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  • 1.
    Barzegar, Hamid Reza
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Xueen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Palladium nanocrystals supported on photo-transformed C-60 nanorods: effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 73, p. 34-40Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis and decoration of high-aspect-ratio crystalline C-60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 +/- 0.66 nm. In their pristine form, C-60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C-60 NRs. Bys measuring the electron mobility of different C-60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C-60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.

  • 2. Gao, Sanshuang
    et al.
    Liu, Jing
    Luo, Jun
    Mamat, Xamxikamar
    Sambasivam, Sangaraju
    Li, Yongtao
    Hu, Xun
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Selective voltammetric determination of Cd(II) by using N,S-codoped porous carbon nanofibers2018In: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 185, article id 282Article in journal (Refereed)
    Abstract [en]

    Porous carbon nanofibers codoped with nitrogen and sulfur (NFs) were prepared by pyrolysis of trithiocyanuric acid, silica nanospheres and polyacrylonitrile (PAN) followed by electrospinning. The NFs were used to modify a glassy carbon electrode (GCE) which then displayed highly sensitive response to traces of Cd(II). Compared to a bare GCE and a Nafion modified GCE, the GCE modified with codoped NFs shows improved sensitivity for Cd(II) in differential pulse anodic sweep voltammetry. The stripping peak current (typically measured at 0.81 V vs. Ag/AgCl) increases linearly in the 2.0–500 μg·L−1 Cd(II) concentration range. This is attributed to the large surface area (109 m2·g−1), porous structure, and high fraction of heteroatoms (19 at.% of N and 0.75 at.% of S). The method was applied to the determination of Cd(II) in (spiked) tap water where it gave recoveries that ranged between 96% and 103%.

  • 3. Gao, Sanshuang
    et al.
    Xu, Chuyang
    Yalikun, Nuerbiya
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Xun
    Liu, Jing
    Luo, Jun
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi 830011, People's Republic of China.
    Sensitive and Selective Differential Pulse Voltammetry Detection of Cd(II) and Pb(II) Using Nitrogen-Doped Porous Carbon Nanofiber Film Electrode2017In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, no 13, p. H967-H974Article in journal (Refereed)
    Abstract [en]

    Carbon matrix materials are regarded as one of the most important electrode materials for heavy metal detection. But even so, optimization procedures of carbon nanofibers (CNFs) for tracing Cd(II) and Pb(II) remains challenging. Here, zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN)-derived nitrogen-doped porous carbon nanofibers (N-PCNFs) were investigated as a new electrode material for determining the concentration of Cd(II) and Pb(II). By optimizing electrochemical conditions such as deposition potential, deposition time, pH of buffer solution, and quantity of N-PCNFs loaded on a glassy carbon electrode (GCE), the linear response curves of Cd(II) and Pb(II) could be obtained. Due to the unique structural feature and N content, the N-PCNFs possess excellent detection limits of 0.8 mu g L-1 for Cd(II) and 0.3 mu g L-1 for Pb(II) (S/N = 3). To manifest the practical use of the sensor platform the concentration of Cd(II) and Pb(II) in normal tap and waste water were monitored. According to the ICP-MS results, the calculated recovery (97.0-107%) indicates that N-PCNFs have potential as a candidate material to monitor the concentration of Cd(II) and Pb(II) in practical samples.

  • 4.
    Gracia-Espino, Eduardo
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Understanding the Interface of Six-Shell Cuboctahedral and Icosahedral Palladium Clusters on Reduced Graphene Oxide: Experimental and Theoretical Study2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 18, p. 6626-6633Article in journal (Refereed)
    Abstract [en]

    Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 +/- 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing similar to 600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdOx shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with fiinctionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.

  • 5. Han, Xin-Bao
    et al.
    Tang, Xing-Yan
    Lin, Yue
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Liu, San-Gui
    Liang, Hai-Wei
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Zhao, Xin-Jing
    Liao, Hong-Gang
    Tan, Yuan-Zhi
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Xie, Su-Yuan
    Zheng, Lan-Sun
    Ultrasmall Abundant Metal-Based Clusters as Oxygen-Evolving Catalysts2019In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 1, p. 232-239Article in journal (Refereed)
    Abstract [en]

    The oxygen evolution reaction is a crucial step in water electrolysis to develop clean and renewable energy. Although noble metal-based catalysts have demonstrated high activity for the oxygen evolution reaction, their application is limited by their high cost and low availability. Here we report the use of a molecule-to-cluster strategy for preparing ultrasmall trimetallic clusters by using the polyoxometalate molecule as a precursor. Ultrafine (0.8 nm) transition-metal clusters with controllable chemical composition are obtained. The transition-metal clusters enable highly efficient oxygen evolution through water electrolysis in alkaline media, manifested by an overpotential of 192 mV at 10 mA cm–2, a low Tafel slope of 36 mV dec–1, and long-term stability for 30 h of electrolysis. We note, however, that besides the excellent performance as an oxygen evolution catalyst, our molecule-to-cluster strategy provides a means to achieve well-defined transition-metal clusters in the subnanometer regime, which potentially can have an impact on several other applications.

  • 6.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cheng, Shaodong
    Shen, Hangjia
    Wang, Chuanyi
    Guo, Shaojun
    Yang, Guang
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Atomistic understanding of the origin of high oxygen reduction electrocatalytic activity of cuboctahedral Pt3Co-Pt core-shell nanoparticles2016In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 6, no 5, p. 1393-1401Article in journal (Refereed)
    Abstract [en]

    PtM-based core-shell nanoparticles are a new class of active and stable nanocatalysts for promoting oxygen reduction reaction (ORR); however, the understanding of their high electrocatalytic performance for ORR at the atomistic level is still a great challenge. Herein, we report the synthesis of highly ordered and homogeneous truncated cuboctahedral Pt3Co-Pt core-shell nanoparticles (cs-Pt3Co). By combining atomic resolution electron microscopy, X-ray photoelectron spectroscopy, extensive first-principles calculations, and many other characterization techniques, we conclude that the cs-Pt3Co nanoparticles are composed of a complete or nearly complete Pt monolayer skin, followed by a secondary shell containing 5-6 layers with similar to 78 at% of Pt, in a Pt3Co configuration, and finally a Co-rich core with 64 at% of Pt. Only this particular structure is consistent with the very high electrocatalytic activity of cs-Pt3Co nanoparticles for ORR, which is about 6 times higher than commercial 30%-Pt/Vulcan and 5 times more active than non-faceted (spherical) alloy Pt3Co nanoparticles. Our study gives an important insight into the atomistic design and understanding of advanced bimetallic nanoparticles for ORR catalysis and other important industrial catalytic applications.

