Nitrogen Defective Engineering of a Metal-Free Carbon Catalyst for Ammonia Electrosynthesis from Nitrate
Shengjun Du, Jun Fang, Minglong Guo, Guangxing Yang, Qiao Zhang, Zhiting Liu, Feng Peng
Abstract
Electrocatalytic nitrate reduction reaction (ENO 3 RR) to NH 3 provides an appealing route to valorize pollutants needed to close the nitrogen cycle. The development of metal-free carbon catalysts with high stability and well-developed active sites for ENO 3 RR is highly desirable, while the role of structural defects (such as vacancies or functional groups) on NH 3 electrosynthesis is not fully understood. Herein, we developed a group of carbon-based catalysts with regulated quaternary-N and N vacancies, and the effect of dual defect sites on the ENO 3 RR to NH 3 process was systematically investigated. The as-prepared NHC-1000 catalyst with atomic-level engineered active sites exhibited a NH 3 Faradaic efficiency of 91.2% associated with a NH 3 yield rate of 2.6 mmol h –1 g –1 at –0.5 V (vs RHE), better than most of the reported metal-free carbon electrocatalysts. According to the structure characterization and theoretical calculations, the yielded NH 3 was dependent on the nitrogen defective involved catalytic sites. The quaternary-N moiety facilitated the potential-determining step of *NO protonation to *NHO and further contributed to the formation of *NH 2 intermediates by the synergistic action of N-vacancies, which enhanced the NO 3 – to NH 3 activity effectively. This work provides a fundamental principle and deeper understanding for designing advanced carbon-based catalysts by defect engineering applied in the ENO 3 RR process effectively.