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

As one of the most popular photoanode materials, hematite (α-FeO) 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-FeO photoanodes are modified with ZnCo-ZIF and ZnCoOOH bimetallic catalysts to obtain FTO/Sn@α-FeO/ZnCo-ZIF and FTO/Sn@α-FeO/ZnCoOOH photoanodes. Their photocurrent densities reach 2.6 mA cm and 2.3 mA cm at 1.23 V, respectively. The detailed mechanism studies demonstrate that both ZnCoOOH and ZnCo-ZIF can effectively decrease the transfer resistance, increase the Fe/Fe ratio and reduce the charge recombination of the α-FeO 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-FeO 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.