Ru-Incorporation-Induced Phase Transition in Co Nanoparticles for Low-Concentration Nitric Oxide Electroreduction to Ammonia at Low Potential

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH₃) represents a potential solution for improving the disrupted nitrogen cycle balance. Unfortunately, designing efficient electrocatalysts for NO reduction reaction (NORR) remains a notable challenge, especially at low concentrations. Herein, a displacement-alloying strategy is reported to successfully induce the phase transition of Co nanoparticles supported on carbon nanosheets from face-centered cubic (fcc) to hexagonal close-packed (hcp) structure through Ru incorporation. The obtained RuCo alloy with hcp phase structure (hcp-RuCo) exhibits apparent NORR activity with a record-high Faraday efficiency of 99.2% and an NH₃ yield of 77.76 µg h^-1 mg_cat ^-1 at -0.1 V versus reversible hydrogen electrode at a NO concentration of 1 vol %, surpassing Co nanoparticles with fcc phase structure and most reported catalysts. Density functional theory calculations reveal that the excellent NORR activity of hcp-RuCo can be attributed to the optimized electronic structure of Co site and lowered energy barrier of the potential rate-determining step through phase transition. Furthermore, the assembled Zn-NO battery using hcp-RuCo as the cathode achieves a power density of 2.33 mW cm^-2 and an NH₃ yield of 45.94 µg h^-1 mg_cat ^-1. This work provides a promising research perspective for low-concentration NO conversion.