Revealing and Optimizing the Dialectical Relationship Between NOR and OER: Cation Vacancy Engineering Enables RuO2 With Unanticipated High Electrochemical Nitrogen Oxidation Performance

The electrochemical N-2 oxidation reaction (NOR) using water and atmospheric N-2 represents a sustainable approach to nitric acid production; while, the parasitic oxygen evolution reaction (OER) usually results in poor conversion selectivity of N-2 oxidation. Although the side-reaction can be partially suppressed by using OER-inactive catalysts or substrates, the optimized performance is usually obtained at the cost of low yield. Revealing the internal relationship between NOR and OER, providing an effective pathway to optimize the dialectical relationship between OER and NOR is desirable and of socio-economic significance. Herein, RuO2, the well-known OER electrocatalyst, is defectively engineered to enhance the cooperation rather than competition between NOR and OER; a Faradaic efficiency (FE) of 6.70% at 1.36 V and a maximum yield of 767.92 mu g h(-1) mg(cat)(-1) at 1.44 V are obtained on D-RuO2 in acid electrolyte, superior to all the previously reported works. Experiments and DFT calculations suggest that the OER intermediates play a crucial role and the real rate-determining step during nitrogen oxidation is the transition from *O to *OOH involved in the formation of *NN(OH). The outstanding NOR activity is ascribed to the enhanced stabilization of *OH and the promotion of O-O bond breakage in the rate determining step of *NN(OH) formation.

Automated summary

In this study, RuO2 electrocatalyst was defectively engineered to enhance the cooperation between NOR and OER, leading to efficient synthesis of nitric acid. The optimized D-RuO2 exhibited outstanding NOR activity in acidic electrolyte, with a maximum yield of 767.92 mu g h(-1) mg(cat)(-1), surpassing previous reports. Experimental and computational results indicated that OER intermediates played a crucial role, and the rate-determining step during nitrogen oxidation was the transition from *O to *OOH involved in the formation of *NN(OH). The enhanced stabilization of *OH and the promotion of O-O bond breakage in the rate determining step of *NN(OH) formation contributed to the excellent NOR activity.