Liquid Metal Dynamic Interface Enabled Reverse Hydrogen Spillover Boosting Electrocatalytic Nitrate Reduction

Abstract Electrochemical nitrate reduction (NO 3 − RR) to ammonia involves intricate and sluggish proton‐coupled electron transfer (PCET) pathways, the active hydrogen (H*) flux regulation are crucial for its efficiency. Here, we demonstrate a liquid metal‐based catalyst, Co@Ga, featuring a dynamic liquid Ga core–solid Co shell interface under operando conditions. This unique architecture enables an unprecedented reverse hydrogen spillover mechanism, where H* generated via facile water dissociation on liquid Ga support spontaneously migrates to adjacent metallic Co for efficient hydrogenation of adsorbed nitrate/intermediates. Moreover, the strong electron donation from Ga to Co also accelerates the rate‐determining NO 3 − → NO 2 − step through a three‐step relay mechanism. Consequently, the synergy of these effects endows Co@Ga with exceptional NO 3 − RR performance, achieving an ultra‐high NH 3 yield rate of 51 mol h −1 g Co −1 , Faraday efficiency of 94.5% at −0.3 V versus RHE, and outstanding stability over 400 h at 1 A cm −2 in a membrane electrode. This work presents the concept of dynamic liquid‐solid‐liquid interfaces for reversing conventional hydrogen spillover, offering a universal strategy to regulate multi‐proton/electron transfers in complex electrocatalytic reactions.