Facet-dependent Chlorine and Oxygen Evolution Selectivity on RuO₂: An Ab initio Atomistic Thermodynamic Study

The chlorine evolution reaction (CER) and oxygen evolution reaction (OER) occur simultaneously due to the low difference (0.13 V) in their standard potentials. RuO₂ is the state-of-art electrocatalyst used for both OER and CER. The activity and selectivity of different RuO₂ low-index facets, namely (100), (110), (111), (001) and (101), are investigated through ab-initio density functional theory (DFT) based calculations. The selectivity of different facets is explored in a mixed OER-CER region by combining Pourbaix diagrams and linear scaling relationships. The difference in limiting overpotential of OER and CER is identified as the selectivity descriptor (SD^CER). The most CER- and OER-selective facets are found to be (101) (SD^CER=0.39 V) and (001) (SD^CER=0.14 V), respectively. The understanding of facet dependent CER selectivity in RuO₂ can be extended as a design strategy to modulate OER and CER activity and selectivity as per design requirements.