Water oxidation on a sustainable polymeric proton relay: the role of post-phosphating of an oxide sub-layer on PCET

Abstract

Lagging proton transfer (PT) toward electron transfer (ET) during multi-step proton-coupled electron transfer (PCET) is one of the humble approaches toward complete biomimicking of artificial leaves. In this work, we synthesized a typical sustainable polymeric interface (poly L-lysine) to investigate the effect of post-phosphating of the metal oxide substrate (NF/CoMoO₄) on the yield of PCET during the electrocatalytic water oxidation reaction (WOR) in alkaline medium. The details of the PCET mechanism are unraveled using the kinetic isotope effect (KIE), proton inventory, Tafel slopes, pH studies, and high-frequency transmission line (Gerischer) impedance. The appealing Gerischer feature unveils an electrochemical reaction preceded and followed by a chemical exchange reaction (CEC mechanism), indicating a proton hopping mechanism that practically blocks natural diffusion of the protonic species (H⁺ and H₂O) and the role of the interfacial phosphate#p-Lys hydrogen bond network (HBN) in PCET. The interfacial HBN can serve as a flexible proton hook to delocalize protons and may polarize the O–O bond, thereby facilitating the overall PCET for the progress of O–O bond formation. Poly L-lysine improved the response stability of the PCET catalyst through corrosion protection of the metallic substrate and also prevention of the spatiotemporal accumulation of protons as a surface corrosion agent. The results show a non-concerted PCET mechanism with the first ET step as the RDS of the heterogeneous WOR.