Green synthesis of Fe-anchored N-doped biochar with highly active FeNx catalytic sites for electrochemical nitrate reduction

Electrocatalytic nitrate reduction reaction is regarded as the promising method to mitigate nitrate pollution and produce ammonia, but cost-effective and efficient electrocatalysts are lacking. In this study, a low-cost Fe- anchored N-doped biochar (Fe-NBC) was synthesized from the N-rich wetland plant and used for electrocatalytic nitrate reduction reaction. At optimal conditions, Fe-NBC could achieve a maximum nitrate removal capacity of 1065 mg N/g Cat, a NH3 yield rate of 78.6 umol mgcat−1 h−1, a Faradaic efficiency of 75.3 %, and an energy consumption of 0.2073 kWh/g. The kinetics results showed that the reaction rate of Fe-NBC was 1.5 times of Fe-embedded biochar, and 3.5 times of bare N-doped biochar. Experimental results and characterizations demonstrated the pyridinic-N in the form of FeNx in Fe-NBCs enhance the electrocatalytic nitrate reduction performance by modulating the electronic properties of the Fe-NBCs surface. Furthermore, the Fe-NBC cathode exhibited an excellent stability due to the coverage of Fe species by deposited carbon during the pyrolysis process. This study deepens our understanding of the role of N species on electrocatalytic nitrate reduction and provides a green strategy for fabricating efficient electrocatalyst through waste biomass.