Ambient Electrosynthesis of Ammonia on a Biomass-Derived Nitrogen-Doped Porous Carbon Electrocatalyst: Contribution of Pyridinic Nitrogen

Abstract

Here we report that alfalfa-derived nitrogen-doped porous carbon (NPC) fabricated by a pyrolysis method is electrochemically active for the N2 reduction reaction (NRR) at ambient conditions. The results demonstrate that the obtained NPC material with a nitrogen content of 6.35 atom % at 500 °C (NPC-500) exhibits high NRR activity with an NH3 yield rate of 1.31 mmol h–1 g–1cat. and a Faradaic efficiency of 9.98% at −0.4 V (vs RHE) in 0.005 M H2SO4 solution. The isotopic labeling experimental results using 15N2 feed gas and 15NPC-500 reveal that the yielded NH3 indeed resulted from the NPC-500 catalyzed NRR, and the doped pyridinic-N also contributes NH3 formation during NRR. The experimental and theoretical calculations results indicate that the doped pyridinic-N in the NPC catalyst during NRR can break away from its surface to form N vacancies in a carbon matrix as the catalytic active sites for N2 adsorption and activation.