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New Vanadium Oxide Fuel Cell Can Both Generate and Store Energy

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Each dark speck within the nine white circles at left is a tiny solid-oxide fuel cell. The AA battery at the right is shown for size comparison.
Photo by Caroline Perry / SEAS

It is now entirely possible for electrical gadgets to keep on running after fuel is depleted. Materials scientists at Harvard have developed a solid-oxide fuel cell (SOFC) that uses hydrogen as fuel to generate electricity, but can store electrochemical energy like a battery as well.

Recent advances in low-temperature operation allowed the thin-film SOFC to incorporate new and more versatile materials.

Previously, the cell used platinum at both anode and cathode. When the fuel cell runs out of fuel, it can continue to generate power for 14 seconds. By replacing platinum with a bilayer of platinum and vanadium oxide (VOx) at the anode, the new cell can continue to operate without fuel for three minutes and thirty seconds at a current density of 0.2 mA/cm2.

The researchers are confident that further improvements in the composition of the VOx-platinum anode will further extend the lifespan of the cell without fuel.

According to principal investigator Shriram Ramanathan, there are three reactions potentially taking place inside the fuel cell due to the VOx.

The first is oxidation of vanadium ions in the anode that was confirmed by x-ray photoelectron spectroscopy. The second is storage of hydrogen inside the VOx lattice that is slowly released and oxidized in the anode and the third reaction is the oxidation of oxygen ions.

All these reactions can release electrons into the circuit after the cell’s fuel is depleted. However, the exact mechanism of how the cell can continue running without fuel is still currently unclear.

It is projected that two years from now, more advanced fuel cells of this type will be available for testing. Possible use of this research is in small-scale, portable energy applications where a very compact and lightweight power supply is important.

It will also be especially useful in applications where it is impossible to refuel immediately or where power supply may be not be interrupted such as in unmanned aerial vehicles. The extra boost of stored energy can extend the device’s lifespan significantly.

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