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1. Thermoelectric Characteristics of Graphene and Aluminum Doped Zinc Oxide Nanopowder Enhanced Cement Composite for Low-Temperature Applications

   Liu, X. ; Qu, M. ( June 2021 , ASHRAE Annual Conference papers)

   Thermoelectric (TE) cement composite is a new type of TE material. Unlike ordinary cement, due to the inclusion of additives, TE cement can mutually transform thermal energy into electrical energy. In extreme weather, the large temperature difference between indoor and outdoor can be harvested by TE cement to generate electricity. In moderate weather, given power input, the same material can provide cooling/heating to adjust room temperature and reduce HAVC load. Therefore, TE cement has energy-saving potential in the application of building enclosures and energy systems. Its ability to convert different forms of energy and use low-grade energy is conducive to the operation of net-zero buildings. In this study, the graphene nanoplatelets and aluminum-doped zinc oxide nanopowder enhanced cement composite, was fabricated. The performance indicator of TE materials includes the dimensionless figure of merit ZT, calculated by Seebeck coefficient, thermal conductivity, and electrical conductivity. These TE properties were measured and calculated by a Physical Property Measurement System at different temperatures. The highest ZT of 15wt.% graphene and 5wt.% AZO enhanced cement composite prepared by the dry method is about 5.93E-5 at 330K.
2. A three-dimensional transient model for evaluating the performance of the cement-based thermoelectric modules.

   Liu, X. ; Qu, M. ; Yazawa, K. ( June 2021 , 2020 International High-Performance Buildings Conference)

   The thermoelectric module (TEM) is a device that integrates multiple thermoelectric (TE) elements to realize the mutual conversion of heat and power. Due to the advantages of no moving parts and flexible expansion, the application of conventional Bi2Te3-based TEM in buildings has attracted the attention of researchers. On the other hand, the TE behavior of hardened cement composites was found by combining conductive additives with cement. Therefore, a new study on cement-based TEM for building energy harvesting and emperature control is proposed. To simulate the performance of cement-based TEM, a three-dimensional heat transfer model considering temperature-dependent TEM characteristics was established. The validity of the model is verified by comparing the results with commercial simulation software and experiments. Different from the existing analytical models and commercial software, the customized model has greater scalability, optimization, and control flexibility. Through parametric studies, the model can guide the design of TEM and the development of TE cement.
3. Development of Nanocomposite Thermoelectric Generators for Body Heat Harvesting

   Chloe Flack, Baiyu Zhang ( January 2019 , Undergraduate Research Symposium)

   This work evaluates wearable thermoelectric (TE) devices consisting of nanocomposite thermoelectric materials, aluminum nitride ceramic headers, and a flexible and stretchable circuit board. These types of wearable systems are part of a broader effort to harvest thermal energy from the body and convert it into electrical energy to power wearable electronics. Thermoelectric generators are made of p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3. The nanocomposite thermoelectric materials investigated in this research address the two fundamental challenges for body heat harvesting. The first challenge is related to the unavailability of high zT n-type materials near the body temperature. The second challenge is related to the thermoelectric power factor. To improve the zT, one has to increase the power factor simultaneously while reducing the thermal conductivity. Our nanocomposites result in enhancement of the TE power factor along with the reduction of the thermal conductivity. The fundamental reason is a nanoscale effect that happens only when the energy distribution function of the carriers does not relax to that of the bulk material in the crystallites. Ten p-type and ten n-type nanocomposite ingots were synthesized and characterized in this research. All ingots were characterized versus their thermoelectric properties and they all showed similarly enhanced properties. Ourmore »nanocomposites, compared to commercial materials, have better zT and thermal resistivity by 40% and 75% for p-type, respectively, and 15% and 140% for n-type. Compared to the state-of-the-art materials, our nanocomposites produce significantly higher power due to their optimized properties for the body temperature.« less
4. Modelling the thermoelectric properties of cement-based materials using finite element method and effective medium theory

   Stella, L. ; Johnston, C. ; Troncoso, J. ; Chudzinski, P. ; Orisakwe, E. ; Kohanoff, J. ; Jani, R. ; Holmes, N. ; Norton, B. ; Liu, X. ; et al ( August 2022 , CERI/ITRN 2022)

   Because of the thermoelectric (TE) effect (or Seebeck effect), a difference of potential is generated as a consequence of a temperature gradient across a sample. The TE effect has been mostly studied and engineered in semiconducting materials and it already finds several commercial applications. Only recently the TE effect in cement-based materials has been demonstrated and there is a growing interest in its potential. For instance, a temperature gradient across the external walls of a building can be used to generate electricity. By the inverse of the TE effect (or Peltier effect), one can also seek to control the indoor temperature of a building by biasing TE elements embedded in its external walls. In designing possible applications, the TE properties of cement-based materials must be determined as a function of their chemical composition. For instance, the TE properties of cement paste can be enhanced by the addition of metal oxide (e.g., Fe2O3) powder. In this paper, a single thermoelectric leg is studied using the finite element method. Metal oxide additives in the cement paste are modelled as spherical inhomogeneities. The thermoelectric properties of the single components are based on experimental data, while the overall thermoelectric properties of the composites aremore »obtained from the numerical model. The results of this numerical study are interpreted according to the effective medium theory (EMT) and its generalisation (GEMT).« less
5. ZnO ‐Embedded Expanded Graphite Composite Anodes with Controlled Charge Storage Mechanism Enabling Operation of Lithium‐Ion Batteries at Ultra‐Low Temperatures

   https://doi.org/10.1002/eem2.12662  

   Ryu, Kun ; Lee, Michael J. ; Lee, Kyungbin ; Lee, Seung Woo ( July 2023 , ENERGY & ENVIRONMENTAL MATERIALS)

   As lithium (Li)‐ion batteries expand their applications, operating over a wide temperature range becomes increasingly important. However, the low‐temperature performance of conventional graphite anodes is severely hampered by the poor diffusion kinetics of Li ions (Li⁺). Here, zinc oxide (ZnO) nanoparticles are incorporated into the expanded graphite to improve Li⁺diffusion kinetics, resulting in a significant improvement in low‐temperature performance. The ZnO–embedded expanded graphite anodes are investigated with different amounts of ZnO to establish the structure‐charge storage mechanism‐performance relationship with a focus on low‐temperature applications. Electrochemical analysis reveals that the ZnO–embedded expanded graphite anode with nano‐sized ZnO maintains a large portion of the diffusion‐controlled charge storage mechanism at an ultra‐low temperature of −50 °C. Due to this significantly enhanced Li⁺diffusion rate, a full cell with the ZnO–embedded expanded graphite anode and a LiNi_0.88Co_0.09Al_0.03O₂cathode delivers high capacities of 176 mAh g⁻¹at 20 °C and 86 mAh g⁻¹at −50 °C at a high rate of 1 C. The outstanding low‐temperature performance of the composite anode by improving the Li⁺diffusion kinetics provides important scientific insights into the fundamental design principles of anodes for low‐temperature Li‐ion battery operation.