Wearable Research Articles

Exceptional thermoelectric and mechanical performance in (Bi, Sb)2Te3 matrix facilitated by AgInSe2 alloying

The emerging fields of the Internet of Things, intelligent robotics, and smart biomedical devices have sparked an increasing demand for high-performance thermoelectric (TE) devices due to their efficient conversion of thermal energy into electrical power, and vice versa. The environmentally friendly (Bi, Sb)2Te3 (BST) system, which displays superior performance near room temperature, offers a promising solution for optimizing thermoelectrics to meet the needs of commercial applications. Here, we utilized AgInSe2 alloying to enhance the TE and mechanical properties of BST, aiming to optimize electron and phonon transport and elucidate the underlying mechanisms. The synergistic optimization resulted in a peak zT of ∼ 1.3 at 353 K and an average zTave of ∼ 1.11 from 303 K to 503 K in BST-0.1 %AgInSe2, as well as a high Vickers hardness of ∼ 105 Hv. Through rational optimization of the TE device, we achieved a maximum conversion efficiency of ∼ 6 % at a temperature difference of 210 K. Leveraging the robust TE output of the device, we further evaluated its potential as a self-powered information interaction wristband device based on ASCII codes. We envisage this versatile TE device being extensively applied in power generation and human–machine interaction, with promising potential in wearable electronics, telecommunications, and healthcare monitoring.

Advanced In-Situ functionalized conductive hydrogels with high mechanical strength for hypersensitive soft strain sensing applications

Conductive hydrogels are used in wearable electronics, soft robotics and artificial skin due to their flexibility, biocompatibility and multifunctionality. However, combining high mechanical strength, conductivity and sensitivity in these hydrogels remains a challenge. This paper proposes a novel in-situ conductive functionalization technology for hydrogels with high mechanical strength, achieving high conductivity (3223.727 S·m−1) and low resistance (0.92 Ω) without sacrificing mechanical properties. Comprehensive experiments reveal the mechanisms and optimal parameters for conductive functionalization. AgNO3 and ascorbic acid (VC) concentrations influence the distribution, reaction rate and aggregation of Ag particles on hydrogel surfaces. Sodium carboxymethylcellulose (CMC) enhances mechanical strength and Ag+ adsorption capacity. Optimal parameters are 1.00 M AgNO3 and 0.08 M VC. An in-situ reduction reaction of silver particles establishes strong interfacial bonding between the silver layer and hydrogel matrix, forming the basis for strain sensing. The hypersensitized sensing mechanism, involving the appearance and recovery of microcracks on the silver layer via the tunneling effect, enables high sensitivity (gauge factor = 36.65). The conductive hydrogels can monitor human physiological signals, tiny strain signals from water droplets (0.01 g) and airflow, with an average response time of 12.7 ms. The developed conductive hydrogels meet the technical requirements for combining high mechanical strength and sensitivity, offering an efficient new approach for conductive hydrogel-based soft strain sensors.

Efficient Zn-Ion Pouch Cell Assembling Based on Aramid Nanofiber Hydrogel

With the fast advancement of portable and wearable electronics, it is urgent to develop safe, stable and flexible power supply devices. Safe and environmentally friendly aqueous zinc-ion batteries (AZIBs) have a low-cost and are perfect candidates for energy storage device in such applications [1-4]. Giving the general challenges, such as the formation of the dendrites on the Zn anodes and hydrogen evolution and side reactions, extensive and wide research has focused on building stable AZIBs with high performance, but less attention was paid to making Zn ion pouch cells which are flexible and with high capacity In this presentation, we developed an efficient method to assemble Zn-ion pouch cells based on the process of formation of the aramid nanofiber hydrogel. The method involves the dipping precursor solution, solvent exchanging, and in-situ electrodeposition of MnO2. The assembled Zn-ion pouch cells exhibit excellent mechanical performance, flexibility and electrochemical performance, which are ideal for portable and wearable electronics. Based on this method, we successfully assembled 3-layer (cathode/anode/cathode, A/C/A) and 5 layer (A/C/A/C/A) pouch cells with over 100 times higher capacity compared with coin cell. In addition, the pouch cell with aramid nanofiber hydrogel and in-situ electrodeposited MnO2 cathode on carbon nanotube mat demonstrates superior cycling stability [5,6]. More details about our assembling method for flexible and stable pouch cells for AZIBs and experimental measurements related to the cycling and stability characteristics, will be presented at the meeting.[1] Yu, Peng, et al. "Flexible Zn‐ion batteries: recent progresses and challenges." Small 15.7 (2019): 1804760.[2] Li, Yingbo, et al. "Recent advances in flexible zinc‐based rechargeable batteries." Advanced Energy Materials 9.1 (2019): 1802605.[3] Li, Chunyang, et al. "High-rate and high-voltage aqueous rechargeable zinc ammonium hybrid battery from selective cation intercalation cathode." ACS Applied Energy Materials 2.10 (2019): 6984-6989.[4] Yu, Feng, et al. "Aqueous alkaline–acid hybrid electrolyte for zinc-bromine battery with 3V voltage window." Energy Storage Materials 19 (2019): 56-61.[5] Wang, Peng, and Petru Andrei. "High Performance Separator and Hydrogel Based on Aramid Fibers for Zn Ion Batteries." Electrochemical Society Meeting s 242. No. 4. The Electrochemical Society, Inc., 2022.[6] Xu, Lizhi, et al. "Water‐rich biomimetic composites with abiotic self‐organizing nanofiber network." Advanced Materials 30.1 (2018): 1703343.