  • 7.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mikolajczuk, Ania
    Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Tai, Cheuk-Wai
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Borodzinski, Andrzej
    Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Palladium nanocrystals supported on helical carbon nanofibers for highly efficient electro-oxidation of formic acid, methanol and ethanol in alkaline electrolytes2012In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 209, p. 236-242Article in journal (Refereed)
    Abstract [en]

    We present the synthesis of palladium nanocrystals self-assembled on helical carbon nanofibers functionalized with benzyl mercaptan (Pd-S-HCNFs) and their electrocatalytic activity toward the oxidation of formic acid, methanol and ethanol. Helical carbon nanofibers (HCNFs) were first functionalized with benzyl mercaptan based on the pi-pi interactions between phenyl rings and the graphitic surface of HCNFs. Palladium nano crystals (PdNC) were fixed on the surface of functionalized HCNF by Pd-S bonds in a simple self-assembly method. The as-prepared materials were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and fuel cell tests. CV characterization of the as-prepared materials shows a very high electrocatalytic activity for oxidation of formic acid, ethanol and methanol in strong alkaline electrolyte. In comparison to commercial catalyst Vulcan XC-72 decorated with Pd nanoparticles, the proposed Pd-S-HCNFs nano composite material shows oxidation currents for formic acid, ethanol and methanol at the Pd-S-HCNF-modified electrode that are higher than that at the Pd/XC-72 modified electrode with a factor of 2.0, 1.5, and 2.3, respectively. In a formic acid fuel cell the Pd-S-HCNF modified electrode yields equal power density as commercial Pd/XC-72 catalyst. Our results show that Pd-decorated helical carbon nanofibers with diameters around 40-60 nm have very high potential as active material in fuel cells, electrocatalysts and sensors. (C) 2012 Elsevier B.V All rights reserved.

  • 8.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ma, Jingyuan
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Xueen
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lu, Lu
    Ma, Chuansheng
    Yang, Guang
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, p. Article number: 5253-Article in journal (Refereed)
    Abstract [en]

    The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium: tungsten = 1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are similar to 1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.

  • 9.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Chalmers University of Technology.
    Jia, Xueen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reduction free room temperature synthesis of a durable and efficient Pd/ordered mesoporous carbon composite electrocatalyst for alkaline direct alcohols fuel cell2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 2, p. 676-682Article in journal (Refereed)
    Abstract [en]

    The development of easy and environmentally benign synthesis methods of efficient electrocatalysts for use in energy conversion applications motivates researchers all over the world. Here we report a novel and versatile method to synthesize well-dispersed palladium-functionalized ordered mesoporous carbons (Pd/OMCs) at room temperature without any reducing agent by one-pot mixing of tri(dibenzylideneacetone)palladium(0) (Pd2DBA3) and OMCs together in a common N,N-dimethylformamide (DMF) solution. The formation of Pd nanoparticles and their crystallization on the OMC is catalyzed by protons in the solution and can thus be controlled by the solution pH. The complete process and the as-prepared nanocomposite was characterized by UV-spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (HTEM), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The electrocatalytic property of the as-decorated material was examined with cyclic voltammetry (CV). The Pd/OMC composite shows up to two times higher electrocatalytic ability with a significantly better durability towards ethanol and methanol oxidation in alkaline media compared to commercial high surface area conductive carbon black Vulcan XC-72 decorated with equivalent Pd nanoparticles. Our described method provides new insight for the development of highly efficient carbon based nanocatalysts by simple and environmentally sound methods.

  • 10.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Self-assembled palladium nanocrystals on helical carbon nanofibers as enhanced electrocatalysts for electro-oxidation of small molecules2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 17, p. 8541-8548Article in journal (Refereed)
    Abstract [en]

    We present a novel approach to prepare helical carbon nanofibers homogeneously functionalized with single crystal palladium nanoparticles via a phase-transfer method. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and electrochemical measurements. We find that homogeneous and small single-crystal Pd nanoparticles can be easily functionalized with phenyl mercaptan, transferred into the toluene phase from the dimethyl sulfoxide (DMSO) phase and then non-covalently self-assembled onto the surface of helical carbon nanofibers with a very good dispersion and homogeneous diameters of 4.5 +/- 0.6 nm. The palladium-helical carbon nanofiber composite exhibits significantly higher electrochemical active area and electrocatalytic activity towards the electrooxidation of formic acid, ethanol and methanol than the commercial electrocatalyst Pd/Vulcan XC-72. Our results show that the prepared material can be potentially used as an advanced nano-electrocatalyst in a direct alkaline fuel cell system.

  • 11.
    Hu, Guangzhi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, Stockholm, Sweden.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Phase-transfer synthesis of amorphous palladium nanoparticle-functionalized 3D helical carbon nanofibers and its highly catalytic performance towards hydrazine oxidation2012In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 543, p. 96-100Article in journal (Refereed)
    Abstract [en]

    Amorphous palladium nanoparticles functionalized helical carbon nanofibers (ApPd-HCNFs) were synthesized using a phase-transfer method. Palladium nanoparticles (Pd-NP) were first prepared using n-dodecyl sulfide as reducing agent and stabilizing ligands in ethanol. The Pd-NPs were then modified with benzyl mercaptan and transferred into a toluene solution with HCNFs which were decorated with amorphous palladium. The materials were characterized with high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry showing that amorphous palladium nanoparticles were uniformly anchored at the HCNFs surface and that the ApPd-HCNFs exhibit high electrocatalytic activity towards hydrazine oxidation. (C) 2012 Elsevier B.V. All rights reserved.

