Cellular heterojunctions fabricated through the sulfurization of MOFs onto ZnO for high-efficient photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting offers a promising way for producing clean and renewable hydrogen fuel, but how to improve the solar conversion efficiency is still a challenge. Herein, the sulfurization of metal organic frameworks (MOFs) onto the semiconductor ZnO to fabricate heterojunctions for PEC water oxidation was proposed. Cellular ZnO@ZnS, ZnO@CoS, and ZnO@ZnS/CoS heterostructured catalysts thus obtained through the direct sulfurization of ZnO@zeolitic-imidazolate-frameworks (ZnO@ZIFs) composites exhibit excellent PEC performances. Particularly, the ZnO@ZnS/CoS represents a largely improved photoconversion efficiency (0.65% at 0.14 V) and photocurrent density (2.46 mA cm(-2) at 0.6 V) under full spectrum illumination, outperforming those of previously reported ZnO-based catalysts in neutral medium. Clearly, their special cellular structure affords rich exposed active sites and long incident photon transport pathway for well light absorption. And, the suitable band matching with strong electronic coupling in the integrated heterojunctions facilitates the effective electron-hole separation. Furthermore, CoS acting as co-catalyst can speed up the hole transfer and simultaneously participate in the surface water oxidation, which leads to the lower oxygen evolution barrier for ZnO@CoS and ZnO@ZnS/CoS. This MOF-derivative decoration approach could be expanded to fabricate other composite photoanodes for a variety of energy storage and conversion applications.