Coordination Structure Modulation in Group-VIB Metal Doped Ag₃PO₄ Augments Active Site Density for Electrocatalytic...

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag₃PO₄ to enhance the active site density, accompanied by d-p orbital mixing at the active site/N₂ interface. Doping induces compressive strain in the Ag₃PO₄ lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N₂ adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N₂H₄, which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N₂ to NH₃ on Mo/Ag₃PO₄-10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR.