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Kwong, Wai Ling
Publications (6 of 6) Show all publications
Kwong, W. L., Gracia-Espino, E., Lee, C. C., Sandström, R., Wågberg, T. & Messinger, J. (2017). Cationic Vacancy Defects in Iron Phosphide: A Promising Route toward Efficient and Stable Hydrogen Evolution by Electrochemical Water Splitting. ChemSusChem, 10(22), 4544-4551
Open this publication in new window or tab >>Cationic Vacancy Defects in Iron Phosphide: A Promising Route toward Efficient and Stable Hydrogen Evolution by Electrochemical Water Splitting
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2017 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 22, p. 4544-4551Article in journal (Refereed) Published
Abstract [en]

Engineering the electronic properties of transition metal phosphides has shown great effectiveness in improving their intrinsic catalytic activity for the hydrogen evolution reaction (HER) in water splitting applications. Herein, we report for the first time, the creation of Fe vacancies as an approach to modulate the electronic structure of iron phosphide (FeP). The Fe vacancies were produced by chemical leaching of Mg that was introduced into FeP as "sacrificial dopant". The obtained Fe-vacancy-rich FeP nanoparticulate films, which were deposited on Ti foil, show excellent HER activity compared to pristine FeP and Mg-doped FeP, achieving a current density of 10 mAcm(-2) at overpotentials of 108 mV in 1 m KOH and 65 mV in 0.5 m H2SO4, with a near-100% Faradaic efficiency. Our theoretical and experimental analyses reveal that the improved HER activity originates from the presence of Fe vacancies, which lead to a synergistic modulation of the structural and electronic properties that result in a near-optimal hydrogen adsorption free energy and enhanced proton trapping. The success in catalytic improvement through the introduction of cationic vacancy defects has not only demonstrated the potential of Fe-vacancy-rich FeP as highly efficient, earth abundant HER catalyst, but also opens up an exciting pathway for activating other promising catalysts for electrochemical water splitting.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2017
Keywords
artificial photosynthesis, cation vacancy, iron phosphide, sacrificial dopant, solar fuels
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-143610 (URN)10.1002/cssc.201701565 (DOI)000416158500031 ()28980427 (PubMedID)
Available from: 2018-01-04 Created: 2018-01-04 Last updated: 2018-06-09Bibliographically approved
Melder, J., Kwong, W. L., Shevela, D., Messinger, J. & Kurz, P. (2017). Electrocatalytic Water Oxidation by MnOx/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O2/CO2 Monitoring by Membrane-Inlet Mass Spectrometry. ChemSusChem, 10(22), 4491-4502
Open this publication in new window or tab >>Electrocatalytic Water Oxidation by MnOx/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O2/CO2 Monitoring by Membrane-Inlet Mass Spectrometry
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2017 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 22, p. 4491-4502Article in journal (Refereed) Published
Abstract [en]

Layers of amorphous manganese oxides were directly formed on the surfaces of different carbon materials by exposing the carbon to aqueous solutions of permanganate (MnO4- ) followed by sintering at 100-400 °C. During electrochemical measurements in neutral aqueous buffer, nearly all of the MnOx /C electrodes show significant oxidation currents at potentials relevant for the oxygen evolution reaction (OER). However, by combining electrolysis with product detection by using mass spectrometry, it was found that these currents were only strictly linked to water oxidation if MnOx was deposited on graphitic carbon materials (faradaic O2 yields >90 %). On the contrary, supports containing sp3 -C were found to be unsuitable as the OER is accompanied by carbon corrosion to CO2 . Thus, choosing the "right" carbon material is crucial for the preparation of stable and efficient MnOx /C anodes for water oxidation catalysis. For MnOx on graphitic substrates, current densities of >1 mA cm-2 at η=540 mV could be maintained for at least 16 h of continuous operation at pH 7 (very good values for electrodes containing only abundant elements such as C, O, and Mn) and post-operando measurements proved the integrity of both the catalyst coating and the underlying carbon at OER conditions.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
Keywords
carbon materials, electrocatalysis, manganese, mass spectrometry, oxides
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-142795 (URN)10.1002/cssc.201701383 (DOI)000416158500025 ()28869720 (PubMedID)
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2018-06-09Bibliographically approved
Kwong, W. L., Lee, C. C. & Messinger, J. (2017). Scalable Two-Step Synthesis of Nickel Iron Phosphide Electrodes for Stable and Efficient Electrocatalytic Hydrogen Evolution. The Journal of Physical Chemistry C, 121(1), 284-292
Open this publication in new window or tab >>Scalable Two-Step Synthesis of Nickel Iron Phosphide Electrodes for Stable and Efficient Electrocatalytic Hydrogen Evolution
2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 1, p. 284-292Article in journal (Refereed) Published
Abstract [en]