Chitin and Cellulose as Constituents of Efficient, Sustainable, and Flexible Zinc-Ion Hybrid Supercapacitors

A zinc-ion hybrid supercapacitor (ZIHS) is a prospective energy storage device featuring cost-effectiveness, operational safety, environmental friendliness, high-power performance, and satisfied energy density.1 The sustainability of this ZIHS technology is even improved by introducing biopolymer constituents into the cell construction.2 Herein, efficient, sustainable, and flexible ZIHSs employing polysaccharide (chitin- or cellulose-based) components are developed.3 Using green ionic liquid solvents, biopolymer-bound, activated carbon-based cathode materials and hydrogel biopolymer electrolytes containing conductive zinc salts are obtained. According to systematical characterization results, the prepared materials possess favorable functional properties. Biopolymer binders provide homogeneity and integrity within the electrode network and high adhesion to the surface of the current collector. Depending on the type of zinc salt, hydrogel biopolymer electrolytes display high ionic conductivity (up to 46 mS cm−1), expanded electrochemical stability window (up to ca. 2.8 V), and zinc dendrites growth suppression. Biopolymer components assembled with zinc foil electrodes operate efficiently in both coin and pouch ZIHS cell configurations, providing satisfactory energy (45–50 Wh kg−1) and high power (10–20 kW kg−1) density combined with excellent cycle stability. Moreover, these ZIHS pouch-type devices exhibit superior durability and flexibility, withstanding mechanical stress up to 150° bending states with at least 90% of capacitance retention. It suggests a prospect for their application in wearable electronics.4 References(1) Wang, Y.; Sun, S.; Wu, X.; Liang, H.; Zhang, W. Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators. Nano-Micro Lett. 2023, 15 (1), 78.(2) Kasprzak, D.; Mayorga-Martinez, C. C.; Pumera, M. Sustainable and Flexible Energy Storage Devices : A Review. Energy & Fuels 2023, 37, 74–97.(3) Kasprzak, D.; Liu, J. Chitin and Cellulose as Constituents of Efficient, Sustainable, and Flexible Zinc-Ion Hybrid Supercapacitors. Sustain. Mater. Technol. 2023, 38, e00726.(4) Dubal, D. P.; Chodankar, N. R.; Kim, D. H.; Gomez-Romero, P. Towards Flexible Solid-State Supercapacitors for Smart and Wearable Electronics. Chem. Soc. Rev. 2018, 47 (6), 2065–2129. Figure 1. Graphical abstract of the research on biopolymer-based Zn-ion hybrid supercapacitors. Figure 1

(Invited) Battery-Free Wearable and Implantable Electronics for Chronic Disease Management

60% of Americans live with at least one chronic disease. These diseases and their associated comorbidities are now the leading causes of death in the United States. The effective management of complex chronic diseases requires body-wide, long-term, accurate, and continuous monitoring of multiple physiological signals from wearable and implantable devices to precisely determine the pathological state. Wearable physiological signal monitoring can dramatically reduce the demand for physician visits and increase patients' engagement and treatment adherence rates. Specifically, battery-free wearables and implantable electronics reduce device volume and mechanical stiffness, significantly improving wear comfort, which is highly desirable for next-generation wearable and implantable electronics. However, battery-free wearables and implantable electronics still face many challenges, mainly wireless energy and data transfer. To address these challenges, my research has been involved in the exploration of rational system design concepts, material and device fabrication innovation, and tailored algorithms to enable smart battery-free wearables and implantable electronics targeting next-generation chronic disease management.Here, I would like to discuss two of my developed technology platforms to elaborate on the concept of battery-free wearable and implantable systems. First, I will describe an RFID-based body area sensor network technology platform. This technology uses electromagnetic waves and RF antennas as energy and data transmission media and has broad applications in sleep tracking, workout monitoring, chronic wound healing, and inflammation management. Second, I will describe a triboelectric transducer-based implantable battery-free device. This technology platform uses ultrasound waves and triboelectric transducers as energy and data transmission media and has broad applications in implantable sensing. Overall, the developed technology platforms can assess multiple health outcomes and treatment responses to various chronic diseases. Ultimately, this technology will help reduce the burden of chronic diseases, lower medical costs, and provide a better quality of life for patients. (1,2,3,4)

