Dual-active-site-designed NiO/Co₃O₄ heterostructures for high-efficiency electroreduction of ultralow-concentration NO to NH₃

Electrochemical nitric oxide (NO) reduction reaction (NORR) is promising for NO removal in exhausts and ammonia synthesis. However, the ultralow-concentration NO in exhaust gas (<0.5%) brings great challenges for activation of NO and suppression of competitive hydrogen evaluation reaction (HER). Herein, a NiO/Co₃O₄ heterostructure catalyst with Ni/Co dual-active sites is designed and exhibits a high ammonia yield rate of 0.364 mmol cm−2 h−1 with 97.6% Faraday efficiency at −0.7 V (vs. RHE) for electroreduction of ultralow-concentration NO (0.3%). Furthermore, even for lower-concentration NO (0.05%), a continuous experiment coupled denitrification and NORR processes presents the above 95% NO removal ratio for 50 h. A comprehensive program of experimental and theoretical calculations reveals that the Ni site accelerates water dissociation to release active hydrogen (H*) while the Co site boosts the activation of ultralow concentration NO to generate NO*. The electron redistribution in the Co-Ni heterointerface realizes the synergetic catalysis via reducing the activation energy of hydrogenation of NO* and promoting the transformation of H*. This work not only provides an alternative protocol for sustainable NH₃ synthesis using the ultralow-concentration NO but also cast a light on insights into the design of high-efficiency catalysts for NORR.