Nickel-metal-orgsanic framework coupled with Cu sub-nanometer clusters enables reverse hydrogen spillover for efficient electrocatalytic nitrate reduction to ammonia

Sub-nanometer Cu are clusters are anchored on Ni-MOF offer abundant active sites. • Cu@Ni-MOF acts as a highly efficient tandem electrocatalyst for NO 3 ¯ reduction. • DFT calculations confirm the *H adsorption energy difference on Cu versus Ni sites. • Ni–O–Cu bridges enable reverse *H spillover from the Ni-MOF to Cu sites. Electrocatalytic nitrate reduction (NO 3 − RR) to ammonia offers a sustainable strategy for wastewater treatment and the balance of the nitrogen cycle. However, this process has long faced challenges from competing side reactions, low selectivity, and sluggish hydrogenation kinetics. Herein, we present a Cu@Ni-MOF catalyst, fabricated by anchoring Cu sub-nanoclusters onto a nickel-metal-organic framework (Ni-MOF) support, which demonstrates exceptional performance for NO 3 − RR. The catalyst achieves a peak NH 4 + Faradaic efficiency (FE) of 96.8% with a production rate of 0.44 mmol h −1  cm −2 and minimal NO 2 − accumulation, and near-total FE (∼100%), which indicates high selectivity and minimal side products. Integrating electrochemical analysis with theoretical calculations establishes a cooperative tandem mechanism: the Cu sites promote NO 3 − adsorption and conversion to NO 2 − , while the Ni-MOF efficiently dissociates water to generate hydrogen species (*H), which migrate via reverse hydrogen spillover through Ni − O − Cu bridges to facilitate further hydrogenation of NO 2 − intermediates on Cu sites. This synergistic process enhances intermediate conversion and overall catalytic efficiency, providing a promising strategy for sustainable electrocatalytic ammonia synthesis. Download: Download high-res image (155KB) Download: Download full-size image