Coal tar pitch-derived nitrogen-doped carbon hosting iron for enhanced ammonia electrosynthesis

Abstract

Renewable electricity powered N₂ electroreduction provides a clean strategy for sustainable NH₃ production, of which the fabrication of electrocatalysts with excellent performance, stability, and cost-effectiveness is vital for its real applications. Herein, we for the first time confined Fe species to the coal tar pitch derived nitrogen-doped porous carbon (denoted as Fe₂O₃/FeNC) by pyrolyzing a uniform mixture of medium temperature coal tar pitch, FeCl₃·6H₂O, urea and NaCl. The obtained Fe₂O₃/FeNC exhibits an excellent N₂ electroreduction activity in neutral media, evidenced by an NH₃ yield of 38.17 ± 0.88 μg·h^-1·mg_cat^-1 at -0.5 V versus reversible hydrogen electrode (vs. RHE) in 0.1 M Na₂SO₄ with a Faradaic efficiency of 22.01% (-0.3 V vs. RHE), surpassing most Fe-based N₂ reduction electrocatalysts reported to date. The detailed electrochemical investigations indicate that the improved N₂ electroreduction performances are mainly due to the following reasons. One is the highly dispersed Fe species provide sufficient active sites for N₂ electroreduction. Another is the existence of both pyridinic-N and pyrrolic-N species facilitates N₂ adsorption. In addition, the interconnected porous carbon matrix accelerates the electron and mass transfer during the electrolysis. Importantly, the in-situ formation of Fe-N-C and Fe₂O₃ nanoparticles on carbon substrate prevents the aggregation and leaching of the Fe species and increases the stability of Fe₂O₃/FeNC. This work presents an ingenious strategy for the mass fabrication of metal-based electrocatalyst for N₂ electroreduction, enabling the high value utilization of coal tar pitch.

Keywords

N₂ electroreduction / iron / coal tar pitch / electrocatalysis / N-doped carbon

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