Mechanistic Insights into Electrocatalytic Nitrogen Reduction Reaction on the Pd-W Heteronuclear Diatom Supported on C₂N Monolayer: Role of H Pre-Adsorption

The electrocatalytic N₂ reduction reaction (eNRR) is a potential alternative to the Haber–Bosch process for ammonia (NH₃) production. Tremendous efforts have been made in eNRR catalyst research to promote the practical application of eNRR. In this work, by means of density functional theory calculations and the computational hydrogen electrode model, we evaluated the eNRR performance of 30 single metal atoms supported on a C₂N monolayer (M@C₂N), and we designed a new thermodynamically stable Pd-W hetero-metal diatomic catalyst supported on the C₂N monolayer (PdW@C₂N). We found that PdW@C₂N prefers to adsorb H over N₂, and then, the pre-generated hydrogen-terminated PdW@C₂N selectively adsorbing N₂ behaves as the actual functioning “catalyst” to catalyze the eNRR process, exhibiting excellent performance with a low overpotential (0.31 V), an ultra-low NH₃ desorption free energy (0.05 eV), and a high selectivity toward eNRR over hydrogen evolution reaction (HER). Moreover, PdW@C₂N shows a superior eNRR performance to its monomer (W@C₂N) and homonuclear diatom (W₂@C₂N) counterparts. The revealed mechanism indicates that the preferential H adsorption over N₂ on the active site may not always hamper the eNRR process, especially for heteronuclear diatom catalysts. This work encourages deeper exploration on the competition of eNRR and HER on catalyst surfaces.