Characterizing the evolution in electronic structure of energy materials systems, e.g., (photo)electrochemical, electrocatalytic, etc., during operation is essential for fully understanding their behavior; the structure-property relationships derived from operando studies of functioning energy systems is critical for informing the tailored design of materials with enhanced performance as part of a feedback loop. Synchrotron-based soft x-ray spectroscopies, including both x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES), are ideally suited to the in situ/operando study of energy material structure. As element specific probes of the unoccupied and occupied electronic density of states, XAS and XES can yield insight into the bonding and composition/structure of materials across multiple length scales; moreover, these techniques are equally applicable to ordered and amorphous systems, and have the sensitivity to address structural changes in low concentration additives/dopants and bulk materials alike. Significantly, the advantages of XAS/XES are only fully realized via the close coupling of in situ experimental methods and advanced ab initio modeling, especially for highly complex, multi-component systems, to identify and interpret key spectroscopic signatures. We demonstrate the benefits of a combined experiment/simulation approach via the investigation of nanostructured carbon aerogel (CA) electrodes operating in prototypical electric double-layer capacitors. Simulations are leveraged to interpret spectral changes consistent with complex, reversible, and highly influential structural transformations: profound bias- and time-dependent evolution of the electronic structure under applied bias connotes both mesoscale (distortion of the porous networks) and nanoscale (specific adsorption) phenomena central to device performance. Although XAS/XES have the potential for impact across multiple EMN consortia, further discussion will focus on ongoing work centered around our combined experiment/simulation node within HydroGEN.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.