Abstract
Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires.
Highlights
Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future
The planar ZB gallium phosphide (GaP) surface is not insulated during experiments; it is expected from absorption measurements performed on nanowires, after transfer onto a poly-dimethyl-siloxane (PDMS) film (Supplementary Figs 3 and 4), that o15% of the current is due to the substrate
We note that our reference planar ZB GaP sample already shows similar VOC and ISC values compared with recently reported best values for planar ZB GaP21
Summary
Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Most semiconductors are limited to one side of the reaction[8,9] (Fig. 1a), due to their electronic band structure, or require an external bias to achieve water splitting[10,11,12,13] VOC ZB of 0.71 V (versus GaP21, and an reversible ISC of hydrogen electrode (RHE)) for 1.5 mA cm À 2 under AM1.5
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