Daniel Kröger

 

Structural and electrochemical investigation of carbonized air-cathodes

Figure 1: Microscopic picture of the breakage of a carbonized fiber using transmission electron microscopy (TEM) (left). The breaking edge shows crystalline domains of the carbon (right). Copyright: D. Kröger Figure 1: Microscopic picture of the breakage of a carbonized fiber using transmission electron microscopy (TEM) (left). The breaking edge shows crystalline domains of the carbon (right)

The Institute for Energy and Climate Research - Fundamentals of Electrochemistry (IEK-9) designs and investigates new concepts of energy storage and conversion. The concept of metal-air batteries is developed further as they have potentially high energy storage densities. In this type of battery a base metal is oxidized at the anode whereas atmospheric oxygen is absorbed and deoxidized at the cathode. This reaction takes place at the three-phase boundary of oxygen, carbon and the electrolyte. Thus the air-cathode needs to be permeable for oxygen and while offering a maximum wetting surface impermeable for the electrolyte. At the IEK-9 carbonic fiber tissues are tested in order to be used as air-cathode. The fiber tissues are first spun as polymeric fiber in an electro spinner and carbonized in the following step. Former studies of individual fibers revealed the semi-crystalline structure of the fibers (see Figure 1).

In this Master thesis electron energy loss spectroscopy (EELS) as well as impedance-spectroscopy and potentiometry are used to investigate on one hand the nanostructure and material composition of the fibers, on the other hand the electrochemical behavior of the tissue. In particular a relation between degree of carbonization, chemical structure and electrical or chemical properties of the cathode should be found.