Atomically Dispersed Mo for Efficient Electrocatalytic Nitrogen Reduction: Nitrogen-Doped Defective Graphene Support

Efficient electrochemical nitrogen reduction reaction (NRR) under mild conditions is highly desired for achieving cost-effective application but is challenging to realize in practice. Previous studies have shown that atomically dispersed Mo on a graphene-like two-dimensional (2D) support can be a promising catalyst for NRR. Here, we show the outstanding electrocatalytic performance of a Mo-based atomically dispersed metal catalyst (ADMC) on a N-doped defective graphene support (Mo_<i>x</i>-N₆-gra (<i>x</i> = 1-3)) by using density functional theory computations. Particular attention is paid to the underlying reaction mechanism for NRR. The computed formation energy and <i>ab initio</i> molecular dynamics simulation suggest that the N atoms doped on the graphene support can firmly anchor the Mo atoms in both Mo₁-N₆-gra and Mo₂-N₆-gra configurations, which are highly beneficial for NRR. In particular, Mo₁-N₆-gra exhibits high catalytic activity toward NRR via the distal mechanism with a limiting potential of -0.23 V, even higher than that of many ADMCs with a graphene-like support. Importantly, Mo₁-N₆-gra enables effective suppression of the competing hydrogen evolution reaction (HER). Additionally, Mo₂-N₆-gra is another high-performance ADMC for NRR with a limiting potential of -0.35 V and different catalytic mechanisms (i.e., the split-alternating and split-mixed mechanism). This computational study suggests two highly efficient ADMCs for N₂ fixation, notably more efficient than previously reported ADMCs, and provides a design strategy for seeking a more optimal ADMC/support combination.