Development of Dual-Gel System for Wearable Electrochemical Sensors

With the innovation of materials and rapid development of wearable technology, wearable electronics—particularly textile-based systems—have broadened perspectives in health monitoring, therapy, and disease diagnosis.Bioelectronics interpret analyte information into real-time electrical signals with high sensitivity. Realizing the selective detection of analytes in biofluids often requires bioreceptors, such as enzymes, antibodies, and DNA, along with corresponding electrochemical detection techniques.Enzymatic sensors have relatively complex sensing structures among others. Enzymes function as biocatalysts at the sensing interface, facilitating electron transfer from analytes to the electrode surface. To enhance overall data acquisition, redox mediators are typically incorporated into these systems.Wearable bioelectronics are currently fabricated by depositing functional materials onto conformal flexible substrates using techniques such as spin coating, spray coating, printing, etching, and other technologies. However, seamlessly integrating multi-layer textile-based biosensors necessitates specific screen mesh and inkjet angles that ultimately limit the manufacturing process.Here, we propose a dual-gel system consisting of a base gel embedding functional materials (redox mediators and bioreceptors) and an encapsulation gel to stabilize the base gel while offering antifouling properties. The thin dual-gel film is fabricated through blade-casting followed by photo-initiated Chemical Vapor Deposition (piCVD) and can seamlessly adhere to various rough fabric surfaces. Moreover, this solvent-free process largely prevents bioreceptor degradation, promising better manufacturing sustainability.Glucose detection on flexible electrodes utilizing such a dual-gel system is exemplified as a proof-of-concept. This unique dual-gel system is expected to contribute to the development of textile-based electronics with greater versatility and improved sensing performance.

Electrochemical Characterization of Non-Aqueous and Aqueous Gel Polymer Electrolytes for Zinc-Ion Fiber Batteries

The increasing miniaturization of integrated circuits has enabled a wide variety of new applications for embedded sensors and smart devices. Miniaturization of their power sources, however, has lagged in comparison. There are many challenges to devising a space-conscious battery, including the power density, mechanical stability, and chemical safety. Batteries made in fiber formats are of interest for use in wearable electronics. Recent studies have shown the feasibility of Li-ion battery chemistries in drawn polymer fibers via thermally induced phase separation (TIPS)1,2 but key performance gaps in safety and reliability of these fiber batteries remain.In addition to Li-ion, zinc-manganese dioxide (Zn-MnO2) chemistries are particularly good candidates for fiber format batteries due to their relatively low raw material cost, low reactivity, and tolerance of environmental contaminants such as water. Our work has focused on two Zn-MnO2 gel polymer electrolyte (GPE) cell formats: one non-aqueous polyvinylidene fluoride (PVDF) based gel polymer electrolyte, the other an aqueous polyvinyl alcohol (PVA) based GPE. In this work, we synthesize, characterize, and compare these two electrolyte formats head-to-head in both Zn-Zn symmetric cells and Zn-MnO2 full cells.After the GPEs were synthesized, thermo-gravimetric analysis was used to characterize the gels and evaluate the feasibility of drawing the GPE of interest into fibers. We synthesized zinc salt containing PVDF-based GPEs and characterized them in ionic blocking cells via electrochemical impedance spectroscopy (EIS), achieving conductivities of 1.8 mS/cm2. We also assembled Zn-Zn symmetric cells, investigated key performance characteristics such as the transport number and the electrochemical stability window, and stably cycled them for over 500 hours at 0.5 mA/cm2. Lastly, we assembled Zn-MnO2 full cells to confirm the battery performance.

