Metal-Metal Bonding Dynamics of Anode Materials for Oxygen Evolution Reaction (OER) in Basic Electrolyte Studied By Using in Situ Surface Stress Measurements

The electrochemical splitting of water offers an attractive way to provide a carbon-free source of hydrogen, however the efficiency is limited primarily by the overpotential of the anodic oxygen evolution reaction (OER, 4OH^-→ 2H₂O + 4e^- + O₂).¹

Knowledge of oxide formation prior and during the OER is essential for understanding the mechanism and electrocatalysts. Extensive studies on the composition and morphology of metal and oxide electrodes in the OER by Raman,² XAS,³ and QCM⁴have been reported. However, there is no reported technique to directly interrogate the oxide film during potential cycling or its evolution over time and multiple electrochemical cycles.            

In this work, in situ electrochemical stress measurements are used to interrogate changes in oxide structure before and during the oxygen evolution reaction (OER) from Ir, Ni, Co, Au, and Pt electrodes in alkaline electrolyte. Stress evolution during potential cycling reports on changes in oxidation state and oxide forms. Hysteresis observed in the potential - dependent stress from Ir, Au, and Pt electrodes is associated with chemical irreversibility in electrode composition and roughness. Alternatively, Ni and Co exhibit reversible conversion between hydroxide and oxyhydroxide forms during cycling. From the experimentally determined stress, charge passed during electrode oxidation, and Young’s modulus, the change in strain exhibited by Ni and Co electrodes during hydroxide-oxyhydroxide conversion is calculated to be 7.0% and 8.4%, respectively. We also show that the magnitude of change in stress is proportional to the amount of material that is further oxidized. The similarity between processes yielding higher oxides and those involved with the OER mechanism yields are a rough correlation between film thickness and OER onset.⁵

Finally, we report the effect of electrodeposition additives to modify electrodeposited OER-active films to achieve high electrocatalyst efficiency for this reaction.

References

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(5) Hoang, T. T. H.; Cohen, Y.; Gewirth, A. A. Analytical Chemistry 2014, 86, 11290-11297.