Gradient-free thermo-electrochemical energy conversion based on ceramic intercalation materials

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Although technical facilities, geothermal sources and humans themselves permanently emit heat of considerable power, the temperature level of these heat sources is too low for economic recovery using common technologies for direct heat to electricity conversion. Recently, electrochemical processes attracted intense attention as a possible alternative to existing technologies for heat to electricity conversion, since they have the potential to be much more effective and less expensive. In the framework of the proposed project and based on very promising preliminary tests, a novel electrochemical cell-concept for heat to electricity conversion using ceramic intercalation compounds is investigated. Substoichiometric intercalation compounds (e.g. based on Li, Na, K) with similar electrode potentials and as high as possible opposite reaction entropy are used as the anode and cathode material. A change in the cells’ temperature (no gradient!) induces a cell voltage according to the respective entropies of the anode and cathode reaction. The cell is literally charged by the temperature change (analogously to a pyroelectric material). During discharging (power generation), the host lattices of the intercalation compounds are oxidized and reduced, respectively, accompanied with the extraction and insertion of the alkali metal ion, until the cell voltage tends towards 0 V. This process is completely reversible. After polarity reversal and return to the initial temperature, the cell can be discharged again and the initial state is restored. The described working principle might have significant benefits compared to existing technologies for waste heat utilization and energy harvesting. However, in light of its novelty and the absence of basic research and experimental data, this statement cannot be confirmed at the moment. Based on very promising preliminary investigations, the applicants strive for a fundamental understanding of the thermo-electrochemical heat to electricity conversion using typical ceramic intercalation materials. This includes mechanistic studies regarding the working principle as well as basic relationships between the properties of the intercalation compounds used and the resulting thermo-electrochemical cells. Finally, based on the experimental insights, a model will be developed describing the thermo-electrochemical heat to electricity conversion, which might be used prospectively for the identification of suitable material and design properties.