  • 12.
    Jia, Xueen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sharifi, Tiva
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tai, Cheuk-Wai
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection2013In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 22, p. 12017-12022Article in journal (Refereed)
    Abstract [en]

    We report on a novel sensing platform for H2O2 and glucose based on immobilization of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostnictures and glucose oxidase (GOx) with Nafion on a glassy carbon electrode (GCE). HCNFs were synthesized by a chemical vapor deposition process on a C-60-supported Pd catalyst. Pd-HCNF nanocomposites were prepared by a one-step reduction free method in dimethylformamide (DMF). The prepared materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits excellent electrocatalytic sensitivity toward H2O2 (315 mA M-1 cm(-2)) as probed by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified electrodes significantly reduce the overpotential and enhance the electron transfer rate. A linear range from 5.0 mu M to 2.1 mM with a detection limit of 3.0 mu M (based on the S/N = 3) and good reproducibility were obtained. Furthermore, a sensing platform for glucose was prepared by immobilizing the Pd-HCNFs and glucose oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting biosensor exhibits a good response to glucose with a wide linear range (0.06-6.0 mM) with a detection limit of 0.03 mM and a sensitivity of 13 mA M-1 cm(-2). We show that small size and homogeneous distribution of the Pd nanoparticles in combination with good conductivity and large surface area of the HCNFs lead to a H2O2 and glucose sensing platform that performs in the top range of the herein reported sensor platforms.

  • 13. Jiang, Linhai
    et al.
    Yao, Mingguang
    Liu, Bo
    Li, Quanjun
    Liu, Ran
    Lv, Hang
    Lu, Shuangchen
    Gong, Chen
    Zou, Bo
    Cui, Tian
    Liu, Bingbing
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Controlled Synthesis of CeO2/Graphene Nanocomposites with Highly Enhanced Optical and Catalytic Properties2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 21, p. 11741-11745Article in journal (Refereed)
    Abstract [en]

    In this paper, CeO2 nanocubes with the (200)-terminated surface/graphene sheet composites have been prepared successfully by a simple hydrothermal method. It is found that the CeO2 nanocubes with high crystallinity and specific exposed surface are well dispersed on well-exfoliated graphene surface. The (200)-terminated surface/graphene sheet composites modified electrode showed much higher sensitivity and excellent selectivity in its catalytic performance compared to a CeO2 nanoparticle-modified electrode. The photoluminescence intensity of the CeO2 anchored on graphene is about 30 times higher than that of pristine CeO2 crystals in air. The higher oxygen vacancy concentration in CeO2 is supposed to be an important cause for the higher photoluminescence and better electrochemical catalytic performance observed in the (200)-terminated surface/graphene sheet composites. Such ingenious design of supported well-dispersed catalysts in nanostructured ceria catalysts, synthesized in one step with an exposed high-activity surface, is important for technical applications and theoretical investigations.

  • 14. Jiang, Ruyuan
    et al.
    Liu, Niantao
    Gao, Sanshuang
    Mamat, Xamxikamar
    Su, Yuhong
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Li, Yongtao
    Hu, Xun
    Hu, Guangzhi
    A Facile Electrochemical Sensor Based on PyTS-CNTs for Simultaneous Determination of Cadmium and Lead Ions2018In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 18, no 5, article id 1567Article in journal (Refereed)
    Abstract [en]

    A simple and easy method was implemented for the contemporary detection of cadmium (Cd2+) and lead (Pb2+) ions using 1,3,6,8-pyrenetetrasulfonic acid sodium salt-functionalized carbon nanotubes nanocomposites (PyTS-CNTs). The morphology and composition of the obtained PyTS-CNTs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results confirmed that the fabricated PyTS-CNTs exhibited good selectivity and sensitivity for metal ion-sensing owing to the insertion of sulfonic acid groups. For Cd2+ and Pb2+, some of the electrochemical sensing parameters were evaluated by varying data such as the PyTS-CNT quantity loaded on the pyrolytic graphite electrode (PGE), pH of the acetate buffer, deposition time, and deposition potential. These parameters were optimized with differential pulse anodic sweeping voltammetry (DPASV). Under the optimal condition, the stripping peak current of the PyTS-CNTs/Nafion/PGE varies linearly with the heavy metal ion concentration, ranging from 1.0 mu g L-1 to 90 mu g L-1 for Cd2+ and from 1.0 mu g L-1 to 110 mu g L-1 for Pb2+. The limits of detection were estimated to be approximately 0.8 mu g L-1 for Cd2+ and 0.02 mu g L-1 for Pb2+. The proposed PyTS CNTs/Nafion/PGE can be used as a rapid, simple, and controllable electrochemical sensor for the determination of toxic Cd2+ and Pb2+.

  • 15. Jiang, Ruyuan
    et al.
    Liu, Niantao
    Su, Yuhong
    Gao, Sanshuang
    Mamat, Xamxikamar
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Li, Yongtao
    Hu, Xun
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, State Key Lab Basis Xinjiang Indigenous Med Plant, Key Lab Chem Plant Resources Arid Reg, Urumqi 830011, Peoples R China.
    Polysulfide/Graphene Nanocomposite Film for Simultaneous Electrochemical Determination of Cadmium and Lead Ions2018In: NANO, ISSN 1793-2920, Vol. 13, no 8, article id 1850090Article in journal (Refereed)
    Abstract [en]

    An integrative electroanalytical method was developed for detecting Cd2+ and Pb2+ ions in aqueous solutions. Polysulfide/graphene (RGO-S) nanocomposites were prepared and their performance as electrochemical sensors for Cd2+ and Pb2+ was evaluated. The RGO-S nanocomposite was carefully characterized by scanning electron microscopy with energy-dispersive X-ray spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The as-prepared RGO-S was incorporated into a pyrolytic graphite electrode (RGO-S/PGE) and used for detecting trace amount of Cd2+ and Pb2+ by differential pulse anodic stripping voltammetry. Under optimal conditions, the stripping peak current of RGO-S/PGE varies linearly with heavy metal ion concentration in the ranges 2.0-300 mu g L-1 for Cd2+ and 1.0-300 mu g L-1 for Pb2+. The limits of detection for Cd2+ and Pb2+ were estimated to be about 0.67 mu g L-1 and 0.17 mu g L-1, respectively. The prepared electrochemical heavy-metal-detecting electrode provides good repeatability and reproducibility with high sensitivity, making it a suitable candidate for monitoring Cd2+ and Pb2+ concentrations in aqueous environmental samples.

