A homogeneous cobalt complex mediated electro and photocatalytic O2/H2O 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.