A Universal Approach To Determine the Free Energy Diagram of an Electrocatalytic Reaction

Abstract

Extended Tafel plots at various temperatures for an electrocatalyzed reaction and (possibly) its reversed reaction on single-crystalline model electrodes allow for constructing the (essential part of the) free energy surface, in particular the free energies of the transition states (TS). Free energies of the reaction intermediates (RIs) including the chemical nature of active surface sites (S) are hardly accessible to experiment and need therefore to be taken from constrained ab initio thermodynamics calculations. The compact compilation of experimental kinetic data in the form of a free energy diagram enables a critical assessment and validation of theoretical free energy landscapes based on first-principles kinetics. For three prototypical electrocatalyzed reactions, namely the chlorine evolution reaction (CER) and oxygen evolution reaction (OER) over RuO2(110) as well as hydrogen evolution reaction (HER) on Pt(111), we exemplify this universal approach and discuss potential benefits for theoretical modeling of electrocatalyzed reaction.

Activity‐Stability Volcano Plots for Material Optimization in Electrocatalysis

“…Figure a) are conducted and combined with the ab initio Pourbaix diagram (cf. Figure b) within the free energy diagram approach to obtain the free energy landscape along the reaction coordinate as function of the applied overpotential (cf. Figure c). The free energy diagram allows quantifying the rate‐determining reaction step in dependence of the applied overpotential, whose knowledge if useful for further DFT calculations, in which the chemical environment of the active surface configuration and the precursor is varied in order to obtain linear scaling relationships for activity and stability (cf.…”

“…Figure a) are conducted and combined with the ab initio Pourbaix diagram (cf. Figure b) within the free energy diagram approach to obtain the free energy landscape along the reaction coordinate as function of the applied overpotential (cf. Figure c).…”

“…Even though the manual appears long, the outlined procedure consists only of the combination of simple ab initio thermodynamics DFT calculations and experimental Tafel measurements, both affordable and well‐established methods in electrocatalysis. Therefore, the outlined procedure of activity‐stability volcano plots in conjunction with the free energy diagram approach may serve as a valuable tool for researchers in material optimization in order to gain in‐depth insights into the overpotential‐dependent performance of electrode surfaces at low (computational and experimental) costs. As the outlined framework is not restricted to the CER over RuO 2 (110) model system, it is strongly encouraged to apply the concept of activity‐stability volcano plots to any electrocatalytic reaction of potential interest.…”

Recent Advancements Towards Closing the Gap between Electrocatalysis and Battery Science Communities: The Computational Lithium Electrode and Activity–Stability Volcano Plots

“…Therefore, furtherm odel development in ab initio electrochemistry is called for that facilitates the incorporation of the appliede lectrode potentiald irectly into the underlying calculations, such as in ar ecent contribution of Melander et al, [124] in whichagrand canonical approach was used to investigatee lectrocatalyticsystems at constant ionand electrode potentials. [65,66] In this regard,f urther modeld evelopment is required to evaluate thermodynamicsi nab initio theory,s uch as by ac omparison of ab initio Pourbaix diagrams with CV measurements. [127] Hence, acombination of DFT calculations and ab initio or classical MD simulations is indispensable for developing novel approaches that go beyondthe CHE approach, [11] as discussed recently by Oberhofer.…”

“…[65] Hence, the constrained ab initio thermodynamics approachp lays ac entral role in both experimental investigations and kinetic studies from first principles. [66] Therefore, future model developmenti na bi nitio electrochemistry can be benchmarked by the free-energy diagram along the reaction coordinate, consisting of highly accurate experimental transition-state free energies. [66] Therefore, future model developmenti na bi nitio electrochemistry can be benchmarked by the free-energy diagram along the reaction coordinate, consisting of highly accurate experimental transition-state free energies.…”