Fe-Single-Atom Catalysts on Nitrogen-Doped Carbon Nanosheets for Electrochemical Conversion of Nitrogen to Ammonia

Electrochemical nitrogen reduction reaction (NRR) has been established as a promising and sustainable alternative to the Haber-Bosch process, which requires intensive energy to produce ammonia. Unfortunately, NRR is constrained by the high adsorption/activation of the N-2 energy barrier and the competing hydrogen evolution reaction, resulting in low faradic efficiency. Herein, a well-dispersed iron single-atom catalyst was successfully immobilized on nitrogen-doped carbon nanosheets (Fe-SAC-N-C) synthesized from pre-hydrothermally derived Fe-doped carbon quantum dots with an average particle size of 2.36 nm and used for efficient electrochemical N-2 fixation at ambient conditions. The as-synthesized Fe-SAC-N-C catalyst records an onset potential of 0.12 V-RHE, exhibiting a considerable faradic efficiency of 23.7% and an NH3 yield rate of 3.47 mu g h(-1) cm(-2) in aqueous 0.1 M KOH electrolyte at a potential of -0.1 V-RHE under continuous N-2 feeding conditions. The control experiments assert that the produced NH3 molecules only emerge from the dissolved N-2-gas, reflecting the remarkable stability of the nitrogen-carbon framework during electrolysis. The DFT calculations showed the Fe-SAC-N-C catalyst to demonstrate a lower energy barrier during the rate-limiting step of the NRR process, consistent with the observed high activity of the catalyst. This study highlights the exceptional potential of single-atom catalysts for electrochemical NRR and offers a comprehensive understanding of the catalytic mechanisms involved. Ultimately, this work provides a facile synthesis strategy of Fe-SAC-N-C nanosheets with high atomic-dispersion, creating a novel design avenue of Fe-SAC-N-C that can vividly have a potential applicability in the large spectrum of electrocatalytic applications.