A homogeneous cobalt complex mediated electro and photocatalytic O2/H2O interconversion in neutral water

Abstract

The O2/H2O redox couple is vital in various renewable energy conversion strategies. This work delves into the Co(L-histidine)2 complex, a functional mimic of oxygen-carrying metalloproteins, and its electrochemical behavior driving the bidirectional oxygen reduction (ORR) and oxygen evolution (OER) activity in neutral water. This complex electrocatalyzes O2 via two distinct pathways: a two-electron O2/H2O2 reduction (catalytic rate= 250 s-1) and a four-electron O2 to H2O production (catalytic rate= 66 s-1). The formation of the key trans-μ-1,2-Co(III)-peroxo intermediate expedites this process. Additionally, this complex effectively oxidizes water to O2 (catalytic rate= 15606 s-1) at anodic potentials via a Co(IV)-oxo species. Additionally, this complex executes the ORR and OER under photocatalytic conditions in neutral water in the presence of appropriate photosensitizer (Eosin-Y) and redox mediators (triethanolamine/ORR and Na2S2O8/OER) at an appreciable rate. These results highlight one of the early examples of both electro- and photoactive bidirectional ORR/OER catalysts operational in neutral water.