Auxiliary Linker-Enabled Local Protonation Boosts the Ammonia Electrosynthesis in Heterometallic Metal–Organic Frameworks

Controlling the local proton environment is a powerful strategy for accelerating proton-coupled electron transfer reactions, but realizing this within stable heterogeneous catalysts remains challenging. Herein, we report a series of metal–organic frameworks (MOFs), PCN-800M-L, featuring precisely placed proton relays adjacent to catalytic sites for boosting electrocatalytic nitrate reduction to ammonia (NO 3 RR). PCN-800M-L series was constructed by sequentially installing catalytically active metal sites (M = Ni 2+ or Co 2+ ) and auxiliary nitrogen-donor linkers (L = L1–L5) into a robust Zr 4+ -based framework. Auxiliary linkers reversibly dissociate upon protonation, transiently exposing active metal sites while functioning as localized proton relays. By systematically varying the metals and linkers, we uncover a volcano-type dependence of NO 3 RR activity on linker p K a, with the PCN-800Co-L3 achieving the highest turnover frequency (1863 h –1 ) and Faradaic efficiency (97.9%). This work establishes a molecular-level design principle that harnesses auxiliary linkers as programmable proton sources in MOFs, enabling efficient multielectron electrocatalysis.