Rather than using three layers, including an electrolyte, a working fuel cell is created that employs only one homogenous layer with mixed conductivity. The layer is a composite made from a mixture of metal oxide, Li0.15Ni0.45Zn0.4 oxide, and an ionic conductor; ion-doped ceria. The single-component layer has a total conductivity of 0.1-1 S cm(-1) and exhibits both ionic and semiconducting properties. This homogenous one-layer device has a power output of more than 600 mW cm(-2) at 550 degrees C operating with H-2 and air. Overall conversion is completed in a similar way to a traditional fuel cell, even though the device does not include the electrolyte layer critical for traditional fuel-cell technologies using the three-component anode-electrolyte-cathode structure.