Reduction Behavior of Oxidized Iron Particles used as Energy Storage Material

• Applicants: Professor Dr. Olaf Deutschmann; Professor Dr.-Ing. Hermann Nirschl; Professor Dr.-Ing. Dimosthenis Trimis
• Subject Area: Technical Chemistry ; Chemical and Thermal Process Engineering ; Mechanical Process Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558715615

Reactive metals such as iron and aluminum have recently gained tremendous attention as carbon-free chemical energy carriers of renewable electrical energy in a circular economy. These metals can store large amounts of energy over extended periods with minimal loss by reducing their oxides using electrolytic hydrogen. The stored energy can then be released through oxidation, offering both temporal and spatial flexibility. Therefore, reactive metals have the potential to meet significant energy demands (hundreds of TWhs) currently fulfilled by fossil fuels. For instance, utilizing iron powder in fossil-fuel-based power plants could potentially reduce global CO2 emissions by up to 30%. Iron, in particular, stands out as an energy storage material due to its high volumetric energy density, non-toxicity, ease of transportation, long-term storage capability, low hazard potential, minimal material losses throughout the cycle, and low water requirements. Furthermore, iron is relatively inexpensive and widely available, reducing political risks in the energy supply chain. With burning velocities and reaction temperatures similar to those of natural gas and coal powder, iron powder is an attractive clean fuel option for retrofitting existing power plants. However, advancing this concept faces significant challenges calling for a better understanding of the complex oxidation states, morphological changes, and the interactions of kinetics, mass, and heat transport in both the oxidation and reduction processes. This research project focuses on the oxidation-reduction cycle of iron powders, with a particular emphasis on the reduction of iron oxide particles using hydrogen. The study will investigate the mechanisms and kinetics of reducing iron oxide particles, ranging from 10 to 100 micrometers in size, through a comprehensive approach that integrates oxidation and reduction experiments, detailed particle characterization, as well as advanced modeling and simulation. The project will be conducted by three collaborating groups, each of them being experienced in one of the methods relevant. Cyclization without substantial efficiency and material losses is a crucial factor for utilizing iron as energy carrier. Based on a fundamental understanding, this project will provide optimized particle characteristics such as particle size (distribution), morphology and porosity as well as suitable process conditions for high efficiency and longevity of the iron oxidation-reduction cycle. The insights gained from this research will lay the groundwork for optimizing the reduction-oxidation cyclability of iron-based particles, enhancing their performance in technical applications.

• DFG Programme: Research Grants