A bio-inspired coordination polymer as outstanding water oxidation catalyst via second coordination sphere engineering

Abstract First-row transition metal-based catalysts have been developed for the oxygen evolution reaction (OER) during the past years, however, such catalysts typically operate at overpotentials ( η ) significantly above thermodynamic requirements. Here, we report an iron/nickel terephthalate coordination polymer on nickel form ( NiFeCP/NF ) as catalyst for OER, in which both coordinated and uncoordinated carboxylates were maintained after electrolysis. NiFeCP/NF exhibits outstanding electro-catalytic OER activity with a low overpotential of 188 mV at 10 mA cm −2 in 1.0 KOH, with a small Tafel slope and excellent stability. The pH-independent OER activity of NiFeCP/NF on the reversible hydrogen electrode scale suggests that a concerted proton-coupled electron transfer (c-PET) process is the rate-determining step (RDS) during water oxidation. Deuterium kinetic isotope effects, proton inventory studies and atom-proton-transfer measurements indicate that the uncoordinated carboxylates are serving as the proton transfer relays, with a similar function as amino acid residues in photosystem II (PSII), accelerating the proton-transfer rate.