Self-supported nickel phosphide electrode for efficient alkaline water-to-hydrogen conversion via urea electrolysis

Electrochemical water splitting is an attractive technique to produce renewable hydrogen gas. However, considerable challenges remain before the catalytic anodic oxygen evolution reaction (OER) can occur at a satisfactory rate due to its sluggish kinetics, thus hampering the overall efficiency of this technology. Urea electrolysis provides opportunities for energy-conserving hydrogen production and the concurrent remediation of urea-enriched sewage water. Therefore, developing advanced electrocatalysts with a reduced cost and improved efficiency for the urea oxidation reaction (UOR) is key to the implementation of this technique. Herein, we present a three-dimensional (3D) self-supported nickel phosphide/Ni foam electrode (P-NF) that can be prepared by adopting a straightforward low-temperature phosphorization treatment of commercially available Ni foam. As a result, compared with the pristine Ni foam, the as-prepared 3D P-NF catalyst presents obviously enhanced activity for the electrocatalytic UOR, and a small potential of 1.32 V (versus the reversible hydrogen electrode (RHE)) is required to achieve a current density of 10 mA cm^-2. When the P-NF electrode is employed to catalyze the hydrogen evolution reaction (HER), it shows equally satisfactory performance. Moreover, a two-electrode electrolyzer system made of the as-obtained P-NF as the bifunctional electrocatalyst can deliver 10 mA cm^-2 at a cell voltage of only 1.37 V with remarkable operational stability.