A microstructured p-Si photocathode outcompetes Pt as a counter electrode to hematite in photoelectrochemical water splitting

Herein, we communicate about an Earth-abundant semiconductor photocathode(p-Si/TiO2/NiOx) as an alternative for the rare and expensive Pt as a counter electrode for overall photoelectrochemical water splitting. The proposed photoelectrochemical (PEC) water-splittingdevice mimics the “Z”-scheme observed in natural photosynthesis by combining two photoelectrodes in a parallel-illumination mode. A nearly 60% increase in the photocurrentdensity (Jph) for pristine α-Fe2O3 and a 77% increase in the applied bias photocurrentefficiency (ABPE) were achieved by replacing the conventionally used Pt cathode with an efficient, cost effective p-Si/TiO2/NiOx photocathodeunder parallel illumination. The resulting photocurrentdensity of 1.26 mA cm−2 at 1.23VRHE represents a new record performance for hydrothermally grown pristine α-Fe2O3 nanorod photoanodes in combination with a photocathode, which opens the prospect for further improvement by doping α-Fe2O3 or by its decoration with co-catalysts. Electrochemical impedance spectroscopy measurements suggest that this significant performance increase is due to the enhancement of the space-charge field in α-Fe2O3.