Adv. Funct. Mater. doi:10.1002/adfm.201002471 (2011)

Fuel cells can convert chemical energy into electricity, and are typically composed of an anode and a cathode separated by an electrolyte membrane. In solid oxide fuel cells, the electrolyte is an oxide that can conduct negative oxygen ions from the cathode to the anode. These fuel cells work at high temperatures (up to around 1,000 °C), but reducing the thickness of the electrolyte can decrease their operating temperatures and nanoscale membranes have previously been fabricated. Bin Zhu and colleagues at the Royal Institute of Technology (KTH), Stockholm, have now been able to remove the electrolyte altogether, creating a fuel cell from a single homogenous layer.

The layer is made from a mixture of samarium-doped ceria and nanoparticles of a LiNiZn-based oxide, and has both ionic and semiconducting properties. Moreover, when hydrogen and air are supplied to either side of the layer, the composite can act as a catalyst for both the oxidation of hydrogen and the reduction of oxygen. On one side, hydrogen is broken down into protons and electrons, a function similar to that of the anode of a typical fuel cell; whereas on the other, electrons are received through an external circuit and oxygen from the air is split into negative oxygen ions, just like a fuel cell's cathode. Water is then thought to be generated through the direct combination of protons and oxygen ions on the surface of the particles.

The exact nature of the underlying processes is still unclear, but the Swedish team show that the one-layer fuel cells can convert hydrogen and air into electricity and water with a power output of more than 600 mW cm−2 at 550 °C.