Scientists at Stanford University have designed an electrocatalytic mechanism that works like a mammal's lung to turn water into fuel. Their research, published Dec. 20 in Joule magazine, could help existing clean energy technologies work more efficiently.
The act of inhaling and exhaling is so automatic for most organisms that it could be mistaken for simplicity, but the mammalian respiration process is actually one of the most sophisticated systems for two-way gas exchange in nature.
With each breath, air moves through the tiny bronchioles in the lungs, like a passage, until it reaches tiny sacs called alveoli. From there, the gas must pass into the bloodstream without simply diffusing, which would cause harmful bubbles to form. It is the unique structure of the alveoli, which includes a one-micron-thick membrane that repels the water molecules inside and attracts them to the outside surface, which prevents those bubbles from forming and makes gas exchange smooth. highly efficient.
Scientists in lead author Yi Cui's laboratory at Stanford University's Department of Materials Science and Engineering were inspired by this process to develop better electrocatalysts - materials that increase the speed of a chemical reaction in an electrode. "Clean energy technologies have demonstrated the ability to rapidly deliver reactant gas to the reaction interface, but the reverse pathway, efficient evolution of the gas product from the catalyst / electrolyte interface, remains a challenge," he says. Jun Li, the first author of the study.
The team's mechanism structurally mimics the alveolus and carries out two different processes to enhance 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 oxidizing water molecules at the anode of a battery and reducing them at the cathode. Oxygen gas (along with hydrogen gas) is produced and transported rapidly through a thin, cell-like membrane made of polyethylene, without the energy costs of forming bubbles.
The second process is more like inhalation and generates energy through an oxygen-consuming reaction. Oxygen gas is delivered to the catalyst on the surface of the electrode, so it can be used as a reagent during electrochemical reactions.
Although still in the early stages of development, the design looks promising. The exceptionally thin nano-polyethylene membrane remains hydrophobic longer than conventional carbon-based gas diffusion layers, and this model can achieve higher current density rates and lower overpotential than conventional designs.
However, this lung-inspired design still has room for improvement before it is ready for commercial use. Since the nano-polyethylene membrane is a polymer-based film, it cannot tolerate temperatures above 100 degrees Celsius, which could limit its applications. The team believes that this material can be replaced by hydrophobic nanoporous membranes, similarly thin, capable of withstanding greater heat. They are also interested in incorporating other electrocatalysts into the design of the device to fully explore its catalytic capabilities.
"The structure that mimics respiration could be coupled with many other leading-edge electrocatalysts, and further exploration of the gas-liquid-solid triphasic electrode offers interesting opportunities for catalysis," says Jun Li.
More information: Joule, Li and others: “Respiration-Imitation Electrocatalysis for Oxygen Evolution and Reduction” https://www.cell.com/joule/fulltext/S2542-4351(18)30564-6, DOI: 10.1016 / j .joule.2018.11.015
Original article (in English):