RESUMEN
Correlative methods to characterize single entities by electrochemistry and microscopy/spectroscopy are increasingly needed to elucidate structure-function relationships of nanomaterials. However, the technical constraints often differ depending on the characterization techniques to be applied in combination. One of the cornerstones of correlative single-entity electrochemistry (SEE) is the substrate, which needs to achieve a high conductivity, low roughness, and electrochemical inertness. This work shows that graphitized sputtered carbon thin films constitute excellent electrodes for SEE while enabling characterization with scanning probe, optical, electron, and X-ray microscopies. Three different correlative SEE experiments using nanoparticles, nanocubes, and 2D Ti3C2Tx MXene materials are reported to illustrate the potential of using carbon thin film substrates for SEE characterization. The advantages and unique capabilities of SEE correlative strategies are further demonstrated by showing that electrochemically oxidized Ti3C2Tx MXene display changes in chemical bonding and electrolyte ion distribution.
RESUMEN
2D layered materials, such as transition metal carbides or nitrides, known as MXenes, offer an ideal platform to investigate charge transfer processes in confined environment, relevant for energy conversion and storage applications. Their rich surface chemistry plays an essential role in the pseudocapacitive behavior of MXenes. However, the local distribution of surface functional groups over single flakes and within few- or multilayered flakes remains unclear. In this work, scanning X-ray microscopy (SXM) is introduced with simultaneous transmission and electron yield detection, enabling multimodal nanoscale chemical imaging with bulk and surface sensitivity, respectively, of individual MXene flakes. The Ti chemical bonding environment is found to significantly vary between few-layered hydrofluoric acid-etched Ti3C2Tx MXenes and multilayered molten salt (MS)-etched Ti3C2Tx MXenes. Postmortem analysis of MS-etched Ti3C2Tx electrodes cycled in a Li-ion battery further illustrates that simultaneous bulk and surface chemical imaging using SXM offers a method well adapted to the characterization of the electrode-electrolyte interactions at the nanoscale.