Electrochemical Performance and Characterisation of Chemically Treated Conductive PLA Fused Deposition Modelling (FDM) Current Collectors within Additively Manufactured (3D-Printed) Symmetric Carbon Supercapacitors

Within the fields of materials science, producing reliable, long-lasting, and efficient energy storage devices to meet the world’s energy needs remains a foremost research goal. 3D-printing (also known as Additive Manufacturing) provides many benefits to this research [1-8], allowing for excellent customization and freedom of design, while eliminating waste material in the manufacturing process. Wearable electronics, medical implants, and the Internet of Things will doubtless benefit from the advantages provided by additive manufacturing.Our previous work compared the electrochemical performances of symmetric carbon-based supercapacitor devices made using two 3D-printing techniques, SLA (stereolithography) and FDM (fused deposition modelling). Though possessing excellent cycle life, the conductive polylactic acid (PLA) FDM printed current collectors suffered from relatively high resistance and poor cyclic voltammetry curves (far from the rectangular shape of ideal electronic double-layer capacitors). This study aims to improve the conductivity of the FDM current collectors via chemically induced surface modification [9]. Both dimethylformamide (DMF) and aqueous potassium hydroxide (KOH) treatments are used for this purpose. The untreated, DMF-treated, and KOH-treated FDM current collectors are loaded with 1:1 by mass single-walled carbon nanotubes and graphene nanoplatelets carbon slurry, placed within stereolithography (SLA) 3D-printed casings [10], and assembled as supercapacitor cells (separated by glass microfiber filter separators soaked in 6 M aqueous KOH electrolyte).This works shows how DMF treatment method results in little change in electrochemical performance compared to the untreated FDM current collector cells, but pre-treatment in a solution of KOH identical to the cell electrolyte markedly improves the current collector conductivity. The KOH treatment provides a tenfold decrease in the FDM current collector resistance, which correlates with the improved cyclic voltammetric response. Galvanostatic charge-discharge tests reveal the effect of these treatments on specific capacitance, charge-discharge response, efficiency, and rate capability for these printed cells. The pre-treatment confirms that the cell electrolyte does not limited long term performance by interacting with the PLA current collector in 3D printed supercapacitor cells and tests using other inorganic active materials will also be shown.

3D-Printed Hydrogel-Based Flexible Electrochromic Device for Wearable Displays.

Flexible electrochromic devices (FECDs) are widely explored for diverse applications including wearable electronics, camouflage, and smart windows. However, the manufacturing process of patterned FECDs remains complex, costly, and non-customizable. To address this challenge, a strategy is proposed to prepare integrated FECDs via multi-material direct writing 3D printing. By designing novel viologen/polyvinyl alcohol (PVA) hydrogel inks and systematically evaluating the printability of various inks, seamless interface integration can be achieved, enabling streamlined manufacturing of patterned FECDs with continuous production capabilities. The resultant 3D-printed FECDs exhibit excellent electrochromic and mechanical properties, including high optical contrast (up to 54% at 360nm), nice cycling stability (less than 5% electroactivity reduction after 10000 s), and mechanical stability (less than 19% optimal contrast decrease after 5000 cycles of bending). The potential applications of these 3D-printed hydrogel-based FECDs are further demonstrated in wearable electronics, camouflage, and smart windows.

(Digital Presentation) Temporal Evolution of the Threshold Voltage in Organic Thin Film Memory Transistors

We present a procedure to monitor the temporal evolution of the trapped charge in floating gates of organic thin film transistors (OTFTs) based memories in dynamic regimes. The potential applications of organic semiconductors in flexible and wearable electronics and their known features such as low-temperature and solution fabrication make the OTFTs be considered as candidates also in the field of non-volatile memories. Past efforts have been devoted on the preparation and optimization of floating gates [1]. In the present work, we focus on the modelling of this kind of devices, in particular, on a model for the threshold voltage useful in dynamic experiments, such as hysteresis and transient regimes. The information extracted from the modelling and simulation of these devices can be related to technological parameters with the objective of finding a better memory design.Current-voltage curves impacted by hysteresis are usually reproduced assuming the threshold voltage to be constant or piecewise constant. Nevertheless, despite positive outcomes [2], this is not a precise approach since it does not consider the actual temporal evolution of the threshold voltage. Thus, a time dependent threshold voltage is mandatory in order to interpret hysteresis phenomena and transient experiments, which in turn can be associated to trapping and de-trapping mechanisms over time.In this work, a model that describes the evolution of the threshold voltage with the time, which is linked to the variation of the trapped charge in the channel, is proposed.The evolution of the trapped charge is described with a first-order linear differential equation with a term controlled by a time constant t, and another term, similar to the generation term in a typical continuity equation, which is proportional to the drain current flowing through the transistor channel. This model is introduced in a compact model previously developed for OTFTs that include contact effects [3–6]. The resulting model is combined with an evolutionary parameter extraction procedure, which is applied to experimental current–voltage curves taken from the literature that show both contact and hysteresis effects [7]. Figures (a) and (b) show the best fitting of our calculations (solid lines) and experimental output and transfer characteristics (symbols), respectively, of a pentacene-based organic thin film memory transistor using poly (methyl methacrylate) (PMMA) as the insulator [7]. Figures (c) and (d) show the time evolution of the threshold voltage during the experiments (a) and (b), respectively.The authors acknowledge support from the project PID2022-139586NB-44 funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR.

