The characterization of electrochemical cells or cell constituents is one of our main research tasks. In electrochemical devices that may range from thin film model systems to a full battery, fuel or electrolysis cell stack, the current passing through the cells is a direct measure for the electrochemical reaction rate. Aim is to gain insight into rates and mechanisms of the electrochemical reaction.
In our team, we have long-term experience and excellent equipment for electrochemical impedance spectroscopy (EIS), where a variable frequency AC signal is applied to the sample in order to differentiate between different processes or reaction steps by their different characteristic time scales. Additional combination of EIS with DC bias voltages, or complementary DC techniques, as well as variation of sample temperature, atmosphere, illumination, etc. gives further insight into materials and reaction mechanisms. Electrochemical techniques are a central aspect in all research topics of our group: In the development of novel setups, electrochemical in-situ characterization is a central functionality (e.g. in-situ impedance PLD). Furthermore, electrolytes and mixed conducting materials for lithium ion batteries, solid oxide fuel cells (SOFCs), or H2O and CO2 electrolysis are thoroughly characterized by EIS. Advanced model cell designs and mathematically rigorous equivalent circuit modelling allow precise and detailed insight into individual reaction steps, which may include electrolyte conduction, interfacial ion transfer, electron conduction and electrochemical surface reactions in fuel cells as well as batteries. It is therefore possible to quantify the overpotentials associated to the individual processes and thus gaining information on the defect chemistry and partial ion/electron conduction in mixed ionic and electronic conductors (MIECs).