Alloyed Rhodium-Copper Nanocavities with Optimized Chemisorption of Hydrogen Radicals for Efficient Nitrate-to-Ammonia Electrocatalysis

Electrocatalytic reduction of waste nitrate (NO₃⁻) in water represents a sustainable and economic route for selective electrosynthesis of recycled ammonia (NH₃), but their performance still falls behind the needed. Herein, bimetallic rhodium-copper nanocavities (RhCu NCs), featuring open nanocavities in mesoscopic structure and well-alloyed composition at atomic level, are demonstrated as a high-performance electrocatalyst for efficient nitrate-to-ammonia (NO₃⁻-to-NH₃) electrocatalysis in a neutral condition. In comparison to other counterpart electrocatalysts, the best RhCu NCs deliver superior NO₃⁻-to-NH₃ performance at a very positive potential of −0.10 V versus RHE with Faradaic efficiency of 97.5%, yield rate of 8.1 mg h⁻¹ mg⁻¹, energy efficiency of 39%, and cycling stability of reaching 15 cycles. The combination of kinetic analysis, in situ Raman spectroscopy, and density functional theory calculation reveals that active hydrogen radicals can be kinetically formed and selectively consumed by the nitrogen intermediates to promote the [2e + 6e] tandem pathway of NO₃⁻ reduction for efficient NH₃ electrosynthesis. The work thus provides some insights into designing functional tandem electrocatalysts for selective electrosynthesis of multi-electron products from various electrocatalytic reactions.