Transient phenomena of electrochemical hydrogen pumps, permeation of hydrogen on passing a direct current through a proton-conducting electrolyte, were investigated. Variations of proton transport in electrochemical hydrogen permeation by changing the anode gas were investigated potentiostatically at 900 degrees C using a SrCe0.95Yb0.05O3-alpha proton-conducting solid electrolyte. Changes in direct current and charge carriers were examined on changing the anode gas from Ar to H-2 and back while keeping Ar as the cathode gas. In another variation of the anode gas with the two hydrogen isotopes, H-2 and D-2, the time dependence of the evolution of hydrogen isotope species at the cathode was analyzed to estimate the mobilities of protons and deuterons in the electrolyte.