The origin of selective nitrate-to-ammonia electroreduction on metal-free nitrogen-doped carbon aerogel catalysts

Electrocatalytic nitrate reduction reaction (NitRR) to NH3 provides an appealing route to reform the energyconsuming ammonia industry. Considerable studies have demonstrated transition-metal-based catalysts for the NitRR, while most of them suffer from high cost, poor stability, and unsatisfactory selectivity. In this work, a group of carbon-based aerogel catalysts with regulated N species have been developed for highly efficient nitrateto-ammonia reduction. The results show that the electrocatalytic performance is dependent on the graphitic-N moiety, where the catalyst with the highest content of graphitic-N moiety exhibits a maximum NH3 yield rate of 1.33 mgNH3 h-1 cm-2 with the faradaic efficiency of ca. 95%. The theoretical investigation further reveals the strong adsorption of nitrate on graphitic-N moiety as the reason for the enhanced NO3 ˉ-to-NH3 activity. This study, thus, provides a fundamental understanding of the intrinsic mechanism of the NitRR on nitrogen-doped carbon structures, facilitating the rational design of metal-free catalysts for advanced electrosynthesis.