EFFECT OF ALKALINE CATIONS ON HYDROGEN EV OLUTION REACTION AT PD CATHODE

The effect of alkaline cations on the electrocatalytic activities of P d cathodes for hydrogen evolution reaction has been studied by the pot ential seep method and the impedance spectroscopy in H2SO4, LiOH, NaOH and KOH aqueous solutions. It took long time to get the steady state because of the surface change by the hydrogen ahsorption and the adsor ption or alkaline cations. At the region of low current density, longe r electrolysis time was necessary to get the steady state in alkaline solutions than in H2SO4. In KOH solution, two Tafel slopes were obtain ed in logarithmic current vs. potential curve by the potential step me thod. By the impedance spectroscopy, two Tafel slopes were also observ ed in NaOH and KOH solutions. The slopes changed at ca. -200 mV and -3 00 mV vs. RHE in NaOH and KOH solutions, respectively. These potential s were well agreed with the changes of the bode plots and the capacity . These changes were discussed to be caused by the change of the Pd ca thode surface such as UPD of alkaline cations. In LiOH solution, the c hange of the Tafel slope was nut observed clearly, possibly because th e change of the surface would take place at more positive potentials.