Research on hydrogen separation membranes is motivated by the increasing demand for an environmentally benign, inexpensive technology for separating hydrogen from gas mixtures. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, the addition of metal to these oxides increases their hydrogen permeability and improves their mechanical stability. This study began by determining hydrogen permeation properties of SrCe0.8Yb0.2O3-delta (SCYb). The results showed that at the investigated temperatures (600-900 degrees C), the hydrogen permeation rate is limited by electron flow. To further enhance hydrogen permeability, a cermet (i.e., ceramic-metal composite) membrane was made by adding Ni to the SCYb. At 900 degrees C, with 20% H-2/balance He as a feed gas (p(H2O) = 0.03 atm), the hydrogen permeation rate was 0.105 cm(3)/min cm(2) for 0.25-mm-thick Ni/SCYb and 0.008 cm(3)/min cm(2) for SCYb (0.7-mm thick). The dependence of hydrogen permeability on temperature and hydrogen partial-pressure gradients was also determined. The proton conductivity (approximate to ambipolar conductivity) was extracted from the dependence of hydrogen permeability on hydrogen potential gradients. The results demonstrate that adding Ni to SCYb considerably increases its hydrogen permeability by increasing its electron conductivity. (c) 2005 The Electrochemical Society.