  • 16.
    Klechikov, Alexey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sun, Jinhua
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zheng, Mingbo
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr V.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Graphene decorated with metal nanoparticles: Hydrogen sorption and related artefacts2017In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 250, p. 27-34Article in journal (Refereed)
    Abstract [en]

    Hydrogen sorption by reduced graphene oxides (r-GO) is not found to increase after decoration with Pd and Pt nanoparticles. Treatments of metal decorated samples using annealing under hydrogen or air were tested as a method to create additional pores by effects of r-GO etching around nanoparticles. Increase of Specific Surface Area (SSA) was observed for some air annealed r-GO samples. However, the same treatments applied to activated r-GO samples with microporous nature and higher surface area result in breakup of structure and dramatic decrease of SSA. Our experiments have not revealed effects which could be attributed to spillover in hydrogen sorption on Pd or Pt decorated graphene. However, we report irreversible chemisorption of hydrogen for some samples which can be mistakenly assigned to spillover if the experiments are incomplete.

  • 17. Liu, Niantao
    et al.
    Mamat, Xamxikamar
    Jiang, Ruyuan
    Tong, Wei
    Huang, Yudai
    Jia, Dianzeng
    Li, Yongtao
    Wang, Lei
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Facile high-voltage sputtering synthesis of three-dimensional hierarchical porous nitrogen-doped carbon coated Si composite for high performance lithium-ion batteries2018In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 343, p. 78-85Article in journal (Refereed)
    Abstract [en]

    Various kinds of efforts have been devoted to ameliorate the serious volume-expansion effect and low electron conductivity of silicon-based materials in lithium ion batteries. Here, we report a facile high voltage sputtering process to prepare three-dimensional hierarchical porous nitrogen-doped carbon coated Si microsphere to significantly improve the lithium storage performance. The structure and morphology of the as-obtained samples are characterized by X-ray diffraction, transmission electron microscope and scanning electron microscope. The results indicate that the as-prepared composite is composed of silicon nanoparticles (similar to 100 nm) coated with conductive thin carbon layer (similar to 8.5 nm). The composite shows excellent lithium storage performance with a reversible capacity of 1565 mAh g(-1) after 100 cycles at a current density of 0.5 A g(-1), as well as a long cycling performance at the high current density of 2 A g(-1). The facile preparation process and highly silicon-loading (similar to 78%) makes the prepared material be a great potential application in lithium-ion batteries.

  • 18.
    Nitze, Florian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mazurkiewicz, Marta
    Malolepszy, Artur
    Mikolajczuk, Anna
    Kedzierzawski, Piotr
    Tai, Cheuk-Wai
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kurzydlowski, Krzysztof Jan
    Stobinski, Leszek
    Borodzinski, Andrzej
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Synthesis of palladium nanoparticles decorated helical carbon nanofiber as highly active anodic catalyst for direct formic acid fuel cells2012In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 63, p. 323-328Article in journal (Refereed)
    Abstract [en]

    We present a single metal approach to produce highly active catalyst materials based on Pd-decorated helical carbon nanofibers. Helical carbon fibers are synthesized by a chemical vapor deposition process on a C-60 supported Pd catalyst and the obtained fibers are functionalized by H2O2 followed by a decoration with Pd nanoparticles. Although transmission electron microscopy images show that the decoration is relatively inhomogeneous the electrocatalytic activity for formic acid oxidation is very high. Cyclic voltammetry measurements (CV) show that the generated current peak value for Pd-decorated helical carbon nanofibers is 300 mA/mg(Pd) for a scan rate of 10 mV/s. This is significantly higher than the corresponding value of a reference sample of multiwalled carbon nanotubes decorated with Pd nanoparticles by the same process. Fuel cell tests for our Pd-decorated helical carbon nanofibers also displayed a high power density, although not as superior to Pd-decorated multiwalled nanotubes as measured by CV. Our results show that helical carbon nanofibers have several good properties, such as a rigid anchoring of catalyst nanoparticles and a suitable structure for creating functionalization defects which make them an interesting candidate for electrochemical applications. (C) 2012 Elsevier Ltd. All rights reserved.

  • 19.
    Nitze, Florian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Chemical and Biological Engineering, Chalmers University of Technology, Sweden.
    Sandström, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mazurkiewicz, Marta
    Malolepszy, Artur
    Stobinski, Leszek
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Direct support mixture painting, using Pd(0) organo-metallic compounds - an easy and environmentally sound approach to combine decoration and electrode preparation for fuel cells2014In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 48, p. 20973-20979Article in journal (Refereed)
    Abstract [en]

    An inventive, fast and straight-forward approach for the direct preparation of fuel cell electrodes has been developed and tested. Our approach avoids long catalyst preparation and post-synthesis treatment. It reduces the use of chemicals and thereby concomitantly lowers the environmental impact and improves cost efficiency. It combines decoration of the support by palladium nanoparticles with electrode preparation through a simple one-step ink-painting and annealing process. Composites have been investigated by high resolution transmission electron microscopy, scanning electron microscopy, and Xray diffraction. Crystalline particles are well-attached and well-distributed on the support. Particles are of few nanometers in size and spherical for decorated Vulcan whereas they are larger and irregularly shaped for decorated helical carbon nanofibers (HCNFs). Electrodes with a metal loading of 0.8 mg cm(-2) have been tested in a direct formic acid fuel cell. Both the Vulcan and the HCNF electrodes show a similar and high power output of up to 120 mW mg(-1). They also show similar performances in deactivation experiments conducted at 200 mA cm(-2) even when using only high purity grade formic acid. After deactivation the electrodes show no structural damage, making them superior to most commercial catalysts. The electrodes can be completely regenerated to initial activity by simple treatment with water. The easy regeneration process indicates that CO-adsorption on the fuel cell anode catalyst is not the main poisoning mechanism responsible for electrode degeneration.

