Materials Screening by the Descriptor G_max(η): The Free-Energy Span Model in Electrocatalysis

Abstract

To move from fossil-based energy resources to a society based on renewables, electrode materials free of precious noble metals are required to efficiently catalyze electrochemical processes in fuel cells, batteries, or electrolyzers. Materials screening operating at minimal computational cost is a powerful method to assess the performance of potential electrode compositions based on heuristic concepts. While the thermodynamic overpotential in combination with the volcano concept refers to the most popular descriptor-based analysis in the literature, this notion cannot reproduce experimental trends reasonably well. About two years ago, the concept of G max (η), based on the idea of the free-energy span model, has been proposed as a universal approach for the screening of electrocatalysts. In contrast to other available descriptor-based methods, G max (η) factors overpotential and kinetic effects by a dedicated evacuation scheme of adsorption free energies into an analysis of trends. In the present perspective, we discuss the application of G max (η) to different electrocatalytic processes, including the oxygen evolution and reduction reactions, the nitrogen reduction reaction, and the selectivity problem of the competing oxygen evolution and peroxide formation reactions, and we outline the advantages of this screening approach over previous investigations.

A general but still unknown characteristic of active oxygen evolution electrocatalysts

“…Furthermore, at a potential of 1.23 V vs. RHE ( η OER = 0) the average values of the span, denoted G max ( η OER = 0), 42,43 are 1.15 ± 0.44, 1.68 ± 0.72, and 1.14 ± 0.25 eV for materials with n = 1, 2, 3, respectively. Because of the number of electrons transferred within the span, as the overpotential grows, the average G max ( η OER ) should decrease faster as a function of n .…”

“…Furthermore, at a potential of 1.23 V vs. RHE (h OER = 0) the average values of the span, denoted G max (h OER = 0), 42,43 are 1.15 ± 0.44, 1.68 ± 0.72, and 1.14 ± 0.25 eV for materials with n = 1, 2, 3, respectively. Because of the number of electrons transferred within the span, as the overpotential grows, the average G max (h OER ) should decrease faster as a function of n. Indeed, when the applied potential is 1.60 V vs. RHE (h OER = 0.37 V) the average values of G max (h OER = 0.37 V) are 0.78 ± 0.44, 1.03 ± 0.67, and 0.27 ± 0.21 eV for materials with n = 1, 2, 3, respectively.…”

“…Recent works have highlighted the insights offered by the freeenergy span model in electrocatalysis. [42][43][44] The model is based on the largest positive free-energy difference between the species involved in a given catalytic pathway. Interestingly, the model can be used to anticipate the kinetic behavior of a catalyst on the basis of its reaction energies.…”

“…Interestingly, the model can be used to anticipate the kinetic behavior of a catalyst on the basis of its reaction energies. We calculated the energy span of each catalyst in our database following the procedure in previous works 42,43 (see Section S2 †). We nd that the most frequent span for catalysts with n = 1 is between *OOH and *O (DG 3 ), which involves one electron transfer.…”

Is there any correlation between impedance shapes and electrocatalytic activity?

“…A mathematical analysis on the potential-dependency of volcano plots has been published recently. 42,43 respectively. Focusing on the shape, we omit the magnitude of impedance.…”