Enhancing hydrogen evolution through urea electrolysis over Co-doped Ni-P-O film on nickel foam

Abstract

A Co-doped Ni-P-O film supported on nickel foam is successfully prepared. It exhibits high activity toward urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Regarding UOR, the onset potential of Ni-P-O is reduced by the introduction of Co and gradually decreases with the incremental of Co content in the film ascribed to the reduction of conversion potential of Ni2+/Ni3+. Concerning HER, the incorporated Co in Ni-P-O film not only increases the amounts of active sites, but also boost the synergetic effect on water dissociation and hydrogen desorption. Particularly, the optimum activity of Ni-P-O is achieved by the introduction of an 8% cobalt source (8% Co:Ni-P-O/NF), which offers the highest activity with the lowest overpotential of 94 mV and Tafel slope of 46.2 mV·dec−1. Furthermore, the efficiency of hydrogen generation is further improved by urea-assistance over the electrolyzer coupled with 8% Co:Ni-P-O/NF electrode. Only 1.481 V is needed to afford 20 mA·cm−2 in urea-mediated electrolysis cell, much lower than that for urea-free electrolyte with 1.689 V.