Direct oxygen isotope effect identifies the rate-determining step of electrocatalytic OER at an oxidic surface

Abstract

Understanding the mechanism of water oxidation to dioxygen represents the bottleneck towards the design of efficient energy storage schemes based on water splitting. The investigation of kinetic isotope effects has long been established for mechanistic studies of various such reactions. However, so far natural isotope abundance determination of O2 produced at solid electrode surfaces has not been applied. Here, we demonstrate that such measurements are possible. Moreover, they are experimentally simple and sufficiently accurate to observe significant effects. Our measured kinetic isotope effects depend strongly on the electrode material and on the applied electrode potential. They suggest that in the case of iron oxide as the electrode material, the oxygen evolution reaction occurs via a rate-determining O−O bond formation via nucleophilic water attack on a ferryl unit.

The FeIVO• oxyl unit as a key intermediate in water oxidation on the FeIIIhydroxide: DFT predictions

“…The authors of cited work showed that the rate‐determining step of the OO bond formation is the nucleophilic water attack on a ferryl unit rather than a direct coupling of two ferryl units. Our computational data from the present and previous work are in a perfect agreement with these findings [20].…”

“…The same mechanism for water oxidation on iron oxide electrode was identified by means of direct isotope effect in a recent work by Haschke et al [20]. The authors of cited work showed that the rate‐determining step of the OO bond formation is the nucleophilic water attack on a ferryl unit rather than a direct coupling of two ferryl units.…”

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives

“…This hypothetical reaction mechanism was later supported by isotope labelling experiments and analyzing the O 2 products using isotope ratio mass spectroscopy. 203 With the combination of photoinduced absorption spectroscopy (PIA) and transient photocurrent spectroscopy (TPS), a first-order reaction was actually observed by Durrant et al when the illumination intensity was weak (Fig. 10c).…”

Dynamic oxygen adsorption on single-atomic Ruthenium catalyst with high performance for acidic oxygen evolution reaction

“…18), and the average Ru-N bond distance is obtained as 2.02 Å, which is in good agreement with the EXAFS fitting value. Generally, the conventional OER in an acidic medium involves four concerted proton–electron transfer steps on surface metal sites, generating three different intermediate adsorbates: OH * , O * , and OOH * (the asterisk denotes the adsorption site) 40 . As the Ru site is believed to be the catalytically active center, Fig.…”