A homogeneous cobalt complex mediated electro and photocatalytic O/HO interconversion in neutral water.

The O/HO redox couple is vital in various renewable energy conversion strategies. This work delves into the Co(L-histidine) 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 O via two distinct pathways: a two-electron O/HO reduction (catalytic rate = 250 s) and a four-electron O to HO production (catalytic rate = 66 s). The formation of the key -μ-1,2-Co(III)-peroxo intermediate expedites this process. Additionally, this complex effectively oxidizes water to O (catalytic rate = 15606 s) 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 NaSO/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.