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-Fe 2 O 3 ) 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-Fe 2 O 3 photoanodes are modified with ZnCo-ZIF and ZnCoOOH bimetallic catalysts to obtain FTO/Sn@α-Fe 2 O 3 /Zn 0.5 Co 0.5 -ZIF and FTO/Sn@α-Fe 2 O 3 /Zn 0.46 Co 0.54 OOH 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 Fe 2+ /Fe 3+ ratio and reduce the charge recombination of the α-Fe 2 O 3 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-Fe 2 O 3 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. A hematite photoanode modified with a ZnCo-ZIF bimetallic catalyst exhibits a higher photocurrent density than that with ZnCoOOH due to the larger binding energy between ZnCo-ZIF and α-Fe 2 O 3 for facilitating charge transfer.