Method to Determine the Bifunctional Index for the Oxygen Electrocatalysis from Theory

Abstract

Metal‐air batteries are encountered as a promising solution for energy storage due to their high energy density, cost effectiveness, and environmental benefits. Yet, the application of metal‐air batteries in practice is still not mature, which is also related to the bifunctional oxygen electrocatalysis at the cathode, comprising the oxygen reduction (ORR) and oxygen evolution (OER) reactions during discharge and charge of the battery, respectively. Experimentally, the performance of electrocatalysts in the OER and ORR is described by bifunctional index (BI), but, so far, there is no direct approach to capture the BI on the atomic scale. Herein, we present a method to ascertain the BI from ab initio theory, thereby combining a data‐driven methodology with thermodynamic considerations and microkinetic modeling as a function of the applied overpotential. Our approach allows deriving the BI from simple adsorption free energies, which are easily accessible to electronic structure theory in the density functional theory (DFT) approximation. We outline how our methodology may steer the design of efficient bifunctional catalysts on the atomic scale.

Rapid Screening of Mechanistic Pathways for Oxygen‐Reduction Catalysts

“…Equation ( 8) indicates that electrocatalytic activity is a function of ΔG 1 and SRI serving as the descriptors, and thus, a data-science approach in the spirit of recent works by the author and his group is applied. [13] The data-science model relies on the definition of a basis set, corresponding to the parameter space of available materials (cf. SI, section 4).…”

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

“…As is evident from the above summary, so far, the application of the descriptor G max (η) has focused on comprehending the activity or selectivity of electrode compositions. ,,,,, The stability aspect of electrocatalysts is often overlooked from the viewpoint of theory, which is mainly related to the fact that powerful concepts to understand degradation processes are yet missing, albeit urgently needed. − Hitherto, mainly bulk-related properties have been used to comprehend catalyst stability on the atomic scale. , This picture is, of course, rather simplistic because chemical information on the decomposition products would be required to gain a profound insight into catalyst degradation. A major step forward in this regard represents a recent study by Andreussi and co-workers, who modeled the oxygen evolution and reduction reactions over two-dimensional transition-metal dichalcogenides in conjunction with different decomposition pathways for highly active OER materials .…”

“…The meaning of the term Δ G RDS-max # is further explained in section 2.3 . Reproduced with permission from ref ( 64 ).…”

“…The bifunctional performance of electrocatalysts in the oxygen electrocatalysis can be assessed by the difference in electrode potential between j OER = 10 mA/cm 2 and j ORR = −1 mA/cm 2 , denoted BI. Reproduced with permission from ref ( 64 ).…”

Implications of the M-OO∙∙OO-M recombination mechanism on materials screening and the oxygen evolution reaction

“…Given that the concept of G max (U) allows deriving potential-dependent activity trends, volcano plots are constructed for applied electrode potentials of U = 1.40 V, 1.50 V, and 1.60 V vs. RHE. In contrast to the common practice of calculating the ∆G j values for a certain material class, we make use of a data-driven methodology by defining a basis set [36] for the free-energy change ∆G 1 , which serves as the descriptor in the analysis. Following the perspective by Rossmeisl and coworkers on a decade of atomic-scale simulations in the OER [10], a typical value range for ∆G 1 corresponds to [−0.50, 2.50] eV.…”