  • 20. Qin, Danfeng
    et al.
    Gao, Shanshuang
    Wang, Le
    Shen, Hangjia
    Yalikun, Nuerbiya
    Sukhrobov, Parviz
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhao, Yujie
    Mamat, Xamxikamar
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang indigenous medicinal plants resource utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi, China.
    Three-dimensional carbon nanofiber derived from bacterial cellulose for use in a Nafion matrix on a glassy carbon electrode for simultaneous voltammetric determination of trace levels of Cd(II) and Pb(II)2017In: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 184, no 8, p. 2759-2766Article in journal (Refereed)
    Abstract [en]

    The authors describe the preparation of carbon nanofibers (CNFs) with a three-dimensional network structure by one-step carbonization of bacterial cellulose at 800 degrees C. The 3D CNFs wrapped with Nafion polymer were cast on a glassy carbon electrode (GCE) which then enables sensitive detection of Cd(II) and Pb(II). Under optimized conditions and at typical stripping peaks of around -0.80 and -0.55 V (vs Ag/AgCl), the electrode exhibits high sensitivity and a wide analytical range of 2-100 mu g.L-1 for both Cd(II) and Pb(II). The detection limits are 0.38 mu g.L-1 for Cd(II) and 0.33 mu g.L-1 for Pb(II), respectively. The modified GCE was successfully employed to the determination of trace amounts of Cd(II) and Pb(II) in both tap water and waste water.

  • 21. Qin, Danfeng
    et al.
    Hu, Xun
    Dong, Yemin
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    An Electrochemical Sensor Based on Green gamma-AlOOH-Carbonated Bacterial Cellulose Hybrids for Simultaneous Determination Trace Levels of Cd(II) and Pb(II) in Drinking Water2018In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 165, no 7, p. B328-B334Article in journal (Refereed)
    Abstract [en]

    An eco-friendly gamma-AlOOH-carbonated bacterial cellulose (gamma-AlOOH-CBC) hybrids material was fabricated by simple pyrolysis and hydrothermal treatments. The obtained hybrids possess an intrinsic 3D nanofibrous structure decorated with chaff-like gamma-AlOOH particles. Owing to the good adsorption property and conductive, gamma-AlOOH-CBC hybrids were used to modified the glass carbon electrode (GCE) for simultaneous determination of Cd(II) and Pb(II) in aqueous samples by differential pulse anodic stripping voltammetry (DPASV) method. Various parameters affected Cd(II) and Pb(II) measurement were optimized. Under the optimal conditions, the limit of detection (S/N = 3) of the gamma-AlOOH-CBC modified electrode was evaluated to be 0.17 mu g.L-1 for Cd(II) and 0.10 mu g.L-1 for Pb(II) with the linear range of the calibration curves ranged 0.5-250 mu g.L-1 for Cd(II) and Pb(II). Furthermore, the developed electrode was also successfully utilized for monitoring trace Cd(II) and Pb(II) in drinking water samples with satisfactory results.

  • 22. Qin, Danfeng
    et al.
    Wang, Le
    Gao, Sanshuang
    Wang, Ying
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cheng, Hao
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in AridRegions, State Key Laboratory Basis of Xinjiang indigenousmedicinal plants resource utilization, Xinjiang Technical In-stitute of Physics and Chemistry, Chinese Academy of Science,Urumqi 830011, China.
    N-Doped Hollow Porous Carbon Spheres/Bismuth Hybrid Film Modified Electrodes for Sensitive Voltammetric Determination of Trace Cadmium2018In: Electroanalysis, ISSN 1040-0397, E-ISSN 1521-4109, Vol. 30, no 9, p. 1906-1912Article in journal (Refereed)
    Abstract [en]

    In this work, N-doped hollow porous carbon spheres (N-HPCSs) were synthesized by silicon dioxide template-assisted polybenzoxazine (PB) coating strategy. The prepared N-HPCSs have a smooth hollow ball structure surrounded by a well-defined porous shell. Combining with in-situ plating of Bi film, the N-HPCSs were further fabricated a sensitive electrochemical platform for determination trace levels of Cd(II) by differential pulse anodic stripping voltammetry (DPASV). Under the optimized conditions, the Bi-N-HPCSs based sensor displays a linear response to Cd(II) over the range of 0.5gL(-1) to 150gL(-1). Meanwhile, the limit of detection (LOD, S/N=3) is estimated to be around 0.16gL(-1) for Cd(II), which is 31 times lower than the safety values set by United States Environmental Protection Agency (EPA) for the drinking water. Moreover, the proposed method was successfully applied to detection of Cd(II) in tap water and lake water, and the analytical results of the presented method are agreed well with inductively coupled plasma-mass spectrometry (ICP-MS) data. Due to the excellent analytical performance, the fabricated electrode is promised for future development in monitoring of cadmium pollution in the environment.

  • 23.
    Sandström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ma, Jingyuan
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yttria stabilized and surface activated platinum (PtxYOy) nanoparticles through rapid microwave assisted synthesis for oxygen reduction reaction2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 46, p. 141-149Article in journal (Refereed)
    Abstract [en]

    The enhancement of platinum (Pt) based catalysts for the oxygen reduction reaction (ORR) by addition of rare earth metals represents a promising strategy to achieve high activity yet low content of the precious metal and concurrently addresses stability issues experienced by traditional late transition metal doping. Improvement in Pt utilization is essential for vehicular applications where material cost and abundancy is a great concern. Here we report a fast and efficient production route of yttria-stabilized platinum nanoparticles (PtxYOy) using a conventional household microwave oven. ORR performance showed a significant improvement and an optimum activity at a 3:1 Pt:Y ratio outperforming that of commercial Pt-Vulcan with a doubled specific activity. Incorporation of Y is evidenced by extended X-ray absorption fine structure and energy dispersive X-ray analysis, while significant amounts of integrated Y2O3 species are detected by X-ray photoelectron spectroscopy. Density functional theory calculations suggest surface migration and oxidation of Y, forming stable superficial yttrium oxide species with low negative enthalpies of formation. The robustness of PtxYOy is shown experimentally and through theoretical arguments demonstrating that surface yttria acts as a stabilizing agent and promoter of highly active ORR sites on the remaining Pt surface, surpassing even the Pt3Y alloy configuration.

