Haiyu Fang

Bio: Haiyu Fang is an academic researcher from Purdue University. The author has contributed to research in topics: Thermoelectric effect & Seebeck coefficient. The author has an hindex of 20, co-authored 21 publications receiving 1915 citations. Previous affiliations of Haiyu Fang include University of Science and Technology of China & University of California, Santa Barbara.

Flexible thermoelectric materials and device optimization for wearable energy harvesting

Abstract: In this paper, we review recent advances in the development of flexible thermoelectric materials and devices for wearable human body-heat energy harvesting applications. We identify various emerging applications such as specialized medical sensors where wearable thermoelectric generators can have advantages over other energy sources. To meet the performance requirements for these applications, we provide detailed design guidelines regarding the properties of the material, device dimensions, and gap fillers by performing realistic device simulations with important parasitic losses taken into account. For this, we review recently emerging flexible thermoelectric materials suited for wearable applications, such as polymer-based materials and screen-printed paste-type inorganic materials. A few examples among these materials are selected for thermoelectric device simulations in order to find optimal design parameters for wearable applications. Finally we discuss the feasibility of scalable and cost-effective manufacturing of thermoelectric energy harvesting devices with desired dimensions.

Hierarchical assembly of micro-/nano-building blocks: bio-inspired rigid structural functional materials

Abstract: The huge diversity of hierarchical micro-/nano-rigid structures existing in biological systems is increasingly becoming a source of inspiration of materials scientists and engineers to create next-generation advanced functional materials. In the past decades, these multiscale hierarchical structures have been intensively investigated to show their contributions to high performance in mechanical properties. Recently, accompanied with the development of nanotechnology, some biologically hierarchical rigid structures have been duplicated and mimicked in artificial materials through hierarchical organization of micro-/nano-building blocks. In this critical review, we will present biological rigid structural models, functional micro-/nano-building blocks, and hierarchical assembly techniques for the manufacture of bio-inspired rigid structural functional materials (177 references).

Artificial Nacre-like Bionanocomposite Films from the Self-Assembly of Chitosan-Montmorillonite Hybrid Building Blocks

Abstract: In the last decade, there has been a trend in chemistry to reduce the human impact on the environment. Special attention has been paid to the replacement of conventional petroleum-based plastics by materials based on biopolymers. However, the mechanical and thermal properties and functionalities of these biopolymers have to be enhanced to be competitive with the petroleum-based plastics from the viewpoint of practical applications. One of the most promising solutions to overcome these drawbacks is the elaboration of bionanocomposite, namely the dispersion of nanosized filler into a biopolymer matrix. Because of their functional properties, bionanocomposites as green nanocomposites based on biopolymers and layered silicates (clays) have received intensive attention in materials science. 4] Chitosan and montmorillonite (MTM), an abundant polysaccharide and a natural clay respectively, have been widely used as the constituents of bionanocomposites. The intercalation of chitosan into MTM and the dispersion of MTM nanosheets in the chitosan matrix have been systematically investigated. Bionanocomposites based on chitosan intercalation into MTM can be used as a sensor applied in the potentiometric determination of several anions. Bionanocomposite films formed through the dispersion of MTM nanosheets in the chitosan matrix have shown enhancement of the mechanical and thermal properties compared with the pure chitosan film. Unfortunately, the enhancement of the tensile strength and thermal stability of the chitosan–MTM bionanocomposite film is still low far from the expectations in industry. Systematic studies are carried out in materials science on natural materials with the objective of duplicating their properties in artificial materials. Natural nanocomposites provide prime design models of lightweight, strong, stiff, and tough materials due to the hierarchical organization of the micro and nanostructures. One attractive biological model for artificial material design is nacre (mother-of-pearl). The microscopic architecture of nacre has been classically illustrated as a “brick-and-mortar” arrangement that plays an important role in the amazing mechanical properties of the nacre. This arrangement is constituted of highly aligned inorganic aragonite platelets surrounded by a protein matrix, which serves as a glue between the platelets. Recently, the microstructure of the nacre has been mimicked by several innovative techniques to fabricate the artificial nacre-like materials with high mechanical performance. For example, layer-by-layer (LBL) deposition combining with cross-linking yielded poly(vinyl alcohol)/MTM nacre-like nanocomposites with a tensile strength of up to 400 MPa; the ice-crystal templates of the microscopic layers were designed to form a brick-and-mortar microstructured Al2O3/poly(methyl methacrylate) composite that is 300 times tougher than its constituents; the assembly of Al2O3 platelets on the air/water interface and sequent spincoating was developed into the fabrication of lamellar Al2O3/ chitosan hybrid films with high flaw tolerance and ductility; the self-assembly of nanoclays with polymers coating by a paper-making method resulted in the nacre-mimetic films; and nacre-like structural MTM–polyimide nanocomposites were fabricated by centrifugation deposition-assisted assembly. Our group has also fabricated nacre-like chitosanlayered double hydroxide hybrid films with a tensile strength of up to 160MPa by sequential dipping coating and the LBL technique. The concept of mimicking nacre and recently developed innovative techniques inspired us to fabricate the highly sustainable artificial nacre-like chitosan–MTM bionanocomposite film with high performance to seek a promising material for the replacement of conventional petroleumbased plastics. Herein, we introduce a novel approach to fabricate artificial nacre-like chitosan–MTM bionanocomposite films by self-assembly of chitosan–MTM hybrid building blocks (Scheme 1). The chitosan molecules are very easily coated onto exfoliated MTM nanosheets to yield the hybrid building blocks by strong electrostatic and hydrogen-bonding interactions. These hybrid building blocks can be dispersed in distilled water and then aligned to a nacre-like lamellar microstructure by vacuum-filtrationor water-evaporationinduced self-assembly because of the role that the orientation of the nanosheets and linking of the chitosan play. The fabrication process is simple, fast, time-saving, and easily scaled up compared with the LBL, ice-crystal-template, and other techniques. [*] H. B. Yao, Z. H. Tan, H. Y. Fang, Prof. Dr. S. H. Yu Division of Nanomaterials and Chemistry Hefei National Laboratory for Physical Sciences at Microscale Department of Chemistry National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) Fax: (+ 86)551-360-3040 E-mail: shyu@ustc.edu.cn Homepage: http://staff.ustc.edu.cn/~ yulab/

