Unlocking Ampere-Level Nitrate Electroreduction to Ammonia Via the Built-In Electric Field in Monometallic Catalysts

Bimetallic/multimetallic catalysts for nitrate reduction reaction (NO₃^–RR) have been extensively investigated benefiting from their synergistic effects in optimizing various intermediate adsorptions; however, the interphasic synergistic effects in monometallic catalysts are often overlooked. Here we report an interphasic synergy between electron-rich Co(OH)₂ and electron-deficient CoO, in which the asymmetric charge distribution in monometallic cobalt-based heterojunction derived from the built-in electric field (BEF) significantly accelerates electron transfer and lowers the energy barriers for NO₃^–RR. Theoretical calculations reveal that the chemical affinities of Co atoms toward NO₃^– and NO₂^– are significantly enhanced and even NO₃^– adsorption switches to a spontaneous process. Simultaneously, the BEF in monometallic Co-based heterostructures greatly reduces the energy barrier of the rate-determining step (*NO→*NOH) in the NO₃^–RR. Therefore, the resultant catalyst exhibits ampere-level NO₃^–RR performance, achieving a record NH₃ yield up to 73.9 mg h^–1 cm^–2 at a low potential of −0.2 V with a Faradaic efficiency (FE) of 95.6%.