A Universal Descriptor for the Screening of Electrode Materials for Multiple-Electron Processes: Beyond the Thermodynamic Overpotential

On the way toward a sustainable energy economy, electrode materials that do not contain scarce noble metals need to be developed. Operating at low computational costs, material screening is a powerful tool to assess the performance of potential electrode compositions by categorizing materials into active and inactive. Most commonly, linear scaling relationships are analyzed by the construction of a volcano plot, in which the thermodynamic overpotential, eta(TD), serves as activity descriptor. Even if this descriptor identifies the majority of active electrode materials, it has been reported that eta(TD) lacks thorough sorting of catalysts according to their activity. This failure is mainly related to the fact that eta(TD) is defined by a single free-energy change (thermodynamics), whereas the applied overpotential and kinetics are not factored in the analysis. Based on the discussion of free-energy diagrams and the rate-determining reaction step, this Viewpoint introduces an alternate activity descriptor, G(max)(eta), for multiple-electron processes, thereby including the applied overpotential and kinetic effects in the evaluation. On the example of the oxygen evolution reaction, the application of G(max)(eta) for the screening and optimization of electrode materials is discussed, providing a different perspective compared with the conventional scheme of eta(TD).