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We show how structurally ordered L1₀ face-centered tetragonal (fct) FePt nanoparticles are produced by a solid-state microwave-assisted synthesis method. The structural phase as well as the incorporated Fe into the nanoparticles is confirmed by X-ray diffraction and high resolution high-angle annular dark field scanning transmission electron microscopy experiments. The prepared particles exhibit a remarkable resilience toward crystallite growth at high temperatures. Directly correlated to the L1₀ phase, the best oxygen reduction reaction (ORR) characteristics are achieved for particles with a 1:1 Fe:Pt atomic ratio and an average size of ~2.9 nm where Pt-specific evaluation provided a high mass and specific activity of ~570 A/g_Pt and ~600 μA/cm²_Pt respectively. Our results demonstrate that well-structured catalysts possessing activities vastly exceeding Pt/C (~210 A/g_Pt & ~250 μA/cm²_Pt), can be synthesized through a fast and highly eco-friendly method. We note that the achieved mass activity represent a significant leap toward the theoretical maximum for fully ordered FePt nanoparticles.

Worldwide significant efforts are ongoing to develop devices that store solar energy as fuels. In one such approach, solar energy is absorbed by semiconductors and utilized directly by catalysts at their surfaces to split water into H₂ and O₂. To protect the semiconductors in these photo-electrochemical cells (PEC) from corrosion, frequently thin TiO₂ interlayers are applied. Employing a well-performing photoanode comprised of 1-D n-Si microwires (MWs) covered with a mesoporous (mp) TiO₂ interlayer fabricated by solution processing and functionalized with α-Fe₂O₃ nanorods, we studied here the function of this TiO₂ interlayer by high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy, along with X-ray emission spectroscopy (XES) and standard characterization techniques. Our data reveal that the TiO₂ interlayer not only protects the n-Si MW surface from corrosion, but that it also acts as a template for the hydrothermal growth of α-Fe₂O₃ nanorods and improves the photocatalytic efficiency. We show that the latter effect correlates with the presence of stable oxygen vacancies at the interface between mp-TiO₂ and α-Fe₂O₃, which act as electron traps and thereby substantially reduce the charge recombination rate at the hematite surface.

Herein, we communicate about an Earth-abundant semiconductor photocathode (p-Si/TiO₂/NiO_x) as an alternative for the rare and expensive Pt as a counter electrode for overall photoelectrochemical water splitting. The proposed photoelectrochemical (PEC) water-splitting device mimics the "Z"-scheme observed in natural photosynthesis by combining two photoelectrodes in a parallelillumination mode. A nearly 60% increase in the photocurrent density (J_ph) for pristine α-Fe₂O₃ and a 77% increase in the applied bias photocurrent efficiency (ABPE) were achieved by replacing the conventionally used Pt cathode with an efficient, cost effective p-Si/TiO₂/NiO_x photocathode under parallel illumination. The resulting photocurrent density of 1.26 mA cm⁻² at 1.23V_RHE represents a new record performance for hydrothermally grown pristine α-Fe₂O₃ nanorod photoanodes in combination with a photocathode, which opens the prospect for further improvement by doping α-Fe₂O₃ or by its decoration with co-catalysts. Electrochemical impedance spectroscopy measurements suggest that this significant performance increase is due to the enhancement of the space-charge field in α-Fe₂O_3. 

The use of graphene oxide (GO) based membranes consisting of self-assembled flakes with a lamellar structure represents an intriguing strategy to spatially separate reactants while facilitating proton transport in proton exchange membranes (PEM). Here we chemically modify GO to evaluate the role of fluorine and sulfonic acid groups on the performance of H₂/O₂ based PEM fuel cells. Mild fluorination is achieved by the presence of hydrogen fluoride during oxidation and subsequent sulfonation resulted in fluorine and SO₃^- co-functionalized GO. Membrane electrode assembly performance in low temperature and moderate humidity conditions suggested that both functional groups contribute to reduced H₂ crossover compared to appropriate reference membranes. Moreover, fluorine groups promoted an enhanced hydrolytic stability while contributing to prevent structural degradation after constant potential experiments whereas sulfonic acid demonstrated a stabilizing effect by preserving proton conductivity.

