Ni-MoO2 Composite Coatings Electrodeposited at Porous Ni Substrate as Efficient Alkaline Water Splitting Cathodes

Abstract

To obtain highly efficient yet easily produced water-splitting cathodes, Ni-MoO2 composite coatings were electrodeposited at a Ni foam substrate with an open-pore structure, pore size of 450 µm, in a Watts-type bath. The concentration of MoO2 particles (about 100 nm) was varied, while the intensive mixing of the solution was provided by air bubbling with 0.5 L min−1. Electrodeposition was performed at different constant current densities at room temperature. The morphology and composition of the coatings were investigated by SEM and EDS. The hydrogen evolution reaction (HER) was tested in KOH of different concentrations, at several temperatures, in a three-electrode H-cell by recording polarization curves and EIS measurements. The lowest achieved HER overpotential was −158 mV at −0.5 A cm−2. Up-scaled samples, 3 × 3.3 cm2, were tested in a single zero-gap cell showing decreasing cell voltage (from 2.18 V to 2.11 V) at 0.5 A cm−2 over 5 h in 30% KOH at 70 °C with electrolyte flow rate of 58 mL min−1. Compared to pure Ni foams used as both cathode and anode under the same conditions, the cell voltage is decreased by 200 mV, showing improved electrode performance.