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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Summary of cutting-edge research, latest advances, and future directions in low carbon and renewable energy systems
Renewable Energy Technologies for Low-Carbon Development provides a comprehensive overview of recent and cutting-edge research progress in a variety of current renewable energy and low carbon development research areas, focusing on sustainable energy from various perspectives such as thermoelectric power generation, organic solar cells, Na-ion, solar thermochemical energy storage, and nano-friction power generation. The book discusses the methodologies and research development of each renewable energy route based on its unique characteristics.
Following a brief overview of renewable energy, this book also reviews low-carbon research in traditional fossil energy and promotes the development of renewable energy with the sustainable recovery and utilization of carbon. Because of the uniqueness of CO2 in low-carbon development, CO2 storage and application are discussed separately.
Written by three highly qualified authors, Renewable Energy Technologies for Low-Carbon Development explores sample topics including:
- Thermoelectric power generators and their applications, application of nanomaterials in organic solar cells, and advances in low-temperature Na-ion battery energy storage
- Thermochemical energy storage for renewable solar energy utilization, and recent progress and new challenges in triboelectric nanogenerators
- Manufacturing, recovery, and reuse of wind turbine blades in wind power generation and electrocatalysts for oxygen reduction in fuel cells
- Carbon fiber in renewable energy development, sustainable carbon nanofluids of petroleum extraction, and carbon dioxide capture and chemical conversion into fuels
Renewable Energy Technologies for Low-Carbon Development is an essential reference on the subject for materials scientists, power engineers, electrochemists, electronics engineers, and all professionals working at energy supplying companies and in the broader chemical industry.
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Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Title Page
Copyright
Dedication
Editors Bio Section
Bio Section of Chunbao Du
Bio Section of Yuan Cheng
Bio Section of Gang Zhang
Preface
Acknowledgments
1 Thermoelectric Power Generators and Their Applications
1.1 Introduction
1.2 Principles of Thermoelectric Conversion
1.3 Thermoelectric Materials
1.4 Preparation of Thermoelectric Materials
1.5 Thermoelectric Devices and Their Applications
1.6 Conclusions and Outlook
Acknowledgment
References
2 Application of Nanomaterials in Organic Solar Cells
2.1 Introduction
2.2 Application of Carbon Materials in OSCs
2.3 Application of Silver Nanowire‐based Nanoarrays in OSCs
2.4 Emerging Trends and Future Outlook
2.5 Conclusions
References
3 Advances in Low‐temperature Na‐ion Battery Energy Storage
3.1 Introduction
3.2 LT NIB Cathode Materials
3.3 LT NIB Anode Materials
3.4 LT Organic Electrolyte Research
3.5 Summary and Outlook
References
4 Thermochemical Energy Storage for Renewable Solar Energy Utilization
4.1 Introduction
4.2 Materials/Chemical Reactions and Systems for TCES Technology
4.3 Solar Receivers/Reactors for TCES Systems
4.4 Conclusion
Acknowledgment
Conflict of Interest
References
5 Recent Progress in Triboelectric Nanogenerators and New Challenges
5.1 Introduction
5.2 Recent Research on Potential Mechanism and Four Working Modes of TENG
5.3 Conclusion
Conflict of Interest
References
6 Wind Turbine Blades in Wind Power Generation: Manufacturing, Recovery and Reuse
6.1 Introduction
6.2 Recycling of Waste WTBs
6.3 Application Procedure for WTBs after Recycling
6.4 Future Direction of WTB Improvement
Conflict of Interest
References
7 Electrocatalysts for the Oxygen Reduction Reaction in Fuel Cells
7.1 Introduction
7.2 Classification
7.3 Electrocatalysts
7.4 Future Outlook
7.5 Conclusion
Acknowledgments
Conflict of Interest
References
8 Carbon Fiber in Renewable Energy Development
8.1 Introduction
8.2 Carbon Fiber Classification: Pitch‐Based, Viscose Based, PAN Based
8.3 Application of Carbon Fiber
8.4 Application of Carbon Fiber in Wind Power
8.5 Application of Carbon Fiber in the Photovoltaic Industry
8.6 Application of Carbon Fiber in the Hydrogen Production Industry
8.7 Redox Fluid Flow Batteries
8.8 Phase Change Energy Storage
8.9 Biofuel Cells
8.10 Emerging Trends and Future Outlook
8.11 Recycling of Carbon Fiber
8.12 Summary
References
9 Sustainable Carbon Nanofluids of Petroleum Extraction
9.1 Introduction
9.2 Carbon Nanofluids for EOR
9.3 Influencing Factors of Carbon Nanofluids on EOR
9.4 Mechanisms
9.5 Emerging Trends and Future Outlook
9.6 Conclusions
Acknowledgment
Conflict of Interest
References
10 Carbon Dioxide Capture and Chemical Conversion into Fuels
10.1 Introduction
10.2 CO
2
Capture
10.3 Chemical Conversion of CO2 into Fuels
10.4 Conclusions
Acknowledgment
Conflict of Interest
References
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Properties of carbon allotropes.
Table 2.2 Parameters based on the optimization of binary and ternary OSCs.
Table 2.3 Comparison of the figure of merit of various electrode combinations...
Chapter 3
Table 3.1 Carbon and Ti‐based interlayer material representatives.
Chapter 4
Table 4.1 Common materials/chemical reactants for TCES technology.
Table 4.2 The performance of the carbonates used for TCES.
Table 4.3 The performance of the metal hydrides materials used for TCES.
Table 4.4 The performance of the metal oxide redox pairs used for TCES.
Table 4.5 The performance of the mixed metal oxide redox systems compared wit...
Table 4.6 The solar receivers/reactors used for solar methane reforming.
Table 4.7 The solar receivers/reactors used for solar thermal decomposition o...
Chapter 6
Table 6.1 Product distribution during depolymerization of carbon fiber reinfo...
Chapter 7
Table 7.1 Fuel cells are categorized according to their types of electrolytes...
Chapter 8
Table 8.1 Technical problems of glass fiber materials caused by increasing bl...
Table 8.2 Comparison of noise intensity of various engine types.
Table 8.3 Carbon fiber composite recycling technology developed by different ...
List of Illustrations
Chapter 1
Figure 1.1 Diagram of the Seebeck effect.
Figure 1.2 Diagram of the Peltier effect.
Figure 1.3 GeTe thermoelectric features. Crystal structures of R‐GeTe (a) an...
Figure 1.4 (a) Crystal structures of Bi
2
Te
3
crystal. Photo image of the sing...
Figure 1.5 Geometrical (a) and lattice thermal conductivity (b) of half‐Heus...
Figure 1.6 Two‐dimensional (2D) materials for thermoelectric conversion.
Figure 1.7 Images of Bi
0.5
Sb
1.5
Te
3
(BST) particle in photoresin (a), Bi
2
Te
3
...
Figure 1.8 (a) Schematic diagram of the Bridgeman method. Pictures of SnSe (...
Figure 1.9 Schematic diagram of the melting method.
Figure 1.10 (a) Schematic diagram of mechanical alloying.Scanning electr...
Figure 1.11 (a) Schematic diagram of the solvothermal synthesis process, (b)...
Figure 1.12 (a) Schematic diagram of printing synthesis.(b) Cross‐sectio...
Figure 1.13 Diagram of π‐ (a), O‐ (b) and Y‐type....
Figure 1.14 Structure of the vertical (a), lateral (b) and hybrid (c) miniat...
