Electrochemical nitrogen reduction reaction (NRR) technology is a viable alternative to reducing the energy and greenhouse gas footprint from the current ammonia (NH3) production technology. Most NRR catalysts operate by using 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 evokes the Mars-van Krevelen (MvK) mechanism to increase the selectivity of NRR towards NH3. The MvK mechanism reduces the competition between NRR and HER by eliminating the adsorption and dissociation processes of nitrogen gas (N2) at the active sites for NH3 synthesis. 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. 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 support an MvK mechanism. These results can be expanded to a broad class of systems evoking the MvK mechanism and constitute the foundation of NRR technology based on MXenes.

Evoking the Mars-van Krevelen mechanism on Ti2N Nitride MXene to achieve high selectivity for nitrogen reduction reaction

ACS Spring 2022

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