Optically passive thin films of mixed cerium/titanium and cerium/zirconium oxides have been prepared by electron beam reactive evaporation. Different oxidation levels have been achieved using different oxygen flows in the deposition process. The samples have been optically and electrochemically characterized. Performances are discussed in view of a future utilization in a electrochromic device as thin film counter electrode. Different materials have been tested to identify the best solution to be used as an optically passive ion storage layer in an existing electrochromic device in alternative to an optically active V2O5 counter electrode. Process conditions and materials performances are reported, related to each other and discussed. Development studies are still in progress towards the optimization of the device and its future scaling up.