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

Electrochemical nitrate reduction (NO₃ ^-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 NO₃ ^- → NO₂ ^- step through a three-step relay mechanism. Consequently, the synergy of these effects endows Co@Ga with exceptional NO₃ ^-RR performance, achieving an ultra-high NH₃ 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.