Constructing AgNi biphase catalysts with a hierarchical pore structure for efficient nitrate reduction to ammonia at low potentials

Abstract

The electrocatalytic nitrate reduction to ammonia (NO₃RR) offers an energy-saving and environmentally friendly technological pathway as an alternative to the traditional high-energy-consumption and high-emission Haber–Bosch process. The hydrogen-assisted reduction pathway in the NO₃RR has gradually become a research hotspot due to its significant advantages in both selectivity and reaction kinetics. To suppress the competing hydrogen evolution reaction (HER), catalysts designed based on this pathway typically facilitate the NO₃RR process at low overpotentials. Therefore, achieving high-current NO₃RR catalysis at low overpotentials has become the key challenge for the practical application of the hydrogen-assisted reduction pathway. Herein, we designed and constructed a 7Ag3Ni bimetallic catalyst with a hierarchical pore structure through a combined dissolution-pore-forming and electrochemical corrosion approach. Benefiting from the engineered porosity, the catalyst enables high-current-density electrocatalytic NO₃RR at low potentials. The 7Ag3Ni bimetallic catalyst exhibits exceptional electrocatalytic performance with a high current density of 400 mA cm⁻² at −0.38 V vs. RHE, achieving an outstanding ammonia production rate of 32.6 mg h⁻¹ cm⁻² and a remarkable 93.5% faradaic efficiency for NH₃ generation. Electrocatalytic mechanism studies reveal that in the 7Ag3Ni bimetallic catalyst, Ag governs the two-electron transfer process from NO₃⁻ to NO₂⁻, while Ni provides active sites for hydrogen-adsorbate species, enabling rapid conversion of NO₂⁻ to NH₃ through the hydrogen-assisted reduction pathway.