Swift Assembly of Adaptive Thermocell Arrays for Device-Level Healable and Energy-Autonomous Motion Sensors

Recent Advances in Nanomaterial-Based Self-Healing Electrodes Towards Sensing and Energy Storage Applications

Nanomaterial-based self-healing electrodes have demonstrated significant potential in sensing and energy storage applications due to their ability to withstand electrical breakdowns at high electric fields. However, such electrodes often face mechanical challenges, such as cracking under stress, compromising stability and reliability. This review critically examines nanomaterial-based self-healing mechanisms, focusing on properties and applications in health monitoring, motion sensing, environmental monitoring, and energy storage. By comprehensively reviewing research conducted on dimension-based nanomaterials (OD, 1D, 2D, and 3D) for self-healing electrode applications, this paper aims to provide essential insights into design strategies and performance enhancements afforded by nanoscale dimensions. This review paper highlights the tremendous potential of harnessing dimensional nanomaterials to develop autonomously restoring electrodes for next-generation sensing and energy devices.

MXene Hollow Microsphere-Boosted Nanocomposite Electrodes for Thermocells with Enhanced Thermal Energy Harvesting Capability

Thermal energy, constantly being produced in natural and industrial processes, constitutes a significant portion of energy lost through various inefficiencies. Employing the thermogalvanic effect, thermocells (TECs) can directly convert thermal energy into electricity, representing a promising energy-conversion technology for efficient, low-grade heat harvesting. However, the use of high-cost platinum electrodes in TECs has severely limited their widespread adoption, highlighting the need for more cost-effective alternatives that maintain comparable thermoelectrochemical performance. In this study, a nanocomposite electrode featuring Ti3C2Tx with hollow microsphere structures is rationally designed. This design addresses the restacking issue inherent in MXene nanosheets, increases the electrochemically active surface area, and modifies the original MXene surfaces with oxygen terminations, leading to improved redox kinetics at the electrode-electrolyte interface, particularly in n-type TECs employing Fe2+/3+ redox ions. The optimized n-type TEC achieved an output power of 84.55 μW cm-2 and a normalized power density of 0.53 mW m-2 K-2 under a ΔT of 40 K, outperforming noble platinum-based TECs by a factor of 5.5. An integrated device consisting of 32 TEC units with a p-n connection is also fabricated, which can be successfully utilized to power various small electronics. These results demonstrate the potential of MXene-based composite electrodes to revolutionize TEC technology by offering a cost-effective, high-performance alternative to traditional noble metal electrodes and contributing to efficient low-grade heat harvesting.

Recent Advances in Self-Powered Sensors Based on Ionic Hydrogels

After years of research and development, flexible sensors are gradually evolving from the traditional "electronic" paradigm to the "ionic" dimension. Smart flexible sensors derived from the concept of ion transport are gradually emerging in the flexible electronics. In particular, ionic hydrogels have increasingly become the focus of research on flexible sensors as a result of their tunable conductivity, flexibility, biocompatibility, and self-healable capabilities. Nevertheless, the majority of existing sensors based on ionic hydrogels still mainly rely on external power sources, which greatly restrict the dexterity and convenience of their applications. Advances in energy harvesting technologies offer substantial potential toward engineering self-powered sensors. This article reviews in detail the self-powered mechanisms of ionic hydrogel self-powered sensors (IHSSs), including piezoelectric, triboelectric, ionic diode, moist-electric, thermoelectric, potentiometric transduction, and hybrid modes. At the same time, structural engineering related to device and material characteristics is discussed. Additionally, the relevant applications of IHSS toward wearable electronics, human-machine interaction, environmental monitoring, and medical diagnostics are further reviewed. Lastly, the challenges and prospective advancement of IHSS are outlined.

Giant Power Output from Ionic/electronic Hybrid Nanocomposite Thermoelectric Converter Under Constant Temperature Gradient

Thermoelectric (TE) materials that directly convert heat to electricity are of great significance for sustainable development. However, TE generators (TEGs) made from electronic TE materials suffer from low Seebeck coefficient (10-2-100 mV K-1). While ionic TE capacitors based on ionic conductors exhibit high thermovoltage (100-102 mV K-1), ionic TE capacitors provide power discontinuously only under variation of temperature gradient as ions cannot transport across electrodes to external circuits. Herein, an ionic/electronic hybrid nanocomposite TE converter (NCTEC) by integrating carbon nanotube/polylactic acid nanofibrous fabrics (CPNF) with gelatin ionogel is reported. The resulting NCTEC exhibits a record-high output power density normalized by squared temperature gradient (Pave/ΔT2) of 1.72 mW m-2 K-2 and realizes continuous power output (over 12 h) at a constant temperature gradient, which is among the highest reported power output for TE converters and can be attributed to the combination of substantial increase in interfacial capacitive effect between ionogel and CPNF and an optimized electrical property of the CPNF. The work provides an effective strategy to overcome the limitations of both TEGs and ionic TE capacitors.

