Bifunctional catalysis on water splitting reaction by graphitic carbon supported NiO, NiS and NiSe nanoparticles

In this work, we have synthesized NiO, NiS and NiSe nanoparticles by similar hydrothermal method and the electrocatalytic activities of the graphite carbon-supported synthesized materials have been compared in reference to hydrogen and oxygen evolution reactions (HER and OER) in aqueous acidic and alkaline media respectively. The as-synthesized nanoparticles have been characterized by using powder X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopic studies. The best electrocatalyst, NiSe provides a current density of 10 mA cm⁻² at 259 mV overpotential for OER in 1.0 M KOH, which is superior to that of the state-of-the-art catalyst RuO₂ in the same environment. For HER the best electrocatalyst, NiSe provides a current density of 10 mA cm⁻² at 49.5 mV overpotential in 0.5 M H₂SO₄, which is again superior to Pt wire electrode. The order of electrocatalytic activity in both HER and OER has been found to follow the sequence: NiSe > NiS > NiO under the same electrochemical conditions, as have been evident from cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopic studies. While the electrochemical surface area is increased by 16.4 % and 37.3 % on changing the electrocatalyst from NiO to NiS and NiSe respectively, the chronoamperometric current densities are increased by 429 % and 635 % at 0.8 V for OER and 548 % and 9733 % at −0.4V for HER on changing the same materials. Thus, the enhancement in catalytic activity hangs mainly on the material characteristics besides the morphological improvement.