(Invited) In Situ and Operando Scattering Studies on Quantum Dot-Based Devices

Colloidal quantum dots (QDs) made e.g. of PbS are attractive for various optoelectronic applications due to their tunable band gap with a large absorption wavelength range from the visible to the near-infrared region. Moreover, due to the high intrinsic permittivity, the exciton binding energy of PbS is smaller than in cadmium chalcogenide QDs and polymer materials, which is beneficial for devices driven by charge carrier generation and transport, e.g. photovoltaics and photodetectors.In this work, we introduce wet chemical deposition methods beyond spin coating such as printing and spray deposition of QDs as a facile and potentially large-scale deposition method for high-performance photodetectors. The inner structures including the inter-dot distance of neighboring QDs and the structure, in the deposited QD solids, are studied by grazing-incidence small-angle X-ray scattering (GISAXS). In addition, the facet orientation of the QDs in the QD solids is characterized by grazing-incidence wide-angle X-ray scattering (GIWAXS). In particular, in situ GISAXS/GIWAXS studies during film formation are able to provide detailed information about the complex kinetic processes [1,2]. Operando GISAXS/GIWAXS studies on QD-based devices such as solar cells bring an in-depth understanding of the degradation mechanisms, which is key for improving the device stability and thereby bringing these novel materials into real-world applications [3]. Superlattice deformation in QD films on flexible substrates via uniaxial strain is followed in situ with GISAXS, providing a fundamental understanding of the impact of strain on the performance of flexible devices based on QD films, such as wearable electronics and next-generation solar cells on flexible substrates [4]. Nanoscale Horiz. 5, 880-885 (2020)Nano Energy 78, 105254 (2020)Energy Environ. Sci. 14, 3420-3429 (2021)Mater. Horizon 8, 383-395 (2023)

Compact Energy Storage Devices Developed from Waste-Derived Electrodes via Facile Recycling Technology

Indeed, the development of sustainable and renewable energy technologies is a critical aspect of addressing the challenges posed by pollution and climate change. Electrochemical energy storage devices, such as batteries and supercapacitors, play a crucial role in this transition by enabling the efficient storage and utilization of energy. The mention of nanomaterials-based electrodes highlights a fascinating area of research and innovation. Nanomaterials offer unique properties and advantages due to their small size, high surface area, short-diffusion path, rapid kinetics, enhanced conductivity, making them highly desirable for energy storage applications.Recycling waste to electrodes in compact energy storage device represents a particularly exciting frontier. Integrating energy storage into advance technology can enhance the portability and convenience of power sources, especially in the context of emerging technologies like wearable electronics and smart devices. However, challenges such as scalability, cost-effectiveness, and environmental impact must also be addressed to ensure the widespread adoption of these technologies. The emphasis on carbon-based nanomaterials, including graphene, carbon quantum dots, and activated carbon, as electrode materials is noteworthy. These materials show promise not only as negative electrodes but also as positive electrodes when combined with metal oxides, hydroxides, or sulphides, demonstrating their versatility in energy storage applications. Additionally, the innovative use of waste recycling, such as tires, shoots, and dry cells, for extracting carbon aligns with the broader goal of creating an eco-friendly environment. The focus on developing carbon-based electrodes from recycled waste for energy storage devices is commendable, as it not only addresses environmental concerns but also contributes to the creation of stable and efficient energy storage systems. In conclusion, this work on the generation of efficient carbon-based electrodes (graphene derived from different waste materials) for energy storage devices, showcases a multidisciplinary approach that considers both environmental sustainability and technological advancement. This research has the potential to contribute significantly to the ongoing efforts to create a more sustainable and efficient energy landscape.Key words: Recycling, Electrochemical, Carbon, Metal oxides, Energy storage, Compact devices

