S3E13

Xin Qian

Xinpeng Zhang

Abstract of Talk 1

Low-grade heat made up more than half of human’s energy rejection, and harvesting low-grade heat is a promising route that could effectively reduce carbon emissions. Yet it remains a challenging task due to the low Carnot efficiency limit and the distributed feature of low-grade heat sources. In addition, harvesting human’s body heat is also an interesting direction for powering biomedical sensors or wearable devices. However, conventional electronic thermoelectric (e-TE) devices have a limited Seebeck coefficient (102 μV/K) with coupled electronic properties, making it challenging for achieving the desired voltage or efficiency using low-grade heat or body-heat. Electrochemical methods including the Soret effect (also known as thermodiffusion or ionic Seebeck effect) and thermogalvanic effect provide alternative routes for low-grade heat harvesting, due to their magnitude-larger Seebeck coefficient (1 ~ 10 mV/K), low cost, and the convenience of synthesis. In this talk, we discuss two types of electrochemical devices for harvesting low-grade heat: a hybrid device of thermionic capacitors and thermogalvanic cell, based on gelatin electrolytes with giant thermopower (12.7 mV/K) and a thermally regenerative flow battery with pH-neutral electrolytes which can continuously harvest low-grade heat. The hybrid device can achieve high voltage (2V) with only 25 serially connected modules, which greatly simplified the device fabrication compared with wearable e-TE devices integrating hundreds of modules. The pH-neutral thermally regenerative redox flow battery marks an important advance towards the stable operation of continuous electrochemical heat engines. Finally, future directions will be discussed for further improving power density and energy conversion efficiency.

Biosketch of Speaker 1

Abstract of Talk 1

Commercial and residential buildings account for ~ 40% of the total energy use in the United States. Amongst various building components, windows are the weakest thermal barrier between indoor and outdoor environments due to the high thermal conductivity and emissivity of float glass, which are responsible for 40 ~ 60% of the total energy loss from buildings. Minimizing the heat loss through windows needs to increase the thermal resistance of windowpanes and regulate the radiative heat transfer between windowpanes and the environment. My talk centers on developing easy-to-install and energy-efficient window retrofitting materials that can efficiently regulate thermal and optical transport across windowpanes. The first section includes the design of a nanofiber-based thermally insulating aerogel, which can significantly reduce heat loss across windowpanes through heat conduction. The second section focuses on the design and fabrication of thermally insulating and optically switchable films that simultaneously address not only the heat conduction, but also the solar radiation heat transfer through windows. We demonstrate a promising pathway toward energy-efficient windows and provide guidance for the design of transparent insulation materials for window applications.

Biosketch of Speaker 1