| 1. |
- Kawde, Anurag, et al.
(författare)
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Photo-electrochemical hydrogen production from neutral phosphate buffer and seawater using micro-structured p-Si photo-electrodes functionalized by solution-based methods
- 2018
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 2:10, s. 2215-2223
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Tidskriftsartikel (refereegranskat)abstract
- 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%
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| 2. |
- Kwong, Wai Ling, et al.
(författare)
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Critical Role of {002} Preferred Orientation on Electronic Band Structure of Electrodeposited Monoclinic WO3 Thin Films
- 2018
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Ingår i: Sustainable Energy & Fuels. - 2398-4902. ; 2:10, s. 2224-2236
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Tidskriftsartikel (refereegranskat)abstract
- Monoclinic WO3 films with tunable (002) and (200) orientations parallel to fluorinedoped tin oxide substrates were electrodeposited from peroxotungstic acid (PTA) solutions and subjected to annealing (≤500°C). It is concluded that the crystallographic orientations of the films are dependent on the nucleation density and the thermal-induced recrystallisation kinetics, which can be controlled respectively by the tungsten concentration of the PTA solution and the annealing conditions. This approach allows the fabrication of films with preferred (002), equally mixed (002) and (200), and (200) orientations, which were characterised in terms of the associated mineralogical, nanostructural, optical, chemical, photoelectrochemical, and photocatalytic properties. The present work decouples the concurrent effects of crystallographic orientation and trend in oxygen vacancy concentration on the optical indirect band gap of WO3 thin films, where the linear correlation between these three variables can be used as a diagnostic tool to engineer the electronic band structure of films for applications requiring photosensitivities in different regions of the solar spectrum. In effect, a low valence band maximum, low oxygen vacancy concentration, and resultant low band gap associated with (002) preferred orientation results in the highest photoelectrochemical performance, which is relevant to applications under solar illumination. In contrast, a high concentration of oxygen vacancies, which act as surface reaction sites associated with (200) preferred orientation, results in the highest efficiency in the photodegradation of methylene blue, which is relevant to applications under UV illumination.
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| 3. |
- Kwong, Wai Ling, et al.
(författare)
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High-performance iron (III) oxide electrocatalyst for water oxidation in strongly acidic media
- 2018
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Ingår i: Journal of Catalysis. - : Academic Press. - 0021-9517 .- 1090-2694. ; 365, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Stable and efficient oxygen evolution reaction (OER) catalysts for the oxidation of water to dioxygen in highly acidic media are currently limited to expensive noble metal (Ir and Ru) oxides since presently known OER catalysts made of inexpensive earth-abundant materials generally suffer anodic corrosion at low pH. In this study, we report that a mixed-polymorph film comprising maghemite and hematite, prepared using spray pyrolysis deposition followed by low-temperature annealing, showed a sustained OER rate (>24 h) corresponding to a current density of 10 mA cm−2 at an initial overpotential of 650 mV, with a Tafel slope of only 56 mV dec−1 and near-100% Faradaic efficiency in 0.5 M H2SO4 (pH 0.3). This performance is remarkable, since iron (III) oxide films comprising only maghemite were found to exhibit a comparable intrinsic activity, but considerably lower stability for OER, while films of pure hematite were OER-inactive. These results are explained by the differences in the polymorph crystal structures, which cause different electrical conductivity and surface interactions with water molecules and protons. Our findings not only reveal the potential of iron (III) oxide as acid-stable OER catalyst, but also highlight the important yet hitherto largely unexplored effect of crystal polymorphism on electrocatalytic OER performance.
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