Formation of porous Ni surface by electrodeposition and dissolution in molten salt

In a NaCl–KCl-3.5 mol%AlF3 molten salt bath, Al deposition and Al dissolution were performed at the bath temperatures of 750 °C and 900 °C to form a porous Ni surface . Furthermore, in order to investigate the hydrogen evolution behavior of the prepared porous Ni, the cathode polarization curve was measured in 10% KOH. When the Al was dissolved after the Al deposition, a porous layer was formed on the Ni surface of the substrate. When the electrodeposition potential of Al was lowered, it formed a thicker layer. Observations of the porous surface showed that the sample at 900 °C had a finer morphology than at 750 °C. The cathode polarization curve in an alkaline aqueous solution was measured. The porous Ni showed a higher cathode current density at a potential higher than the untreated Ni. The cathode current density increased in the order of untreated Ni, 750 °C treatment, and 900 °C treatment. Therefore, it was found that the 900 °C treatment generated the most hydrogen. The sample with the higher porosity showed a higher cathode current density based on the cathode polarization curve. The activation energies for the hydrogen evolution reaction were 10.3 kJ/mol for the untreated Ni, 10.1 kJ/mol at 750 °C, and 11 kJ/mol at 900 °C. There is no difference in the reaction mechanism, and it is considered that the performance was improved by increasing the surface area.