Underwater drones can be mighty useful for exploring the oceans, finding fish or filming scuba divers but they do have some drawbacks, namely how far they can travel on each charge. A startup spun out of MIT has built what could be a game-changer for these types of watercraft, in the form of a power system that drinks in seawater to activate a battery that offers a tenfold increase on range.

Unpiloted underwater vehicles (UUVs) are generally powered by lithium-based batteries which pose a few problems. One is that they are a fire hazard, and therefore they are generally not shipped by air. They are instead carried out to sea by larger ships, which also means that the range that they do have isn't wasted on transport beforehand. The team members at Open Water Power say they have come up with a better way of doing things, and liken their solution to a car engine. But where a car engine relies on air to act as an oxidizer to feed the chemical reactions, its new power system instead relies on seawater.

"Our power system can drink sea water and discard waste products," says Open Water Power co-inventor Ian Salmon McKay. "But that exhaust is not harmful, compared to exhaust of terrestrial engines."

The new battery consists of an alloyed aluminum anode, a primarily nickel alloyed cathode and an alkaline electrolyte in between. As seawater is drawn into the system, the cathode splits it into hydroxide anions and hydrogen gas. The anions react with the aluminum anode to create aluminum hydroxide and release electrons, which are then donated to the circuit.

The team claims this system can offer a tenfold increase on range over conventional lithium-ion batteries, and that it is both safer and more durable. The process is only triggered when the system is flooded with water, and while the researchers note that corroding of the aluminum anode is a problem, it can still be replaced at low cost.

And they should learn soon enough how well these claims check out. The company is currently working with the US Navy to deploy these batteries in the acoustic sensors used to detect enemy submarines. Another pilot will kick off this summer (US) with a company called Riptide Autonomous Solutions, whose underwater surveying drones currently travel around 100 nautical miles (185 km) on one charge. It hopes that this new tech can extend this range to 1,000 nautical miles (1,852 km).

And that could be just the tip of the iceberg. Other areas where Open Water Power's new device could be put to use include basically anywhere we want a better idea of what is under the sea. It could power vehicles that dive deeper to map the ocean floor or shipwrecks, it could make long-range oil prospecting easier, or the search for missing airplanes such as that lost in the Malaysian Airlines crash in 2014.

"In looking for the debris, a sizeable amount of the power budget for missions like that is used descending to depth and ascending back to the surface, so their working time on the sea floor is very limited," McKay says. "Our power system will improve on that."

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