Figure 1.15 (a) Schematic diagram and optical image of fabricating chain‐lik...
Chapter 2
Figure 2.1 Schematic diagram of OSCs working mechanism, from left to right i...
Figure 2.2 Schematic diagram of OSCs (a), conventional structure (b), invert...
Figure 2.3 (a), PM6 and Y6 structure (b), Y6 simple four‐step synthesis stra...
Figure 2.4 Chemical structure of Y6 series receptors.
Figure 2.5 Schematic diagram of the architecture of a traditional inverted O...
Figure 2.6 (a) Schematics of the acid‐doped CNT film‐based OSC. (b) Graph re...
Figure 2.7 (a) Schematic Describing the Two‐Step Fabrication Process of PI@G...
Figure 2.8 Blending effect of fullerene derivative PC71BM in binary and tern...
Figure 2.9 J‐V curves (a) EQE (external quantum efficiency) spectra of four ...
Figure 2.10 Fullerene receptors and non‐fullerene performance relationship....
Figure 2.11 NFA receptors represent (a) the energy levels of PM6, BTIC and N...
Figure 2.12 The diffraction grating capturing light and the buried nanoelect...
Figure 2.13 (a) Structure of traditional ITO electrode on the left, modified...
Chapter 3
Figure 3.1 (a) Schematic illustration of the Na
+
hopping transportation ...
Figure 3.2 (a) Schematic illustration of the effect of Ni and Co doping on t...
Figure 3.3 The crystal structure of the PB obtained by DFT calculations.
Figure 3.4 (a,b) Schematic illustration and microstructure of the preparatio...
Figure 3.5 (a) ΔG between Na
2
Se/Mo and MoSe
2
under...
Figure 3.6 The electrolyte of Na‐ion batteries: solvents, electrolyte salts,...
Figure 3.7 (a) DSC heating curves of electrolytes at LT.(b) Nyquist plot...
Figure 3.8 (a) Overview of electrolytes from high to low concentrations....
Figure 3.9 (a,b) Solvation structure and desolvation energy calculation of N...
Chapter 4
Figure 4.1 A schematic of the steps involved in thermochemical energy storag...
Figure 4.2 Schematics of the solar‐driven CH
4
/CO
2
or CH
4
/H
2
O reforming syste...
Figure 4.3 A schematic of the ammonia‐based TCES system.
Figure 4.4 Schematics of (a) the SO
3
/O
2
/SO
2
TCES system, and (b) the sulfur‐...
Figure 4.5 A schematic of the TCES system based on carbonates calcination/ca...
Figure 4.6 Principles of the CaO/PbO/CO
2
chemical heat pump of heat transfor...
Figure 4.7 A schematic of the CaL TCES system in a solar thermal power plant...
Figure 4.8 A schematic of the endothermic dehydration and exothermic hydrati...
Figure 4.9 A schematic diagram of the Ca(OH)
2
/CaO chemical heat pump system....
Figure 4.10 Operation schematics of the metal hydrides‐based TCES system dur...
Figure 4.11 A schematic of the two‐step metal oxides‐based thermochemical cy...
Figure 4.12 A schematic of the isopropanol/acetone/hydrogen chemical reactio...
Figure 4.13 Schematic diagrams of directly heated reactors for solar methane...
Figure 4.14 The monolithic ceramic structures explored as volumetric receive...
Figure 4.15 The SOLASYS ceramic foam‐based directly irradiated solar steam m...
Figure 4.16 Schematic diagrams of the indirectly heated reactors for solar m...
Figure 4.17 The CSIRO's reformers and their operating principles: (a) the si...
Figure 4.18 Sketches of (a) a vortex flow reactor and (b) a particle flow re...
Figure 4.19 Schematics of (a) a direct ammonia dissociation receiver/reactor...
Figure 4.20 (a) Design of the cavity receiver with 15‐kW solar ammonia disso...
Figure 4.21 A schematic of a novel entire synthesis system for ammonia‐based...
Figure 4.22 Schematics of (a) a single concentric tube heat recovery reactor...
Figure 4.23 (a) A schematic and (b) actual solar reactors for sulfuric acid ...
Figure 4.24 (a) A schematic diagram of the indirect contact fixed/packed bed...
Figure 4.25 The experimental system for testing the performance of a packed ...
Figure 4.26 Fixed/packed bed reactors with (a) spiral fins and (b) metal foa...
Figure 4.27 (a) A schematic diagram of the direct contact fixed/packed bed a...
Figure 4.28 (a) Honeycombs and (b) foams used in direct‐heat transfer reacto...
Figure 4.29 Schematics of the (a) endothermic and (b) exothermic fluidized b...
Figure 4.30 (a) Final design and (b) gas velocities simulation of a fluidize...
Figure 4.31 A schematic diagram of shell and tube type of moving bed reactor...
Figure 4.32 A schematic diagram of an industrial rotary kiln.
Figure 4.33 Schematics of (a) the mini‐plant in the solar furnace and (b) th...
Figure 4.34 (a) A photograph of the rotary solar reactor installed in the fo...
Figure 4.35 A schematic diagram of a screw extruder moving‐bed reactor.
Chapter 5
Figure 5.1 Schematic illustration of the applications and working modes of T...
Figure 5.2 (a) The working mechanism of CS‐TENG.(b) Illustration of leaf...
Figure 5.3 (a) Working principle of LS‐TENG.(b) Configuration and applic...
Figure 5.4 (a) Working mechanism of the SE‐TENG.(b) Illustration of fabr...
Figure 5.5 (a) Working principles of FT‐TENG.(b) TENG based wind energy ...
Chapter 6
Figure 6.1 Wind turbine blade section.
Figure 6.2 Closed‐loop process of HT
3
/TCF composites for recycling both resi...
Figure 6.3 Pyrolysis conversion pathway of resin binder and its change with ...
Figure 6.4 Main components and flow directions of the fluidized bed CFRP rec...
Figure 6.5 Schematic presentation of reclamation process of waste composite ...
Figure 6.6 Schematic diagram of the microwave‐assisted chemical recycling (M...
Figure 6.7 Schematic view of electrochemical recycling system for CFRP.
Figure 6.8 Innovative reuse of WTBs: Amusement park.
Figure 6.9 Pure PLA, recycled fabricated filaments, and corresponding scanni...
Figure 6.10 Recycling schemes of mechanical grinding and FFF 3D printing....
Chapter 7
Figure 7.1 Schematic illustration of the fuel cell unit.
Figure 7.2 Fuel cell vehicles and buses utilizing fuel cell technology.
Figure 7.3 Working principles of (a) DMFC, (b) PEMFC, (c) AFC, (d) SOFC.
Figure 7.4 (a) The status of fuel cell power systems for light‐duty vehicles...
Figure 7.5 Characterizations of Pt‐Fe‐N‐C electrocatalyst via (a) HAADF‐STEM...
Figure 7.6 A schematic depiction demonstrates the ionomer distribution and t...
Figure 7.7 (a) The comparison displays the predicted activity from DFT simul...
Figure 7.8 (a and b) TEM images of Co
3
O
4
/N‐rmGO hybrid under low‐magnificati...
Figure 7.9 (a) The diagram illustrates the correlation between surface free ...
Figure 7.10 (a) The FT‐EXAFS fitting curves for Fe‐IICSAC are illustrated, w...
Figure 7.11 (a) A high‐resolution X‐ray photoelectron spectroscopy (XPS) sca...
