Apparatus for the measurement of the a‐c admittance of electrodes using sweep‐frequency techniques is described. Measurements of the interface are reported for the hydrogen adsorption, double‐layer, and oxide regions. Rotating disk electrodes were used, and necessary corrections for nonuniform current distributions are discussed. A single relaxation time closely characterizes the hydrogen adsorption process at all potentials. No evidence for Faradaic processes was evident in either the double‐layer or oxide regions, but the double layer capacitance exhibits a dispersion resembling that of a diffusional process.