A homogeneous cobalt complex mediated electro and photocatalytic O(2)/H(2)O interconversion in neutral water

The O(2)/H(2)O 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 O(2) via two distinct pathways: a two-electron O(2)/H(2)O(2) reduction (catalytic rate = 250 s(−1)) and a four-electron O(2) to H(2)O 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 O(2) (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 Na(2)S(2)O(8)/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.