The current response of an electrode which absorbs reactant on a potential step was computed by digital simulation and by Boltzmann substitution under assumption of diffusion coefficient being a linear function of concentration. The results were expressed as an correction factor [I in Sand equation i = -aF AC(D/rt)1'3. Similar results were obtained for admittance of such electrodes. Results were tested on absorption of hydrogen in sodium tungsten bronze Na,_,2 WO,. The potential step method is suitable for evaluation of concentration-potential-diffusion coefficient profiles. NOMENCLATURE AH+/RT, slope of By plot concentration and its crystallographic limit true and chemical diffusion coefficient value D at x = 0 (surface) standard potential, Armand potential initial and final potential in potential step method potential for y = 0 and y = 1 current imaginary unit time coordinate dimensionless concentration 0 Q y d 1, 7 = YIYmax complex impedance and admittance constant term for Warburg impedance relative value of Warburg impedance, 2, = z/z, correction term in Cotrell equation activity coefficient