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 Mo 2 C, W 2 C, Mo 2 N, and W 2 N MXenes with F, N, and O functionalization and investigated distal and alternative associative pathways. We analyzed these MXenes for eNRR based on N 2 adsorption energy, NH 3 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 NH 3 binding (>-1.0 eV) and thus will be covered with NH 3 during operating conditions. Amongst all considered MXenes, only W 2 NF 2 is found to have a low NH 3 desorption energy along with low eNRR overpotential and selectivity towards eNRR. The obtained eNRR overpotential and NH 3 desorption energy on W 2 NF 2 are superior to those reported for pristine W 2 N 3 as well as functionalized MXenes.