Chapter 8
Figure 8.1 Comparison of specific strength/specific modulus of carbon fiber ...
Figure 8.2 Preparation process of carbon fiber.
Figure 8.3 Application of carbon fiber.
Figure 8.4 Development trend of wind power blade diameters.
Figure 8.5 Carbon fiber crucible furnace.
Figure 8.6 Carbon fiber solar photovoltaic carrier for improving the convers...
Figure 8.7 Carbon fiber roller.
Figure 8.8 Hydrogen fuel cell.
Figure 8.9 Carbon fiber recycling.
Chapter 9
Figure 9.1 Geographic distribution of nanotechnology in the oil industry....
Figure 9.2 Reasons for wettability change of sandstone: structural separatio...
Figure 9.3 IFT of nanofluids with different concentrations (a); Relationship...
Figure 9.4 Determination of IFT of water, MWCNT/SiO
2
, SWCNT/SiO
2
and activat...
Figure 9.5 Schematic diagram of α‐olefin sulfonate...
Figure 9.6 TEM images of MWCNTs before (a) and after (b) interacting with ac...
Figure 9.7 Time evolution of the desorption process of SDS (top row) and C
12
Figure 9.8 Preparation process of GO Janus nanosheets (a); A stable emulsion...
Figure 9.9 Schematic of the interfacial film in the presence of amphiphilic ...
Figure 9.10 Preparation process of CQDs (a); Transmittance of CQDs nanofluid...
Figure 9.11 The contact angle of the paraffin‐treated glass sheets aged in N...
Figure 9.12 Schematic diagram of the mechanism of CQDs stabilizing foam liqu...
Chapter 10
Figure 10.1 Schematic illustration for the pre‐combustion carbon capture pro...
Figure 10.2 Schematic illustration for the oxy‐fuel combustion carbon captur...
Figure 10.3 Schematic illustration for the post‐combustion carbon capture pr...
Figure 10.4 Condensation reactions of boronic acids and HHTP (2,3,6,7,10,11‐...
Figure 10.5 Structure of MUF‐16: (a) infinite secondary building units (iSBU...
Figure 10.6 Graphene nanosheets: (a) the heat treatment process, (b) Scannin...
Figure 10.7 Mechanisms of the RWGS Reaction: (a) surface redox mechanism, (b...
Figure 10.8 Schematic illustration of the photoexcitation and electron trans...
Figure 10.9 Schematic illustration of the electrochemical CO
2
reduction proc...
Guide
Cover
Table of Contents
Title Page
Copyright
Dedication
Editors Bio Section
Preface
Acknowledgments
Begin Reading
Index
End User License Agreement
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Renewable Energy Technologies for Low‐Carbon Development
Edited by Chunbao Du, Yuan Cheng, and Gang Zhang
Editors
Dr. Chunbao Du
Yangtze Delta Region Academy of Beijing Institute of Technology
Jiaxing 314019
China
Prof. Yuan Cheng
Monash University
Melbourne
VIC 3800
Australia
Prof. Gang Zhang
Institute of High Performance Computing
Singapore 138632
Singapore
Cover Image: © Miha Creative/Shutterstock
All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.d-nb.de.
© 2025 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany
The manufacturer's authorized representative according to the EU General Product Safety Regulation is Wiley‐VCH GmbH, Boschstr. 12, 69469 Weinheim, Germany, e‐mail: [email protected].
All rights reserved (including those of translation into other languages, text and data mining and training of artificial technologies or similar technologies). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
Print ISBN: 978‐3‐527‐35252‐4
ePDF ISBN: 978‐3‐527‐84355‐8
ePub ISBN: 978‐3‐527‐84354‐1
oBook ISBN: 978‐3‐527‐84356‐5
This book is dedicated to the many individuals who have inspired, supported, and guided us throughout our professional and personal journeys.
From Dr. Chunbao Du:
To my PhD supervisor, Professor Xiaoling Hu, for her unwavering support and insightful guidance, which have been pivotal throughout my academic journey. Her mentorship has not only shaped my career but has also deepened my passion for the pursuit of knowledge. To Mr. Fei Qu, whose wisdom and encouragement helped me overcome moments of confusion and setbacks, providing clarity and inspiration that have profoundly shaped both my career and personal growth.
From Prof. Yuan Cheng:
To my mentors and colleagues, who have continuously challenged and inspired me to explore new horizons in renewable energy research. Your collaboration and support have been invaluable throughout this endeavor. To my family, for their unconditional love and patience, which have been a source of strength and motivation.
From Prof. Gang Zhang:
To my academic advisors and friends, for their guidance, encouragement, and shared passion for scientific discovery. Your contributions have been instrumental in shaping my academic and professional journey. To the broader scientific community, whose dedication to advancing knowledge in renewable energy has inspired the vision for this book.
Finally, to all researchers and innovators working tirelessly to make renewable energy a cornerstone of a sustainable future, this book is dedicated to you. May it serve as a source of inspiration and a valuable resource in the collective pursuit of low‐carbon development.
Editors Bio Section
Bio Section of Chunbao Du
Dr. Chunbao Du is an associate research fellow in Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing. He received his PhD in 2017 from School of Natural and Applied Science, Northwestern Polytechnical University. He was a visiting scholar at the National University of Singapore and Institute of High Performance Computing, A*STAR prior to his PhD. After one year in Northwest Agriculture & Forestry University as a post‐doctoral fellow, he joined Xi'an Shiyou University in 2019 where he was promoted to an associate professor in 2023. His research interests are mainly focused on the controlled synthesis and application of functional materials.
Bio Section of Yuan Cheng
Prof. Yuan Cheng is the Principal Research Fellow of Monash Suzhou campus, Full Professor of Materials Science and Engineering, Monash University. She received her Bachelor degree from the Department of Mechanics and Engineering Science, Fudan University, China in July 2003, and PhD degree from the Department of Mechanical Engineering, National University of Singapore in April 2008. Before join in Monash Suzhou, she worked at the Institute of High Performance Computing (IHPC) in Singapore from 2007 till February 2021 as a Senior Scientist and Group Manager. During February till June 2009, she visited Brown University, USA as a visiting scholar. Dr. Yuan Cheng's research interest involve mechanical properties of biomaterials, machine learning for material science and skin research with applications in consumer care industry and wearable device. She has published more than 100 journal papers in the leading journals including Prog. Polym. Sci., Adv. Mater., Nature. Comm., ACS Appl. Mater. Interfaces, J. Am. Chem. Soc., etc. with an H‐index of 36. She has edited two books and has been serving as the Guest Editor of International Journal of Computational Methods, Journal of Applied Physics and Nanoscale Advances. She is elected as Fellow of International Association for Computational Mechanics.
Bio Section of Gang Zhang
Prof. Gang Zhang is a senior principal scientist in Institute of High Performance Computing (IHPC), A*STAR, Singapore. He has published more than 340 referred papers, with citations over 28,000 and an h‐index of 87. He serves as advisory board member of Nanoscale and Nanoscale Advances, advisory board member of ES Energy & Environment, technical committee member of IEDM, associate editor of Journal of Electronic Materials, associate editor of Frontiers in Physics, guest editor of Advanced Functional Materials and Science China. He is elected Fellow of American Physical Society (APS), and fellow of Institute of Physics (IOP), United Kingdom.
