Triggering synergistic electronic promoting effect through oxygen doping to promote electrochemical nitrogen reduction on metal-free electrocatalyst

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) as an alternative approach to the energy-intensive Haber–Bosch process for artificial ammonia synthesis has attracted extensive attention. Previous reports have suggested that metal-free electrocatalysts, such as nitrogen-doped carbon featuring modified electronic structure and charge polarization, are able to eliminate the nitrogen chemisorption barrier and achieve ammonia synthesis with a certain performance. However, the NRR process involves not only adsorption but also subsequent nitrogen cleavage and hydrogenation, which still pose great challenge. Herein, through doping oxygen as a secondary heteroatom into nitrogen-doped carbon, a synergistic electronic promoting effect is triggered to boost ambient ammonia synthesis. The electronic structure and the polarity of adjacent carbon atoms are further optimized, significantly lowing the energy barrier of the overall nitrogen reduction process. As expected, the proof-of-concept oxygen-enriched nitrogen-doped carbon catalyst delivers a much enhanced performance compared to its counterpart, with an ammonia yield rate of 67.3 μg h⁻¹ mg⁻¹ and the corresponding Faradaic efficiency of 36.2% at −0.2 V versus the reversible hydrogen electrode. This study emphasizes the superiority of oxygen doping and sheds light on the rational design of heteroatom-modified carbon materials for artificial ammonia synthesis under ambient conditions.