Electronic state modulation via electrochemical reconstruction enhances dilute nitrate-to-ammonia reduction efficiency

Abstract

The electrochemical reduction of NO₃⁻ to NH₃ represents a promising approach for producing a renewable fuel with high energy density. However, problems such as low activity and/or selectivity in low-concentration solutions (≤100 ppm NO₃⁻-N) and instability of active sites still require to be overcome. In this work, Cu/ZnO heterostructure composite materials were synthesized for the NO₃RR. During the electrocatalysis process, Cu/ZnO undergoes electrochemistry-driven structural reconstruction, generating the CuZn bimetallic alloy phase. In a dilute NO₃⁻-N solution of 100 ppm, the optimal Cu₇₅Zn₂₅ catalyst exhibits an FE_NH3 of 94.1% at −0.7 V vs. RHE, and a high NH₃ yield of 414 mmol h⁻¹ g_cat⁻¹. Density functional theory calculations and a series of characterization studies unveiled that the CuZn alloy phase alters the electronic state surrounding Cu, leading to the regulation of the Cu d-band center and thereby optimizing the adsorption of intermediates. Meanwhile, forming a new alloy phase inhibits the competitive HER as well. This study shows the prospect of the CuZn composite catalyst in sustainable NH₃ synthesis, which holds a certain guiding significance for the efficient and eco-friendly conversion of effluents in the future.