Hydrogen absorption/diffusion into Pd80Rh20 alloy (50 mu m foil) was studied using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 0.1 M H2SO4 at 25 degrees C in the absence and presence of crystal violet. The double layer capacitance, charge transfer resistance, diffusion coefficient and mass transfer coefficient of hydrogen were determined. The mechanism of hydrogen absorption was discussed. Hydrogen adsorption inhibits the kinetics of hydrogen absorption and, in the presence of crystal violet, it proceeds much faster. At more positive potentials crystal violet is probably desorbed and the kinetics of absorption in the absence and in the presence of crystal violet proceeds with similar rate.