Unlocking sustainable nitrate reduction: Earth-abundant bimetallic electrodes under galvanostatic evaluation

Abstract

Electrochemical reduction of nitrate (ERN) has emerged as a green alternative to alleviate the NH3 production via the Haber-Bosch process. Harnessing earth-abundant materials for electrocatalysts is a logical strategy, minimizing dependence on the cost-prohibitive platinum group elements. While previous research has delved into the preparation and evaluation of electrodes for NH3 generation, much of it has been mainly focused on potentiostatic conditions and mechanisms elucidation, overlooking real-world scenarios and precluding the advancement towards technology implementation. This study addresses this gap by screening the performance of earth-abundant bimetallic electrodes, leveraging Cu foam as a substrate and modifying it with Cu2O, Ni(OH)2, SnO2, and Co(OH)x through electrodeposition. A comprehensive characterization encompassing morphological, structural, and electrochemical analysis was performed on the novel bimetallic surfaces. Electrolysis experiments targeting 30 mg L−1 NO3−-N were conducted under galvanostatic conditions (2.5, 5, 10, 20, and 40 mA cm−2), revealing the following trend in NH3 yield (mmol NH3 gcat−1 h−1): Cu/Co(OH)x > Cu/Cu2O > Cu foam > Cu/SnO2 > Cu/Ni(OH)2. Engineering figures of merit required for techno-economic analysis, such as Faradic efficiency, electrical energy per order, kinetic constants, and NH3 generation efficiency, were estimated for each configuration. This study not only sheds light on the operational conditions of ERN but also offers a roadmap toward sustainable and economically viable NH3 production.