Efficient hydrogen production via urea electrolysis with cobalt doped nickel hydroxide-riched hybrid films: Cobalt doping effect and mechanism aspect

The exploration of earth-abundant catalysts that are highly active and robustly stable for urea electro-oxidation is critical for energy-efficient hydrogen production associated with urea-rich wastewater purification. Herein, Co-doped alpha-Ni(OH)(2) hybrid films with unique ultrafine nanoparticles assembled network structure are constructed as efficient bifunctional electrocatalysts for urea-assisted water electrolysis. By employing a facile potentiodynamic deposition route carried out in a deep eutectic solvent (Ethaline), ultrafine Ni-based nanoparticles with a alpha-Ni(OH)(2) rich surface doping by Co are in-situ grown on Cu foam substrate (Co-x-Ni(OH)(2) NPs/CF), creating an integrated electrode full of intimate contact interfaces. The doping of Co triggers a structural transition with electronic structure changes at the electrode surface and lowers the onset potential required for Ni(OH)(2)/NiOOH, which strongly enhances the urea electrolysis activity. Through potential conditioning procedure, the optimized Co-0.26-Ni(OH)(2) NPs/CF catalyst (with a Ni/Co proportion of 1:0.26) manifests excellent electrocatalytic performance for urea electrolysis in 1.0 M KOH with 0.5 M urea, presenting a low onset potential of 1.27 V vs. RHE for urea oxidation and an overpotential of 106 mV for the hydrogen evolution reaction at 10 mA cm(-2). Impressively, the constructed alkaline urea electrolyzer based on Co-0.26-Ni(OH)(2) NPs/CF delivers 10 mA cm(-2) at a stable output voltage of 1.42 V with robust durability over 38 h and high selectivity. (C) 2019 Elsevier Inc. All rights reserved.