Scaling Relation between the Reduction Potential of Copper Catalysts and the Turnover Frequency for the Oxygen and Hydrogen Peroxide Reduction Reactions

Abstract

Changes in the electronic structure of copper complexes can have a remarkable impact on the catalytic rates, selectivity, and overpotential of electrocatalytic reactions. We have investigated the effect of the half-wave potential (E 1/2) of the CuII/CuI redox couples of four copper complexes with different pyridylalkylamine ligands. A linear relationship was found between E 1/2 of the catalysts and the logarithm of the maximum rate constant of the reduction of O2 and H2O2. Computed binding constants of the binding of O2 to CuI, which is the rate-determining step of the oxygen reduction reaction, also correlate with E 1/2. Higher catalytic rates were found for catalysts with more negative E 1/2 values, while catalytic reactions with lower overpotentials were found for complexes with more positive E 1/2 values. The reduction of O2 is more strongly affected by the E 1/2 than the H2O2 rates, resulting in that the faster catalysts are prone to accumulate peroxide, while the catalysts operating with a low overpotential are set up to accommodate the 4-electron reduction to water. This work shows that the E 1/2 is an important descriptor in copper-mediated O2 reduction and that producing hydrogen peroxide selectively close to its equilibrium potential at 0.68 V vs reversible hydrogen electrode (RHE) may not be easy.

A cobalt molecular catalyst for hydrogen evolution reaction with remarkable activity in phosphate buffered water solution

“…3) suggesting that the same reaction mechanism is reasonably active and the structural differences of complexes systematically tune the free energies of intermediates and reaction steps of the catalytic cycle. 89–94 Our DFT computational results are in line with this hypothesis ( vide infra ).…”

Integrated Experimental and Theoretical Investigation of Copper Active Site Properties of a Lytic Polysaccharide Monooxygenase from Serratia marcescens

“…A recent investigation has reported that binding of the polysaccharidic substrate increases the redox potential of a fungal AA9 LPMO . Interestingly, the E 1/2 of the Cu­(II)/Cu­(I) redox couple of small copper-containing complexes was shown to correlate with the binding energy of O 2 to Cu­(I) with more electron-rich copper centers (lower redox potentials) binding O 2 more strongly . In the same study, a relation has been established between the E 1/2 and the ability to electrochemically reduce O 2 vs H 2 O 2 and it was observed that increasing E 1/2 lowers the electrocatalytic rate for both O 2 and H 2 O 2 reduction but in a different extent, leading to a change in the relative magnitude between both reactions.…”