Power-source-free energy conversion by first-order phase transforming ferroelectric materials

Abstract

Due to the overwhelming development of modern technology, human beings so far have faced the most severe energy shortage than ever. We daily consume magnificent amount of energy while generating vast waste heat. In order to recycle the wasted energy, many researchers are focusing on utilizing the heat to electricity through thermoelectric devices. Statistics show that the majority of wasted thermal energy is the low-grade heat less than 200℃. Utilizing and recycling this low-grade waste heat is very important and profound. Though the performance enhancement of energy conversion by thermoelectrics has been improved by a large margin in nanostructured composites, the ability to harvest and conduct electricity in low temperature range is still not satisfactory. In this thesis, we propose a new way of energy harvesting directly from heat to electricity by the first-order phase transformation. The key is to use the singular sensitivity of certain ferroic property on crystal structure change at the first-order phase transformation. Here, the energy is converted from heat by phase transforming ferroelectric materials whose polarization jumps at phase transformation temperature. Through specified electric system, the heat can be converted to electricity. However, conventional ways of ferroelectric energy conversion are mostly based on Olsen's cycle, which depends on an external power source. It brings confusion where the true energy comes from. Instead, we designed a power-source-free energy conversion by ferroelectric materials. We conduct the in-depth thermodynamic analysis and propose the governing equation, Figure of Merit for our energy conversion design. The Figure of Merit guides the material development for high performance candidates and system optimization. We further designed an experimental platform to demonstrate heat to electricity conversion by the synthesized ferroelectric materials. Our work removes the confusion and build up the fundamentals in ferroelectric energy conversion by eliminating the impact of power source. In future, the power-source-free energy conversion system plays an important role in harvesting low-grade waste heat and serve as one of the main forces in renewable energies.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology