In situ transmission electron microscopy on operating electrochemical cells

Solid oxide fuel/electrolysis cells (SOFC/SOEC) will play an important role in future efficient and environmentally friendly energy systems if a better long term performance of the cells can be achieved. In a solid oxide fuel cell (SOFC) a fuel such as hydrogen, methane, synthesis gas, etc. is oxidized over a solid oxygen ion-conducting electrolyte which physically separates fuel and air.
The electron transfer in this chemical reaction takes place via an external circuit and electricity is therefore a product of the reaction. Catalysts are used on both sides of the ion conducting electrolyte to activate the splitting of fuel and oxygen molecules.
Impressive performance improvements have recently been reported for cells with specific multiphase nano-structures, but structural and compositional nano-scaled changes can also lead to deactivation. On the other hand, deactivation processes due to nano-scaled structural and compositional changes (segregations followed by nano-particle precipitation in some cases) can be observed near the material interfaces in the electrodes. Neither the mechanisms of the initial fast electrode process nor the development and dynamics of these critical structures are understood. Further studies of these dynamical changes are hampered since there are no available methods which offer in situ characterization of operating cells with nano-scale spatial resolution.
The project will develop a method for in situ transmission electron microscopy (TEM) of operating solid oxide electrochemical cells. Until now, knowledge of the nanoscale SOFC/SOEC dynamics is entirely based on observations performed post mortem, when the cells have been cooled down and de-mounted. To obtain direct insight into the dynamics of the active nanostructures of a SOFC/SOEC in operation can therefore have significant importance for our understanding of the cell dynamics during activation and deactivation.
The aim is to record TEM image sequences (movies) with atomic resolution of the active nanostructures in the SOFC/SOEC during operation. To do this, model SOFC/SOEC systems will be developed and integrated into a TEM holder so that heating, electrical currents and exposure to reactive gas environments all are integrated at the same time. In addition the model systems will need to be highly compact and the thickness of the imaged area should be approximately 100 nm. The project will therefore push the limits of in situ TEM experiments.
The goal is direct insight into the nano-scale dynamics of the operating SOFC/SOEC during exposure to elevated temperatures, electrical currents and a reactive gas environment. This will be a key factor in developing more efficient and stable SOFCs/SOECs. Therefore, micro-SOFC will be developed and characterized by thin layer, especially regarding the electrolyte layer which will have a thickness lower than one micrometre. This will allow to work at temperature lower than 600°C.
The project will be carried out as a PhD project in collaboration between the two applicant institutions (DTU Energy Conversion and DTU Cen) and with the in situ group from Nagoya University with Prof. Shunsuke Muto. The work will primarily be carried out by the PhD student with support and supervision from the project team. The principal supervisor is Head of Section Luise T. Kuhn. The TEM work will be carried out under the guidance of Søren Bredmose Simonsen and Prof. Jakob B. Wagner. Prof. Mogens B. Mogensen will contribute to the project as an internal consultant when analyzing and linking the observed physical properties to the electrochemical performance.