Optimization of the Activity of Ni-Based Nanostructures for the Oxygen Evolution Reaction

Ni-based compounds have been widely used for catalytic water splitting in alkaline media. NiO-based nanostructures supported on carbon nanotubes (CNTs) were synthesized by atomic layer deposition (ALD) using NiCp2 and O-3 as precursors. NiO-coated CNTs display enhanced catalytic activity for the oxygen evolution reaction. The recorded overpotential of 315 mV at the current density of 10 mA cm(-2) in Ar-saturated 1 M KOH is lower than any reported values so far for NiO-based catalysts. Moreover, the overpotential is constant for 12 h electrolysis at current density of 10 mA cm(-2), highlighting the stability of our materials. The Tafel slopes of 50 mV dec(-1) are also lower than other Ni-based nanostructures previously reported. The study of CVs in the redox region in Fe(III)-free and Fe(III)-saturated 1 M KOH solutions proves that the high catalytic activity is intrinsic of the NiO/carbon composite and is not influenced by iron precipitation. The enhanced catalytic activities could be attributed to the conformal and well-distributed NiO layer by ALD and the large surface area and good conductivity of the CNTs network.