Engineering interfacial water activation via synergistic defects and an aggregate carbon dot layer for efficient nitrate-to-ammonia electrocatalysis

Abstract

Ammonia synthesis from nitrate via electrocatalysis offers a sustainable alternative to the energy-intensive Haber–Bosch process, yet achieving high efficiency is challenging due to sluggish multi-electron transfer and unstable intermediates. Here, we report a TaON@CL hybrid electrocatalyst (CL denotes an aggregate carbon dot-derived carbon layer), which integrates oxygen vacancy-rich TaON with the carbon layer to synergistically engineer interfacial water activation and electron transfer, leveraging a sustainable and waste-valorizing carbon source. The defect-engineered TaON@CL enhances nitrate adsorption and stabilizes key hydrogenated intermediates while concurrently promoting interfacial charge transfer, lowering the free energy requirement of the rate-determining step (RDS), and facilitating water activation at the catalyst–electrolyte interface. This synergistic design achieves an NH₃ yield of 2843.1 mmol g_cat.⁻¹ h⁻¹ with a faradaic efficiency of 86.4%. Operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), transient photovoltage (TPV) analysis, and density functional theory (DFT) calculations collectively reveal that the defect-engineered TaON and the biomass-derived carbon layer act cooperatively to enhance interfacial water activation, facilitate electron transfer, and lower the rate-determining energy barrier, thereby establishing the mechanistic basis for the high activity and selectivity of the catalyst.