Advancing Kesterite-Based Photocathodes for Water Splitting and Beyond

Converting the solar energy to storable and transportable chemicals via photoelectrochemical (PEC) reactions offers unique advantages of overcoming the intermittence features of solar irradiation. Kesterites have long been ideal candidates standing as cost-efficient, environmental-friendly, and efficient semiconductor photoelectrode materials for PEC solar fuel production. With significant progress made in hydrogen production, there is increasing attention paid to extending the applications in CO₂ reduction, ammonia synthesis, etc. However, when designing efficient kesterite based photoelectrodes (i.e. Cu₂ZnSnS₄ (CZTS)) for water splitting and beyond, it is crucial to make comprehensive consideration on both photoelectrode activity and reaction selectivity.<br/>Our works elaborate the strategies on rationally design the kesterite based photoelectrodes by both optimising photoactivity in terms of photogenerated charge migration and regulating the surface catalytic sites. Specifically, it demonstrates the successful application of CZTS photocathode in CO₂ reduction with enhanced photoactivity by post heat treatment and controllable selectivity towards CO and alcohols by surface S vacancy regulation. In addition, it also extends the application of CZTS photocathode into NOx reduction to ammonia by rationally incorporating a TiOx cocatalyst with optimal surface oxygen vacancy. Powered by the CZTS based solar cells, standalone solar to ammonia synthesis was achieved with Co-TiOx/Ag/TiOx/CdS/CZTS photocathode, leading to nearly 100% of ammonia faradaic efficiency. More recently, by replacing the toxic CdS buffer layer with the environmental-friendly and cost-effective ZnSnO buffer layer, a competitive half-cell solar to hydrogen conversion efficiency of more than 5.2 % has been achieved.<br/>These findings have brought important insights into rationally designing kesterite based photoelectrodes for advancing their PEC applications to achieve both enhanced activity and target product selectivity.