  • 24.
    Sandström, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Compositional Evaluation of Coreduced Fe-Pt Metal Acetylacetonates as PEM Fuel Cell Cathode Catalyst2018In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, no 12, p. 7106-7115Article in journal (Refereed)
    Abstract [en]

    Platinum iron nanoparticles were produced by solvothermal coreduction of organic Fe and Pt precursor compounds and supported on conventional Vulcan XC 72. Evaluation of oxygen reduction performance reveals a highly active surface with up to 5 times the specific activity of commercial Pt Vulcan measured in O-2-saturated 0.1 M HClO4. A particle size of 5.5 nm for the best performing sample, produced from an initial metal ratio of 1:1, provided 28% higher mass activity than the commercial reference. Membrane electrode assemblies, optimized for both H-2/O-2 and direct formic acid fuel cells, were produced, and the PEM fuel cell cathodic performance displayed results with similar enhancements as its ex situ measured mass activity, although a delamination of the catalyst layer from the membrane could be observed even when employing a hot-pressing procedure during MEA fabrication. Physical characterizations including X-ray photoelectron spectroscopy and in situ X-ray diffraction reveal oxidized states of Fe incorporated into the disordered face-centered cubic Pt nanoparticles, supported by composition-dependent morphological changes as observed by transmission electron microscopy. The provided insight into fuel cell performance as well as CO-oxidation attributes are expected to assist in selecting suitable applications and operating conditions for such FePt type nanoparticles.

  • 25.
    Sharifi, Tiva
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Barzegar, Hamid Reza
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Xueen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nitze, Florian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nordblad, Per
    Department of Engineering Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden.
    Tai, Cheuk-Wai
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic gamma-Fe2O3 nanoparticles2013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, p. 2319-Article in journal (Refereed)
    Abstract [en]

    Graphene nanoscrolls are Archimedean-type spirals formed by rolling single-layer graphene sheets. Their unique structure makes them conceptually interesting and understanding their formation gives important information on the manipulation and characteristics of various carbon nanostructures. Here we report a 100% efficient process to transform nitrogen-doped reduced graphene oxide sheets into homogeneous nanoscrolls by decoration with magnetic gamma-Fe2O3 nanoparticles. Through a large number of control experiments, magnetic characterization of the decorated nanoparticles, and ab initio calculations, we conclude that the rolling is initiated by the strong adsorption of maghemite nanoparticles at nitrogen defects in the graphene lattice and their mutual magnetic interaction. The nanoscroll formation is fully reversible and upon removal of the maghemite nanoparticles, the nanoscrolls return to open sheets. Besides supplying information on the rolling mechanism of graphene nanoscrolls, our results also provide important information on the stabilization of iron oxide nanoparticles.

  • 26.
    Sharifi, Tiva
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Chen, Anran
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Oxygen Reduction Reactions on Single- or Few-Atom Discrete Active Sites for Heterogeneous Catalysis2019In: Advanced Energy Materials, ISSN 1614-6832, article id 1902084Article in journal (Refereed)
    Abstract [en]

    The oxygen reduction reaction (ORR) is of great importance in energy-converting processes such as fuel cells and in metal-air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O-2 adsorption, dissociation, and subsequent electron transfer. Single- or few-atom motifs based on earth-abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon-based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal-coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single- and few-atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.

  • 27.
    Sharifi, Tiva
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Xueen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Formation of active sites for Oxygen reduction reactions by transformation of Nitrogen functionalities in Nitrogen-doped Carbon nanotubes2012In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 6, no 10, p. 8904-8912Article in journal (Refereed)
    Abstract [en]

    Heat treating nitrogen-doped multiwalled carbon nanotubes containing up to six different types of nitrogen functionalities transforms particular nitrogen functionalities into other types which are more catalytically active toward oxygen reduction reactions (ORR). In the first stage, the unstable pyrrolic functionalities transform into pyridinic functionalities followed by an immediate transition into quaternary center and valley nitrogen functionalities. By measuring the electrocatalytic oxidation reduction current for the different samples, we achieve information on the catalytic activity connected to each type of nitrogen functionality. Through this, we conclude that quaternary nitrogen valley sites, N-Q(valley), are the most active sites for ORR in N-CNTs. The number of electrons transferred in the ORR is determined from ring disk electrode and rotating ring disk electrode measurements. Our measurements indicate that the ORR processes proceed by a direct four-electron pathway for the N-Q(valley) and the pyridinic sites while it proceeds by an indirect two-electron pathway via hydrogen peroxide at the N-Q(center) sites. Our study gives both insights on the mechanism of ORR on different nitrogen functionalities in nitrogen-doped carbon nanostructures and it proposes how to treat samples to maximize the catalytic efficiency of such samples.

  • 28. Shen, Hangjia
    et al.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Jingyuan
    Tang, Haodong
    Mamat, Xamxikamar
    Wagberg, Thomas
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China.
    Guo, Shaojun
    Atomically FeN2 moieties dispersed on mesoporous carbon: A new atomic catalyst for efficient oxygen reduction catalysis2017In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 35, p. 9-16Article in journal (Refereed)
    Abstract [en]

    Earth-abundant materials with Fe-N-C centers have been identified as promising catalysts for oxygen reduction reaction (ORR), but these alternatives for Pt catalysts are usually the porphyrin-like FeN4 configuration. The density functional theory (DFT) calculations reveal that FeN2 outperforms FeN4 due to its lower interaction with *O-2 and *OH intermediates and enhanced electron transport, however, achieving an optimum design of these earth-abundant materials with the enriched FeN2 catalytic centers is still a great challenge. Here, we report an intriguing template casting strategy to introduce a mass of atomically dispersed FeN2 moieties onto the surface of N-doped ordered mesoporous carbon for boosting ORR electrocatalysis. One of unique parts herein is to pre anchor Fe precursor on the surface of template (SBA-15) during catalyst synthesis, preventing Fe from penetrating into the carbon skeleton and facilitating the removal of excessive Fe-based particles during silica elimination by HF etching, resulting in a desirable model structure comprising only highly active atomically dispersed FeN2 sites, as confirmed by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), extended X-ray absorption fine structure (EXAFS) and Mossbauer spectroscopy analysis. The well-defined structure prompts us to understand the nature of the catalytic active sites, and to demonstrate that the catalyst activity is linearly proportional to the concentration of FeN2 sites. The obtained atomic electrocatalyst exhibits superior electrocatalytic performance for ORR with a more positive half-wave potential than that of Pt/C catalyst. We further establish a kinetic model to predict the ORR activity of these single-atom dispersed catalysts. The present work elaborates on a profound understanding for designing low-cost, highly efficient FeN2-based electrocatalyst for boosting ORR.

