Waste-derived cobalt Electrocatalysts for high-efficiency nitrate-to-Ammonia conversion and sustainable resource...

Electrochemical nitrate reduction (NO₃RR) is a promising route to sustainable ammonia production, but suffers from inefficient catalysts. Here, we synthesize a high-performance cobalt-based electrocatalyst derived from spent batteries and brewery waste. The catalyst achieves an ammonia yield of 75.32 mg h^-1 mgₚₜₙ^-1 and NH₄⁺-N recovery efficiency of 88.36 % at -1.5 V vs. Hg/HgO. In situ Fourier transform infrared (In situ FTIR) spectroscopy and density functional theory (DFT) calculations reveal that optimized electron redistribution near the Fermi level accelerates the rate-limiting NO₂^- → NH₃ step. Critically, the catalyst demonstrates scalability in treating actual fertilizer wastewater (NO₃^--N = 3573.30 mg L^-1) via continuous flow. Over 10 h operation, cumulative ammonia production reached 172.11 mg with an energy consumption of 96.75 kWh kg^-1 for NH₄⁺-N recovery, surpassing existing systems. This "waste-for-waste" strategy establishes a closed-loop process that reduces energy/carbon costs while enabling resource circularity, delivering dual economic and environmental benefits.