Artificial gills for ocean gliders

This is the first prototype of the new energy system. It is still too big to fit into an ocean glider. The scientists are continuing to optimize it. Photo: Hereon/Steffen Niemann

Ocean gliders can autonomously navigate the ocean for several weeks. Their sensors measure parameters like temperature, pressure, salinity, oxygen concentration, and currents. Capable of diving to depths of up to 1,000 metres, they facilitate measurements that are challenging to achieve with research vessels. Additionally, gliders can be operated at a much lower costs than research vessels. However, lithium batteries pose challenges for research teams. Classified as hazardous materials, they can only be transported under strict safety regulations, complicating logistics and increasing project costs.

Nature as inspiration

Dr Lucas Merckelbach and Dr Prokopios Georgopanos from the Helmholtz-Zentrum Hereon have developed an alternative. Instead of using batteries, they propose powering gliders with a fuel cell that generates electricity from hydrogen and oxygen. A glider can then be filled up with hydrogen at the deployment site. A container with metal hydrides serves as a safe and efficient storage medium. These hydrides store hydrogen by bonding hydrogen to the metal hydrides at the atomic level. Oxygen, on the other hand, is not stored but extracted directly from seawater. “Nature is a great source of inspiration for us”, says Merckelbach. He works at the Institute of Coastal Ocean Dynamics and uses ocean gliders in his own research.

The concept was developed by Lucas Merckelbach in collaboration with Prokopios Georgopanos from the Institute of Membrane Research. Georgopanos identified an oxygen-permeable silicone membrane that functions as artificial gills when integrated into the glider’s hull. Exposed to oxygen-rich seawater on the outside, the membrane enables oxygen to diffuse into an internal recirculating airflow. The fuel cell then extracts oxygen from this airflow, where it reacts with hydrogen to generate electrical energy.

Greater range and sustainability

“This system eliminates the need for onboard oxygen storage. The weight and volume saved can be used for additional hydrogen storage, enabling higher energy density and lower operating costs compared to current battery solutions,” explains Georgopanos. This would allow the gliders to operate for longer periods. Furthermore, hydrogen is a more sustainable energy source than batteries.

Schematic representation of the power supply system: The fuel cell and the circulating air flow are located in a pressurized container. The membrane, the artificial gill, is located at the interface between the device and the water and allows oxygen to pass through, which enters the circulating air flow and is consumed by the fuel cell. The hydrogen is fed to the fuel cell from a metal hydride container. A passive heat exchanger dries the gas flow sufficiently to prevent condensation of the generated water vapor. Source: Hereon/Lucas Merckelbach/Prokopios Georgopanos

Georgopanos and Merckelbach have already patented their new energy system. In their paper, A Fuel Cell Power Supply System Equipped with Artificial Gill Membranes for Underwater Applications, they present their first prototype. The paper was recently published in the journal Advanced Science. Over the coming years, they will further optimize the system as part of the MUSE project. Hereon will strengthen its teams at the Institutes of Membrane Research and Hydrogen Technology for this effort. MUSE is a collaborative project with the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, and GEOMAR Helmholtz Centre for Ocean Research Kiel, aiming to advance marine technology and infrastructure. “This interdisciplinary work combines knowledge from coastal research, membrane research, and hydrogen technology – a rare combination, but one that exists at Hereon,” says Georgopanos.