Underwater power

Drones and submersibles are increasingly used for surveillance and other military purposes, but researchers are still looking for the best way extend their mission range and capabilities.

Funding from the Office of Naval Research will allow Vijay Ramani to create better fuels for the U.S. Navy’s unmanned undersea vehicles such as these. Photo credit: U.S. Navy

Vijay Ramani, an electrochemical engineer at Washington University in St. Louis, has received a three-year, $468,087 grant from the Office of Naval Research to create a stable, bipolar membrane for fuel cell propulsion systems that would enable the U.S. Navy's unmanned undersea vehicles (UUVs) to fulfill challenging mission requirements.

Ramani's group works with batteries and fuel cells that convert energy via the addition and release of electrons from chemicals. The focus of this project is on sodium borohydride-hydrogen peroxide fuel cells. Sodium borohydride is a high-energy-density fuel not commonly used in fuel cells, but has several advantages for UUV applications, Ramani said.

"The operational needs for this platform necessitate a very high-energy-density fuel that won't evolve gas bubbles during reaction and that won't flash spontaneously, which is an important consideration when such UUVs are hosted on vessels with ordnance on them," Ramani said.

Ramani and his team will investigate structure-property relationships in a class of membranes and interfaces that transport both negatively and positively charged ions.

Since sodium borohydride is only stable in an alkaline environment, the membranes intended for such fuel cells also will need to be stable in alkali, which is not the case. Ramani intends to draw on fundamental research done in his lab over the past several years studying how his candidate membranes degrade in alkaline environments to design high-performance degradation-resistant membranes for the Navy.

Vijay Ramani
"We're now incorporating the mechanistic insights grained in or prior findings to make the fuel cell separator membranes more alkali resistant," he said. "These efforts will enhance the operational range of the UUVs."

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