Preface
In the face of global climate change and the ongoing energy crisis, low‐carbon development has become an irreversible trend. As energy remains a crucial driving force for social and economic progress, the transition from traditional fossil fuels to renewable energy has garnered significant attention from both academic and industrial sectors. This book, Renewable Energy Technologies for Low‐Carbon Development, emerges within this context, offering a comprehensive exploration of cutting‐edge technologies in renewable energy research and applications.
Through several representative technological topics, the book presents the latest advancements and challenges in the renewable energy field. It begins by discussing thermoelectric conversion technology, which focuses on converting the vast amount of waste heat from industrial processes into usable electrical energy – a promising solution to the current energy shortage. Building on this, the book delves into the application of nanomaterials in organic solar cells, highlighting research breakthroughs in materials like silver nanowires and gold nanorods that significantly enhance photovoltaic performance, laying a solid foundation for future energy harvesting technologies.
Energy storage is another critical area of focus, with particular emphasis on the development of low‐temperature sodium‐ion batteries. These batteries, due to their low cost and exceptional performance in extreme environments, show potential as replacements for lithium‐ion batteries. Additionally, the book explores thermochemical energy storage technology, which provides efficient means of storing and utilizing solar energy, making it highly suitable for solar thermal power generation systems. The discussion also covers triboelectric nanogenerators, which offer innovative ways to harness mechanical energy from the environment, driving the development of self‐powered devices.
As the importance of large‐scale renewable energy deployment grows, wind power has become a significant player. The recycling and reuse of wind turbine blades are crucial to achieving sustainable wind power development, and this book provides an in‐depth analysis of potential solutions in this area. Fuel cell technology, particularly oxygen reduction reaction (ORR) electrocatalysts, is also thoroughly examined, showing promise for the low‐carbon transportation systems of the future.
Beyond energy production and storage, the book also addresses the wide‐ranging applications of carbon fiber in renewable energy. As a lightweight and strong material, carbon fiber plays an essential role in wind energy, photovoltaics, and hydrogen energy, contributing to the efficiency and lightweighting of energy systems. Moreover, the book touches on the green development of traditional fossil energy, exploring the application of carbon nanofluids in enhanced oil recovery. The final chapter discusses carbon dioxide capture and its chemical conversion into renewable fuels, a key technological pathway for achieving carbon neutrality.
Through its rigorous scientific approach and broad technological coverage, this book highlights the immense potential and practical applications of renewable energy technologies in driving low‐carbon development. Scholars, engineers, and policymakers alike will find inspiration and valuable insights within its pages. We are confident that this book will make significant contributions to the advancement and application of renewable energy technologies and help realize the global goal of low‐carbon development.
Chunbao Du
Jiaxing, China
Yuan Cheng
Clayton, Australia
Gang Zhang
Singapore, Singapore
Acknowledgments
We extend our heartfelt thanks to Wiley Publishing for their kind invitation and for the friendly and efficient support they provided throughout the editing process. Their professionalism, attention to detail, and dedication to excellence have been instrumental in bringing this book to fruition. We deeply appreciate the seamless collaboration and guidance they offered at every stage, which ensured the smooth progression of this project.
We also wish to express our sincere gratitude to the chapter authors of this multiauthor volume, who generously shared their valuable expertise and cutting‐edge insights. Their dedication, meticulous research, and passionate contributions were the backbone of this book. Each chapter reflects their commitment to advancing knowledge in renewable energy technologies and serves as a testament to their scholarly excellence.
Additionally, we recognize the broader academic and professional communities whose ongoing innovation and dialogue have inspired the topics and themes explored in this book. It is our hope that their collective efforts will continue to drive transformative progress toward a sustainable, low‐carbon future.
Finally, to all those who supported this endeavor behind the scenes – whether through discussions, feedback, or encouragement – we are deeply indebted. Your belief in the importance of this work has been a source of strength and motivation for us throughout this journey.
Chunbao Du Jiaxing, China Yuan Cheng Clayton, Australia Gang Zhang Singapore, Singapore
1Thermoelectric Power Generators and Their Applications
Jianxu Shi and Ke Wang
School of Automation, Xi'an University of Posts & Telecommunications, Xi'an, 710121, China
1.1 Introduction
Energy is a fundamental requirement for the development of human society. In recent decades, the rapid increase in energy demand has led to the emergence of an energy crisis. Moreover, in the industrial production process, the majority of energy is wasted in the form of heat, which further exacerbates theis crisis. Therefore, knowing how to convert these waste heat into effective electrical energy is beneficial to solving current energy problems. Thermoelectric conversion technology, achieving the conversion between heat or temperature gradients and electrical energy, may be a promising strategy. Thermoelectric conversion technology covers multiple stages, including material preparation, materials forming, device fabrication, and system integration. Among them, thermoelectric materials are the basis, while thermoelectric devices are the core that allows the leap from thermoelectric materials to thermoelectric conversion technology. Meantime, device design and fabrication covers such interdisciplinary scientific and technological issues as thermodynamics, thermal processing, interface physics and engineering, and reliability design.
In this section, we introduce the principle of thermal conversion technology, then discuss various thermoelectric materials, the preparation and forming of thermoelectric materials, and multifunctional thermoelectric devices. Finally, a conclusion and insightful outlook is given. Here, we present the advanced understanding of thermoelectric materials and some new‐type preparation and forming methods, which can provide new opportunities for the further advancement of thermoelectric conversion technology in a wide variety of applications.
1.2 Principles of Thermoelectric Conversion
1.2.1 Seebeck Effect
In 1823, Thomas Seebeck discovered that the compass pointer would slowly deflect when it was placed near a circuit composed of two different metals with a temperature gradient. This is the first observation of the phenomenon of electricity induced by temperature difference. Subsequently, he implemented comparative studies on various metals, and identified the existence of electromotance induced by temperature difference, which provides the fundamental principle for sensing temperature using thermocoupling. To commemorate his contributions, this phenomenon is called the Seebeck effect (Figure 1.1). With the Seebeck effect, the circuit is composed of two metals, A and B. In this circuit, metals A and B come into contact to form two nodes. Interestingly, there is a temperature difference ΔT between these two nodes, and then an electrical potential difference between the two nodes can be detected by a voltmeter connected in the circuit. With this effect, the generated thermoelectric electromotance has two fundamental properties: (i) the thermoelectric electromotance is only related to the temperature difference between the two nodes and does not rely on the temperature of the wire between the two nodes; (ii) the electromotance formed by the contact between conductors A and B, is independent of whether a third metal, C, is connected between the two nodes. These two fundamental properties render the wide application of the Seebeck effect in wearable devices, wireless sensor networks, and the aerospace field [1].
Figure 1.1 Diagram of the Seebeck effect.
1.2.2 Peltier Effect
Twelve years after the Seebeck effect was discovered, another fantastic thermoelectric phenomenon was observed by Peltier (Figure 1.2). It can be found that the contact junction in the circuit will surfer endothermic or exothermic experience, after powering on the circuit composed of two conductors, A and B. Considering that conductors A and B have different electron concentrations and the Fermi level, the contact between conductors A and B will cause unequal electron diffusion at the junction, resulting in the establishment of an electric field between the two metals at the junction, thus establishing the electrical potential difference. This thermoelectric phenomenon is calledsthe Peltier effect, which is the foundation of thermoelectric refrigeration. The Peltier electrical potential difference is a function of temperature, and the dependence of the Peltier electrical potential difference on temperature also varies for different junctions. When the current is reversed, the endothermic or exothermic behaviors of two junctions would also be reversed, thus it is suggested that the direction of heat flux (JQ) is dependent on the electrical current (JE) flow. After hundreds of years of research in thermoelectric materials, it is well known that if current flows from N‐type materials to P‐type materials, carriers willeconduct away the thermal energy and reduce temperature, thereby cooling the junction. Conversely, if electrical current flows from the P‐type conductor material into the N‐type conductor material, the temperature of the junctionwwill increase. The relationship between the thermal energy (Q) and electrical current (I) is dQ/dt = ПI with the Peltier coefficient (П), suggesting that the rate of heat generation is directly proportional to the intensity of the electrical current passed through the junction. The Peltier electrical potential of general metal junctions is µV level, while semiconductor junctions can be several orders of magnitude larger than it.
