Electrochemical Nitrate Production via Nitrogen Oxidation with Atomically Dispersed Fe on N-Doped Carbon Nanosheets

Electrocatalytic N-2 oxidation (NOR) into nitrate is a potential alternative to the emerging electrochemical N-2 reduction (NRR) into ammonia to achieve a higher efficiency and selectivity of artificial N-2 fixation, as O-2 from the competing oxygen evolution reaction (OER) potentially favors the oxygenation of NOR, which is different from the parasitic hydrogen evolution reaction (HER) for NRR. Here, we develop an atomically dispersed Fe-based catalyst on N-doped carbon nanosheets (AD-Fe NS) which exhibits an exceptional catalytic NOR capability with a record-high nitrate yield of 6.12 mu mol mg(-1) h(-1) (2.45 mu mol cm(-2) h(-1)) and Faraday efficiency of 35.63%, outperforming all reported NOR catalysts and most well-developed NRR catalysts. The isotopic labeling NOR test validates the N source of the resultant nitrate from the N-2 electro-oxidation catalyzed by AD-Fe NS. Experimental and theoretical investigations identify Fe atoms in AD-Fe NS as active centers for NOR, which can effectively capture N-2 molecules and elongate the N.N bond by the hybridization between Fe 3d orbitals and N 2p orbitals. This hybridization activates N-2 molecules and triggers the subsequent NOR. In addition, a NOR-related pathway has been proposed that reveals the positive effect of O-2 derived from the parasitic OER on the NO3- formation.

Automated summary

A novel atomically dispersed Fe-based catalyst on N-doped carbon nanosheets exhibits exceptional catalytic N-2 oxidation capability, outperforming all reported NOR and most NRR catalysts. Experimental and theoretical investigations confirm the active role of Fe atoms in initiating N-2 electro-oxidation and unveil a positive effect of O-2 derived from parasitic OER on the formation of nitrate in the NOR process.