Challenges and Opportunities in Understanding Proton Exchange Membrane Fuel Cell Materials Degradation Using In‐Situ Electrochemical Liquid Cell Transmission Electron Microscopy

Abstract Environmental pollution at the current state of fossil fuel consumption has led clean energy devices like proton exchange membrane fuel cells (PEMFCs) to emerge as alternative energy generation solutions. However, the performance, durability, and efficiency limitations of PEMFCs have hindered their widespread adoption. Improving their performance and durability can be achieved by fundamentally understanding and tuning their catalyst layer structures and compositions. Transmission electron microscopy and scanning transmission electron microscopy have proven to be among the best characterization tools available to analyze the microstructural features of the catalyst layers of PEMFC devices. The ability to directly observe changes in catalyst materials during operation with high spatial and temporal resolutions by the means of In‐situ techniques can accelerate material development in the PEMFC field. In this article, structure, properties, and performance of PEMFC materials are reviewed, and their known degradation mechanisms are introduced. Available In‐situ TEM techniques are presented to guide the selection of suitable methods and approaches for studying the PEMFC systems. Finally, the current literature is presented on PEMFC research that has used In‐situ electrochemical liquid cell TEM to study materials evolution and degradation, highlighting the specific challenges and opportunities for applying the technique in the PEMFCs’ field.