Multiphase electrochemical reactions at the gas/liquid/solid phase boundary are often limited by the low solubility of the gaseous component in the electrolyte, leading to slow reaction rates. A particularly striking example is the electrochemical synthesis of ammonia from atmospheric dinitrogen and a proton source, which occurs at 0.148 V vs. NHE and hence strongly competes with the hydrogen evolution reaction (HER) occurring at 0 V vs. NHE.[1] Since the kinetics of the nitrogen reduction reaction (NRR) are intrinsically sluggish as compared to that of the HER, high overpotentials must be applied to yield ammonia in measurable quantities so that achieving a selectivity towards NRR becomes a key challenge in the field.[2] On top, solubility of nitrogen in the commonly used aqueous electrolytes is low, while protons are ubiquitous, rendering the HER the dominating reaction in such systems. On the other hand, due to their unique structure, ionic liquids exhibit high gas solubilities, typically by an order of magnitude higher than water.[3] Hence, the utilization of composites between microporous carbons and room-temperature ionic liquids (RTILs) as electrocatalysts is an efficient way to tailor the electrode/electrolyte interface in a way that protons are prevented from accessing the electrode surface and at the same time increased amounts of nitrogen can accumulate near the catalytically active centers to enable electrochemical NRR.

This approach was performed using a literature-known iron oxide-based catalyst, deposited on activated ultramicroporous carbon via a wet impregnation technique and employing it on a gas-diffusion electrode cell. This setup ensures the direct contact between gaseous N₂ molecules, solid electrocatalyst and the protons in the electrolyte, creating an ideal environment for e-NRR under ambient conditions. Ion Chromatography was used to measure the amount of produced ammonia. The resulting NH₃ yield rate and Faradaic Efficiency (FE) confirm the compatibility and the synergetic effect of nanoporous AC and iron oxide towards e-NRR, paving the way for further investigation for example of the effects of pore size, hydrophilicity of the RTIL.

References:

[1] F. Qu et al., J. Mater. Chem. A, 2019, 7, 3531,

[2] J. K. Nørskov et al., ACS Catal. 2017, 7 (1), 706–709.

[3] D. R. MacFarlane et al., Energy Environ. Sci. 2017, 10 (12), 2516–2520.