Solid-oxide fuel cells work by separating a fuel cell's cathode and anode with a solid electrolyte that passes positively-charged oxygen ions in an equal number to the negatively-charged electrons passing through the electronic circuit. The circuit is connected externally to the fuel cell's electrodes. The solid electrolyte performs the same function as the polymer electrolyte membrane used in fuel cells being developed by Ford, Volkswagen, GE, Dupont and others.
The efficiency of solid-oxide fuel cells is limited by the electrolyte's ability to transport oxygen ions, which must pass from atom to atom through the solid electrolyte. To achieve higher efficiencies, solid-oxide fuel cells are typically operated at above 1,000 degrees F.
The new superlattice electrolyte material opens wider gaps through which the oxygen ions can pass without having to be handed from atom to atom. This advance accounts for the huge increase in ionic conductivity near room temperature.
The new material uses alternating layers of zirconium oxide and titanium strontium oxide, which have mismatched crystalline lattices that account for the membrane material's greater permeability for oxygen ions. Oak Ridge researchers said they observed the mismatched lattices and resultant gaps with its 300-kilovolt, z-contrast scanning transmission electron microscope with a resolution of almost 0.6 angstroms.
"We observed that there are many more pathways opened up by the lattice mismatch between the layers," said Varela.
The researchers will pass along their results to development teams who will seek to demonstrate a solid-oxide fuel cell using the new alternating-layer superlattice electrolyte.