The Fuel Cells and Solid State Chemistry Division at Risø DTU is among the world’s research leaders in solid oxide fuel cells (SOFCs) – a technology for clean and efficient conversion of chemical energy (in the form of, e.g., natural gas, hydrogen, biogas, ammonia or methanol) into electricity and heat. 

In addition we have activities within a number of related topics in functional ceramics, including high-temperature electrolysis, oxygen and hydrogen separation membranes, electrochemical flue gas purification, electronic/ionic heterostructure oxides, thermoelectrics and magnetic refrigeration.

In the present talk I will concentrate on our activity within the areas of heterostructure interfaces, high temperature thermoelectric oxides and magnetic refrigeration.

Stacking for example two electrically insulating crystalline compounds such as LaAlO3 (LAO) and SrTiO3 (STO) can lead to a metallic or even a superconducting interface. Other unexpected properties of such interfaces include ferromagnetism, ferroelectricity and multiferroic behavior. More and more evidence, including our own work, indicates that the oxygen vacancies on STO side control the conductivity at the interface. We have recently discovered a new type of heterostructure based on strontium titanate that has a conducting interface even though it includes a non-crystalline overlayer, which challenges current understandings of the effect. Some recent results will be presented.

A large amount of thermal energy is available from the waste heat associated with many industrial and social activities of mankind. This heat is difficult to reclaim due to the dispersed nature and relative small size 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 Risø DTU.

Magnetic refrigeration is an emerging technology that has the potential to significantly reduce the energy consumption in the refrigeration sector. The technology relies on the heating and cooling of magnetic materials upon the application and removal of a magnetic field, respectively. The thermodynamically reversible nature of the magnetocaloric effect holds out the promise of a more energy efficient method of refrigeration compared to conventional compressor technology. Coupling this with an absence of ozone depleting and greenhouse contributing gasses gives magnetic refrigeration the potential to become an environmentally sustainable technology. The practical implementation of magnetic refrigeration requires optimisation of magnetocaloric materials and permanent magnet circuits in order to design and construct a working prototype magnetic refrigeration device. The magnetic refrigeration group at Risø DTU covers all these areas and recently such a working prototype has been constructed and tested. Results from these tests will be presented and discussed.