  • 29. Shen, Hangjia
    et al.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Jingyuan
    Zang, Ketao
    Luo, Jun
    Wang, Le
    Gao, Sanshuang
    Mamat, Xamxikamar
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions State Key Laboratory Basis of Xinjiang indigenous medicinal plants resource utilization Xinjiang Technical Institute of Physics and Chemistry Chinese Academy of Sciences.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Guo, Shaojun
    Synergistic Effects between Atomically Dispersed Fe-N-C and C-S-C for the Oxygen Reduction Reaction in Acidic Media2017In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, no 44, p. 13800-13804Article in journal (Refereed)
    Abstract [en]

    Various advanced catalysts based on sulfur-doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur-doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template-sacrificing method. The incorporated sulfur gives a thiophene-like structure (C-S-C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4e(-) ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur-free variant (Fe/NC) in 0.5m H2SO4.

  • 30. Shen, Hangjia
    et al.
    Gracia-Espino, Eduardo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Le
    Qin, Danfeng
    Gao, Sanshuang
    Mamat, Xamxikamar
    Ren, Wei
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, Urumqi 830011, Peoples R China.
    Microwave-assisted synthesis of multimetal oxygen-evolving catalysts2017In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 81, p. 116-119Article in journal (Refereed)
    Abstract [en]

    Oxygen evolution reaction (OER) plays a pivotal role in water-splitting. Here, we report a facile method to synthesize multimetal supported on commercial carbon black via a time-saving microwave process. Crystalline FeNi3 nanoparticles homogeneously doped with Mo are formed via a microwave treatment and activated to metal oxyhydroxide in-situ during cyclic voltammetry test with overpotential of only 280 mV at 10 mA cm(-2) for OER in alkaline electrolyte, outperforming RuO2. Our synthesis methodology is a promising alternative for large-scale production, delivering a valuable contribution to catalyst preparation and electrocatalytic water oxidation research.

  • 31. Shen, Hangjia
    et al.
    Qin, Danfeng
    Li, Yuzhen
    Li, Shouzhu
    Yang, Chi
    Yuan, Qunhui
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    In situ magnesiothermal synthesis of mesoporous MgO/OMC composite for sensitive detection of lead ions2016In: Electroanalysis, ISSN 1040-0397, E-ISSN 1521-4109, Vol. 28, no 12, p. 2939-2946Article in journal (Refereed)
    Abstract [en]

    Mesoporous materials have exceptional properties for application owing to their ability to absorb and interact with guest species. A novel MgO/OMC composite with mesoporous structure was successfully synthesized via in situ magnesiothermic reduction. The structure was confirmed by N-2 sorption isotherms, X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). By using nafion and bismuth films as co-modifiers, the MgO/OMC composite material shows high sensitivity of 0.113 mu A.L mu g(-1) and lower background current for electrochemical determination of lead ion (Pb2+) by using anodic stripping voltammetry. The high specific surface area and good mass transfer on the proposed mesoporous material, as well as the outstanding adsorption abilities of MgO to metal ions and the excellent conductivity of the carbon skeleton contribute to the enhanced electrochemical response of Pb2+. As the stripping response of Bi/MgO/OMC-Nafion/PGE is highly linear (R-2 = 0.998) over a Pb2+ concentration range of 2 to 300 mg/L, it was successfully used to analyse Pb2+ in real tap-water samples with good recoveries.

  • 32. Sukhrobov, Parviz
    et al.
    Numonov, Sodik
    Gao, Sanshuang
    Mamat, Xamxikamar
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Guo, Yufen
    Liu, Liwei
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous, Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, P. R. China.
    Nonenzymatic Glucose Biosensor Based on NiNPs/Nafion/Graphene Film for Direct Glucose Determination in Human Serum2018In: NANO, ISSN 1793-2920, Vol. 13, no 7, article id 1850075Article in journal (Refereed)
    Abstract [en]

    This study describes a type of novel nickel nanoparticles (NiNPs) decorated on Nafiongraphene composite film by using the electrochemical deposition method. It was used to fabricate electrochemical biosensors for sensitive nonenzymatic glucose detection. Compared with the Nafion-graphene film and NiNPs-modified glassy carbon electrode (NiNPs-GCE), the NiNPs/Nafion/graphene/GCE showed the best electrocatalytic activity towards glucose oxidation in alkaline medium. The NiNPs/Nafion/graphene/GCE at an applied potential of +0.55 V in a linear range of 1-200 mu M presented a high sensitivity of 3437.25 mu A center dot mM(-1) cm(-2) with coefficient of correlation R-2 = 0.999; and in a linear range of 200-10800 mu M it performed the best sensitivity of 2848.6 mu A center dot mM(-1) cm(-2) with coefficient of correlation R-2 = 0.995 towards glucose oxidation. For a concentration up to 200 mu M, a linear range was obtained with a limit of detection of 0.6 mu M (signal to noise = 3) and as much as 10 800 mu M with a limit of detection of 0.82 mu M (signal to noise = 3). The time of responses was about 1-1.5 s with the addition of 0.1-1 mM glucose. In addition, NiNPs/Nafion/graphene/GCE also has a high anti-interference ability toward common oxidative interfering species, such as uric acid, ascorbic acid and dopamine. More importantly, NiNPs/Nafion/graphene/GCE was successfully used for the determination of glucose concentration in human serum samples in comparison with a local hospital. The NiNPs/Nafion/graphene/GCE exhibited high sensitivity, low working potential, good stability, excellent electrical properties, enhanced selectivity and fast amperometric responses to glucose oxidation. Thus, as a nonenzymatic sensor, it is promising for future glucose determination development.

