Chicken eggs are used worldwide in large quantities in the food, pharmaceutical and manufacturing industries. After the eggs have been used, however, the shells are thrown away and disposed of as bio-waste in landfills. The shell consists of a composite of calcium carbonate (CaCO3) and a protein-rich fibre membrane. "Surprisingly, there are always new examples in which natural substances have good to very good prerequisites for producing materials for electrochemical storage," explains Professor Maximilian Fichtner from the Helmholtz Institute Ulm, an institution run by the Karlsruhe Institute of Technology (KIT).
Together with Australian colleagues, Fichtner discovered the promising electrochemical properties of chicken egg shells that are able to store lithium well due to their high CaCO3 content. The eggshell powder was used as an electrode against a metallic lithium anode in a non-aqueous electrolyte. After over 1,000 charging and discharging cycles, the test cell maintained a capacity of 92 percent. Both the calcified shell and the inner and outer shell membranes of the eggshells were used. The researchers washed, dried and crushed the shells into a powder – the result was a conductive material.
So far, egg shell waste has been used in a number of applications, including bioceramics, cosmetics and the dyestuff industry. The protein-rich, fibrous egg shell membrane also served as a separator in supercapacitors. However, biowaste was used as an electrode for the first time worldwide. According to the research team, further research and a detailed understanding of the electrochemical and physical behaviour of the material are now required in order to improve the performance of the material and enable it to be used widely.
The results of the research work have now been presented in the journal Dalton Transactions of the Royal Society of Chemistry .
More information: https://www.energy.kit.edu/index.php