For a modern gasoline engine it is only about one third of the energy (for diesel engines this is about 40%) contained in fuel which is converted into mechanical work required to move the vehicle. Unused energy escapes into the environment in the form of hot exhaust gases, hot air, or thermal energy emitted from the surface of hot engine parts and accessories. The proposed project seeks to design a complex system for unused heat utilization, leading to increased engine efficiency and thus also reduction in the concentration of undesirable greenhouse gases. It is a combination of direct heat recovery (e.g. we use the heat from the exhaust gases to faster warm the engine and the interior after starting the engine) and the indirect “thermoelectric conversion of heat energy” recovery method, where the engine is already sufficiently warmed-up and thus we can use the heat from the exhaust gases to generate electricity to run electrical devices in the car.
The project is directed to a new class of intercalation systems Ln(x)CoO2 (Ln=La,Y,rare-earth), prepared by an ionic exchange from the isostructural sodium cobaltate. Their structure is based on hexagonal layers of the edge-sharing CoO6 octahedra that alternate along the c-axis with layers of lanthanide ions. Through the variable content of Ln3+ (x<1/3), an electronic behavior of the cobalt subsystem, in particular the conduction and thermopower, is effectively controlled. Our aim is to optimize the technology of the ionic-exchange using the rare-earth nitrates or halides, to vary the mixed valency Co3+/Co4+ by deintercalation or alkali-earth substitution, and to explore systematically the structural, magnetic and electric properties of the products. For a theoretical analysis, the ab-initio and effective Hamiltonian calculations will be undertaken. It is expected that the insertion of magnetic rare-earths will make the electric transport sensitive to external magnetic field.
Direct thermal to electric power generation represents a very prospective method for recovery of the high temperature waste heat. In this context the development of chemically stable and efficient thermoelectric ceramics, composed of nontoxic and price affordable elements, has a key role for extensive application of thermoelectric materials. The project is thus aims to investigate and characterize oxide materials, which form efficient thermoelectric unicouple. The targeted materials are principally derived from layered oxide cobaltates (as p-type legs) and Mn-based perovskites or ZnO (as n-type legs). Apart of the standard thermoelectric requirements for relevant materials, namely the low thermal conductivity, the special care will be focused, given the intense thermal strain and oxidation-reduction conditions at high temperatures, on the functionalization of thermal and electrical interfaces. In this respect we plan to utilize conducting oxide nanotubes, which are able to release mechanical stresses.
The project deals with a fundamental research on novel oxide thermoelectric materials of p-type considered for the electric power generation using waste heat. As concerns the conversion efficiency of such thermoelectric generators, the materials should operate in wide temperature range and keep at the same time a high figure of merit, ZT =(S2
R)T, where S is the Seebeck coefficient, R is the ratio of electric resistivity and thermal conductivity and T is the actual temperature of the thermoelectric segment. In this respect, some cobalt oxides have been found promising, especially thanks to the pioneering work of Terasaki on thermoelectric properties of Na0.6
in 1997. The present project is focused on material research of a broad class of complex cobaltites, based both on the hexagonal and tetragonal arrangements of the thermoelectrically active CoO2
layers. The properties of the cobaltites will be optimized by an improvement of their intrinsic properties through modification of the chemical composition, as well as by a control of morphology and microstructure of the prepared materials.
Energy conversion by thermoelectric effect: from theory to applications
The objective of this course is to present the basics of energy conversion by thermoelectric effects. Starting from thermal conduction, electrical resistivity and the origin of thermoelectric power in solids, we will see that the coupling between these properties, in a certain category of materials, gives rise to effects that can be exploited advantageously to cool the body or generate electricity.
From theory to practice: