Influence of hydrogen absorption in amorphous Ni-P electrodes on double layer capacitance and charge transfer coefficient of hydrogen evolution reaction

Hydrogen evolution reaction (HER) was studied by ac impedance spectroscopy on electrolytically prepared amorphous Ni-P(3) layers with the phosphorus content about 3 wt%, The method allowed two equivalent circuits to be found which are different for the low (up to E greater than or equal to - 0.10 V RHE) and high (E less than or equal to - 0.150 V) potentials. It did not allow evaluation of the rate constants of possible reaction steps. Impedance spectroscopy and the analysis of previously published results obtained by potential decay method confirmed that the high double layer capacitances (around 10 mF cm(-2)) are characteristic for the active Ni-P(3) electrodes. Further measurements proved that the double layer capacitance of these electrodes depends on the amount of absorbed hydrogen and it can change in the range of two orders. It was also found that the charge transfer coefficient beta also varied in the range beta approximate to 0.5-1 according to the content of absorbed hydrogen. Poisoning the electrodes by thiourea caused a decrease in the amount of absorbed hydrogen and an increase in the overvoltage of the HER mainly at higher current densities. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.