Operando IR: a less-travelled path towards molecular insight into electrochemical reactions

Abstract Operando spectroscopy is a powerful tool that enables mechanistic understanding of materials but often requires advanced and expensive characterization tools. Infrared spectroscopy (IR) can directly probe bond-specific changes during electrochemical reactions using widely available instrumentation. Nevertheless, operando IR remains underutilized due to complex interpretation and the lack of commercial characterization setups. In this tutorial, we aim to offer basic guidance to non-specialists interested in the use of operando IR for the investigation of energy-related materials. This tutorial covers basic experimental design, cell setup, data treatment and interpretation, as well as more advanced IR techniques such as synchrotron-based IR (SR-IR) and surface-enhanced IR absorption spectroscopy (SEIRAS). Examples from different electrochemical applications, ranging from batteries to electrocatalysts, are provided for illustration. Current literature offers a broad range of operando cell setups suitable for different electrochemical conditions and applications. Operando spectroelectrochemical cells are typically customized in-house, and their electrochemical performance must be carefully cross-checked with conventional cells to detect potential side reactions caused by cell modification. After measuring experimental spectra, subtraction or multivariate analysis can be used to resolve features and identify relevant IR-active changes. Assigning IR bands and understanding mechanisms can be facilitated by computational modeling, which assists in interpreting results by calculating IR spectra of different species when experimental reference spectra are difficult to measure. Improved data treatment and modeling enhance the analytical power of operando IR spectroscopy and make it more user-friendly. The concurrent development of spatially resolved and optic fiber IR spectroscopy, as well as the combination of IR with other developing non-linear spectroscopies offer exciting opportunities for the future of this technique.