Design principle of telluride-based nanowire heterostructures for potential thermoelectric applications.

Abstract: We present a design principle to develop new categories of telluride-based thermoelectric nanowire heterostructures through rational solution-phase reactions. The catalyst-free synthesis yields Te–Bi2Te3 “barbell” nanowire heterostructures with a narrow diameter and length distribution as well as a rough control over the density of the hexagonal Bi2Te3 plates on the Te nanowire bodies, which can be further converted to other telluride-based compositional-modulated nanowire heterostructures such as PbTe–Bi2Te3. Initial characterizations of the hot-pressed nanostructured bulk pellets of the Te–Bi2Te3 heterostructure show a largely enhanced Seebeck coefficient and greatly reduced thermal conductivity, which lead to an improved thermoelectric figure of merit. This approach opens up new platforms to investigate the phonon scattering and energy filtering.

Flexible and conductive MXene films and nanocomposites with high capacitance

Abstract: MXenes, a new family of 2D materials, combine hydrophilic surfaces with metallic conductivity Delamination of MXene produces single-layer nanosheets with thickness of about a nanometer and lateral size of the order of micrometers The high aspect ratio of delaminated MXene renders it promising nanofiller in multifunctional polymer nanocomposites Herein, Ti 3 C 2 T x MXene was mixed with either a charged polydiallyldimethylammonium chloride (PDDA) or an electrically neutral polyvinyl alcohol (PVA) to produce Ti 3 C 2 T x /polymer composites The as-fabricated composites are flexible and have electrical conductivities as high as 22 × 10 4 S/m in the case of the Ti 3 C 2 T x /PVA composite film and 24 × 10 5 S/m for pure Ti 3 C 2 T x films The tensile strength of the Ti 3 C 2 T x /PVA composites was significantly enhanced compared with pure Ti 3 C 2 T x or PVA films The intercalation and confinement of the polymer between the MXene flakes not only increased flexibility but also enhanced cationic intercalation, offering an impressive volumetric capacitance of ∼530 F/cm 3 for MXene/PVA-KOH composite film at 2 mV/s To our knowledge, this study is a first, but crucial, step in exploring the potential of using MXenes in polymer-based multifunctional nanocomposites for a host of applications, such as structural components, energy storage devices, wearable electronics, electrochemical actuators, and radiofrequency shielding, to name a few

Nanostructured metal chalcogenides: synthesis, modification, and applications in energy conversion and storage devices

Abstract: Advanced energy conversion and storage (ECS) devices (including fuel cells, photoelectrochemical water splitting cells, solar cells, Li-ion batteries and supercapacitors) are expected to play a major role in the development of sustainable technologies that alleviate the energy and environmental challenges we are currently facing. The successful utilization of ECS devices depends critically on synthesizing new nanomaterials with merits of low cost, high efficiency, and outstanding properties. Recent progress has demonstrated that nanostructured metal chalcogenides (MCs) are very promising candidates for efficient ECS systems based on their unique physical and chemical properties, such as conductivity, mechanical and thermal stability and cyclability. In this review, we aim to provide a summary on the liquid-phase synthesis, modifications, and energy-related applications of nanostructured metal chalcogenide (MC) materials. The liquid-phase syntheses of various MC nanomaterials are primarily categorized with the preparation method (mainly 15 kinds of methods). To obtain optimized, enhanced or even new properties, the nanostructured MC materials can be modified by other functional nanomaterials such as carbon-based materials, noble metals, metal oxides, or MCs themselves. Thus, this review will then be focused on the recent strategies used to realize the modifications of MC nanomaterials. After that, the ECS applications of the MC/modified-MC nanomaterials have been systematically summarized based on a great number of successful cases. Moreover, remarks on the challenges and perspectives for future MC research are proposed (403 references).

Graphene nanosheet: synthesis, molecular engineering, thin film, hybrids, and energy and analytical applications

Abstract: The emergence of graphene nanosheet (GN, 2010 Nobel Prize for Physics) has recently opened up an exciting new field in the science and technology of two-dimensional (2D) nanomaterials with continuously growing academic and technological impetus. GN exhibits unique electronic, optical, magnetic, thermal and mechanical properties arising from its strictly 2D structure and thus has many important technical applications. Actually, GN-based materials have enormous potential to rival or even surpass the performance of carbon nanotube-based counterparts, given that cheap, large-scale production and processing methods for high-quality GN become available. Therefore, the studies on GN in the aspects of chemistry, physical, materials, biology and interdisciplinary science have been in full flow in the past five years. In this critical review, from the viewpoint of chemistry and materials, we will cover recent significant advances in synthesis, molecular engineering, thin film, hybrids, and energy and analytical applications of the “star-material” GN together with discussion on its major challenges and opportunities for future GN research (315 references).

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

Abstract: Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.