Ni3S2/MWCNTs/NF Hybrid Nanostructure as Effective Bifunctional Electrocatalysts for Urea Electrolysis Assisted Hydrogen Evolution

Substituting the smaller theoretical applied potential of the urea oxidation reaction (UOR) for the larger theoretical potential of anodic water electrolysis (oxygen evolution reaction (OER)) is critical for the energy requirement in the evolution of hydrogen. In this work, a brief and scalable strategy was presented to synthesize nickel sulfide and multi-walled carbon nanotube composites on Ni foam, denoted as Ni3S2/MWCNTs/NF. Electrochemical measurements show that Ni3S2/MWCNTs/NF can be an efficient electrocatalyst for UOR. A potential of 1.338 V was required at a current density of 10 mA·cm−2 for UOR with Ni3S2/MWCNTs/NF. This UOR catalyst was used to replace OER for hydrogen production, which reduced the overpotential required for H2-production and reduced overall power consumption. Also, the Ni3S2/MWCNTs/NF catalyst exhibited high electrocatalytic efficiency to evolve hydrogen, which provided a low overpotential of only 104 mV at 10 mA·cm−2. As a proof of concept, a water-urea electrolysis measurement was carried out in 1 M KOH with 0.5 M urea using Ni3S2/MWCNTs/NF as the cathode and anode, respectively. Ni3S2/MWCNTs/NF∣∣Ni3S2/MWCNTs/NF electrodes provided a current density of 10 mA·cm−2 at a voltage of 1.509 V, which was 149 mV lower than that of water splitting, which proved that this catalyst may be commercially viable in energy-saving hydrogen production.