Future Trends in Alternative Sustainable Materials for Low-Temperature Thermoelectric Applications

In the evolution of pervasive electronics, it is imperative to significantly reduce the energy consumption of power systems and embrace sustainable materials and fabrication processes with minimal carbon footprint. Within this context, thermoelectric generators (TEGs) have garnered substantial attention in recent years because of the readily available thermal gradients in the environment, making them a promising energy-harvesting technology. Current commercial room-temperature thermoelectrics are based on scarce, expensive, and/or toxic V-VI chalcogenide materials, which limit their widespread use. Thermoelectric polymers partially address this issue, and as such, they have been intensively studied in the field in the past decade. However, less popular materials have recently appeared to respond to the challenges of room-temperature thermoelectrics in terms of sustainability and cost. In this contribution, we comprehensively review the latest advancements in emerging alternative materials with the potential to pave the way for the next generation of sustainable TEGs. This upcoming generation includes flexible and printed TEGs for applications like wearables or the Internet of Things.

Advances in flexible ionic thermal sensors: present and perspectives

Ionic thermal sensors (ITSs) represent a promising frontier in sensing technology, offering unique advantages over conventional electronic sensors. Comprising a polymer matrix and electrolyte, these sensors possess inherent flexibility, stretchability, and biocompatibility, allowing them to establish stable and intimate contact with soft surfaces without inducing mechanical or thermal stress. Through an ion migration/dissociation mechanism similar to biosensing, ITSs ensure low impedance contact and high sensitivity, especially in physiological monitoring applications. This review provides a comprehensive overview of ionic thermal sensing mechanisms, contrasting them with their electronic counterparts. Additionally, it explores the intricacy of the sensor architecture, detailing the roles of active sensing elements, stretchable electrodes, and flexible substrates. The decoupled sensing mechanisms for skin-inspired multimodal sensors are also introduced based on several representative examples. The latest applications of ITS are categorized into ionic skin (i-skin), healthcare, spatial thermal perception, and environment detection, regarding their materials, structures, and operation modes. Finally, the perspectives of ITS research are presented, emphasizing the significance of standardized sensing parameters and emerging requirements for practical applications.

Metal-organic framework based self-powered devices for human body energy harvesting

The shift from traditional bulky electronics to smart wearable devices represents a crucial trend in technological advancement. In recent years, the focus has intensified on harnessing thermal and mechanical energy from human activities to power small wearable electronics. This vision has attracted considerable attention from researchers, with an emphasis on the development of suitable materials that can efficiently convert human body energy into usable electrical form. Metal-organic frameworks (MOFs), with their unique tunable structures, large surface areas, and high porosity, emerge as a promising material category for human body energy harvesting due to their ability to be precisely engineered at the molecular level, which allows for the optimization of their properties to suit specific energy harvesting needs. This article explores the progressive development of MOF materials, highlighting their potential in the realm of self-power devices for wearable applications. It first introduces the typical energy harvesting routes that are particularly suitable for harvesting human body energy, including thermoelectric, triboelectric, and piezoelectric techniques. Then, it delves into various research advances that have demonstrated the efficacy of MOFs in capturing and converting body-generated energy into electrical energy, emphasizing on the conceptual design, device fabrication, and applications in medical health monitoring, human-computer interaction, and motion monitoring. Furthermore, it discusses potential future directions for research in MOF-based self-powered devices and outlines perspectives that could drive breakthroughs in the efficiency and practicality of these devices.

Progress on Material Design and Device Fabrication via Coupling Photothermal Effect with Thermoelectric Effect

Recovery and utilization of low-grade thermal energy is a topic of universal importance in today's society. Photothermal conversion materials can convert light energy into heat energy, which can now be used in cancer treatment, seawater purification, etc., while thermoelectric materials can convert heat energy into electricity, which can now be used in flexible electronics, localized cooling, and sensors. Photothermoelectrics based on the photothermal effect and the Seebeck effect provide suitable solutions for the development of clean energy and energy harvesting. The aim of this paper is to provide an overview of recent developments in photothermal, thermoelectric, and, most importantly, photothermal-thermoelectric coupling materials. First, the research progress and applications of photothermal and thermoelectric materials are introduced, respectively. After that, the classification of different application areas of materials coupling photothermal effect with thermoelectric effect, such as sensors, thermoelectric batteries, wearable devices, and multi-effect devices, is reviewed. Meanwhile, the potential applications and challenges to be overcome for future development are presented, which are of great reference value in waste heat recovery as well as solar energy resource utilization and are of great significance for the sustainable development of society. Finally, the challenges of photothermoelectric materials as well as their future development are summarized.

