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, Δ E O , has been established as a descriptor in such analyses. In the present article, it is demonstrated that Δ E O is not suitable to assess activity trends in the OER over transition‐metal oxides, such as RuO 2 (110) and IrO 2 (110). Quite in contrast, the free‐formation energy of oxygen with respect to hydroxide, Δ G O−OH , reproduces activity trends of RuO 2 (110) and IrO 2 (110) in the CER and OER correctly. Consequently, re‐investigation of the CER versus OER selectivity issue, using Δ G O−OH as a descriptor, is strongly suggested.