Hydrogen generation from electrolysis of water using renewable energy sources provides a sustainable pathway toward storing electrical energy from renewable sources in the form of chemical bonds. Among the two half-cell reactions involved in water splitting, the anodic oxygen evolution reaction (OER) requires electric potentials significantly higher than the thermodynamic limit to achieve desirable electrochemical rates on the state-of-the-art IrO2 electrocatalysts, making it a prime source of inefficiency. As such development of cost effective, active, and stable electrocatalyst for oxygen evolution has been of central interest in the recent years. We have focused on the use of non-stoichiometric mixed ionic and electronic conducting metal oxide electrocatalysts as potential alternatives to IrO2. In alkaline OER, we show through variations in the A- and B-sites of non-stochiometric mixed metal oxides (n = 1 (A2BO4) or n = ∞ (ABO3); A = La, Sr, Ca; B = Mn, Fe, Co, Ni), that surface restructuring universally governs their OER performance and is influenced by their initial composition. Irreversible A-site cation dissolution is observed which triggers surface restructuring resulting in the in-situ generation of a transition metal-based oxyhydroxide shell on top of the parent oxide. This newly generated surface structure serves as the active surface for OER. Among the generated 3d transition metal oxyhydroxide structures from An+1BnO3n+1 oxides, Co-based structures are found to exhibit superior OER performance, indicating the generation of active surface structures through oxide restructuring. In the case of acid OER, through A-site variations in Ru-based mixed metal oxides (ABO3 or A2B2O7; A = alkaline earth metal and/or lanthanide cation; B = Ru), we find that A2Ru2O7 oxides provide the best compromise between activity and stability, and this highly depends on the composition of the A site cation. Using a combination of electrochemical measurements, mass spectrometry, and X-ray based spectroscopic analyses, we provide an understanding of the structural evolution of these oxide surfaces in relation to their structure. In general, our findings suggest that under oxidative potentials at solid/liquid interfaces, the surface of non-stoichiometric mixed metal oxides is dynamic and evolves which makes understanding of the evolution mechanism critical toward developing effective design criteria for optimizing their OER performance.

Dynamic behavior of non-stoichiometric mixed metal oxides under oxygen evolution reaction conditions

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.