Electrochemistry of thin films with operando grazing incidence X-ray scattering: bypassing electrolyte scattering for high fidelity time resolved studies

Electroactive polymer thin films undergo repeated reversible structural change during operation in electrochemical applications. While synchrotron X-ray scattering is powerful for the characterization of stand-alone and ex-situ organic thin films, in situ structural characterization has been underutilized--in large part due to complications arising from supporting electrolyte scattering. This has greatly hampered the development of application relevant structure property relationships. Therefore, we have developed a new methodology for in situ and operando X-ray characterization that separates the incident and scattered X-ray beam path from the electrolyte. As a proof of concept, we demonstrate the in situ structural changes of weakly-scattering, organic mixed ionic-electronic conductor thin films in an aqueous electrolyte environment, enabling access to previously unexplored changes in the pi-pi peak and diffuse scatter in situ, while capturing the solvent swollen thin film structure which was inaccessible in previous ex situ studies. These in situ measurements improve the sensitivity to structural changes, capturing minute changes not possible ex situ, and have multimodal potential such as combined Raman measurements that also serve to validate the true in situ/operando conditions of the cell. Finally, we examine new directions enabled by this operando cell design and compare state of the art measurements.