High-temperature Electrochemical Impedance Spectroscopy Transmission electron microscopy on energy materials

ended

The great challenge for humankind is to mitigate climate changes by replacing fossil fuels with renewables. We will have to store excess energy produced by solar and wind power for usage in dark and calm weather. Excess energy can be stored electrochemically by high-temperature electrolysis cells as they have the potential to store vast amounts of electrical energy by conversion to chemical fuels. Solid oxide electrolysis cell (SOEC) technology is well known and proven, but not price competitive with storage of fossil fuels. To drive the SOEC research towards a breakthrough, it is critical to determine relations between electrochemical activity and structure/composition in the cells. Electrochemical impedance spectroscopy (EIS) is a very powerful method for determining the contribution from processes in the cell to the overall activity. EIS cannot show structure/composition which is offered by transmission electron microscopy (TEM). Conventional TEM, however, does not offer insight into active cells, but only post mortem analysis. High-temperature electrochemical TEM is extremely challenging because this requires a) that hard and brittle ceramic cells are thinned to electron transparency (ca. 100 nm), b) that the cells are carefully designed to allow for characterization of the layer interfaces, and c) that the cells are characterized during exposure of i) reactive gasses, ii) electrical potentials and iii) temperatures up to ca. 800 °C. The aim of HEIST is to cover step a) to c), i.e. to transform TEM into an electrochemical lab for high-temperature electrochemical experiments including EIS. HEIST will give us “live” images of nanostructures and composition during operation of the electrochemical cells and thus disclose structure-activity relations. This is important, because the structures of nanomaterials will transform depending on the electrochemical environment, and post mortem analysis does not offer a correct representation of the active nanostructures.