Photo-electrochemical hydrogen production from neutral phosphate buffer and seawater using micro-structured p-Si photo-electrodes functionalized by solution-based methods
SUSTAINABLE ENERGY & FUELS 2018, 2(19):2215-2223
Kawde A, Annamalai A, Amidani L, Boniolo M, Kwong WL, Sellstedt A, Glatzel P, Wagberg T, Messinger J

Abstract
Solar fuels such as H-2 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 photo-electrodes (p-Si/TiO2) that were functionalized with CoOx and NiOx for H-2 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 cm(-2) at zero bias (0 V-RHE), 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 H-2 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 K-1 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 H-2-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 cm(-2) at an applied potential of -0.7 V-RHE, and of 20 mA cm(-2) at -0.9 V-RHE. The applied bias photon-to-current conversion efficiency (ABPE) at -0.7 V-RHE and 10 mA cm(-2) was found to be 5.1%.

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