Improving the Selectivity of Nitrogen Reduction Reaction through the Mars-Van Krevelen Mechanism

Abstract

The electrochemical nitrogen reduction reaction (NRR) process is an attractive alternative to minimizing the energy and greenhouse gas footprint from current ammonia (NH3) production processes. Most NRR catalysts operate through utilizing an associative or dissociative mechanism, during which the NRR competes with the hydrogen evolution reaction (HER), resulting in low selectivity. In this presentation, we report on a new active catalyst for NRR that operates through the Mars-van Krevelen (MvK) mechanism to increase the selectivity of NRR towards NH3. This new catalyst, two-dimensional (2D) Ti2N nitride MXene, was synthesized via an oxygen-assisted molten salt fluoride etching technique. We confirmed its phase purity and stability in aqueous electrolytes using various characterization techniques, including Raman, X-ray diffraction, and UV-Vis. The Ti2N nitride MXene catalyst achieved a high Faradaic efficiency (FE) of 19.85% towards NH3 at an applied potential of –250 mV vs. RHE with a yield of 11.33 μg/cm2/hr in a 0.1 m hydrochloric acid (HCl) N2-saturated electrolyte. Electrocatalytic activity and selectivity obtained in an Ar-saturated electrolyte confirm that the new catalyst operates through an MvK mechanism. These results can be expanded to a broad class of systems enabling the MvK mechanism and constitute the foundation of NRR technology based on MXenes.