Electron-deficient Co modulated by the construction of heterojunctions Co@NC boosts the electroreduction of nitrate to ammonia

Abstract

The electrochemical conversion of nitrate (NO₃⁻) to ammonia (NH₃) appears to be a promising approach for achieving carbon-free production of NH₃ while balancing the nitrogen cycle. However, the design of efficient electrochemical catalysts remains one of the main challenges in realizing this strategy. Here, with g-C₃N₄ as the N source, a series of heterojunction Co@NC-x (x = 0.5, 1, 2, 4) catalysts with adjustable N contents was effectively created. The as-prepared Co@NC-4 catalysts show a significant faradaic efficiency (FE_NH3) of 99.1% at −0.5 V vs. RHE and an excellent NH₃ yield of 1392.8 mmol h⁻¹ g_cat⁻¹ at −0.8 V vs. RHE when used for the electrochemical nitrate reduction reaction (NO₃RR). Both theoretical and experimental data indicate that the increased N content (especially pyridinic N) promotes electron flow via the heterojunction interface, resulting in the formation of a more pronounced electron-deficient Co atom with a comparatively high N content. Electron-deficient Co stimulates NO₃⁻ adsorption, which is the rate-determining step (RDS) of the electrochemical NO₃RR. Moreover, a linear link was built between the N content and the catalytic activity, further demonstrating the promotion of electronic state regulation for the NO₃RR.