Unveiling the effect of the structural transformation of CoZn-MOF on BiVO4 photoanode for efficient photoelectrochemical water oxidation

Abstract

Photoelectrochemical (PEC) water splitting has been widely investigated for solar-to-hydrogen conversion. However, issues like high charge recombination rate and slow surface water oxidation kinetics severely hinder its (PEC) conversion efficiency. Herein, we constructed MOF-derived CoOOH cocatalyst on BiVO4 photoanode, using a feasible electrochemical activation strategy. The BiVO4-based photoanode obtained shows a high photocurrent density of 3.15 mA/cm2 at 1.23 VRHE and low onset potential. Detailed experiments and theoretical calculations show that during the activation of CoZn-MOFs, there was a partial breakage of 2-methylimidazole (mIM) linker, an increase in the oxidation state of Cobalt ion (Co), and increased O2–. The high PEC performance is mainly attributed to the MOF-derived CoOOH, which provides rich active sites for hole extraction and reduces the overpotential for oxygen evolution reaction. Furthermore, when CoZnNiFe-LDHs were decorated on BiVO4 using the ions exchange method, the photocurrent density of BiVO4/CoZnNiFe-LDHs photoanode got to 4.0 mA/cm2 at 1.23 VRHE, accompanied with high stability. This study provides insights into understanding the key role played by the structural transformation of MOF cocatalyst in PEC water splitting processes.