Figure 1.2 Diagram of the Peltier effect.
1.2.3 Thomson Effect
In 1851, W. Thomson derived the relationship between the Seebeck coefficient (S) and Peltier coefficient (П): S = П/T, and predicted that there should be a third thermoelectric phenomenon based on the thermodynamics. If a current goes across a uniform conductor with a certain temperature gradient, in addition to generating irreversible Joule heat, the conductor would also absorb or release amounts of heat. This phenomenon is called the Thomson effect, and the heat absorbed or released is called Thomson heat. Unlike the Seebeck and Peltier effects, the Thomson effect acts on the same conductor. Assuming the electrical current flows through a uniform conductor I, there will be a corresponding temperature difference (ΔT) in the direction of the electrical current. So the endothermic rate of the electrical current on this conductor can be written as dQ/dt = βIΔT with the Thomson coefficient (β). Subsequently, W. Thomson derived the relationship between the Seebeck coefficient (S), Peltier coefficient (П), and Thomson coefficient (β) using the theoretical approximation of balanced forces:
Thomson heat is also reversible, but it is difficult to measure the Thomson heat experimentally, due to the difficulty of distinguishing Thomson heat from Joule heat.
1.2.4 Evaluation Indicators for Thermoelectric Materials and Devices
In 1911, Altenkirch proposed a theoretical expression for the figure of merit (ZT) of thermoelectric materials, which is as follows [2, 3]:
where S, σ, and k are the Seebeck coefficient, electrical conductivity, and thermal conductivity of thermoelectric materials, respectively. The thermal conductivity is contributed by the carriers (kC and kB) and lattice vibration. Meantime, the multiple of S and σ2 is called the power factor. From Eq. (1.2), it is known that the value of ZT varies with temperature for a thermoelectric materias, and the value of ZT is proportional to the power factor but inversely proportional to the thermal conductivity of the material. To obtain high‐performance thermoelectric materials, i.e. thermoelectric materials with high ZT, the materials should have high conductivity and a large Seebeck coefficient.hHigh conductivity can reduce the heat loss caused by Joule heat, and a large Seebeck coefficient ensures the large electromotance of thermoelectric materials under specific temperature gradients. In addition, the low thermal conductivity is beneficial foe maintainingf the temperature gradient.
For a thermoelectric device, its maximum conversion efficiency (ηmax) is determined by the efficiency of the Carnot cycle and the ZT value of thermoelectric materials [4], as follows:
From Eq. (1.3), we can find the maximum conversion efficiency of thermoelectric devices increases with the increase of ZT and temperature difference. Therefore, increasing the value of ZT is usefulofor improvine the maximum thermoelectric conversion efficiency of thermoelectric devices.
1.3 Thermoelectric Materials
1.3.1 Traditional Thermoelectric Materials
GeTe material: GeTe is an extensively used thermoelectric material for working in the mid‐temperature range. GeTe is a semiconductor with a narrow band gap and large hole carrier concentration of ∼1021 cm−3[5]. When the temperature increases over approximately 600–700 K, GeTe undergoes a phase transition from rhombohedral structure (R‐GeTe) with lattice parameters of a = 4.156 Å and c = 10.663 Å and the space group of R3m to cubic structure (C‐GeTe) with a lattice parameter of a=5.996 Å and the space group of (Figure 1.3a–d) [6]. In Figure 1.3e, the photograph of (GeTe)x(AgSbTe2)100−x (commonly called TAGS‐x) pellets is presented, which was prepared bhe gas‐atomization followed by spark plasma sintering (SPS) [7]. The temperature‐dependent ZT and average ZT (zTavg) of the GeTe family materials have been studied in a large temperature region (Figure 1.3f,g) [8]. To achieve an ultralow lattice thermal conductivity, high‐entropy engineering for thermoelectrics is one of the latest promising strategies. The large strains can be caused in high entropy materials due to the severely distorted lattices, which strengthens the phonon scattering and reduced lattice thermal conductivity significantly [9]. He and coworkers [10] have improved the ZT value of GeTe to 2.7 at 750 K usithe high‐entropy engineering.
Figure 1.3 GeTe thermoelectric features. Crystal structures of R‐GeTe (a) and C‐GeTe (b) as well as the corresponding primitive cells of R‐GeTe (c) and C‐GeTe (d).
Source: Hong et al. [6]/Reproduced with permission from John Wiley & Sons.
(e) Photograph of (GeTe)x (AgSbTe2)100−x (commonly called TAGS‐x) pellets prepared by gas‐atomization (GA) plus spark plasma sintering (SPS).
Source: Reproduced with permission from Kim et al. [7]/ELSEVIER.
(f) Representative temperature‐dependent zT, and (g) the average value of zT (zTavg).
Source: Hong et al. [8]/John Wiley & Sons/CC BY 4.0.
Bi2Te3material: Since 1954, Goldsmid firstly proposed and verified bismuth telluride (Bi2Te3) as potential thermoelectric materials [11]. Bi2Te3 is a semiconductor material with the highest thermoelectric performance at room temperature, and it has been commercially produced. Therefore, Bi2Te3 has become one of the most developed and most frequently used thermoelectric materials, and its binary crystal structure belongs to triangular crystal systems. Bi atoms and Te atoms are along the crystallographic c‐axis, forming Te(1)‐Bi‐Te(2)‐Bi‐Te(1) five atomic sublayers (Figure 1.4a). Meantime, these atomic layers are alternately arranged and stacked to form a hexagonal layered structure. Te(1) and Bi atoms are bonded by both the covalent bond and ionic bond, while Te(2) and Bi atom are bonded only by the covalent bond. There is the non‐bond Van der Waals coupling between adjacent Te(1) and Te(1) sublayers. In Bi2Te3 compound, the ionic covalent bonds are the strongest, while the van der Waals coupling is the weakest. Therefore, Bi2Te3 alloys are prone to slip in the Te(1)‐Te(1) layer and dissociate perpendicular to the c‐axis. Hence, the dimension of Bi2Te3 can be decreased to two dimensionl (2D). At present, The single crystal of Bi2Te3 compound is common, and can be cleaved (Figure 1.4b,c) [12]. According to the stoichiometric ratio of Bi2Te3, the alloy prepared by meltinod or zon‐ melting method exhibits p‐type conductivity. Because elemental Te has a high saturated vapor pressure, and it is volatize during the melting process, this resungs in a large number of Te vacancies in the Bi2Te3 compound. Subsequently, Bi occupies the Te vacancies to form antisite defects, which increases the hole concentration, resulting in p‐type conduction. The lattice parameters of Bi2Te3 are a = 4.395 Å and c = 30.44 Å. The band gap of Bi2Te3 is ∼0.13 eV at room temperature, and its molar mass, density and melting point are 800.76 g mol−1, 7.74 g cm−3, and 580 °C, respectively. In order to improve the thermoelectric properties of Bi2Te3he doping can be employed. For instance, p‐type Bi2−xSbxTe3 can be formed by the doping of Sb element, and n‐type Bi2−xSbxTe3 is formed by Se element doping. Meantime, the lattice thermal conductivity of bismuth telluride can be reduced by nanostructure, which is also useful to improve the thermoelectric performance of Bi2Te3 compounds [13].
