Overpotential‐Dependent Volcano Plots to Assess Activity Trends in the Competing Chlorine and Oxygen Evolution Reactions

Abstract

The selectivity problem of the competing chlorine evolution (CER) and oxygen evolution (OER) reactions at the anode in chlor−alkali electrolysis is a major challenge in the chemical industry. The development of electrode materials with enhanced stability and CER selectivity could result in a significant reduction of the overall process costs. In order to gain an atomic‐scale understanding of the CER versus OER selectivity, commonly, density functional theory (DFT) calculations are employed that are analyzed by the construction of a volcano plot to comprehend trends. Herein, the binding energy of oxygen, ΔEO, has been established as a descriptor in such analyses. In the present article, it is demonstrated that ΔEO is not suitable to assess activity trends in the OER over transition‐metal oxides, such as RuO2(110) and IrO2(110). Quite in contrast, the free‐formation energy of oxygen with respect to hydroxide, ΔGO−OH, reproduces activity trends of RuO2(110) and IrO2(110) in the CER and OER correctly. Consequently, re‐investigation of the CER versus OER selectivity issue, using ΔGO−OH as a descriptor, is strongly suggested.

Recent Progress in the Development of Screening Methods to Identify Electrode Materials for the Oxygen Evolution Reaction

“…Using the concept of overpotential-dependent volcano plots with a scaling relation's offset of 2.93 eV at a target overpotential of η target = 0.40 V, the volcano curve unequivocally indicates that RuO 2 is more active than IrO 2 in the OER. [20,53] This may corroborate the suggested procedure of overpotential-dependent volcano plots, particularly for thorough sorting of highly active electrode materials. Additionally, this outcome suggests that general scaling relations by summing up several classes of materials should be treated with some caution.…”

“…Section 2.3). [ 53 ] Actually, binding energies (thermodynamics) are already sufficient to recognize inactive materials, whereas close to the top of the volcano microkinetic details of the underlying reaction rather than binding energies are decisive. Since the kinetics and applied overpotential are enclosed in the unifying methodology, the concept of ESSI‐descriptor activity maps excels the conventional volcano scheme, particularly for a profound assessment of highly active electrode materials.…”

“…An offset of 2.93 eV describes the energetics in the class of TMOs better than the offset of 3.2eV. [53] Several ab initio studies in the literature addressed activity trends of RuO 2 and IrO 2 , corresponding to the most active TMOs in the OER and CER, by the conventional volcano scheme. [54,55] However, in none of these studies, the trend RuO 2 > IrO 2 , as reported by experimentalists, [9,56] could be reproduced.…”

Computational Design of Copper doped Indium for electrocatalytic Reduction of CO2 to Formic Acid

“…In addition, the HCOO* adsorbate and the H* adsorbate determine the activity of the FAP or the HER, respectively, and hence also the selectivity ratio of the competing processes. Therefore, the selectivity ratios of Cu‐In (101) surfaces for the equilibrium potential of the FAP pathway (−0.16 V vs. RHE) is calculated with the model used in the previous literatures by Kai S. Exner and Vijay Ramani et al [17b,c] (See calculation equations in Supporting Information). As for the Cu‐In (101) surface, it can be clearly found that there is a positive correlation between high FE HCOO − (70 %) and better selectivity ratio of FAP vs.…”

“…It should be noticed that the thermodynamics of the competing HCOOH and CO pathways and the HER are qualitatively calculated by ignoring the effects of surrounding adsorbates in this work. Generally, Ab‐initio Pourbaix diagrams can be employed to resolve the surface structure as a function of the applied electrode potential and pH [17b,c] . However, since we pay more attention on the effect of Cu doping, the Pourbaix diagrams are not included here.…”