Evaluation of Sputtered Nickel Oxide, Cobalt Oxide and Nickel-Cobalt Oxide on n-type Silicon Photoanodes for Solar-Driven O2(g) Evolution from Water

Thin films of nickel oxide (NiOx), cobalt oxide (CoOx) and nickel-cobalt oxide (NiCoOx) were sputtered onto n-Si(111) surfaces to produce a series of integrated, protected Si photoanodes that did not require deposition of a separate heterogeneous electrocatalyst for water oxidation. The p-type transparent conductive oxides (p-TCOs) acted as multi-functional transparent, antireflective, electrically conductive, chemically stable coatings that also were active electrocatalysts for the oxidation of water to O-2(g). Relative to the formal potential for water oxidation to O-2,E-o '(O-2/H2O), under simulated Air Mass (AM)1.5 illumination the p-TCO-coated n-Si(111) photoanodes produced mutually similar open-circuit potentials of -270 +/- 20 mV, but different photocurrent densities atE(o)'(O-2/H2O), of 28 +/- 0.3 mA cm(-2)for NiOx, 18 +/- 0.3 mA cm(-2)for CoO(x)and 24 +/- 0.5 mA cm(-2)for NiCoOx. The p-TCOs all provided protection from oxide growth for extended time periods, and produced stable photocurrent densities from n-Si in 1.0 M KOH(aq) (ACS grade) under potential control atE(o)'(O-2/H2O) for >400 h of continuous operation under 100 mW cm(-2)of simulated AM1.5 illumination.