Doping‐Engineered Fe‐Co Tandem Sites Balance Hydrogen and Nitrite Intermediates for Efficient Nitrate to Ammonia Conversion at Low Potential

Why It Matters

The breakthrough offers a low‑energy route to produce ammonia while cleaning nitrate‑laden water, opening cost‑effective pathways for fertilizer manufacturing and decentralized wastewater treatment.

Key Takeaways

• Fe‑Co tandem sites achieve 98% NH₃ selectivity at –0.33 V vs. RHE.
• Dynamic *H balance suppresses HER and maintains hydrogenation efficiency.
• Adjacent Co sites instantly reduce Fe‑generated NO₂⁻ to NH₃, avoiding accumulation.
• Catalyst powers Zn‑NO₃⁻ battery at 6.63 mW cm⁻², showing scalability.

Pulse Analysis

Nitrate contamination of water bodies and the global demand for sustainable ammonia production have converged on electrocatalytic nitrate reduction (NO₃⁻RR) as a promising dual‑solution. Traditional catalysts struggle with high overpotentials, low Faradaic efficiencies, and poor selectivity because they cannot simultaneously manage the supply of active hydrogen (*H) and the rapid removal of nitrite intermediates. These limitations have kept NO₃⁻RR from scaling beyond laboratory proof‑of‑concept, despite its potential to replace energy‑intensive Haber‑Bosch processes and remediate polluted streams.

The Fe‑Co tandem catalyst (FeCo/C‑0.5) sidesteps these bottlenecks by engineering adjacent iron and cobalt sites that act in concert. Iron centers efficiently dissociate water, generating a controlled *H reservoir that fuels nitrate hydrogenation without triggering the hydrogen evolution reaction (HER). Meanwhile, cobalt sites positioned next to iron rapidly convert the generated NO₂⁻ into ammonia, preventing the buildup of toxic intermediates. This synergy yields an unprecedented 98% NH₃ selectivity and 89.7% Faradaic efficiency at a modest –0.33 V vs. RHE, with a specific ammonia yield of 14.1 mg h⁻¹ mg⁻¹ catalyst. In situ spectroscopies and DFT modeling confirm the dynamic *H balance and the spatially resolved reduction pathway, establishing a new design paradigm for tandem electrocatalysts.

Beyond laboratory metrics, the catalyst’s robustness in simulated wastewater containing chloride and sulfate, and its ability to deliver 6.63 mW cm⁻² in a Zn‑NO₃⁻ battery, signal clear commercial relevance. Industries ranging from fertilizer manufacturing to decentralized water treatment can leverage this low‑potential technology to cut energy costs and lower carbon footprints. Moreover, integrating the catalyst into flow‑cell or battery architectures could enable on‑site ammonia generation paired with renewable electricity, aligning with circular‑economy goals and emerging green‑hydrogen markets. The Fe‑Co tandem approach therefore marks a pivotal step toward economically viable, environmentally responsible ammonia synthesis.