Journal of Applied Electrochemistry, Vol.34, No.5, 507-516, 2004
Effect of heat-treatment on the mechanism and kinetics of the hydrogen evolution reaction on Ni-P+TiO2+Tielectrodes
Composite Ni-P + TiO2 + Ti layers were prepared by codeposition of Ni -P alloy with TiO2 and Ti powders from a solution containing suspension of TiO2 and Ti particles. The electrodeposition was carried out under galvanostatic conditions at room temperature. The layers exhibited an amorphous Ni - P matrix in which crystalline TiO2 and Ti were embedded. On the deposit surface, the nonstoichiometric Ti oxide, Ti10O19, and intermetallic compounds, NiTi, formed during the electrodeposition, were also present. The heat treatment of these layers in argon leads to the crystallization of Ni - P matrix and formation of nonstoichiometric Ti oxides, detected by XRD. Electrolytic activity towards the hydrogen evolution reaction ( HER) was studied on these electrode materials before and after heat treatment. The mechanism of the HER was also studied, and the kinetic parameters were determined using steady-state polarization and electrochemical impedance spectroscopy (EIS). An increase in activity occurring after heating of Ni - P + TiO2 + Ti layers is related to TiO2 reduction and formation of nonstoichiometric Ti oxides: Ti10O19 (400 degreesC), Ti7O13 (500 degreesC) and Ti4O7 (800 degreesC). It is postulated that the increase in electrochemical activity is related to the properties of these oxides and a facility for H reduction/adsorption on their surface, as well as to the presence of NiTi intermetallics as compared with the Ni - P + TiO2 + Ti electrode.
Keywords:hydrogen evolution reaction;impedance modelling;nickel based electrodes;titanium;titanium dioxide