Robust, Efficient, and Recoverable Thermocells with Zwitterion-Boosted Hydrogel Electrolytes for Energy-Autonomous and Wearable Sensing

The rapid growth of flexible quasi-solid-state thermocells (TECs) provides a fresh way forward for wearable electronics. However, their insufficient mechanical strength and power output still hinder their further applications. This work demonstrates a one-stone-two-birds strategy to synergistically enhance the mechanical and thermoelectrochemical properties of the [Fe(CN)6]3-/4--based TECs. By introducing Hofmeister effect and multiple non-covalent interactions via betaine zwitterions, the mechanical strength of the conventional brittle gelatin hydrogel electrolytes is substantially improved from 50 to 440 kPa, with a high stretchability approaching 250 %. Meanwhile, the betaine zwitterions strongly affect the solvation structure of [Fe(CN)6]3- ions, thus enlarging the entropy difference and raising the thermoelectrochemical Seebeck coefficient from 1.47 to 2.2 mV K-1. The resultant quasi-solid-state TECs exhibit a normalized output power density of 0.48 mW m-2 K-2, showing a notable improvement in overall performance compared to their counterparts without zwitterion regulation. The intrinsic thermo-reversible property also allows the TECs to repeatedly self-recover through sol-gel transformations, ensuring reliable energy output and even recycling of TECs in case of extreme mechanical damages. An energy-autonomous smart glove consisting of eighteen individual TECs is further designed, which can simultaneously monitor the temperature of different positions on any touched object, demonstrating high potential in wearable applications.

Distinguishing thermoelectric and photoelectric modes enables intelligent real-time detection of indoor electrical safety hazards

Due to the prevalence of electronic devices, intelligent sensors have attracted much interest for the detecting and providing alarms with respect to indoor electrical safety. Nonetheless, how to effectively identify various indoor electrical safety hazards remains a challenge. In this study, we fabricated single-walled carbon nanotube/poly(3-hexylthiophene-2,5-diyl) (SWCNT/P3HT) composites with exceptional bifunctional thermoelectric and photoelectric responses. Through synergy of the thermo-/photoelectric effects, the composites yielded greatly enhanced output voltages compared with the use of thermoelectric effects alone. Interestingly, modes of heat transfer can be effectively distinguished using the nominal Seebeck coefficients. Based on the remarkable output voltages and deviations in the nominal Seebeck coefficients, we developed indoor intelligent sensors capable of effectively identifying and monitoring diverse indoor electrical conditions, including electrical overheating, fire, and air conditioning flow. This pioneering investigation proposes a novel avenue for designing intelligent sensors that can recognize heat transfer modes and hence effectively monitor indoor electrical safety hazards.

Enhanced Selective Ion Transport in Highly Charged Bacterial Cellulose/Boron Nitride Composite Membranes for Thermo-Osmotic Energy Harvesting

Significant untapped energy exists within low-grade heat sources and salinity gradients. Traditional nanofluidic membranes exhibit inherent limitations, including low ion selectivity, high internal resistance, reliance on nonrenewable resources, and instability in aqueous solutions, invariably constraining their practical application. Here, an innovative composite membrane-based nanofluidic system is reported, involving the strategy of integrating tailor-modified bacterial nanofibers with boron nitride nanosheets, enabling high surface charge densities while maintaining a delicate balance between ion selectivity and permeability, ultimately facilitating effective thermo-osmotic energy harvesting. The device exhibits an impressive output power density of 10 W m-2 with artificial seawater and river water at a 50 K temperature gradient. Furthermore, it demonstrates robust power density stability under prolonged exposure to salinity gradients or even at elevated temperatures. This work opens new avenues for the development of nanofluidic systems utilizing composite materials and presents promising solutions for low-grade heat recovery and osmotic energy harvesting.

Solvation Engineering via Fluorosurfactant Additive Toward Boosted Lithium-Ion Thermoelectrochemical Cells

Lithium-ion thermoelectrochemical cell (LTEC), featuring simultaneous energy conversion and storage, has emerged as promising candidate for low-grade heat harvesting. However, relatively poor thermosensitivity and heat-to-current behavior limit the application of LTECs using LiPF6 electrolyte. Introducing additives into bulk electrolyte is a reasonable strategy to solve such problem by modifying the solvation structure of electrolyte ions. In this work, we develop a dual-salt electrolyte with fluorosurfactant (FS) additive to achieve high thermopower and durability of LTECs during the conversion of low-grade heat into electricity. The addition of FS induces a unique Li+ solvation with the aggregated double anions through a crowded electrolyte environment, resulting in an enhanced mobility kinetics of Li+ as well as boosted thermoelectrochemical performances. By coupling optimized electrolyte with graphite electrode, a high thermopower of 13.8 mV K-1 and a normalized output power density of 3.99 mW m-2 K-2 as well as an outstanding output energy density of 607.96 J m-2 can be obtained. These results demonstrate that the optimization of electrolyte by regulating solvation structure will inject new vitality into the construction of thermoelectrochemical devices with attractive properties.