(Invited) Laser-Induced Graphene for Improved Electrochemical Biosensors

Laser-induced graphene (LIG) has emerged as a promising technique for fabricating porous graphene electrodes for many applications, including biosensors and medical devices. However, improving electrochemical properties of LIG hinges on not only understanding the kinetics and energetics governing the physicochemical process of lasing, but also the tunability of surface chemistry and morphology of the produced LIG. This talk reveals the spatiotemporal laser control for achieving different LIG morphology and atomic structures with demonstrations of seamless transitions between conductive networked LIG structures and insulating fibrous LIG morphologies. The effect of laser fluence and multi-pass lasing on LIG morphology and properties will be shown. In addition, molecular engineering of the polymer substrate is explored for controlling the chemical and physical properties of the produced LIG. Finally, the electrochemical detection of neurotransmitters in the nanomolar range will be demonstrated. Our results show that heteroatom doping of graphene is possible by including sulfur or fluorine atoms into the backbone of the polyimide synthesized by two-step polycondensation. Accordingly, both the surface hydrophobicity and sensing sensitivity are shown to depend on the heteroatom-doping content. Taken together, our work paves the way for scalable fabrication of functional graphene-based electrodes and coatings on polymers for flexible and wearable electronics, as well as implantable devices, such as neural probes.

Synthesis of Yolk-Shell CoNi2S4 Spheres Modified Flexible Carbon Cloth Electrode for Highly Sensitive Detection of Neurotransmitter Dopamine

Dopamine (DA) is a neurotransmitter that is connected with transitory information in the mammalian central nervous system; changes in its concentration in the body are directly related to mental activity. The absence and/or low level of DA can cause symptoms of several disorders, including Parkinson’s and schizophrenia. As a result, detecting DA in patients is critical for regulating body function. Many efforts have been made to build electrochemical sensing devices to detect DA in human body or biological fluids due to its inherent advantages of high sensitivity, speed, simplicity, and affordability. However, surface modification with nanomaterials, polymers, pretreatments, or simple functionalization are required to improve the performance of these sensing electrodes. Further, exploration of earth-abundant electro-catalysts with high activity and stability is also important for the development of highly selective and sensitive electrochemical sensing interfaces. With these considerations in mind, our study describes the construction of yolk-shell CoNi2S4 spheres modified flexible carbon cloth (CC) electrode for the sensitive detection of DA. The synthesized material's surface and morphological study were examined, and the successful synthesis was confirmed. The yolk-shell CoNi2S4 spheres shown good electrochemical sensing performance towards DA detection due to their unique surface morphology with large specific surface area and synergistic effects. In comparison to unmodified CC, the yolk-shell CoNi2S4 spheres modified CC demonstrated a low detection limit (5.1 nM), great sensitivity, and a wide linear range (0.01 – 5.2 µM). The detection selectivity was also tested in the presence of a high quantity of the common interference ascorbic acid. Selectivity, stability, and repeatability have also been demonstrated to be satisfactory. Furthermore, the fabricated sensor’s flexibility endows it with significant potential in the fabrication of wearable and soft electronics for human healthcare monitoring.

Flexible Aluminum-Air Batteries

Wearable and flexible electronics have a wide range of applications. Making a flexible power source for them is essential. Aluminum-air batteries are attractive for powering portable, lightweight devices due to their inexpensive, light, and powerful energy source. In this project, the Al-air battery was made using activated carbon and aluminum electrodes, chloride-based electrolytes with ionic liquid additives. Various mixtures of 1-ethyl-3-methylimidazolium chloride, aluminum chloride, sodium hydroxide, and sodium chloride were studied. Fundamental properties of room-temperature ionic liquids, such as lower conductivity and density, improved the performance of aluminum-air batteries. Cell capacity, cyclic voltammetry behavior, and cell interfacial impedance with various electrolytes were optimized using the design of experiments. The battery's electrical power output and cell capacity were lower than those obtained using an activated carbon air cathode. The cell capacity over repeated electrochemical reactions was stable. The Al-air battery had regular cyclic voltammetry behavior. Aluminum hydroxide was not found on the anode electrode when an ionic liquid electrolyte was used. The interfacial cell impedance did not decrease after electrochemical reactions over a long time.

