Understanding the lattice nitrogen stability and deactivation pathways of cubic CrN nanoparticles in the electrochemical nitrogen reduction reaction

Transition metal nitrides (TMNs) are predicted to be highly promising electrocatalysts for the nitrogen reduction reaction (NRR) by theoretical calculations. TMNs follow a special Mars-van Krevelen (MvK) mechanism during the NRR, involving surface lattice nitrogen exchange and regeneration. It is hence essential to identify the source of nitrogen, especially taking the stability of lattice nitrogen into consideration. Herein, we investigated the deactivation process of a benchmark CrN nanoparticle catalyst (CrN NPs) with a phase-pure cubic rocksalt (RS) structure for the electrochemical NRR. The current work identifies two possible deactivation pathways for CrN: (i) potential-induced structural collapse of the catalyst including both lattice N leaching and metal dissolution and (ii) ammonia poisoning due to the accumulation and strong chemical bonding of the produced ammonia on the CrN surface. This work provides new perspectives for understanding the structural evolution of nitrogen-containing electrocatalysts for NRR research.