  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.
