Keywords: hydrogen, solar energy, water splitting, Si
Summary:The use of silicon, one of the most earth-abundant materials, for photoelectrochemical water splitting has been intensively studied. To date, however, their practical applications have been limited by the low efficiency and instability related issues. Recently, metal-nitride nanowire photoelectrodes have drawn considerable attention, which exhibit several unique advantages compared to conventional metal-oxide and other semiconductor photocatalysts/photoelectrodes. The energy bandgap of metal-nitrides, e.g. Ga(In)N can be tuned across nearly the entire solar spectrum, and their conduction and valence band edges can straddle water redox potentials over a wide range of alloy compositions. Importantly, Ga(In)N materials have been widely used in the photonics, lighting, and electronics industries, with proven scaled-up production. We have demonstrated that the quantum efficiency of solar-to-hydrogen conversion on Ga(In)N nanowires can be enhanced by nearly two orders of magnitude through careful control of the surface charge properties. We have further demonstrated an integrated Si/GaInN nanowire photoelectrode system that can lead to significantly enhanced efficiency and stability in strong acidic solution. The nanowire/Si photocathode exhibits an applied bias photon-to-current efficiency of 8.7% and nearly unity Faradaic efficiency for H2 production.