Atomic hydrogen provision by cobalt sites in a bimetallic Ni/Co(OH)x and trimetallic Ni/Cu2O/Co(OH)x configurations for superior ammonia production

Abstract

Electrochemical reduction of nitrate provides a green alternative for decentralized ammonia production by selectively transforming a pollutant in an added-value product. Electrocatalysts containing platinum group metals (PGM) present a high selectivity and stability for ammonia production. However, these cost-prohibitive elements motivate the design of catalysts based on earth-abundant elements with comparable performance. Herein, Ni/Co(OH)x and Ni/Cu2O/Co(OH)x interfaces illustrate high competitiveness as PGM-free substitutive electrocatalyst. Evaluation of synergistic effects and mechanisms suggest co-existing direct charge transfer reduction and catalytic hydrogenation by atomic hydrogen provision over Co(OH)x sites. Trimetallic configuration reached high nitrate conversion (90.3 %) in less than 120 min when treating solutions at environmental-relevant concentration of 30 mg L−1 NO3--N. Meanwhile, electrode stability evaluation demonstrated high activity retention (>90 %) and negligible metal leaching after 12 h of sustained use. These results motivate the exploration of electrocatalyst based on earth-abundant materials for electrochemically driven N-resource recovery.