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%.