Developing electrocatalysts that exhibit both high activity and ammonia selectivity for nitrate reduction is a significant and demanding challenge, primarily due to the complex nature of the multiple-electron reduction process involved. An encouraging approach involves coupling highly active precious metals with transition metals to enhance catalytic performance through synergy. Here, we report a ruthenium-nickel alloy catalyst with nanosheets (Ru-Ni NSs) structure that achieves a remarkable ammonia Faradaic efficiency of approximately 95.93%, alongside a yield rate of up to 6.11 g·h⁻¹·cm⁻². Moreover, the prepared Ru-Ni NSs exhibit exceptional stability during continuous nitrate reduction in a flow reactor for 100 h, maintaining a Faradaic efficiency of approximately 90% and an ammonia yield of 37.4 mg·L⁻¹·h⁻¹ using 0.05 M nitrate alkaline electrolyte. Mechanistic studies reveal that the catalytic process follows a two-step pathway, in which HONO serves as a migration intermediate. The presence of a partially oxidized Ru (002) surface enhances the adsorption of nitrate and facilitates the release of the migration intermediate by adjusting the strength of the electrostatic and covalent interactions between the adsorbate and the surface, respectively. On the other hand, the Ni (111) surface promotes the utilization of the migration intermediate and requires less energy for NH₃ desorption. This tandem process contributes to a high catalytic activity of Ru-Ni NSs towards nitrate reduction.

Biochar-based transition metal catalysts have been identified as excellent peroxymonosulfate (PMS) activators for producing radicals used to degrade organic pollutants. However, the radical-dominated pathways for PMS activation severely limit their practical applications in the degradation of organic pollutants from wastewater due to side reactions between radicals and the coexisting anions. Herein, bimetallic Fe/Mn-loaded hydroxyl-rich biochar (FeMn-OH-BC) is synthesized to activate PMS through nonradical-dominated pathways. The as-prepared FeMn-OH-BC exhibits excellent catalytic activity for degrading tetracycline at broad pH conditions ranging from 5 to 9, and about 85.0% of tetracycline is removed in 40 min. Experiments on studying the influences of various anions (HCO₃⁻, NO₃⁻, and H₂PO₄⁻) show that the inhibiting effect is negligible, suggesting that the FeMn-OH-BC based PMS activation is dominated by nonradical pathways. Electron paramagnetic resonance measurements and quenching tests provide direct evidence to confirm that ¹O₂ is the major reactive oxygen species generated from FeMn-OH-BC based PMS activation. Theoretical calculations further reveal that the FeMn-OH sites in FeMn-OH-BC are dominant active sites for PMS activation, which have higher adsorption energy and stronger oxidative activity towards PMS than OH-BC sites. This work provides a new route for driving PMS activation by biochar-based transition metal catalysts through nonradical pathways.