MOF-derived porous ZnO integrated with NiO and colloidal QDs for efficient hydrogen generation via a synergistic photoelectrochemical and electrochemical process

Abstract

Photoelectrochemical (PEC) water splitting is a promising approach for the conversion of solar energy to hydrogen fuel. However, the solar-to-hydrogen (STH) efficiency is still restricted by the kinetically sluggish oxidation reaction on the surface of the photoanode. Herein, a unique composite structure (ZnO@NiO–QDs) was developed as the photoanode, in which the highly dispersed ZnO (d-ZnO) particles derived from the pyrolysis of ZIF-8 serve as the scaffolds to support NiO (cocatalysts) and colloidal CdSe(CdSe_xS_1−x)₄(CdS)₂ QDs (denoted as CAS, a light absorber). Due to the enhanced hole consumption accelerated by NiO cocatalysts, the optimized photoanode (d-ZnO@NiO_0.03–CAS) exhibits a higher saturated current density (J_sc) of 21.7 mA cm⁻² than the d-ZnO–CAS photoanode (15.6 mA cm⁻²) under standard one sun (AM 1.5 G, 100 mW cm⁻²) solar irradiation. More importantly, such an electrode can still work as an electrocatalyst under light-off conditions via a sole electrochemical (EC) process. Thus, a well-designed bifunctional electrode that integrates cocatalysts and light absorbers makes it possible to generate hydrogen efficiently under both light-on and light-off conditions, providing an efficient and low-cost paradigm to improve the hydrogen evolution performance.