The role and evolutionary pathway of spin states in CoFe Prussian blue analogues for photo-assisted water oxidation electrocatalysis

Abstract

The investigation of the mechanism underlying spin crossover (SCO) compounds as oxygen evolution reaction (OER) catalysts has become a novel research area in recent years. The intermetallic charge transfer (IMCT) process, involving transitions between spin states, has been recently reported as an effective method to address the linear-scaling relationships in the OER. However, the impacts of the proportion and variation of spin states on the OER process have not been systematically studied. Here, we synthesized CoFe Prussian blue analogs (PBAs) with different spin states and analyzed the variation of their electrochemical behaviors, spin states, oxidation states, electronic spectrum, and open-circuit potential during the photo-assisted OER process. Our findings reveal that the enhanced current density under irradiation is not only derived from the IMCT process but also from the photoelectrochemical process. The proportion of the two reaction pathways’ contribution to the photo-assisted current density enhancement is directly related to the ratio of the low-spin state in CoFe PBAs. This study provides valuable insights into the role of spin states in the OER process and paves the way for the development of efficient SCO compound-based OER catalysts.