Modulating charge transfer pathway via halide tuning of layered Bi-oxyhalides on an MOF-derived CuO nanorod photocathode

Abstract

Charge transfer pathways in heterojunctions are crucial for determining photoexcited charge generation, separation, and kinetics of surface reactions. Nature-inspired Z-scheme and type-I heterojunctions are the most sought mechanisms in photo-assisted processes aimed at charge separation and achieving higher photovoltages, thereby improving photoconversion efficiencies. Herein, we present a novel strategy to control the charge transfer pathway in p–n heterojunctions by modulating the halide in a metal oxyhalide combined with metal–organic framework (MOF)-templated CuO nanorods (M-CuO NRs). Charge transfer mechanisms and kinetics across p–n heterojunctions were systematically investigated using M-CuO NRs/BiOX (X = Cl, Br, and I) photocathodes for photoelectrochemical (PEC) hydrogen evolution reactions. Varying halide species led to transition in the charge transfer mechanism, resulting in distinct PEC conversion characteristics. Furthermore, J = −5.6 mA cm⁻² at 0 V_RHE and an HC-STH (%) of 0.95% at 0.34 V_RHE were achieved for M-CuO NRs/BiOI, while J = −5.1 mA cm⁻² at 0 V_RHE and an HC-STH (%) of 0.85% at 0.40 V_RHE were obtained for M-CuO NRs/BiOBr. Our findings demonstrate that modulating the halide in BiOX significantly impacts charge transfer pathways, enhancing PEC conversion kinetics and hydrogen evolution under solar irradiation. Comprehensive characterizations of M-CuO NRs/BiOX photoelectrodes were conducted, including crystalline structure, morphology, photoelectrochemical performance, and photophysical properties.