(Invited) Triboelectric Nanogenerators for Self-Powered Sensing and Human-Machine-Interfaces

Wearable and portable electronics are garnering substantial interest for applications ranging from personalized healthcare monitoring to implantable devices and prosthetics. The demand for long-term operation poses significant challenges to their power supply. To address this, the development of novel self-powered systems holds considerable promise. In this talk, I will discuss our recent advancements in crafting triboelectric nanogenerators (TENGs) for self-powered sensing and human-machine interfaces (HMIs). I will first introduce our multifunctional tactile sensors inspired by human skin. These sensors combine a triboelectric nanogenerator layer with a piezoresistive sensing layer, emulating the ability of human skin to detect a variety of static and dynamic stimuli. This sensor can successfully recognize voice patterns, monitor physiological signals, and track human motion in real-time. Then, I will unveil our self-powered smart packaging system, which is driven by a novel desiccant-based triboelectric nanogenerator (D-TENG). This system offers a viable method for continuous monitoring of product conditions and quality control throughout the supply chain, thus minimizing food waste and maintaining a comprehensive log of logistics, especially critical in vaccine transport. Lastly, I will present our novel breath-driven triboelectric sensor in respiratory monitoring. This sensor can precisely detect breath variations and convert different breathing patterns into electrical signals, all without impeding normal breathing. It enables severely disabled individuals to control household appliances through a breath-driven HMI and provides an intelligent monitoring system for emergency situations. This innovative work paves the way for future development in self-powered sensors and advanced HMIs, enhancing assistive technology for individuals with disabilities.

Synthesis and Characterization of a Biocompatible, and Flexible Solid-Electrolyte for Zn-MnO2 Batteries

The new generation of flexible wearable electronics is becoming one of the most in-demand wearable tech in most parts of the world, be it for regular use or for medical reasons, which gives rise to the need for the development of safe and flexible rechargeable batteries. Some of the most basic requirements for such batteries constitute the ease of use, flexibility, mechanical strength, and environmental friendliness. This can be achieved by carefully designing the electrolyte for the battery such that it fulfills the mentioned properties without compromising the electrochemical performance of the battery. This study sheds light on the development of a safe, flexible, and environmentally friendly solid electrolyte film based on a biopolymer. The electrolyte film derived from Chitosan, which is a biocompatible biopolymer, offers various advantages over the conventional liquid electrolytes. When soaked in an alkaline liquid, KOH, this Chitosan-film can be used as an efficient electrolyte for Zn-MnO2 battery chemistry. According to optical imaging, the incorporation of freeze drying for the preparation of the solid electrolyte films provided a lamellar structure with a microporous morphology. Higher concentrations of Chitosan enabled the film to absorb and retain increased amount of KOH because of the hydrogen bonds present between the Chitosan molecules and KOH, which helped in enhancing the ionic conductivity (IC) of the freeze-dried electrolyte, i.e., 300-600 mS/cm, at a thickness of 150-170µm. Additionally, the obtained electrolyte demonstrated exceptional mechanical strength and flexibility which also makes it a promising solid electrolyte for Zinc metal batteries, as it has a potential to impede the progression of Zn dendrites during cycling, thereby improving the stability and lifespan of the battery.

(Battery Student Slam 8 Award Winner) A Simple and Fast Method to Assemble Flexible and Stable Quasi-Solid-State Zn Ion Pouch Cell

Aqueous zinc-ion batteries (AZIBs) have been investigated intensively as effective energy storage devices that are environmentally friendly, safe, and have a lower cost than current Li-ion batteries.[1-5] Being outstandingly safe due to usage of non-organic electrolyte, AZIBs could also be used as power supply for wearable electronics. This also put high standard requirements in terms of flexibility, stability and electrochemical performance to AZIBs. On the other hand, the general challenges, such as the formation of the dendrites on the Zn anodes, hydrogen evolution and side reactions, have been obstructing the practical application of AZIBs. In this presentation, a simple method to assemble quasi-solid-state Zn ion pouch cell with excellent mechanical performance, flexibility and electrochemical performance was developed, combining in-situ electrodeposition of MnO2 cathode and aramid nano fiber-based hydrogel with Zn plate as anode. In-situ and cycling measurements of the electrodeposition of MnO2 on carbon nanotube mat shows excellent capacitance and superior cycling stability. In addition, Kevlar derivatized aramid nanofiber-based hydrogel shows extremely strong strength when combined with polyvinyl alcohol, which prolonged the lifetime of the cell by preventing Zn dendrite growth largely.[5,6] Moreover, the method to assemble the AZIBs pouch cell enables us to optimize the process, decrease the steps, and save time effectively by taking advantage of hydrogel formation stage and avoiding conventional verbose slurry-casting-drying steps. This work paves an efficient path to assemble flexible and stable AZIBs pouch cells with high capacity and cycling stability.[1] Tang, Boya, et al. "Issues and opportunities facing aqueous zinc-ion batteries." Energy & Environmental Science 12.11 (2019): 3288-3304.[2] Li, Chang, et al. "Toward practical aqueous zinc-ion batteries for electrochemical energy storage." Joule 6.8 (2022): 1733-1738.[3] Yu, Feng, et al. "An aqueous rechargeable zinc-ion battery on basis of an organic pigment." Rare Metals 41.7 (2022): 2230-2236.[4] Lin, Yuexing, et al. "Dendrite-free Zn anode enabled by anionic surfactant-induced horizontal growth for highly-stable aqueous Zn-ion pouch cells." Energy & Environmental Science 16.2 (2023): 687-697.[5] Wang, Peng, and Petru Andrei. "High Performance Separator and Hydrogel Based on Aramid Fibers for Zn Ion Batteries." Electrochemical Society Meeting s 242. No. 4. The Electrochemical Society, Inc., 2022.[6] Xu, Lizhi, et al. "Water‐rich biomimetic composites with abiotic self‐organizing nanofiber network." Advanced Materials 30.1 (2018): 1703343.

