Yi Zhou

​Temporal heat harvesting: transverse pyroelectricity

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The non-static heat recovery capability is typically determined by temporal temperature change (∂T/∂t) and spontaneous polarization variation (ΔP). However, conventional out-of-plane heat conduction exhibits small values for ∂T/∂t and ΔP, resulting in low pyroelectric power density. To address this challenge, we unravelled the correlation between non-uniform solar-thermal conversion in thin films and solid-state heat transfer, based on spontaneous polarization anisotropy and temperature nonlinearity in general pyroelectric materials. Specifically, an in-plane topological heat conduction model was proposed, and the decoupling of photothermal confinement and heat propagation was achieved. This approach synergistically enhanced ∂T/∂t and ΔP variation, resulting in a record-high photothermal pyroelectric power density of 38 mW/m² at 1 sun. Furthermore, inspired by high spatial degrees of freedom and photothermal property tunability in non-planar structures, we devised multi-layered dielectrics of transparent optical prisms with various projection ratios. This enabled selective, integrated, and adaptive photothermal waste heat recovery and rain droplet-based triboelectric energy harvesting (achieving a 174% increase in output power density for waste heat recovery and a 65% increase for droplet-based energy harvesting, respectively).

References

[1] Nature Communications, 14, 426, 2023
[2] National Science Review, 10, nwad186, 2023
[3] National Science Review, 10, nwad218, 2023
[4] Next Energy, 1, 100026, 2023

 

Spatial heat harvesting: non-unity thermoelectrics

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Static heat recovery typically relies on Seebeck effect and utilizes electrically connected p- and n-type thermoelectric legs with a unity geometric structure. Therefore, achieving high power density necessitates the integration of more thermoelectric materials and denser units, posing significant challenges to energy sustainability and carbon neutrality. According to the thermoelectric constitutive equation and impedance matching factor, we elucidated the topology manipulation mechanism for peak power and peak power conversion efficiency theoretically and clarified the synergistic modulation fundamentals of non-unity geometric structures on power output and heat flux. Specifically, we effectively increased the output power density of the device by 22% with a less material usage of 44%. Also, the reduction in energy consumption and carbon emissions, associated with the industrial production of non-unity thermoelectric devices were evaluated from a viewpoint of techno-economic sustainability. Furthermore, based on the non-unity structure, we proposed an anisotropic heterostructure strategy for spatial solar heat recovery. This strategy involved constructing spatial separation of photothermal absorption and reflection on a single thermoelectric thin film, leading to an in-plane temperature gradient of over 5 °C and providing a record-high photothermal thermoelectric power density of 4.2 W/m² at 1 sun.

References

[1] Science Advances, 9, eadf5701, 2023
[2] Nature Nanotechnology, 2023, doi.org/10.1038/s41565-023-01457-5
[3] Nature Nanotechnology, 2023, doi.org/10.1038/s41565-023-01464-6
[4] Applied Physics Letters, 116, 043904, 2020

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Integrated environmental energy harvesting

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The synergistic utilization of low-grade environmental thermal fluids and waste heat is an important pathway for achieving efficient conversion of hybrid energies in environmental systems. It has also been an emerging research focus in the field of waste heat harvesting and thermal energy utilization in recent years. In response to different thermal fluid systems, we optimized the macro/micro topological structures and thermal transport across the heterogeneous interfaces towards co-manipulation of heat and mass transport characteristics in the system. This optimization has enabled comprehensive utilization of energy forms such as thermal and mechanical energies. Additionally, a series of piezoelectric and thermoelectric devices have been developed, allowing for stable and efficient thermo-fluid waste heat recovery at the scale of proof-of-concept prototypes. Meanwhile, our approach facilitated the synergistic production of clean water, electricity, and green hydrogen. These achievements provide fundamental principles and technological support for the integration of thermal energy conversion with clean water and energy.

References
[1] Nano Energy, 77, 105102, 2020
[2] Nano Energy, 69,104397, 2020
[3] Materials Today, 42, 178-191, 2021