Figure 1.4 (a) Crystal structures of Bi2Te3 crystal. Photo image of the single Bi2Te3 single crystal (b) and cleavage surface (c) after dissociation.
Source: Reproduced with permission from Lu et al. [12]/Springer Nature.
1.3.2 Half‐Heusler Alloys
Half‐Heusler alloys have attracted extensive attention, due to their stable chemical, good mechanical, and excellent thermoelectric properties in the medium and high temperature range (700–1000 K). Half‐Heusler alloys can be represented by the general formula ABC, where A is the most electronegative transition element, such as Zr, Hf, Ti, V, Nb, etc., and B is a weaker electronegativity transition element, such as Ni, Co, Fe, etc., and C is the main group element, such as Sn, Sb element (Figure 1.5a) [14–17]. Lattice thermal conductivities of major half‐Heusler thermoelectric materials are comparable to other common thermoelectric materials (Figure 1.5b) [18]. Meanwhile, the thermoelectric performance of half‐Heusler alloys can also be evaluated bhe band‐structure manipulation, and the band engineering can be achieved bhe point defect and substitution doping. Li et al. [19] improved the performance of FeNbSb‐based half‐Heusler alloys by band manipulation, and they found the band structure of FeNbSb‐based half‐Heusler alloynsdisplays high band degeneracy near the valence band maximum (VBM), which is beneficial for thermoelectric performance. Subsequently, they manipulated the band structure by doping of Hf on the Nb site, and obtained the maximum ZT is up to ∼1.5 at 1500 K.
Figure 1.5 Geometrical (a) and lattice thermal conductivity (b) of half‐Heusler materials.
Source: Ren et al. [18]/Springer Nature/CC BY 4.0.
1.3.3 2D Thermoelectric Materials
In the past two decades, two‐dimensional (2D) materials received substantial attention since graphene was peeled off by mechanical exfoliation. Compared with bulk materials, 2D materials often display quantum confinement and thickness effects, as well as anisotropic thermal conductivity. However, the electrical properties of 2D insulators are poor, thus unsuitable for thermoelectric conversion. Meantime, 2D metals have extremely low Seebeck coefficients because of the deep Fermi level in the band structure, which is detrimental to the thermoelectric figure of merit [21]. Therefore, researchers studying 2D thermoelectric materials mainly focus on 2D semiconductors. Typical 2D semiconductors include transition metal disulfides (TMDs), black phosphorus, IV‐VI chalcogenides, and MXenes (Figure 1.6).
Figure 1.6 Two‐dimensional (2D) materials for thermoelectric conversion.
Source: Li et al. [20]/Springer Nature/CC BY 4.0.
TMDs are a series of very important materials with the general formula MX2, where M represents transition metal elements and X represents sulfur group elements. The geometrical structures of TMDs is like a sandwich with transition metal elements layered between sulfur group elements. MoS2, the most widely studied semiconductor among TMDs, has low phonon group velocity and large Grüneisen constants, leading to its much lower lattice thermal conductivity than graphene. Moreover, this low lattice thermal conductivity is also layer‐dependent. Both Gu et al. [22] and Xu et al. [23] found that the lattice thermal conductivity of MoS2 clearly decreases with the number of layers reducing from three to one using the phonon Boltzmann transport equation and non‐equilibrium Green's function, respectively. Meanwhile, the band gap of MoS2 can also be tuned in the range of 1.2–1.8 eV by controlling the number of layers [24]. Kayyalha et al. [25] and Hippalgaonkar et al. [26] explored the dependence of thermoelectric performance of 2D MoS2 on the number of layers, and found that the power factor reaches the maximum (up to 8.5 mW [m−1 · K−1]) at bilayer MoS2 while the Seebeck coefficient is insensitive to the number of layers. Besides, other TMDs also have giant potential in thermoelectric conversion, because the thermal conductivity of TMDs can be manipulated effectively by the type of chalcogen [27]. It has been identified by theoretical and experimental studies that the thermal conductivity of TMDs shows a reduction when the type of chalcogen changes from S to Se, which is useful for thermoelectric conversion.
Compared to TMDs, the band gap of black phosphorus can be tailored over a wider range (0.3–2.0 eV) by controlling the number of layers [28]. Due to the corrugated geometrical structure of black phosphorus, as well as its electrical, phononic, mechanical, and thermal properties, it behaves strong in‐plane anisotropy between the armchair (AC) and zigzag (ZZ) directions. In the AC direction, black phosphorus shows stronger anharmonicity, lower group velocity, and phonon relaxation time than in the ZZ direction [29, 30], resulting in the anisotropic ratio of thermal conductivity between the ZZ and AC direction of up to 2.2 times [31]. Interestingly, the anisotropy of electronic properties is opposite to that of thermal conductivity in black phosphorus [32]. In the AC direction with lower thermal conductivity, higher conductivity and Seebeck coefficient occur. This phenomenon that better electrical performance and lower thermal performance occur in the same direction meets the demand for high thermoelectric figures of merit. SnSe is one of IV‐VI chalcogenides, whose structure is similar to black phosphorus. 2D SnSe has strong anisotropy and anharmonicity due to the unequivalent occupations of Sn and Se atoms in its geometrical structure, which is reflected in the large Grüneisen constants. These large Grüneisen constants result in the extremely low thermal conductivity of 2D SnSe, which is beneficial for thermoelectric applications [33–36]. MXene, a new group of 2D materials, is defined as Mn+1AXn, where M represents the early transition metal, while A and X are the element from groups 13–16 in the periodic table and the carbon/nitrogen atoms, respectively. The value of n can be 1, 2, or 3. The electronic properties of MXene can be tuned between metallic, semiconducting, and half‐ metallic states by surface functionalization. Unlike black phosphorus prone to oxidation in the air, MXene possesses excellent thermal stability, and is thus often studied for the high‐temperature thermoelectric conversion. In 2014, Khazaei et al. [37] predicted the thermoelectric properties of more than 35 functionalized MXene monolayers through first‐principles calculations, and proved that monolayer and multilayer Mo2C exhibit a higher power factor than other MXenes. Subsequently, Kim et al. [38] fabricated two kinds of Mo2C‐based MXene flexible thin films, and discovered the power factor of Mo2TiC2Tx film is up to 309 µW mK−2 at 800 K, making this promising for thermoelectric conversion at high temperatures.
2D materials are more sensitive to the surface and geometrical structure than bulk materials, thus the electronic, thermal and thermoelectric properties can be manipulated effectively by doping [39], defect [40, 41], strain [42, 43] and heterostructure [44, 45]. For instance, the thermal conductivity of graphene is measured at about 5000 W (m−1 · K−1) by Balandin [46, 47], which is detrimental for thermoelectric conversion. In 2011, Seol et al. [48] placed the graphene on SiO2 substrate and found the thermal conductivity decreased to 500–600 W (m−1·K−1) at room temperature. This is mainly due to the interaction between acoustic phonons and the substrate, which greatly suppresses the contribution of acoustic phonons to thermal conductivity, resulting in a lower thermal conductivity than suspended graphene. Besides, there is still a long way to go for the practical applications of 2D materials in thermoelectric conversion. Because it is still difficult to prepare 2D semiconductor materials with high mobility on a large scale. Furthermore, complex devices need to be made when measuring the thermoelectric properties of 2D semiconductor materials, which would introduce more defects and other uncertainties and make it challenging to measure the intrinsic properties of 2D materials.
