The effects of phase composition of the nc-Ni thin films upon their catalytic activity is examined.

Nickel thin films (400 nm) were deposited by dc magnetron sputtering onto fused silica, mono-Si and alumina ceramic substrates. The base pressure in the process chamber was 10^-6 - 10^-5 Pa, and the working gas was argon at 1.3 Pa with a small admixture of oxygen. The substrate temperature was varied in the 20 - 700 °C range in order to examine the effects upon the film structure.

The film structure has been investigated using the XRD method and the Grazing Incidence Small Angle X-ray Scattering (GISAXS). The oxygen content was determined by the ERDA method using 35 MeV Cl⁷⁺ ions. The electrocatalytic activity of the nc-Ni electrodes for the Hydrogen Evolution Reaction (HER) was studied in 1.0 mol dm^-3 NaOH solution at 25 °C using polarization and electrochemical impedance spectroscopy techniques.

It was found that the prepared nickel films exhibit nanocrystalline structure in the whole range of examined substrate temperatures. However, with the increase of substrate temperature up to 700 °C the Ni-grain size increases from 12 to 130 nm, while characteristic length of the intergranular matter decreases from 8 to 2 nm. The oxygen content strongly decreases with increase in substrate temperature.

Electrocatalytic activity of the nc-Ni films for the HER significantly decreases (by more than 20 times) with the increasing substrate temperature and corresponding increase of the Ni-grain size. Thus, improved catalytic activity of nc-Ni is in accordance with an increase in the intercrystalline volume fraction at the very small grain size of the sputter deposited nickel.

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