Impact of Vacancy Defects on Electrochemical Nitrogen Reduction Reaction Performance of MXenes

We investigated electrochemical nitrogen reduction reaction (eNRR) on MXenes consisting of the vacancy defects in the functional layer using density functional theory calculations. We considered Mo₂C, W₂C, Mo₂N, and W₂N MXenes with F, N, and O functionalization and investigated distal and alternative associative pathways. We analyzed these MXenes for eNRR based on N₂ adsorption energy, NH₃ desorption energy, NRR selectivity, and electrochemical limiting potential. While we find that most of the considered MXenes surfaces are more favorable for eNRR compared to hydrogen evolution, these surfaces also have strong NH₃ binding (>-1.0 eV) and thus will be covered with NH₃ during operating conditions. Amongst all considered MXenes, only W₂NF₂ is found to have a low NH₃ desorption energy along with low eNRR overpotential and selectivity towards eNRR. The obtained eNRR overpotential and NH₃ desorption energy on W₂NF₂ are superior to those reported for pristine W₂N₃ as well as functionalized MXenes.