Boosting Electrocatalytic Nitrogen Fixation with Co-N3 Site-Decorated Porous Carbon

Electrocatalytic ammonia (NH3) synthesis under ambient temperature and pressure is an emerging sustainable method for dinitrogen (N-2) fixation, providing a potential environmentally benign pathway for N-2 fixation using renewable power of electricity. However, this strategy is subjected to the low activity of electrocatalysts. In this work, a Co-N-x-C hybrid derived from the metal-organic framework with built-in Co-N-x active sites was fabricated. A high NH3 yield (37.6 mu g mg(-1) h(-1) at -0.9 V vs a reversible hydrogen electrode) and favorable faradaic efficiency (17.6% at -0.3 V vs a reversible hydrogen electrode) were achieved in a 0.05 M H2SO4 electrolyte. The dominating coordination environment of Co-N-x was finally determined by combining X-ray absorption fine structure spectroscopy and theoretical calculation. Co-N-3 demonstrated pivotal active centers that facilitated N-2 adsorption, lowered the free energy of the rate-determining step, inhibited hydrogen evolution reaction, and promoted the N-2 reduction reaction (N2RR). The hierarchical pore structure of catalysts also promoted N-2 adsorption, and the produced high pressure contributed to the further reaction of N-2 fixation. This work also provides a new strategy for developing cost-effective electrocatalytic materials for N2RR.