(Invited) Electrochemistry at Metal-Oxide Interfaces: At the Crossroads of Activity and Stability

Abstract

The identification of materials needed for efficient energy conversion and fuel production in electrochemical systems must be guided by two equally important fundamental properties: optimization of their catalytic behavior and their long-term stability in hostile electrochemical environments. This is especially true for the oxygen evolution reaction (OER), the anodic-half cell reaction that takes place at high overpotentials on oxidized metal surfaces in hydrogen-oxygen electrolyzers, metal air batteries and electrometallurgy. The kinetics of the OER have, for the most part, been closely tied to the concept of the volcano plot, which generally expresses the rate of the OER as a function of more fundamental properties of the oxide materials, known as descriptors. These analyses showed that the interaction between the substrate and the reactants, intermediates, and the products has to be optimized for the reaction to proceed efficiently. Although concepts resulting from volcano plot analyses have led to the establishment of important catalytic trends, many fundamental questions still remain open. One key question is what relationship exists between the kinetics of the OER and the stability of oxide materials. The lack of understanding of such stability-activity relationships derives mainly from the fact that research directed to the development of anode materials for the OER has been strongly “activity-centric”, while almost completely ignoring the stability of active components during the OER. Here, we show that this disparity in focus has masked the inherently close ties that exist between the stability and activity of monometallic and complex oxide catalysts. By studying the stability-activity relationships of well-characterized oxide surfaces, we demonstrate that there is a fundamental link between the stability of catalysts and their reactivity for the OER. This trend is observed for many oxide catalysts in both acidic and alkaline electrolytes, indicating that the stability-activity relationship is independent of the specific ionic/molecular species mediating the OER (i.e. OH- vs. H2O). We found that the degree of stability is always inversely proportional to activity and that stable surfaces are, in fact, not reactive.