Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature.

Abstract

The development of electrocatalysts capable of efficient reduction of nitrate (NO₃^-) to ammonia (NH₃) is drawing increasing interest for the sake of low carbon emission and environmental protection. Herein, we present a CuCo bimetallic catalyst able to imitate the bifunctional nature of copper-type nitrite reductase, which could easily remove NO₂^- via the collaboration of two active centers. Indeed, Co acts as an electron/proton donating center, while Cu facilitates NO_x^- adsorption/association. The bio-inspired CuCo nanosheet electrocatalyst delivers a 100 ± 1% Faradaic efficiency at an ampere-level current density of 1035 mA cm^-2 at -0.2 V vs. Reversible Hydrogen Electrode. The NH₃ production rate reaches a high activity of 4.8 mmol cm^-2 h^-1 (960 mmol g_cat^-1 h^-1). A mechanistic study, using electrochemical in situ Fourier transform infrared spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy, reveals a strong synergy between Cu and Co, with Co sites promoting the hydrogenation of NO₃^- to NH₃ via adsorbed *H species. The well-modulated coverage of adsorbed *H and *NO₃ led simultaneously to high NH₃ selectivity and yield.