Exploration of highly ordered electrochemical interfaces of semiconductor and battery electrodes by combined operando impedance and reflection anisotropy spectroscopy

• Applicant: Dr. Matthias May
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576432839

The properties of electrochemical interfaces are to a large extent determined by intermediate phases forming at the phase boundary between the electrode and the electrolyte. This applies in particular to reactive electrode materials such as compound semiconductors or battery electrodes. Even if the electrode is originally in single-crystalline form, initial corrosion typically results in the formation of an amorphous intermediate phase, ranging from a few nanometres in semiconductors in contact with aqueous electrolytes to several hundred nanometres in the case of battery electrodes. While these intermediate phases, also known as solid-electrolyte interphases (SEI), are often beneficial for the functioning of the electrochemical system, their amorphous nature makes it difficult to understand the interface in terms of potential distributions or charge-transport properties. In this project, electrochemical conditions will therefore be identified for two different electrode systems under which highly ordered electrochemical interfaces can be prepared and stabilised to improve the understanding of the respective electrochemical system. Gallium phosphide will represent the class of semiconductor photoelectrodes in contact with aqueous electrolytes, while highly ordered pyrolytic graphite (HOPG) in contact with Al, Li, and Mg-based battery electrolytes will represent the class of battery electrodes. Reflection anisotropy spectroscopy is used here as a spectroelectrochemical method to identify such highly ordered interfaces “operando” in the electrolyte. These interfaces will then be the starting point for in-depth investigations with impedance-based methods. For GaP, the formation and properties of surface states are investigated using electrochemical impedance spectroscopy (EIS), followed by charge transport properties and charge-carrier recombination using intensity-modulated photo spectroscopy (IMPS). For battery electrodes, the nucleation and intercalation behaviour will be examined using structural analysis, and the ion transport properties by means of EIS. The hereby obtained findings can contribute to improving passivation approaches for photoelectrodes and developing charging cycles for batteries to prevent dendrite formation.

• DFG Programme: Research Grants