Charge transfer and reaction coordinate construction based theoretical investigation of the eNRR and HER on cuboidal silver phosphate: a tale of two competing mechanisms†

We have performed systematic electronic structure calculations based on reaction coordinate construction and charge transfer analysis to explore the demarcation between two-competing mechanisms: the electrochemical nitrogen reduction reaction (eNRR) and hydrogen evolution reaction (HER). We have employed density functional theory based first-principles calculations to investigate the eNRR and HER on the cuboidal silver phosphate Ag₃PO₄ surface in an acidic medium. For the eNRR, we have explored all three reaction mechanism pathways named distal, alternating and enzymatic, while the adsorption site selectivity has also been envisaged in this work. Among all the possible catalytic sites of Ag₃PO₄, the Ag site turned out to be the most energetically favourable for the eNRR that suppresses HER activity. The alternating pathway is confirmed to be the best catalytic pathway with a limiting potential of −0.60 V, as compared to −1.4 V and −2.9 V for distal and enzymatic pathways, respectively. The quantitative and qualitative analyses of the charge transfer process corresponding to the alternating pathway of the eNRR are also being explored from the perspective of Bader charge variation and charge density distribution.