Single-Electrode Tandem Electrocatalysis with Dual TiO 2 @Cu and Cu Surfaces Enables Energy-Efficient Ammonia Production from Nitrate

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High Resolution Image Download MS PowerPoint Slide Electrochemical ammonia synthesis from nitrate can complement a hydrogen-based energy system with a liquid, shippable energy carrier. Ammonia (NH 3 ) is attractive because it serves both as an energy vector and as an essential feedstock. However, nitrate reduction is an eight-electron, proton-coupled pathway that forms multiple intermediates; the NO 3 – → NO 2 – step is widely viewed as rate-determining, followed by nitrite reduction and hydrogenation steps, until the formation of NH 3 . Here, we implement a tandem strategy in a flow cell using a double-sided electrode with Cu and TiO 2 @Cu surfaces that cooperatively boost the NO 3 – → NO 2 – and NO 2 – → NH 3 conversions. The system achieves a Faradaic efficiency toward NH 3 of 97%, with an NH 3 selectivity of 80%, and a productivity of 7.7 mg h –1 cm –2 (0.45 mmol h –1 cm –2 ), corresponding to a full-cell energy efficiency of 29%. This integrated electrode–reactor design expands the accessible performance space for the NO 3 RR by combining nitrate adsorption with selective nitrite hydrogenation. These results establish a practical route for the efficient electrochemical synthesis of NH 3 from nitrate.