Electrode reactions of intermediate species (IS), generated by a short pulse of laser photoemission (LPE), result in the time-dependent change of emitted charge Q(t). Analytical expressions for the kinetic curves Q(t) are derived by solving non-stationary diffusion equations for e(aq)(-) and IS. For the IS adsorption Gibbs energy less than -25 kJ mol(-1), kinetic curves art exponential over the very wide range of electrode reaction rate constant W, from 1 up to 10(7) s(-1). The dependence Q(t) alpha t(-1/2) is typical for the case of activated adsorption of IS or their discharge from the non-adsorbed state. Voltammograms of IS generated by pulse radiolysis, modulated photolysis and pulsed or alternating photoemission current are demonstrated to be described by similar expressions. The difference between half-wave and equilibrium potentials depends on the reactant and product lifetimes and rates of desorption. A characteristic trapezoid of Tafel lines is introduced as a new way to characterize completely the kinetics of two-electron electrode reactions. The relations obtained were applied to the analysis of hydrogen evolution reactions and carbon dioxide and formaldehyde reduction, where hydrogen atoms and organic radicals HCO2 and CH2OH adsorbed on a mercury electrode participate as IS.