Fabrication of Ni nanowires for hydrogen evolution reaction in a neutral electrolyte

Hydrogen evolution reaction in 1 M Na2SO4 was investigated using Ni nanowires in diameter of 250 nm with exposed lengths of 20, 35, and 45 μm, respectively. The Ni nanowires were fabricated by a direct-current pulse electrodeposition technique using an anodic aluminum oxide template, followed by selective removal of the supporting pore walls. Scanning Electron Microscope images revealed structural stabilities and X-ray diffraction pattern indicated a polycrystalline fcc phase. In current–potential (i–V) polarizations, the Ni nanowires with longer exposed lengths demonstrated larger current responses. Analysis from impedance spectroscopy confirmed increasing double-layer capacitances with longer Ni nanowires. In galvanostatic lifetime experiments, the free-standing Ni nanowires exhibited a reduced overpotential over that of supported ones. Similar procedures were performed for the oxygen evolution reaction in both i–V and lifetime measurements. For the Ni nanowires of 45 μm length, we estimated the energy cost for hydrogen production was 5.24 × 105 J/mole.