In this paper, the influence of tetravalent dopants such as Si4+, Sn4+, Ti4+, and Zr4+ on the hematite (alpha-Fe2O3) nanostructure for enhanced photoelectrochemical (PEC) water splitting are reported. The tetravalent doping was performed on hydrothermally grown akaganeite (beta-FeOOH) nanorods on FTO (fluorine-doped tin-oxide) substrates via a simple dipping method for which the respective metal-precursor solution was used, followed by a high-temperature (800 degrees C) sintering in a box furnace. The photocurrent density for the pristine (hematite) photoanode is similar to 0.81 mA/cm(2) at 1.23 V-RHE, with an onset potential of 0.72 V-RHE; however, the tetravalent dopants on the hematite nanostructures alter the properties of the pristine photoanode. The Si4+-doped hematite photoanode showed a slight photocurrent increment without a changing of the onset potential of the pristine photoanode. The Sn4+- and Ti4+-doped hematite photoanodes, however, showed an anodic shift of the onset potential with the photocurrent increment at a higher applied potential. Interestingly, the Zr4+-doped hematite photoanode exhibited an onset potential that is similar to those of the pristine and Si4+-doped hematite, but a larger photocurrent density that is similar to those of the Sn4+- and Ti4+-doped photoanodes was recorded. The photoactivity of the doped photoanodes at 1.23 V-RHE follows the order Zr > Sn > Ti > Si. The onset-potential shifts of the doped photoanodes were investigated using the Ab initio calculations that are well correlated with the experimental data. X-ray diffraction (XRD) and scanning-electron microscopy (FESEM) revealed that both the crystalline phase of the hematite and the nanorod morphology were preserved after the doping procedure. X-ray photoelectron spectroscopy (XPS) confirmed the presence of the tetravalent dopants on the hematite nanostructure. The charge-transfer resistance at the various interfaces of the doped photoanodes was studied using impedance spectroscopy. The doping on the hematite photoanodes was confirmed using the Mott-Schottky (MS) analysis. 

Improving interfacial contact between each component in the proton exchange membrane fuel cell (PEMFC) can lead to a significant increase in power density and Pt utilization. In this work, the junction between the catalyst layer and gas diffusion layer (GDL) is greatly enhanced through direct attachment of helical carbon nanofibers, giving rise to a hierarchical structure within the electrical interconnections. The alternative novel GDL is produced by spraying a thin layer of Pd2C60 precursor on commercial carbon paper, followed by chemical vapor deposition growth resulting in a surface morphology of well-attached nanofibers surrounding the microfibers present in the commercial carbon paper. Subsequent solvothermal deposition of platinum nanoparticles allowed evaluation of its suitability as gas diffusion electrode in cathodic H-2/O-2 PEMFC environment. A combination of lowered charge transfer resistance and enhanced Pt-utilization is attributed to its unique wire-like appearance and its robust properties. The fabricated microporous layer - free GDL is suitable for relatively aggressive membrane electrode assembly fabrication procedures and is produced by industrially favorable techniques, rendering it capable of efficiently supporting small amounts of precious metal catalyst nanoparticles in various PEM applications.

To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Solar fuels such as H2 generated from sunlight and seawater using earth-abundant materials are expected to be a crucial component of a next generation renewable energy mix. We herein report a systematic analysis of the photo-electrochemical performance of TiO2 coated, microstructured p-Si photoelectrodes (p-Si/TiO2) that were functionalized with CoOx and NiOx for H2 generation. These photocathodes were synthesized from commercial p-Si wafers employing wet chemical methods. In neutral phosphate buffer and standard 1 sun illumination, the p-Si/TiO2/NiOx photoelectrode showed a photocurrent density of 1.48 mA cm2 at zero bias (0 VRHE), which was three times and 15 times better than the photocurrent densities of p-Si/TiO2/CoOx and p-Si/TiO2, respectively. No decline in activity was observed over a five hour test period, yielding a Faradaic efficiency of 96% for H2 production. Based on the electrochemical characterizations and the high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and emission spectroscopy measurements performed at the Ti Ka1 fluorescence line, the superior performance of the p-Si/TiO2/ NiOx photoelectrode was attributed to improved charge transfer properties induced by the NiOx coating on the protective TiO2 layer, in combination with a higher catalytic activity of NiOx for H2-evolution. Moreover, we report here an excellent photo-electrochemical performance of p-Si/TiO2/NiOx photoelectrode in corrosive artificial seawater (pH 8.4) with an unprecedented photocurrent density of 10 mA cm2 at an applied potential of 0.7 VRHE, and of 20 mA cm2 at 0.9 VRHE. The applied bias photon-to-current conversion efficiency (ABPE) at 0.7 VRHE and 10 mA cm2 was found to be 5.1%

For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (alpha-Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm(2)) compared to pristine alpha-Fe2O3 (0.7 mA/cm(2)), and Sn4+ mono-doped alpha-Fe2O3 photoanodes (1.0 mA/cm(2)). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped alpha-Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure.