Electrical and hydrogen transport properties of SrCe _0.8Yb _0.2O _3-δ/Ni cermet membranes

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 the electrical and hydrogen permeation properties of SrCe _0.8Yb _0.2O _3-δ (SCYb). The results showed that the hydrogen permeation rate is limited by electron flow at the investigated temperatures (600 - 900°C). To further enhance hydrogen permeability, a cermet (i.e., ceramic-metal composite) membrane was made by adding Ni to the SCYb. The cermet showed no phase change after sintering in a reducing atmosphere. At 900°C, with 20% H ₂/balance He as a feed gas (pH ₂O = 0.03 atm), the hydrogen permeation rate was 0.113 cm ³/min-cm ² for Ni/SCYb (0.43-mm thick) and 0.008 cm ³/min-cm ² for SCYb (0.7-mm thick). The dependences of hydrogen permeability on temperature, thickness, and hydrogen partial pressure gradients are also determined. The results demonstrate that adding Ni to SCYb considerably increases its hydrogen permeability by increasing its electron conductivity.