  • 33. Sukhrobov, Parviz
    et al.
    Numonov, Sodik
    Liu, Jing
    Luo, Jun
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, China.
    Rapid Microwave-Assisted Synthesis of Copper Decorated Carbon Black Nanocomposite for Non-Enzyme Glucose Sensing in Human Blood2019In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 13, p. B1238-B1244Article in journal (Refereed)
    Abstract [en]

    The current research performs the novelty fabricated of non-enzymatic biosensor based on copper nanoparticles decorated carbon black nanocomposite modified glassy carbon electrode (Cu/DCB/GCE) by using the microwave method. The prepared nanomaterial was applied for glucose determination in biological fluids and human serum samples. The techniques of SEM, TEM, XPS, XRD, EDS and mapping tests were selected for the morphological, compositions and crystal structure characterizations of the fabricated nanocomposite. In comparison with other electrodes based on metal decorated carbon black, the Cu/DCB/GCE demonstrated the best electrocatalytic property toward glucose oxidation in 0.1 M KOH electrolyte. Cu/DCB/GCE under the optimal potential of +0.5 V in a linear range from 0.5 up to 7000 mu M with a detection limit of 0.1 mu M (S/N=3), the coefficient of correlation R-2=0.999, performed significant high sensitivity of 1595 mu A mM(-1) cm(-2). Rapid amperometric responses of the prepared biosensor in short time with 0.8-2 s were observed by addition of different glucose concentrations in alkaline solution. Modified Cu/DCB/GCE exhibited the best anti-interference property against blood cells and some blood co-existence molecules such as dopamine, uric acid, ascorbic acid, albumin, and globulin. Most importantly, Cu/DCB/GCE biosensor was used for glucose level determination in human blood serum samples. Due to the attractable structure and properties of the fabricated biosensor, it can be suggested for the future development of glucose detection design.

  • 34. Sukhrobov, Parviz
    et al.
    Numonov, Sodik
    Mamat, Xamxikamar
    Li, Yongtao
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang Indigenous Medicinal Plants Resource Utilization, Xinjiang Technical Institute of Physics .
    A New Non-Enzymatic Amperometric Sensor Based on Nickel Decorated ZIF-8 Derived Carbon Nanoframe for the Glucose Determination in Blood Samples2018In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 13, no 7, p. 6550-6564Article in journal (Refereed)
    Abstract [en]

    The present study demonstrated a highly sensitive non-enzymatic glucose biosensor in real blood samples based on simple evaluated nickel deposited on N-doped porous carbon modified glassy carbon electrode (Ni/NPC/GCE) by applying electrochemical deposition method. The prepared material initially were characterized by cyclic voltammetry, the morphology structure of the as-prepared samples was observed by SEM, and composition, crystals structure of Ni/NPC were identified by SEM mapping and EDS tests. The Ni/NPC/GCE compared with NPC/GCE and NiNPs/GCE performed the best electrocatalytic behavior towards oxidation of glucose in 0.1 M KOH medium. By applied potential of +0.6 V Ni/NPC/GCE showed very high sensitivity of 3753.78 mu AmM(-1)cm(-2) in linear range of 1-7940 mu M with the correlation coefficient of R-2=0.995. The linear ranges get views above the concentration up to 7940 mu M with the detection limit of 0.3 mu M (S/N= 3). Amperometric time responses of prepared electrode towards different glucose concentrations are 0.8-1.3s. Finally, several positive characteristics such as very high sensitivity, weak working potential, nice anti-interference properties, long stability, good selectivity, and comparison with some other non-enzymatic sensors Ni/NPC/GCE executed high sensitivity, low detection limit and wide linear range to glucose sensing, thus the selected electrode is supplying for future glucose level determination design.

  • 35. Yalikun, Nuerbiya
    et al.
    Mamat, Xamxikamar
    Li, Yongtao
    Hu, Xun
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, Key Lab Chem Plant Resources Arid Reg, State Key Lab Basis Xinjiang Indigenous Med Plant, Urumqi 830011, Peoples R China.
    Bacterial cellulose-based three-dimensional carbon nanofibers for the sensitive and selective determination of uric acid2018In: Science of Advanced Materials, ISSN 1947-2935, E-ISSN 1947-2943, Vol. 10, no 11, p. 1623-1629Article in journal (Refereed)
    Abstract [en]

    In recent years, the interest in the optimization of novel nanomaterials for electrodes preparation has received tremendous attention. This article describe about develop an electrochemical sensor for to detect the uric acid (UA). Firstly, the sensing materials of carbon nanofibers (CNFs) were prepared through an economical approach under freeze-dried, mainly for CNFs were successfully synthesized through carbonized biomass green bacterial cellulose (BC) at 800 degrees C. The obtained CNFs were used to modify the glassy carbon electrode (GCE), and have an excellent electrochemical response towards the UA. Under the optimized condition, the current response of UA at the CNFs/GCE increased also the peak current linearly with the UA concentration, the limitation of detection (LOD) calculated as 0.29 mu M (S/N = 3), revealing the a high sensitivity and an broader analytical range of the as-prepared CNFs/GCE. Finally, the proposed electrochemical sensor can be used for detection of UA in human urine with the satisfactory result.

  • 36. Zhan, Xuejia
    et al.
    Hu, Guangzhi
    Umeå University, Faculty of Science and Technology, Department of Physics. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi, People’s Republic of China .
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhan, Shenshan
    Xu, Hanchu
    Zhou, Pei
    Electrochemical aptasensor for tetracycline using a screen-printed carbon electrode modified with an alginate film containing reduced graphene oxide and magnetite (Fe3O4) nanoparticles2016In: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 183, no 2, p. 723-729Article in journal (Refereed)
    Abstract [en]

    The authors describe a label-free electrochemical aptasensor for tetracycline (TET). The TET-binding aptamer was immobilized on a composite consisting of reduced graphene oxide, magnetite (Fe3O4) and sodium alginate, and this material was used to modify the surface of a screen-printed carbon electrode (SPCE). Cyclic voltammetry was carried out to characterize the single steps in the preparation of the modified electrode and to optimize the conditions for detection. Differential pulse voltammetry (DPV) was then used to monitor the interaction between aptamer and TET by applying the electrochemical probe thionine. Under optimal conditions, TET can be quantified by DPV in the 1 nM to 5 mu M concentration range, with a detection limit as low as 0.6 nM (at an S/N ratio of 3). The method is rapid, cost-efficient, highly sensitive and specific, and therefore is considered to be a viable platform for TET analysis in food, environmental, and clinical samples.

1 - 36 of 36
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