1.3.4 Thermoelectric Liquid Materials
Thermoelectric liquid materials mainly contain two types, one is slurry and another is ink (Figure 1.7). In 2015, He et al. [49] firstly reported p‐type Bi0.5Sb1.5Te3 (BST) slurry and its photoresins (Figure 1.7a). This slurry was used as 3D printing (sterolithography apparatus, SLA) raw materials, and the printed sample exhibited excellent thermal performance. Compared to thermoelectric slurries, inks have a lower viscosity. The single‐crystalline Bi2Te3 thermoelectric nanowires (BTNWs) eare dispersed in deionized (DI) water (Figure 1.7b), and formed inkjet‐printed BTNWs. Theis inkjet‐printed BTNWs providthe good thermoelectric performances aitstheir Seebeck coefficient reached up to 140 µV K−1[50]. The BiSbTe‐based all‐inorganic inks can be formulated by dispersing BixSb2−xTe3 micro‐particles in the presence of Sb2Te4 as an inorganic binder in glycerol [51] (Figure 1.7c). The Bi2Te3‐based inorganic paints were prepared by employing the molecular Sb2Te3 chalcogenidometalate as a sintered precursor, and possessed ZT values of 0.67 and 1.21 for n‐ and p‐type painted materials [52], respectively. The all‐inorganic viscoelastic Bi2Te3‐based inks were synthesid by using chalcogenidometalate ions as inorganic binders [53], while the single‐crystal nanoplates Bi2Te2.8Se0.2 reas mixed in solvent (α‐Terpineol) using a planetary centrifugal mixer for a uniform mixture.
Figure 1.7 Images of Bi0.5Sb1.5Te3 (BST) particle in photoresin (a), Bi2Te3 nanowire in deionized water (b), as well as the images of all‐inorganic (c).
Sources: (a) Reproduced with permission from He et al. [49]/John Wiley and Sons. (b) Reproduced with permission from Chen et al. [50]/with permission John Wiley & Sons. (c) Reproduced with permission from Yang et al. [51]/ELSEVIER.
1.4 Preparation of Thermoelectric Materials
Generally, thermoelectric materials can be prepared by the Bridgeman method, melting, mechanical alloying, solvothermal synthesis, and printing alloying. A schematic diagram of the Bridgeman method is given (Figure 1.8a), which has been widely used in the preparation of thermoelectric single crystals [54]. SnSe has attracted widespread interess, due to its outstanding thermoelectric performance. By substituting Bi at Sn sites, successful synthesis of n‐type SnSe single crystals was achieved by the temperature gradient growth method. At 773 K, the highly doped n‐type SnSe with carrier density of −2.1 × 1019 cm−3 reached the maximum ZT value of 2.2 along the b‐axis [55] (Figure 1.8b). The single crystal p‐type Bi0.5Sb1.5Te3 and n‐type Bi2Te2.7Se0.3 are synthesized by zone melting and the Bridgman technique with a three‐temperature‐zone furnace. Then, the films are exfoliated from the corresponding single crystal. The power factors of p‐type and n‐type are 42 and 46 µW cm−1 K−1[12] (Figure 1.8c). Layered materials based on Mg3Bi2, composed of non‐toxic and abundantly available elements, are being widely regarded as a highly promising option for thermoelectric applications. Besides, single crystals of Mg3Bi2‐based materials with high quality and precise compositional control are groughusing the Bridgman method [56] (Figure 1.8d).
Figure 1.8 (a) Schematic diagram of the Bridgeman method. Pictures of SnSe (b), Bi2Te3 (c), Mg3Bi2 (d) single crystal.
Sources: (a) Reproduced with permission from Shi et al. [54]/American Chemical Society. (b) Duong et al. [55]/Springer Nature/CC BY 4.0. (c) Reproduced with permission from Shi et al. [54]/American Chemical Society. (d) Reproduced with permission from et al. [56]/ ELSEVIER.
Currently, the most prevalent and widely adopted method to prepare thermoelectric materials is the melting process, due to its high productivity, easy operation, and affordable characteristic. The schematic diagram and basics of the melting process are given (Figure 1.9). This process mainly involves three stages: (i) heating the high‐purity precursors above their melt points in a quartz tube; (ii) keeping the high‐purity precursors at high temperature for an appropriate time; (iii) cooling to the room temperature slowly. At present, the SnSe ingot [57], Bi2Te3 alloys [58], and TiNISn half‐Heusler alloys [59] have been fabricated by this melting process. However, there is a disadvantagefto this method that it is difficult to control the structures and morphologies of synthesized materials.
Figure 1.9 Schematic diagram of the melting method.
Source: Reproduced with permission from Shi et al. [54]/American Chemical Society.
In addition, the ball milling process is also a very common method in the preparation of thermoelectric materials, especially for high‐temperature thermoelectric materials or elements that contain easily gasified elements. The schematic diagram of the ball milling process is shown (Figure 1.10a). Using this mechanical alloying process, here are FeV1−xTixSb half‐Heusler alloyse successfully synthesized [60], and the scanning electron microscope (SEM) image of alloy powder (Figure 1.10b). Followed by hot pressing, powder fabricated by ball milling is transformed into dense bulk. Bi2Te3 samples with the highest thermoelectric figure of merit at temperatures ranging from 573 to 673 K were synthesized using a combination of mechanical alloying [61] (Figure 1.10c). The half‐Heusler Nb0.55Ta0.40Ti0.05FeSb alloyed by ball milling can approach a maximum power factor of 78 µW cm−1 K−2, whose performance is much better than NbFeSb single crystal samples [17].
Figure 1.10 (a) Schematic diagram of mechanical alloying.
Source: Reproduced with permission from Shi et al. [54]/American Chemical Society.
Scanning electron microscope (SEM) images of FeVSb (b) and Bi2Te3 (c) samples.
Source: Reproduced with permission from Hasan and Ur [60]/Springer Nature.
Solvothermal preparation is also a promising method for the synthesis of thermoelectric materials. This technique involves the use of solvents at elevated temperatures and pressures, allowing the precise control of the component, structure, and properties of as‐synthesized materials. Solvothermal synthesis offers the ability to achieve uniform mixing and homogenization of constituents, which is beneficial to improving thermoelectric performance. With the solvothermal synthesis method, the controllable degree of particle size, shape, and distribution is heavily dependent on the solubility of precursors in solvents under the elevated temperature, and the high solubility of precursors can enhance the controllable degree of particle size, shape, and distribution, thereby improving the thermoelectric properties of as‐synthesized materials. Furthermore, solvothermal synthesis enables the incorporation of dopants or the formation of composites, providing opportunities to tailor the properties of thermoelectric materials. With ongoing research and advancements in solvothermal techniques, this method holds great promise for the development of high‐performance thermoelectric materials. The schematic diagram of the solvothermal principle is shown (Figure 1.11a). The microcrystal SnTe synthesized by solvothermal method [62] (Figure 1.11b). Synthesis quality was demonstrated by the energy dispersive spectrometer (EDS) characterization (Figure 1.11c). At 773 K, Sn0.99In0.01Te exhibits an impressive power factor of ∼21.8 µW cm−1 K−2, and concurrently achieves a ZT value of ∼0.78 [62]. The solvothermal method is weor suited to the synthesis of nanostructured thermoelectric materials. The Sb2Te3 nanoplate was fabricated by th sSolvothermal method [63] (Figure 1.11d). 2D bismuth telluride nanosheets were also synthesizedrmalthis method and used as raw material the high‐throughput airgel 3D printing [64] (Figure 1.11e).
