Solar-powered device generates electricity through ion transport and could lead to low-cost for seawater desalination
By binding photosensitive dyes to common plastic membranes and adding water, chemists at the University of California, Irvine have made a new type of solar power generator. The device is similar to familiar silicon photovoltaic cells but differs in a fundamental way: Instead of being produced via electrons, its electricity comes from the motion of ions. Dubbed the “synthetic, light-driven proton pump” by its creators, the innovation – because of its ionic basis – has the added potential capability of taking the salt out of seawater. “The materials used to make such a device can be dirt-cheap,” said Shane Ardo, UCI assistant professor of chemistry, as well as chemical engineering & materials science, and senior author of a paper describing the generator published today in the Cell Press journal Joule. “We’re talking about common polyethylene plastic, light-absorbing dye molecules and water.” In Ardo’s laboratory, researchers devised a system based on dual layers of dye-coated, ion-transporting membranes. When struck with light from a laser pointer – a laboratory simulation of sunlight – the dye releases ions. Positively charged protons, also known as cations, pass through one sheet, while negatively charged hydroxides, also known as anions, pass through the other. These photoactive membranes generate 60 millivolts, on average, occasionally climbing to more than 100 millivolts, as measured by Ardo’s team. “Our results represent considerable progress toward a device that directly converts sunlight into ionic electricity, which has implications for direct desalination of seawater,” Ardo said. When speaking in public about this research, he often holds up an ordinary plastic water bottle and asks, “What if it were possible to dip this container in the ocean, let it sit in full sun for about an hour and then be able to drink the water? The prospect of that is revolutionary.” According to lead author William White, a graduate student in Ardo’s lab, scientists have been trying to develop an ion-exchange power generator for decades with limited success. “There had been other experiments dating back to the 1980s that photo-excited materials so as to pass an ionic current through them,” he said. “Theoretical studies said that those currents should be able to reach the same levels as their electronic analogs, but none of them worked all that well.” The researchers see other possible applications for the technology, including as part of a brain-computer interface system. Silicon-based devices and aqueous environments don’t mix, but the flexible, fluid-permeable structures being developed in the Ardo lab may one day offer a way of integrating living tissue and artificial circuitry. This work was supported by UCI’s School of Physical Sciences and the Gordon and Betty Moore Foundation.