Hydrogen evolution on NiPx alloys: the influence of sorbed hydrogen

NiP_x alloys were formed by electro deposition. P content in the range from 10 to 27 at% was obtained by altering the deposition current and the composition of the deposition electrolyte. For all the alloys the hydrogen evolution was measured in an alkaline solution. The catalytic activity of the alloys varied with several decades. The maximum activity was obtained for a Ni alloy with 12 at% P. The amount of hydrogen adsorbed to the surface and absorbed into the NiP_x alloys was measured. The highest catalytic activity was obtained for the alloys that sorbed a large amount of hydrogen. For the hydrogen reaction a Tafel slope close to 60 mV/dec was observed. The measurement of adsorption isotherms showed the Frumkin isotherm to give the best fit of the data. This isotherm also provided an explanation for the Tafel slopes.