New lung-inspired device turns water into fuel

Scientists at the Standford University in the US have designed an electro-catalytic material that works like a mammalian lung to convert water into fuel. The research, published in the journal Joule, could help existing clean energy technologies run more efficiently.

The mammalian breathing process is one of the most sophisticated systems for two-way gas exchange found in nature. It’s unique structures of the alveoli—including a micron-thick membrane that repels water molecules on the inside while attracting them on the outer surface—that prevents bubbles from forming and makes the gas exchange highly efficient. Scientists in Yi Cui’s lab at the Stanford University drew inspiration from this process in order to develop better electro-catalysts.

The team’s mechanism structurally mimics the alveolus and carries out two different processes to improve the reactions that drive sustainable technologies such as fuel cells and metal-air batteries. The first process is analogous to exhalation. The mechanism splits water to produce hydrogen gas, a clean fuel, by oxidising water molecules in the anode of a battery while reducing them in the cathode. Oxygen gas (along with the hydrogen gas) is rapidly produced and transported through a thin, alveolus-like membrane made from polyethylene—without the energy costs of forming bubbles.

The second process is more like inhalation and generates energy through a reaction that consumes oxygen. Oxygen gas is delivered to the catalyst at the electrode surface, so it can be used as reactant during electrochemical reactions. The uncommonly thin nano-polyethylene membrane remains hydrophobic longer than conventional carbon-based gas diffusion layers, and this model is able to achieve higher current density rates and lower over-potential than conventional designs.

Since the nano-polyethylene membrane is a polymer-based film, it cannot tolerate temperatures higher than 100 degrees Celsius, which could limit its applications. The researchers believe this material can be replaced with similarly thin nanoporous hydrophobic membranes capable of withstanding greater heat.