Biomimetic Second Coordination Sphere Effect within Cu-Peptoid Electrocatalyst Enables Homogeneous Water Oxidation at pH 7

A dinuclear Cu-peptoid, Cu₂(<b>BDiE</b>)₂, having a diol side chain was developed as a homogeneous electrocatalyst for oxygen evolution reaction (OER) at neutral pH. The molecular structure of Cu₂(<b>BDiE</b>)₂ was characterized and concluded by ESI-MS, UV-vis, and single-crystal X-ray diffraction. Electrochemical, spectroscopic, and mechanistic studies revealed that borate buffer (the solution medium) has a minor effect during electrocatalysis; however, the diol side chain promotes a second coordination sphere effect via multiple hydrogen bonds which highly stabilize the complex, leading to an OER. Based on these observations and the collected data, we also suggest two different and unique mechanism pathways: a major one, which involves interactions of radical intermediates, which is buffer independent, and a minor one that resembles water nucleophilic attack (WNA) and is assisted by the borate buffer.