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.
Highlights
First-row transition metal-based catalysts have been developed for the oxygen evolution reaction (OER) during the past years, such catalysts typically operate at overpotentials (η) significantly above thermodynamic requirements
The Ni-Fe coordination polymer (NiFeCP)/Ni foam (NF) electrode was prepared via a repeated doublecurrent pulse chronopotentiometry (Supplementary Fig. 1)
The OER electrocatalytic performances of the NiFeCP/NF prepared with different Ni:Fe ratios in the electrodeposition solution were measured, as presented in the linear sweep voltammograms (LSVs) in Supplementary Fig. 2a
Summary
First-row transition metal-based catalysts have been developed for the oxygen evolution reaction (OER) during the past years, such catalysts typically operate at overpotentials (η) significantly above thermodynamic requirements. The evolution of oxygen by OEC is an integrated process, involving the Mn4CaO5 cluster as catalyst, and is assisted by other functional groups in the first and second coordination spheres, such as carboxylate and imidazole ligands from amino-acid residues of the protein backbone[8,9]. These electron-rich ligands strongly stabilize the high valent states of the Mn4CaO5 cluster and play vital roles in effective water oxidation with low overpotential[7,10]. These secondcoordination-sphere effects can be introduced to the heterogeneous OER catalysts
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