Two-Step Tandem Catalysis for High-Efficiency Ammonia Synthesis Via Nitrate Reduction on Anion-Intercalated CoNi LDH...

Ammonia is essential across industry, agriculture, and as a future carbon-free energy carrier. Electrocatalytic nitrate reduction (NitRR) offers a sustainable path for removing nitrate contaminants from wastewater and groundwater while using abundant nitrate ions as nitrogen sources under eco-friendly conditions. However, the NitRR pathway, which involves sequential reactions, poses challenges in synchronizing the rate of nitrate-to-nitrite conversion with the subsequent reduction of nitrite to ammonia, particularly as the initial reduction step is rate-limiting. This study presents a CoNi layered double hydroxide (LDH) approach to finely control hydrogen radical (*H) supply, paired with Cu/Cu₂O redox coupling, to achieve optimal rate matching. CoNi LDH is engineered with various anion intercalations (NO₃ ^-, Cl^-, SO₄ ^2-, MoO₄ ^2-, WO₄ ^2-) to regulate *H capacity. By integrating Cu/Cu₂O and CoNi LDH, tandem kinetic descriptors, including a volcano curve, are employed to predict rate constants, facilitating ideal kinetic matching for efficient ammonia synthesis. The optimized MoO₄-CoNi LDH/CuO NW/CF electrode demonstrated exceptional performance, achieving a 99.78% Faraday efficiency, a yield of 1.12 mmol cm^-2 h^-1 at -0.2 V vs. RHE, and robust 14-h stability. The model descriptors effectively elucidated the kinetic pathway, linking reaction rates and factors impacting ammonia production.