Kinetics of the hydrogen evolution reaction on Ni-(Ebonex-supported Ru) composite coatings in alkaline solution

The hydrogen evolution reaction (HER) was studied on Ni, Ni-Ebonex and Ni-(Ebonex-Ru) coatings in 1 mol dm(-3) NaOH solution at 25 degrees C. The composite coatings were electro-deposited from a nickel Watts-type bath containing suspended Ebonex (chemical composition mainly Ti4O7) or Ebonex-supported Ru(10 wt.%) particles (0-10 g dm(-3)) onto Ni mesh substrate. The electrodes were investigated by cyclic voltammetry (CV), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), electrochemical impedance spectroscopy (EIS) and polarization measurements. These investigations showed that the roughness factor of the Ni-(Ebonex-Ru) and the Ni-Ebonex coating was 29 and 6 times higher than that of a pure Ni coating, respectively. In the whole potential range of the HER only one Tafel slope of about -120 mV was present at the polarization curves of Ni and Ni-Ebonex electrodes, with increased activity of the latter being attributed only to the increase of the electrochemically active surface area. The Ni(Ebonex-Ru) electrodes exhibited the highest intrinsic catalytic activity with two Tafel slopes, indicating also that the HER takes place exclusively. on Ru active sites.