(448c) Sustainable synthesis of NH3 via electrochemical reduction of N2 on an earth abundant Cu gas diffusion electrode at ambient conditions
AIChE Annual Meeting
Wednesday, November 10, 2021 - 9:50am to 10:10am
The electrochemical reduction of N2 to produce NH3 at ambient conditions is an effective and sustainable route to store H2, balance the N2 cycle, and provide means to produce on-demand fertilizers. The efficient electrosynthesis of NH3 is challenging because of the high energy of N â¡ N triple bond (941 kJ/mol), dominant undesired H2 evolution reaction (HER), and lower solubility of N2 in aqueous solution. Here, we propose theory-guided activity descriptors to identify an efficient N2 reduction reaction (NRR) catalyst, followed by its implementation in a flow through gas diffusion electrode (GDE) to quantify the effects of pH, cation identity, H2O saturation, and N2 concentration on the kinetics of the NRR. The identified Cu catalyst with dominant (111) facets electrodeposited on a carbon paper provides optimal active sites to obtain maximum NH3 Faradaic efficiency (FE) of 18 Â± 3 % at -0.3 V vs RHE and the maximum NH3 current density of 0.25 ± 0.03 mA/cm2 at -0.5 V vs RHE in an alkaline medium. The electrolyte pH, counter cations and the H2O saturation on the catalyst are optimized to suppress the HER. The fixed potential DFT calculations reveal an associative distal mechanism for the NRR over Cu where the hydrogenation of *N2 is the rate limiting step.