Cuprous Oxide Photocathodes For Photoelectrochemical Water Splitting

Photocatalysis has recently received a great deal of attention due to its potential to solve the energy crisis and environmental pollution by directly transforming solar energy into chemical energy,which offers a promising method to use solar energy.Photoelectrochemical?PEC?water splitting is one of the promising technologies for environmental friendly and renewable hydrogen production.Therefore,the design of stable photocatalysts with high activities for PEC hydrogen evolution is urgently needed.Cuprous oxide is considered as one of the most promising p-type semiconductor photocathodes in solar water splitting due to its abundance,nontoxicity and appropriate band gap of 2.0 eV with favorable energy band positions.However,the application of cuprous oxide photocathodes are limited to relatively negative onset potential and their photocurrent densities still fall well below the theoretical value of-14.7 mA/cm² under AM 1.5G.Therefore,it is urgently demanded to enhance the PEC performance of cuprous oxide photocathodes.Firstly,we investigated the property of cuprous oxide homojunction photocathode for solar water splitting.This study describes a facile electrodeposition process to construct the homogenous p-n junction,which can significantly increase the built-in potential and decrease the interface defects for efficient charge separation.Compared with the heterogeneous Schottky junction counterpart,this homojunction can achieve an anodic onset potential shift of 400 mV and a photocurrent of-4.30mA/cm² at 0 V vs.RHE under AM 1.5G.It is a valid method to construct efficient photocathodes with cuprous oxide homojunction that is superior to cuprous oxide Schottky junction.Then,we explored the influence of hole transfer layer for cuprous oxide photocathodes.Cuprous oxide has a large work fuction.It is likely to form Schottky junction with substrate,thus blocking the photogenerated hole and limiting the PEC activity.Nickel oxide is a favourable hole transfer material and it can extract the holes from cuprous oxide rapidly,which can reduce the recombination of photogenerated electrons and holes.The NiO hole transfer layer is introduced to form an Ohmic back contact to Cu₂O,thus achieving a positive onset potential of 0.61 V vs.reversible hydrogen electrode and a two-fold increase of solar conversion efficiency.It is an efficient way to improve the PEC performance of cuprous oxide photocathodes by modifying them with nickel oxide hole transfer layer.