Tandem Cu–Co Sites in MOF-818 for Efficient Ammonia Electrosynthesis from Nitrate in Neutral Media
Hai Sun, Zixiang Xia, Yuanyuan Qi, Qiang Xü, Jingwei Han, Jiahui Wu, Jun‐Sheng Qin, Heng Rao
Abstract
The electrocatalytic reduction of nitrate (NO 3 – ) to ammonia (NH 3 ) is a promising strategy for addressing environmental NO 3 – pollution. However, achieving a high Faradaic efficiency (FE) for NH 3 production over a wide potential range in neutral electrolytes remains a major challenge for NO 3 – reduction reaction (NO 3 – RR). Herein, MOF-818(Cu)–Co was synthesized by immobilizing Co clusters within the porous framework of MOF-818(Cu). MOF-818(Cu)–Co exhibited a superior NH 3 FE and the highest NH 3 yield rate compared to both pristine MOF-818(Cu) and Co nanoparticles (Co NPs). Under neutral conditions, the NH 3 FE exceeded 90% over a wide potential window (−1.3 to −1.8 V vs Ag/AgCl), approaching nearly 100% at −1.5 V (vs Ag/AgCl). Meanwhile, the NH 3 yield rate attained 1.06 mol h –1 g cat –1 at −1.8 V vs Ag/AgCl, corresponding to a CuCo catalytic active sites yield rate of 35.0 mol h –1 g CuCo –1 . In situ characterizations and theoretical calculations showed that the Cu and Co sites in MOF-818(Cu)–Co synergistically lowered the energy barrier of the rate-determining step (RDS, *NO 2 – → *NO) through a synergistic tandem catalytic mechanism. The Cu sites predominantly catalyzed the reduction of NO 3 – to NO 2 –, while the Co sites facilitated the subsequent conversion of NO 2 – to NH 3 . This study demonstrates that synergistic tandem catalytic systems can significantly enhance ammonia electrosynthesis in neutral media.