Wearable Masks Integrated with Conducting Polymer and Carbon-Based Nanomaterials for VOC and Breath Monitoring

There has been considerable effort to develop wearable electronics from life-supporting devices for solders to fashion accessories such as smartwatches. The research of gas sensors has also attempted to adapt wearables with the power of nanotechnology. On the wearable platform, miniature gas sensors will provide real-time information about the atmosphere to protect each personnel from possible hazardous chemical attacks. In addition, wearable gas sensors can be facilitated to monitor human’s breath as medical applications. [1] Continuous monitoring of respiratory rate in real-time can act as a crucial benchmark for non-invasively detecting cardiac or arterial vascular function. Anomalies in respiratory rate serve as a significant indicator of a patient's health deterioration. Furthermore, it has been reported that aberrations in respiratory rate, as a physiological parameter, can be utilized to monitor common COVID-19 symptoms [2]. The analysis of breath through identifying biomarkers in exhaled breath proves to be an effective method for assessing metabolic disorders or dysfunctions in the human body. Conducting polymers (CPs) have generated significant interest in constructing flexible gas sensors. The inherent issue with pure CPs lies in their tendency to deprotonate in the presence of air, leading to a notable decline in long-term stability. Furthermore, limited gas response on diverse gaseous species demands the exploration of hybridizing CPs and other nanomaterials. When nanomaterials are hybridized with CPs, a synergistic effect, which comes from the benefits of each material, can improve sensing performance.In this study, polyaniline (PANI) conducting polymer and carbon-based nanomaterials, including carbon nanotubes (CNTs), graphene, or MXene were synthesized in a composite form and deposited into disposable masks. The developed gas sensor demonstrates remarkable stability attributed to the presence of van der Waals forces and π–π interactions between carbon-based nanomaterials and polyaniline (PANI). This stability is crucial for its reliable performance over time. The sensor's sensitivity is notably improved due to enhanced charge transfer channels and a porous structure that facilitates the adsorption of target gas. Additionally, the composite sensors detect breathing patterns in real-time, which demonstrates noninvasive human breath monitoring. A noteworthy aspect is that a significant portion of breath signals originates from the presence of target gases and moisture in exhaled breath. Although volatile sulfur compounds, CO2, and volatile organic compounds in the exhaled breath have a minimal influence on the sensing signals, the sensor remains highly responsive to the key components, particularly target gas by selecting carbon-based nanomaterials [3, 4]. The proposed gas sensing mechanism of the CP-based composites is discussed.

(Invited) Toward Ultrathin Flexible Quantum Dot Light-Emitting Diodes and Photodetectors for the Wearable Electronics

Flexible optoelectronic devices, encompassing light-emitting diodes (LEDs) and photodetectors, capable of seamlessly transforming their shapes, represent a prominent trend in next-generation electronics. Quantum dots, widely employed as emitters and light absorption layers, are chosen for their high luminous performance, size-dependent color tunability, and excellent light absorption properties. Moreover, their solution processability and ultrathin form factor make them particularly appealing for the development of ultrathin wearable optoelectronic devices.Here, we introduce ultrathin flexible quantum dot light-emitting diodes and photodetectors designed for wearable electronics. Utilizing intaglio transfer printing, we can produce high-definition red-green-blue quantum dot LEDs, suitable for integration into skin-attachable displays. Moreover, our ultrathin, self-powered, heavy-metal-free photodetectors, based on copper indium selenide nanoparticles, showcase outstanding optical performance (specific detectivity: 2.10 × 1012 Jones at zero-bias) and find application in wearable photoplethysmography (PPG) sensors.