Figure 1.11 (a) Schematic diagram of the solvothermal synthesis process, (b) images of SnTe microcrystal, and (c) energy dispersive spectrometer (EDS) maps for prepared SnTe microcrystal. Sb2Te3 nanoplate (d), and Bi2Te3 nanoparticle (e) using solvothermal synthesis.
Sources: (a) Reproduced with permission from Shi et al. [54]/American Chemical Society. (b and c) Reproduced with permission from Moshwan et al. [62]/American Chemical Society. (d) Reproduced with permission from Dun et al. [63]/John Wiley & Sons. (e) Zeng et al. [64]/Springer Nature/CC BY 4.0.
3D printing, also known as additive manufacturing, allows for the precise layer‐by‐layer deposition of materials, enabling the creation of complex geometries and intricate structures. Thus, it is also regarded as a promising approach for the fabrication of thermoelectric materials. By utilizing 3D printing, researchers can personalize the design of thermoelectric devices, optimizing their efficiency and performance. Additionally, 3D printing offers the advantages of reduced material waste and the ability to create intricate thermoelectric architectures, which is difficult to achieve through traditional fabrication methods. Various thermoelectric materials, including semiconductors and composites, have been successfully printed by the fused deposition modeling (FDM), selective laser sintering (SLS), and inkjet printing methods. However, challenges still exist, such as the limited availability of suitable thermoelectric inks and the unsatisfactory thermoelectric properties of printed materials. Nevertheless, the rapid progress in 3D printing technology and raw printing materials still hold great promise for the development of highly efficient and customizable thermoelectric devices in the future.
Research on 3D printing synthetic thermoelectric materials is just getting started. The schematic diagram of printing synthetic thermoelectric materials is shown (Figure 1.12a) [65]. The elemental powdery were first placed into a powder bed, and then a fiber laser was employed to melt these powders and printed alloys. In the whole process, each alloyed layer was melted twice by the fiber laser to form dense thermoelectric ingots under a high‐purity argon environment. In the selective laser melting (SLM) process, a mixture of Sb and Te elemental powders is utilized as the initial materials. The printed sample and its morphology of Sb2Te3 have been given (Figure 1.12f,g) [65]. When the a blend of Bi and Te elemental powders is utilized as the initial materials, the morphology of the molten pool for Bi2Te3 specimens is reported (Figure 1.12b), indicating the feasibility of printing [66]. Thermoelectric compounds, including alloys, intermetallic compounds, and oxides, have been successfully synthesized using laser melting (Figure 1.12c) [67]. The morphology and cross‐section of the single‐pass melt pool of laser printed bismuth telluride are presented (Figure 1.12d,e) [68], suggesting that suitable laser printing parameters can form good surface features.
Figure 1.12 (a) Schematic diagram of printing synthesis.
Source: Reproduced with permission from Shi et al. [65]/ELSEVIER.
(b) Cross‐section of Bi2Te3 molten region.
Source: Reproduced with permission from El‐Desouky et al. [66]/ELSEVIER.
(c) Photo of Bi1−xSbx samples synthesized by laser printing, and melt line on a bismuth telluride (d) and its cross‐section (e), and photo (f) and SEM image (g) of Sb2Te3 sample.
Sources: (c) Reproduced with permission from Kinemuchi et al. [67]/ELSEVIER. (d and e) Reproduced with permission from El‐Desouky et al. [68]/ELSEVIER. (f and g) Reproduced with permission from Shi et al. [65]/ELSEVIER.
1.5 Thermoelectric Devices and Their Applications
1.5.1 Conventional Devices
In a thermoelectric module, a metal electrode is required to connect the p‐ and n‐type thermoelectric materials. To elevate the performance of thermoelectric modules, the type of metal electrode and thermoelectric materials can be chosen optimally, thereby manipulating the contact resistance between them to obtain a better output voltage. However, the output voltage of single thermoelectric module is still low, thus it is necessary to connect several thermoelectric modules in parallel or in series and form a thermoelectric device.
According to geometrical structure, conventional thermoelectric devices are divided into three types: π‐, O‐ and Y‐type [54] (Figure 1.13). Among them, the π‐type thermoelectric device, integrating modules into two plates with large thermal conductivity and electrical insulation, is the mostly frequently‐used. In the π‐type thermoelectric device, heat flow transmits along the axis perpendicular to the two plates, suitable for working environments with flat heat sources. However, the hot (top) and cold (bottom) surfaces are usually constrained in the π‐type thermoelectric device, which results in a vertical temperature difference. Due to the existence of thermal expansion difference, this vertical temperature difference is likely to cause considerable thermal strain, thereby damagins the device reliability. In the O‐type thermoelectric device, n‐ and p‐type thermoelectric materials are arranged in alternating coaxial with cylindrical heat sources. To realize the electrical insulation between adjacent thermoelectric materials, annular insulation materials are employed and placed between each thermoelectric material layer. Meantime, the metal electrodes are also employed to connect adjacent thermoelectric materials. Compared to the π‐type thermoelectric device, the O‐type thermoelectric device is more suitable for working environments withea non‐flat heat source. However, the manufacturing cost of O‐type thermoelectric devices is much higher than the π‐type. Because the soldering between special shaped thermoelectric materials and metal electrodes, as well as the integration technology of devices, are more difficult than flat devices. In the Y‐type thermoelectric device, each n‐ or p‐type thermoelectric materias is sandwichedybetween electrode plates (Figure 1.13c). Based on this unique structure, each electrode plate not only provides conductive paths between adjacent p‐type and n‐type thermoelectric materials, but also serves as collector and heat transfer components.
Figure 1.13 Diagram of π‐ (a), O‐ (b) and Y‐type (c) thermoelectric devices.
Source: Reproduced with permission from Shi et al. [54]/American Chemical Society.
The shape of thermoelectric materials can be rectangular or cylindrical. Compared to the π‐ and O‐type thermoelectric devices, the lateral series in a Y‐type thermoelectric device can eliminate the stress induced by the difference in thermal expansion coefficients of p‐type and n‐type thermoelectric materials significantly. Furthermore, each thermoelectric module in Y‐type structures is allowed to be optimized independently, which is beneficial to the manufacture of segmented structures. However, there are two main concerns in designing the conventional thermoelectric device. One is the choice of thermoelectric materials with robust mechanical properties and high thermoelectric performance, while another concern is how to connect the thermoelectric materials and electrodes. The appropriate selection of thermoelectric and interlayer materials can maintain the high performance of thermoelectric devices for a long time with high stability. With the development of the internet of things (IoT), more and more systems are connected by a network of billions of smart sensors. As a result, knowing how to power these smart sensors becomes an urgent problem to be solved. Thermoelectric energy conversion provides a possible solution to this problem. In particular, micro and flexible thermoelectric devices are required for the wireless sensor networks used for animal tracking and human health monitoring. Hence, researchers are beginning to design and manufacture miniaturized and flexible thermoelectric devices.
