Minimizing energy loss based on ultrathin Co-Ni3S2 for enhanced electrocatalytic nitrate to ammonia

To address the challenge of high energy consumption (EC) in electrocatalytic nitrate reduction (ERN) for ammonia (NH 3 ) synthesis, this study proposes a dual strategy: engineering advanced anode materials and replacing the sluggish oxygen evolution reaction (OER) with the thermodynamically favorable urea oxidation reaction (UOR). A three-dimensional nanosheet Co-doped Ni 3 S 2 /NF (Co-Ni 3 S 2 /NF) self-supporting anode was prepared via a facile hydrothermal method. Co doping transformed the morphology from rod-like (Ni 3 S 2 /NF)) to nanosheet flower-like (Co-Ni 3 S 2 /NF), which quantitatively increased the BET surface area and electrochemical active surface area (ECSA) by approximately 7.6 and 14 times, respectively, thereby exposing a greater number of active sites. XRD revealed a ∼ 0.4° positive shift due to lattice contraction (Co 3+ radius 0.545 Å < Ni 2+ radius 0.69 Å), while a 3.1 cm −1 Raman shift indicated strengthened Ni S bonds and enhanced charge transfer. Consequently, the anode exhibited a large electrochemical active surface area (119.54 cm 2 ) and low charge-transfer resistance. It delivered superior catalytic activity, with an OER overpotential 86 mV lower than commercial Pt at 10 mA cm −2 , and a further 149 mV reduction when switched to UOR. Turnover frequency (TOF) analysis revealed that the enhanced performance originated predominantly from the increased density of active sites rather than their intrinsic activity. In combination with a Mn-CoNiP/NF cathode, UOR substitution reduced EC by 21.7 % while maintaining high NH 3 Faradaic efficiency (FE > 98 %), selectivity (SE > 95 %), and a yield rate of 1289.8 mg h −1  g −1 at −0.58 V vs. RHE. The system also demonstrated stable performance over 76 h. These findings highlight the potential of anode modulation via morphology engineering to lower energy demand in ERN, offering a sustainable strategy for efficient NH 3 production and nitrate remediation.