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Superlattice electrolyte to drive cheaper fuel cells for cars

Posted: 08 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:fuel cell? superlattice electrolyte component? automobile?

Spanish researchers claim that a superlattice electrolyte with far greater conductivity could significantly boost fuel cell efficiency while lowering costs when compared to current solid-oxide fuel cells.

The superlattice electrolyte is touted to achieve almost 100 million times greater ionic conductivity than conventional fuel cell components. The new technique has been successfully characterized by scientists at the Energy Department's Oak Ridge National Laboratory in Tennessee.

Delphi Automotive Systems, BMW and Rolls-Royce have all announced development programs for solid-oxide fuel cells. However, fuel cells based on the new superlattice electrolyte are being touted as far more efficient and cheaper for use in automobiles.

"The Spanish researchers could measure the ionic conductivity of their superlattice material, but they couldn't explain it," said Maria Varela of Oak Ridge's materials science and technology division. "Our direct images show the crystal structure that accounts for the material's conductivity. We can actually see the strained, yet ordered, interface structure and how it opens up much wider pathway for the ions.

"I can't tell you how much more efficient fuel cells using this superlattice will be, but I can tell you that they will be much cheaper to operate," she predicted.

The Spanish researchers work at two Madrid universities: Universidad Complutense and Universidad Politcnica.

Solid-oxide fuel cells require operating temperatures of over 1,000F, but the new superlattice electrolyte design offers not only greater permeability for greater fuel cell efficiency but they also operate near room temperature, thereby lowering their own and eliminating the "warm-up" delay usually associated with solid-oxide fuel cells.

The molecular model of the ion-conducting material explains its greater ionic conductivity by virtue of numerous vacancies at the interface between the layers in a superlattice that creates an open pathway through which many more ions can travel.

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 1,000F.

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 300kV, z-contrast scanning transmission electron microscope with a resolution of almost 0.6?.

"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.

- R. Colin Johnson
EE Times

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