Ni-(Ebonex-supported Ir) composite coatings as electrocatalysts for alkaline water electrolysis. Part I: Hydrogen evolution

Abstract

The hydrogen evolution reaction (HER) was studied at electrodeposited Ni and Ni-(Ebonex/Ir) composite coatings in 1 mol dm(-3) NaOH solution at 25 degrees C. The Ni-(Ebonex/Ir) coatings were electrodeposited from a nickel Watts type bath containing different amounts of suspended Ebonex/Ir(30 wt.%) powder particles (0-2 g dm(-3)) onto a Ni 40 mesh substrate. The electrodes were investigated by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS) and polarization measurements. It was shown that the roughness factor of coatings increased to a maximum value of 27 with increasing the concentration of Ebonex/Ir particles in the deposition bath, while that of a pure Ni coating was found to be 3.2. In the whole potential range of the HER only one Tafel slope of about -120 mV dec(-1) was observed at all polarization curves. Considerably improved intrinsic catalytic activity for the HER compared to pure Ni was achieved with the composite coating deposited from the bath with the lowest concentration of Ebonex/Ir particles (0.1 g dm(-3)). Further enhancement of the apparent catalytic activity for the HER of Ni-(Ebonex/Ir) composite coatings obtained at higher concentrations of suspended Ebonex/Ir particles in the bath was attributed only to the increase of their electrochemically active surface area.