Stable Solar-Driven Water Oxidation to O2(g) by Ni-Oxide-Coated Silicon Photoanodes

Semiconductors with small band gaps (<2 eV) must be stabilized against corrosion or passivation in aqueous electrolytes before such materials can be used as photoelectrodes to directly produce fuels from sunlight. In addition, incorporation of electrocatalysts on the surface of photoelectrodes is required for efficient oxidation of H2O to O-2(g) and reduction of H2O or H2O and CO2 to fuels. We report herein the stabilization of np(+)-Si(100) and n-Si(111) photoanodes for over 1200 h of continuous light-driven evolution of O-2(g) in 1.0 M KOH(aq) by an earth-abundant, optically transparent, electrocatalytic, stable, conducting nickel oxide layer. Under simulated solar illumination and with optimized index-matching for proper antireflection, NiOx-coated np(+)-Si(100) photoanodes produced photocurrent-onset potentials of -180 +/- 20 mV referenced to the equilibrium potential for evolution of O-2(g), photocurrent densities of 29 +/- 1.8 mA cm(-2) at the equilibrium potential for evolution of O-2(g), and a solar-to-O-2(g) conversion figure-of-merit of 2.1%.