MOF-Based Transparent Passivation Layer Modified ZnO Nanorod Arrays for Enhanced Photo-Electrochemical Water Splitting

This study introduces zeolitic imidazolate framework-8 (ZIF-8) as the first metal-organic framework based transparent surface passivation layer for photo-electrochemical (PEC) water splitting. A significant enhancement for PEC water oxidation is demonstrated based on the in situ seamless coating of ZIF-8 surface passivation layer on Ni foam (NF) supported ZnO nanorod arrays photoanode. The PEC performance is improved by optimizing the ZIF-8 thickness and by grafting Ni(OH)₂ nanosheets as synergetic co-catalyst. With respect to ZnO/NF, the optimized Ni(OH)₂/ZIF-8/ZnO/NF photoanode exhibits a two times larger photocurrent density of 1.95 mA cm⁻² and also a two times larger incident photon to current conversion efficiency of 40.05% (350 nm) at 1.23 V versus RHE (V_RHE) under AM 1.5 G. The synergetic surface passivation and the co-catalyst modification contribute to prolonging the charge lifetime, to promoting the charge transfer, and to decreasing the overpotential for water oxidation.