Phase-dependent Electrocatalytic Nitrate Reduction to Ammonia on Janus Cu@Ni Tandem Catalyst

Abstract

Electrosynthesis of NH3 from nitrate anion (NO3-) reduction (NO3-RR) is a cascade reaction, which is considered a great potential alternative to the Haber-Bosch route to reduce CO2 emissions and alleviate the adverse effects of excessive NO3- contamination in the environment. Frequently, solid solution alloys (SSAs) with a single-phase active site may struggle to fully utilize their benefits during the entire process of nitrate (NO3-) reduction, which involves multiple intermediate reactions. In this study, we showed that by separating Cu and Ni in a Janus Cu@Ni catalyst structure, we can achieve high performance in NO3-RR, yielding a high Faradaic efficiency (92.5%) and a production rate of NH3 (1127 mmol h-1 g-1) at −0.2 V versus RHE, compared to CuNi SSA (82.6%, 264 mmol h-1 g-1). Here, we demonstrate that a Janus Cu@Ni catalyst with short-range ordered catalytic sites favors the adsorption of NO through a bridge-bond mode. Simultaneously, a hydrogen spillover process was observed, in which Ni dissociates H2O to generate *H which spontaneously migrates to adjacent catalytic sites to hydrogenate the *NOx intermediates. This facilitates N-O bond cleavage, resulting in the NH3 production rate nearly 5 times higher than that of CuNi SSA, where NO was linearly bonded on its surface. The study of this catalytic effect, a cooperative tandem enhancement, provides insights into the design of multifunctional heterogeneous catalysts for electrochemical NH3 synthesis. © 2024 The Authors. Published by American Chemical Society.