Shattering Conventional Wisdom – The surprising discovery could change the future of electrochemical devices

Artist’s illustration of an electronegative polymer in water that conducts ionic and electronic charges. Credit: Scott T. Kane

Researchers from the University of Cambridge have made a surprising discovery that has the potential to reshape the landscape of electrochemical devices. This new vision opens the door to the creation of advanced materials and paves the way for improvements in sectors such as energy storage, neural computing, and bioelectronics.

Electrochemical devices depend on the movement of charged particles, whether ions or electrons, to function properly. However, understanding how these charged particles move together is a major challenge, which hinders progress in creating new materials for these devices.

In the rapidly evolving field of bioelectronics, soft conductive materials known as conjugated polymers are being used to develop medical devices that can be used outside of traditional clinical settings. For example, this type of material could be used to make wearable sensors that monitor patients’ health remotely or implantable devices that effectively treat disease.

The major benefit of using conjugated polymer electrodes for this type of device is their ability to seamlessly couple the ions responsible for electrical signals in the brain and body with the electrons that carry electrical signals in electronic devices. This synergy improves communication between the brain and medical devices, and efficient translation between the two types of signals.

In this recent study on polymer conjugate electrodes, which was published in nature materialsResearchers report an unexpected discovery. It is traditionally thought that the movement of ions is the slowest part of the charging process because they are heavier than electrons. However, the study revealed that in conjugated polymer electrodes, the movement of ‘holes’ – the empty spaces into which electrons travel – can be the limiting factor in how quickly a material can be charged.

Using a specialized microscope, the researchers closely monitored the charging process in real time, and found that when the charge level is low, the movement of the holes is inefficient, causing the charging process to slow down much more than expected. In other words, contrary to standard knowledge, ions behave faster than electrons in this particular substance.

This unexpected discovery provides valuable insight into the factors that affect charging speed. Interestingly, the research team also determined that by manipulating the microstructure of the material, it is possible to regulate how fast 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, enabling faster and more efficient charging processes.

“Our findings challenge the traditional understanding of the charging process in electrochemical devices,” said first author Scott Kane, from the Cavendish Laboratory in Cambridge and the Department of Electrical Engineering. “The movement of holes, which act as empty spaces for electrons to move into, can be surprisingly inefficient during low charge levels, causing unexpected slowdowns.”

The implications of these findings are far-reaching, and provide a promising avenue for future research and development in 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 initial steps that occur during electrochemical doping of conjugated polymers and highlighting the role of the polymer band structure,” said George Maliaras, senior author of the study and Prince. Philip is Professor of Technology in the Department of Engineering, Department of Electrical Engineering.

“With a deeper understanding of the charging process, we can now explore new possibilities in creating advanced medical devices that can seamlessly integrate with the human body, wearable technologies that provide real-time health monitoring, and new solutions for energy storage with energy storage,” concluded Professor Akshay Rao, co-lead author. “The efficiency is enhanced,” he says, also from the University of Cambridge’s Cavendish Laboratory.

Reference: “Hole-Limited Electrochemical Doping in Conjugated Polymers” by Scott T. Kane, Jonathan EM Laughlinen, Raj Pandya, Maximilian Moser, Christoph Schneiderman, Paul A. Midgley, Ian McCulloch, Akshay Rao and George G Malliaras, July 6, 2023 Available here. nature materials.
doi: 10.1038/s41563-023-01601-5

The research was supported in part by the Engineering and Physical Sciences Research Council (EPSRC), part of the UK Research and Innovation (UKRI), the European Union’s Horizon 2020 research and innovation programme, the NVIDIA Academic Hardware Grants Programme, Clare College and the NVIDIA Academic Grants Programme. Royal Commission for the 1851 Exhibition. Scott Kane is a Marie Skłodowska-Curie Postdoctoral Fellow in the Cavendish Laboratory and Electrical Engineering Department of the Engineering Department.