Regulating a Zn/Co bimetallic catalyst in a metal–organic framework and oxyhydroxide for improved photoelectrochemical water oxidation

Abstract

As one of the most popular photoanode materials, hematite (α-Fe₂O₃) has obvious advantages in the field of photoelectrochemical water splitting (PEC-WS). However, it is difficult to achieve excellent PEC-WS performance without loading a cocatalyst serving as an electron/hole collector to promote photogenerated carrier separation. In this work, FTO/Sn@α-Fe₂O₃ photoanodes are modified with ZnCo-ZIF and ZnCoOOH bimetallic catalysts to obtain FTO/Sn@α-Fe₂O₃/Zn_0.5Co_0.5-ZIF and FTO/Sn@α-Fe₂O₃/Zn_0.46Co_0.54OOH photoanodes. Their photocurrent densities reach 2.6 mA cm⁻² and 2.3 mA cm⁻² at 1.23 V_RHE, respectively. The detailed mechanism studies demonstrate that both ZnCoOOH and ZnCo-ZIF can effectively decrease the transfer resistance, increase the Fe²⁺/Fe³⁺ ratio and reduce the charge recombination of the α-Fe₂O₃ film, which synergistically improves the PEC-WS performance. Compared with ZnCoOOH, the ZnCo-ZIF exhibits better photogenerated carrier transfer efficiency and catalytic performance, which mainly can be attributed to the improved binding energy between the ZnCo-ZIF catalyst and the α-Fe₂O₃ film. This work provides a simple and feasible strategy for constructing bimetallic catalysts and deepens the understanding of different types of bimetallic catalysts for high-performance PEC-WS systems.