Electrochemical ammonia synthesis from nitrate can complement a hydrogen-based energy system with a liquid, shippable energy carrier. Ammonia (NH3) 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 NO3– → NO2– step is widely viewed as rate-determining, followed by nitrite reduction and hydrogenation steps, until the formation of NH3. Here, we implement a tandem strategy in a flow cell using a double-sided electrode with Cu and TiO2@Cu surfaces that cooperatively boost the NO3– → NO2– and NO2– → NH3 conversions. The system achieves a Faradaic efficiency toward NH3 of 97%, with an NH3 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 NO3RR by combining nitrate adsorption with selective nitrite hydrogenation. These results establish a practical route for the efficient electrochemical synthesis of NH3 from nitrate.
Chávez et al. (Thu,) studied this question.