Strongly coupled carbon encapsulated Ni-WO2 hybrids as efficient catalysts for water-to-hydrogen conversion via urea electro-oxidation

Electrochemical water splitting is a sustainable method to produce hydrogen (H2), but it is limited by the large overpotential at anodic reaction. Using urea oxidation reaction (UOR) to replace oxygen evolution reaction (OER) can reduce the potential at anode and simultaneously purify the nitrogen-containing wastewater. Herein, the carbon encapsulated Ni-WO2 hybrids self-supported on nickel foam [denoted as (Ni-WO2)@C/NF] is synthesized via a hydrothermal method and then annealing in high temperature. The physicochemical characterizations indicate that the Ni-WO2 hybrids are encapsulated by carbon layer and the particles are evenly dispersed on the surface of nickel foam. It only needs a potential of 1.31 V and −77 mV for UOR and HER to produce a current density of 10 mA cm−2, exhibited outstanding catalytic activity. Furthermore, it only requires 1.38 V to drive a current density of 10 mA cm−2 for overall urea oxidation and lasting 80 h at 80 mA cm−2 without attenuation, highlighting the stability. This good performance could be originated from the synergistic effect between nickel and tungsten oxide, the carbon-encapsulated and the self-supported structure. This work offers a promising method for cost-effective and energy-saving H2 production and nitrogen-containing wastewater treatment.