Nanoscale Chemical Imaging of MXene Electrochemical Storage by Operando Scanning X-ray Microscopy

Finding efficient ways to store and deliver electrical energy is urgently needed for the large-scale development of renewable energy sources.

The use of pseudocapacitive materials, such as 2D transition metal carbides and nitrides, so-called MXenes, is an extremely promising solution to achieve electrochemical energy storage with high power and energy densities, benefiting from fast redox reactions on transition metal oxides.

Nevertheless, local electrochemical processes occurring at the solid-liquid interface of pseudocapacitors are currently largely unexplored.

The goal of this project is to image for the first time electrochemical processes occurring during pseudocapacitive electrochemical storage on MXenes at the nanoscale with operando Scanning Transmission X-ray microscopy (STXM). Using synchrotron X-ray light, STXM will allow element-selective chemical mapping with <50 nm spatial resolution and bulk-sensitivity, so that transition metal atoms, surface termination and confined electrolyte in single MXene flakes can be probed independently.

The objectives of NANOMXM are to image in operando electrochemical reactions occurring at the MXene-electrolyte interface inside single multi-layered flakes at high cycling rates (up to 10 V/s) and to probe dynamic processes such as charge transfer and ion diffusion with electrical pump-X-ray probe schemes at high repetition rates (>30 kHz).

Redox and intercalation pseudocapacitive charging processes will be investigated directly in acidic or alkali cations-containing electrolytes, respectively.

By offering unprecedented chemical sensitivity, spatial and temporal resolutions in liquid simultaneously, NANOMXM will provide a radically new method to probe pseudocapacitive electrochemical storage in MXene.

Achieving operando imaging of fast electrochemical reactions at the nanoscale would be a major breakthrough that could open new perspectives to investigate further electrochemical processes on metal oxide-based materials.