Revolutionizing Ocean Exploration with Artificial Gill Technology

Scientists at Helmholtz-Zentrum Hereon in Germany have made a groundbreaking advancement in marine robotics. They have created an artificial gill that extracts oxygen from seawater to power fuel cells, revolutionizing the way robotic sea gliders and autonomous underwater vehicles (AUVs) operate on long missions.

How the Artificial Gill Works

This innovative technology, utilizing membrane technology similar to a fish’s gills, allows for the extraction of oxygen directly from seawater. The team built a prototype based on a mathematical model, creating a digital twin to validate its performance. Analysis shows that this system could outperform traditional battery-powered methods.

Battery-Free Exploration: A Vision for the Future

Ocean gliders operate autonomously for weeks at a time, measuring temperature, pressure, salinity, oxygen, and currents with onboard sensors. Their ability to dive up to 1,000 meters provides data that is challenging to obtain otherwise, and they are significantly less expensive to maintain than research vessels.

However, the use of lithium batteries presents logistical challenges. They need to be handled according to strict safety guidelines due to their classification as hazardous materials, increasing costs and complexity. To address this, researchers have developed a new fuel cell system that uses hydrogen and oxygen for power instead of batteries.

The Role of Hydrogen and Metal Hydrides

At the deployment site, hydrogen is added to the glider using metal hydride containers, which provide a safe and efficient storage method. These hydrides store hydrogen by forming an atomic-level bond with the metal, while oxygen is extracted directly from seawater without storing it onboard.

Prokopios Georgopanos from the Institute of Membrane Research at Helmholtz-Zentrum Hereon explained: “This system eliminates the need for onboard oxygen storage, saving weight and volume for additional hydrogen storage. This enables higher energy density and lower operating costs compared to current battery solutions.”

By leveraging hydrogen as an energy source, this system not only enhances operational efficiency but also promotes a more sustainable approach to marine exploration.

The Artificial Gill System

The new system employs a proton-exchange membrane (PEM) fuel cell to convert hydrogen and oxygen into electricity. Hydrogen is safely stored in a low-pressure metal hydride alloy, while oxygen is continuously extracted from seawater through a specialized membrane.

The membranes are crafted from poly(octylmethylsiloxane) (POMS), a hydrophobic polymer renowned for its superior oxygen permeability compared to alternatives like polytetrafluoroethylene (PTFE) or polyolefins. Researchers developed the membrane using a silicone-based mixture with crosslinking agents and a platinum catalyst, casting it onto a porous support coated with polyacrylonitrile. The final membrane, at 4 μm thick, was rigorously tested for oxygen flow using a custom device.

Researchers integrated this innovative membrane into the AUV’s hull, where it allows dissolved oxygen to pass while blocking liquid water. Oxygen diffuses through the membrane due to a pressure gradient created by the fuel cell’s consumption. The process results in waste heat and water vapor, necessitating an air-drying component. However, a heat exchanger was not included in the prototype due to the short duration of the tests.

The Promise of the Future

While the fuel cell and hydrogen storage systems are commercially available, the membrane module represents the key innovation, mimicking fish gills to supply oxygen efficiently. Its performance is crucial for determining power availability, while other system enhancements would focus on increasing endurance.

The team’s research, published in the journal Advanced Science, claims this design offers a promising alternative to batteries for long-duration ocean glider operations, potentially enhancing efficiency and sustainability.

As this technology continues to evolve, it could significantly expand the capabilities of oceanographic research, enabling more comprehensive and extended studies of our world’s oceans.

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