Mixed ionic–electronic conductors are widely used in  electrodes of fuel cells and batteries eg.YSZ-Ni(anode); YSZ-electrolyte(ionic),Ni-electrode(hole) or  

LixTiS2 

you can  use carbonaceous materials or Transparent conductive oxides (TCO).

I don't know what electrochemical device you are referring to, specifically, but this is possible in SOFC/SOECs. In these types of cells, the electrolyte must be conduct either oxygen ions or hydrogen protons, but not electrons. However, the electrodes must necessarily have mixed ionic and electronic conductivity. The most common configuration is YSZ (electrolyte) and YSZ-Ni cermet (H2 electrode). The Ni is added to supply electronic pathway. 

In principle, you can also use gadolinia-doped ceria as it becomes a mixed ionic and electronic conductor under reducing conditions (H2 electrode), but this is rarely if ever the case because it simultaneously lowers cell efficiency because of electronic leakage across the electrolyte. 

Thank u .