Abstract
The heterostructuring and doping concepts have proved to obtain a novel n-InGaN/p-Cu2O nanowire (NW) photoanode by strong enhancement of the photocurrent compared to a bare InGaN NW photoanode in solar water splitting. The large photocurrent is due to the maximized photocarrier separation and hole transfer to the surface in the depletion zone of the p–n heterojunction established by the p-Cu2O layer, forming a thin, uniform shell-layer around the n-InGaN NW core by electrodeposition. For sufficiently thin Cu2O layers, the upward energy band bending in the depletion zone extends up to the surface for optimized hole transport and surface reaction. Thick Cu2O layers on top of the InGaN NWs act as common photocathodes. The functional InGaN/Cu2O heterostructure core-shell NW photoanode is chemically self-stabilized at positive applied voltage by a thin CuO surface layer. Final deposition of the earth-abundant NiOOH co-catalyst boosts the photocurrent of the InGaN/Cu2O/NiOOH complete NW photoanode into the competitive mA/cm2 range.
Highlights
The key strategies to boost the performance of photoelectrodes are nanostructuring, surface catalyst coupling, light management, heterostructuring, and doping to optimize the crucial processes of light absorption, photocarrier separation and transfer, and surface reaction [1, 2]
This is based on a previous study where we showed that Cu2O, a deeply studied p-type metal-oxide, acts as an efficient hole injection and a collection layer on In-rich InGaN NWs, solving the p-type conductivity problem [23]
Large enhancement of the photocurrent is achieved for a novel n-InGaN/p-Cu2O NW photoanode compared to a bare InGaN NW photoanode for the oxygen evolution reaction (OER) in solar water splitting
Summary
The key strategies to boost the performance of photoelectrodes are nanostructuring, surface catalyst coupling, light management, heterostructuring, and doping to optimize the crucial processes of light absorption, photocarrier separation and transfer, and surface reaction [1, 2]. Photogenerated carrier separation and transfer are strongly enhanced in the depletion zone of the p–n heterojunction formed at the n-InGaN/p-Cu2O heterointerface with positive band offset This is based on a previous study where we showed that Cu2O, a deeply studied p-type metal-oxide, acts as an efficient hole injection and a collection layer on In-rich InGaN NWs, solving the p-type conductivity problem [23]. Cu2O is electrodeposited on the InGaN NWs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) reveal that Cu2O forms a uniform shell-layer on the mplane InGaN NW sidewalls while nucleating as isolated Cu2O nanocrystals on the c-plane NW tops. For thin Cu2O layer deposition, the Cu2O shelllayers on the InGaN NWs are fully depleted for thicknesses of ∼10 nm with upward energy band bending up to the surface. CV measurements were performed in the voltage windows of −1 V to +1 V and 0 V to +1 V vs. Ag/AgCl with a 100 mV s−1 scan rate
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