Clean Circles

Kinetic study of the oxidation of iron and the thermochemical reduction of iron oxides


The energy sector emitted around 254 t CO2 equivalents in Germany in 2019. 74 % of the emitted green house gases can be attributed to the burning of solid fossil fuels. To lower the emissions of the energy sector, the increased use of renewable energy is necessary. One of the major challenges regarding the usage of renewable energies, e.g. solar and wind, is the long-term storage and transportation of energy. 

A promising technology solving these problems is the chemical storage of energy in metal fuels. Their safety and high energy density are advantages over the common energy storage technologies like hydrogen or batteries. Energy is released by the combustion of metal powders with air leading only to metal oxides as oxidation product. The obtained solid metal oxides can be recycled via the reduction with green energy and thus leading to a closed COfree cycle. Iron with its high energy density, safety and high occurrence in the earth’s crust is one promising candidate for this technology.

​ Figure 1: Clean Circles – A closed CO2 cycle for the storage of renewable energies. ​

Project Clean Circles:

Beside the oxidation process, the release of energy, the reduction process, e.g. the storage of the energy, plays a major role in the efficiency of the cycle. The reduction can occur via the electrochemical way or via the reduction with green hydrogen. Subject of this investigations is the thermochemical reduction with hydrogen. The aim of future work is the development of detailed reaction mechanisms for reduction and oxidation of Iron and its oxides. The reduction of Iron oxide with hydrogen and the oxidation of Iron powder with oxygen are multistep, heterogeneous reactions containing several phases and phase boundaries as well as different oxides (Fe2O3, Fe4O3, FeO). This work focusses on the detailed understanding of the reaction mechanisms under consideration of the different species, phases and phase boundaries. Thermogravimetric analysis coupled with IR-spectroscopy and massspectrometry is used to get an insight on the reduction and oxidation kinetics. Based on the experimental results a reaction mechanism will be developed, which will further be integrated in simulations to get a validation of model and experiments.

Contact: Prof. Dr. Olaf Deutschmann, Dr. Marion BörnhorstCarola Kuhn


Clean Circles
​ KIT Future Fields ​





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