Measuring ion transport in battery materials at individual electrode interfaces — New method provides guidelines for improving material performance

A collaborative research group, including Yusuke Abe (doctoral student at the time of research), Assistant Professor Kentaro Aoki, Researcher Athchaya Suwansoontorn, and Professor Yuki Nagao from the Materials Chemistry Frontiers Research Area at the Japan Advanced Institute of Science and Technology (JAIST), along with their partners from the University of Calgary in Canada and Associate Professor Isao Shitanda from the Faculty of Science and Technology at Tokyo University of Science, has developed a new measurement method that isolates and quantifies ion (proton) transport at individual interfaces within polymer electrolyte thin films, which make up the electrodes of battery materials. This achievement is expected to provide new guidelines for improving the performance of battery materials. The findings were published in ACS Applied Materials & Interfaces.

By precisely controlling the shape of the electrode structure (specifically, comb-shaped interdigitated electrodes) and combining it with impedance measurements extended to low frequencies, the research group developed a new method to isolate and quantify proton transport components that were previously observed as one overlapped component. This marks the first successful individual evaluation of proton flow at each electrode interface.

As a result, the team clarified that the multiple resistance components included in the measurement signals originate from completely different interfaces. They revealed that the resistance component on the high-frequency side corresponds to proton conduction at the silicon dioxide (SiO₂) interface, while the low-frequency side corresponds to proton conduction at the platinum and carbon interfaces. They discovered that the ease of proton movement varies by up to a factor of two between the oxide interface and the metal/carbon interfaces.

Furthermore, because the same conductivity was obtained even when the length of the electrode pads was altered, the team demonstrated that these resistance components stem from the properties of the "interface itself" rather than the electrode structure.

This represents the first time that proton conductivity, which could previously only be evaluated as a single overall value, has been broken down and quantified for each interface.

This breakthrough makes it possible to clearly identify which specific interface acts as a bottleneck for ion transport. The selection of electrode materials and the optimization of interface structures can be achieved based on a larger body of scientific evidence than was available in the past.

Particularly in the development of fuel cells and water electrolyzers, improving energy conversion efficiency and reducing costs are critical challenges. This method is expected to directly contribute to material development and device design as a foundational technology that provides these design guidelines.

Furthermore, its applications are not limited to fuel cells. It can be applied to various electrochemical devices where ion transport at electrode interfaces is vital, including water electrolysis systems, secondary batteries, and sensors, thereby contributing to their performance enhancement.

Journal Information
Publication: ACS Applied Materials & Interfaces
Title: Decoupling Interfacial Proton Conductivity in Ionomer Thin Films on Pt and Carbon Electrodes
DOI: 10.1021/acsami.6c04425