Oxides gets environmentally-friendly

A large amount of thermal energy is available from the waste heat associated with many industrial and social activities of mankind. However, it is difficult to reclaim this heat due to the dispersed nature and relative smallness of its sources. Thermoelectric conversion offers a very promising method to overcome these difficulties by converting heat directly into electricity at the source.

However, the requirements for the materials are not easily satisfied even by current state-of-the-art thermoelectric materials. Not only must they possess high thermoelectric performance, they must also be stable at high temperatures and be composed of nontoxic and low-cost elements, and must be able to be processed and shaped cheaply.

Oxides are among the strongest candidate materials for this purpose. This talk provides an overview of the development on such materials at DTU Energy Conversion. In order for high temperature oxide thermoelectric (TE) modules to become a viable route for power generation, the overall efficiency of these devices must be improved.

While most research currently focuses on the enhancement of the thermoelectric properties of the p- and n-type elements of the module, it is also necessary to demonstrate a working oxide module and develop stable interconnects with low contact resistance as well as mechanical and the chemical stability.

In this presentation I will also show our latest results on the performance of oxide module made of ZnO doped Al (n-type) and CaCoO 349 (p-type) [1]. In the second part of the presentation I will talk about magnetic cooling/heating. In recent years much effort has been put towards development and improvement of active magnetic regenerator (AMR) refrigerators which represent an alternative to vapor compression technology.

This technology has great potential in realizing cooling devices with high efficiency and low global warming potentials, which are highly desirable for a broad range of applications. The technology relies on the magnetocaloric effect in a solid refrigerant rather than the temperature change that occurs when a gas is compressed.

This talk presents the general considerations for the design and construction of a high frequency rotary AMR device [2]. Recently we have also clearly showed the potential value of the mixed valence manganese ceramics as magnetocaloric materials for application in devices [3]. The strength of the materials lies in the ability to accurately tune the Curie temperature.

The relatively low cost of materials and especially the processing route, compared to conventional materials and processing routes, reduces the price which is otherwise a major obstacle in the way of magnetocaloric applications. Finally, the latest experimental results of our novel rotary magnetic refrigeration device are also presented at various cooling powers for a range of operating conditions near room temperature. [1] N.

Van Nong et al., Advanced Materials, 23(21) (2011) 2484-2490. [2] A. Smith et al. Review, Advanced Energy Materials, (2012), DOI: 10.1002/aenm.201200167 [3] C. R. H. Bahl et al., Appl. Phys. Lett. 100 (2012) 21905.