The development of efficient, durable, and inexpensive hydrogen evolution electrodes remains a key challenge for realizing a sustainable H-2 fuel production via electrocatalytic water splitting. Herein, nickel-iron phosphide porous films with precisely controlled metal content were synthesized on Ti foil using a simple and scalable two-step strategy of spray-pyrolysis deposition followed by low-temperature phosphidation. The nickel-iron phosphide of an optimized Ni:Fe ratio of 1:4 demonstrated excellent overall catalytic activity for hydrogen evolution reaction (HER) in 0.5 M H2SO4, achieving current densities of -10 and -30 mA cm(-2) at overpoteritials of 101 and 123 mV, respectively, with a Tafel slope of 43 mV dec(-1). Detailed analysis obtained by X-ray diffraction, electron microscopy, electrochemistry, and X-ray photoelectron spectroscopy revealed that the superior overall HER activity of nickel iron phosphide as compared to nickel phosphide and iron phosphide was a combined effect of differences in the morphology (real surface area) and the intrinsic catalytic properties (electronic structure). Together with a long-term stability and a near-100% Faradaic efficiency, the nickel-iron phosphide electrodes produced in this study provide blueprints for large-scale H-2 production.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-132028 (URN)10.1021/acs.jpcc.6b09050 (DOI)000392035500031 ()
Available from: 2017-04-02 Created: 2017-04-02 Last updated: 2018-06-09Bibliographically approved
Sharifi, T., Kwong, W. L., Berends, H.-M., Larsen, C., Messinger, J. & Wågberg, T. (2016). Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation. International journal of hydrogen energy, 41(1), 69-78
Open this publication in new window or tab >>Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation
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2016 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 1, p. 69-78Article in journal (Refereed) Published
Abstract [en]

A hybrid catalyst 3D electrode for electrochemical water oxidation to molecular oxygen is presented. The electrode comprises needle shaped maghemite nanorods firmly anchored to nitrogen doped carbon nanotubes, which in turn are grown on a conducting carbon paper that acts as efficient current collector. In 0.1 M KOH this hybrid electrode reaches a current density of 1 mA/cm(2) (geometric surface) at an overpotential of 362 mV performing high chronoamperometric stability. The electrochemical attributes point toward efficient catalytic processes at the surface of the maghemite nanorods, and demonstrate a very high surface area of the 3D electrode, as well as a firm anchoring of each active component enabling an efficient charge transport from the surface of the maghemite rods to the carbon paper current collector. The latter property also explains the good stability of our hybrid electrode compared to transition metal oxides deposited on conducting support such as fluorine doped tin oxide. These results introduce maghemite as efficient, stable and earth abundant oxygen evolution reaction catalyst, and provide insight into key issues for obtaining practical electrodes for oxygen evolution reaction, which are compatible with large scale production processes. 

Keywords
Nitrogen-doped carbon nanotubes, Maghemite, Hybrid catalyst, Water oxidation, 3D electrode
National Category
Materials Chemistry Other Chemistry Topics Other Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-130009 (URN)10.1016/j.ijhydene.2015.11.165 (DOI)000368955300005 ()
Available from: 2017-01-11 Created: 2017-01-11 Last updated: 2018-06-09Bibliographically approved
Sharifi, T., Larsen, C., Wang, J., Kwong, W. L., Gracia-Espino, E., Mercier, G., . . . Edman, L. (2016). Toward a Low-Cost Artificial Leaf: Driving Carbon-Based and Bifunctional Catalyst Electrodes with Solution-Processed Perovskite Photovoltaics. Advanced Energy Materials, 6(20), 1-10, Article ID 1600738.
Open this publication in new window or tab >>Toward a Low-Cost Artificial Leaf: Driving Carbon-Based and Bifunctional Catalyst Electrodes with Solution-Processed Perovskite Photovoltaics
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2016 (English)In: Advanced Energy Materials, ISSN 1614-6832, Vol. 6, no 20, p. 1-10, article id 1600738Article in journal (Refereed) Published
Abstract [en]

Molecular hydrogen can be generated renewably by water splitting with an artificial-leaf device, which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovoltaics. Ideally, this device should operate efficiently and be fabricated with cost-efficient means using earth-abundant materials. Here, a lightweight electrocatalyst electrode, comprising large surface-area NiCo2O4 nanorods that are firmly anchored onto a carbon-paper current collector via a dense network of nitrogen-doped carbon nanotubes is presented. This electrocatalyst electrode is bifunctional in that it can efficiently operate as both anode and cathode in the same alkaline solution, as quantified by a delivered current density of 10 mA cm(-2) at an overpotential of 400 mV for each of the oxygen and hydrogen evolution reactions. By driving two such identical electrodes with a solution-processed thin-film perovskite photovoltaic assembly, a wired artificial-leaf device is obtained that features a Faradaic H-2 evolution efficiency of 100%, and a solar-to-hydrogen conversion efficiency of 6.2%. A detailed cost analysis is presented, which implies that the material-payback time of this device is of the order of 100 days.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2016
Keywords
artificial-leaf devices, bifunctional electrocatalyst, carbon paper, nitrogen-doped carbon nanotubes, perovskite photovoltaics
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-128457 (URN)10.1002/aenm.201600738 (DOI)000387136300001 ()
Available from: 2017-01-11 Created: 2016-12-05 Last updated: 2019-10-17Bibliographically approved
Kwong, W. L., Lee, C. C. & Messinger, J. (2016). Transparent Nanoparticulate FeOOH Improves the Performance of a WO3 Photoanode in a Tandem Water-Splitting Device. The Journal of Physical Chemistry C, 120(20), 10941-10950
Open this publication in new window or tab >>Transparent Nanoparticulate FeOOH Improves the Performance of a WO3 Photoanode in a Tandem Water-Splitting Device
2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 20, p. 10941-10950Article in journal (Refereed) Published
Abstract [en]

Oxygen evolution catalysts (OEC) are often employed on the surface of photoactive, semiconducting photoanodes to boost their kinetics and stability during photoelectrochemical water oxidation. However, the necessity of using optically transparent OEC to avoid parasitic light absorption by the OEC under front-side illumination is often neglected. Here, we show that furnishing the surface of a WO3 photoanode with suitable loading of FeOOH as a transparent OEC improved the photocurrent density by 300% at 1 V versus RHE and the initial photocurrent-to-O-2 Faradaic efficiency from similar to 70 to similar to 100%. The data from the photo-voltammetry, electrochemical impedance, and gas evolution measurements these improvements were a combined result of reduced hole-transfer resistance for water oxidation, minimized surface recombination of charge carriers, and improved stability against photocorrosion of WO3. We demonstrate the utility of transparent FeOOH-coated W(O)3 in a solar-powered, tandem water-splitting device by combining it with a double-junction Si solar cell and a Ni-Mo hydrogen evolution catalyst. This device performed at a solar-to-hydrogen conversion efficiency of 1.8% in near-neutral K2SO4 electrolyte.

National Category
Botany
Identifiers
urn:nbn:se:umu:diva-123072 (URN)10.1021/acs.jpcc.6b02432 (DOI)000376840900022 ()
Available from: 2016-07-01 Created: 2016-06-27 Last updated: 2018-06-07Bibliographically approved
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