Illustration of an electronic polymer in water conducting both ionic and electronic charges. Image: Scott T. Keene.
Illustration of an electronic polymer in water conducting both ionic and electronic charges. Image: Scott T. Keene.

A new study by researchers at the University of Cambridge in the UK has revealed a surprising discovery that could transform the future of electrochemical devices. The findings, reported in a paper in Nature Materials, offer new opportunities for the development of advanced materials and improved performance in fields such as energy storage, brain-like computing and bioelectronics.

Electrochemical devices rely on the movement of charged particles, both ions and electrons, to function properly. However, understanding how these charged particles move together has presented a significant challenge, hindering progress in creating new materials for these devices.

Soft conductive materials known as conjugated polymers are commonly used in electrochemical devices. In particular, they are employed as electrodes in medical devices that can be used outside of traditional clinical settings, such as wearable sensors that monitor patients’ health remotely or implantable devices that actively treat disease.

The great advantage of conjugated polymer electrodes in this kind of device is that they can seamlessly couple ions, which are responsible for electrical signals in the brain and body, with electrons, the carriers of electrical signals in electronic devices. This synergy improves the connection between the brain and the medical device, effectively translating between these two types of signals.

The researchers have now made an unexpected discovery about conjugated polymer electrodes. It had conventionally been believed that the movement of ions is the slowest part of the charging process because they are heavier than electrons. However, the researchers found that in conjugated polymer electrodes, the movement of ‘holes’ – empty spaces for electrons to move into - can be the limiting factor in how quickly the material charges up.

Using a specialized microscope, the researchers closely observed the charging process in real-time, and found that when the level of charging is low, the movement of holes is inefficient, causing the charging process to slow down a lot more than anticipated. In other words, and contrary to what was previously thought, ions conduct faster than electrons in this particular material.

This unexpected finding provides a valuable insight into the factors influencing charging speed. Excitingly, the research team also determined that by manipulating the microscopic structure of conjugated polymers, it is possible to regulate how quickly the holes move during charging. This newfound control and ability to fine tune the material’s structure could allow scientists to engineer conjugated polymers with improved performance, allowing faster and more efficient charging processes.

"Our findings challenge the conventional understanding of the charging process in electrochemical devices,” said first author Scott Keene in Cambridge’s Cavendish Laboratory. “The movement of holes, which act as empty spaces for electrons to move into, can be surprisingly inefficient during low levels of charging, causing unexpected slowdowns."

The implications of these findings are far-reaching, offering a promising avenue for future research and development in the field of electrochemical devices for applications such as bioelectronics, energy storage and brain-like computing.

"This work addresses a long-standing problem in organic electronics by illuminating the elementary steps that take place during electrochemical doping of conjugated polymers and highlighting the role of the band structure of the polymer," said George Malliaras, senior author of the paper and professor of technology in the Department of Engineering’s Electrical Engineering Division.

“With a deeper understanding of the charging process, we can now explore new possibilities in the creation of cutting-edge medical devices that can seamlessly integrate with the human body, wearable technologies that provide real-time health monitoring, and new energy-storage solutions with enhanced efficiency,” said Akshay Rao, a co-senior author in Cambridge’s Cavendish Laboratory.

This story is adapted from material from the University of Cambridge, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.