Harness High-Temperature Thermal Energy via Elastic Thermoelectric Aerogels

Despite notable progress in thermoelectric(TE)materials and devices,developing TE aerogels with high-temperature resistance,superior TE performance and excellent elasticity to enable self-powered high-temperature monitoring/warning in industrial and wearable applications remains a great challenge.Herein,a highly elastic,flame-retardant and high-temperature-resistant TE aerogel,made of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)/single-walled carbon nanotube(PEDOT:PSS/SWCNT)composites,has been fabricated,displaying attractive compression-induced power factor enhancement.The as-fabricated sensors with the aerogel can achieve accurately pressure stimuli detection and wide temperature range monitoring.Subsequently,a flexible TE generator is assembled,consisting of 25 aerogels connected in series,capable of delivering a maximum output power of 400μW when subjected to a temperature difference of 300 K.This demonstrates its outstanding high-temperature heat harvesting capability and promising application prospects for real-time temperature monitoring on industrial high-temperature pipelines.Moreover,the designed self-powered wearable sensing glove can realize precise wide-range temperature detection,high-temperature warning and accurate recognition of human hand gestures.The aerogel-based intelligent wearable sensing system developed for firefighters demonstrates the desired self-powered and highly sensitive high-temperature fire warning capability.Benefitting from these desirable properties,the elastic and high-temperature-resistant aerogels present various promising applications including self-powered high-temperature monitoring,industrial overheat warning,waste heat energy recycling and even wearable healthcare.

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

The evolution of wearable technology has prompted the need for adaptive,self-healable,and energy-autonomous energy devices.This study innovatively addresses this challenge by introducing an MXene-boosted hydrogel electrolyte,which expedites the assembly process of flexible thermocell(TEC)arrays and thus circumvents the complicated fabrication of typical wearable electronics.Our findings underscore the hydrogel electrolyte’s superior thermoelectrochemical performance under substantial deformations and repeated self-healing cycles.The resulting hydrogel-based TEC yields a maximum power output of 1032.1 nW under theΔT of 20 K when being stretched to 500%for 1000 cycles,corresponding to 80%of its initial state;meanwhile,it sustains 1179.1 nW under theΔT of 20 K even after 60 cuthealing cycles,approximately 92%of its initial state.The as-assembled TEC array exhibits device-level self-healing capability and high adaptability to human body.It is readily applied for touch-based encrypted communication where distinct voltage signals can be converted into alphabet letters;it is also employed as a self-powered sensor to in-situ monitor a variety of body motions for complex human actions.The swift assembly approach,combined with the versatile functionality of the TEC device,paves the way for future advancements in wearable electronics targeting at fitness monitoring and human–machine interfaces.

Characteristics of a Type of NTC Thermistors for Cryogenic Applications

A new type of miniature negative temperature coefficient (NTC) thermistors has been developed and manufactured with Mn-Ni-Cu-Fe oxides. The prepared NTC thermistors were calibrated in the temperature range from 77 K to 300 K with 1 μA exciting currents. The automatic calibration apparatus as well as thermometric characteristics, stability, calibration equations and interchangeability of the manufactured thermistors were investigated. A mean fit equation was obtained: 1/T = 8.60 × 10−4 + 6.54 × 10−4 ln(R/Rref) + 2.46 × 10−5 ln(R/Rref)2 + 9.48 × 10−7 ln(R/Rref)3 − 2.16 × 10−8 ln(R/Rref)4. All the prepared NTC thermistors agreed with this fit with an error of 1.5 K. If the greater accuracy is required, a calibration is necessary, and the calibration accuracy is estimated to be ±10 mK.

Regulating Thermogalvanic Effect and Mechanical Robustness via Redox Ions for Flexible Quasi‑Solid‑State Thermocells

The design of power supply systems for wearable applications requires both flexibility and durability.Thermoelectrochemical cells(TECs)with large Seebeck coefficient can efficiently convert lowgrade heat into electricity,thus having attracted considerable attention in recent years.Utilizing hydrogel electrolyte essentially addresses the electrolyte leakage and complicated packaging issues existing in conventional liquid-based TECs,which well satisfies the need for flexibility.Whereas,the concern of mechanical robustness to ensure stable energy output remains yet to be addressed.Herein,a flexible quasisolid-state TEC is proposed based on the rational design of a hydrogel electrolyte,of which the thermogalvanic effect and mechanical robustness are simultaneously regulated via the multivalent ions of a redox couple.The introduced redox ions not only endow the hydrogel with excellent heat-to-electricity conversion capability,but also act as ionic crosslinks to afford a dual-crosslinked structure,resulting in reversible bonds for effective energy dissipation.The optimized TEC exhibits a high Seebeck coefficient of 1.43 mV K−1 and a significantly improved fracture toughness of 3555 J m^(−2),thereby can maintain a stable thermoelectrochemical performance against various harsh mechanical stimuli.This study reveals the high potential of the quasi-solid-state TEC as a flexible and durable energy supply system for wearable applications.

Carbon and carbon composites for thermoelectric applications

The urgent need for consistent,reliable,ecofriendly,and stable power sources drives the development of new green energy materials.Thermoelectric(TE)materials receive increasing attention due to their unique capability of realizing the direct energy conversion between heat and electricity,showing diverse applications in harvesting waste heat and low-grade heat.Carbon materials such as carbon nanotubes(CNTs)and graphene have experienced a rapid development as TE materials because of their intrinsic ultrahigh electrical conductivity and light weight.Besides,polymer-based carbon composites are particularly fascinating as the combination of the merits of polymers and filler materials leads to high TE performance and superior flexibility.Herein,the recent TE advances are systematically summarized in the studied popularity of carbon materials(ie,CNTs and graphene)and the category of polymers.The conducting polymer-based carbon materials are particularly highlighted.Finally,the remaining challenges and some tentative suggestions possibly guiding future developments are proposed,which may pave a way for a bright future of carbon and carbon composites in the energy market.

Construction of a cement-rebar nanoarchitecture for a solution-processed and flexible film of a Bi_(2)Te_(3)/CNT hybrid toward low thermal conductivity and high thermoelectric performance

Solution processability and flexibility still remain major challenges for many thermoelectric(TE)materials,including bismuth telluride(Bi_(2)Te_(3)),a typical and commercially available TE material.Here,we report a new solutionprocessed method to prepare a flexible film of a Bi_(2)Te_(3)/single-walled carbon nanotube(SWCNT)hybrid,where the dissolved Bi_(2)Te_(3) ion precursors are mixed with dispersed SWCNTs in solution and recrystallized on the SWCNT surfaces to form a“cement-rebar”-like architecture.The hybrid film shows an n-type characteristic,with a stable Seebeck coefficient of^(−1)00.00±1.69μVK^(−1) in air.Furthermore,an extremely low in-plane thermal conductivity of∼0.33Wm^(−1) K^(−1) is achieved at 300 K,and the figure of merit(ZT)reaches 0.47±0.02.In addition,the TE performance is independent of mechanical bending.The unique“cement-rebar”-like architecture is believed to be responsible for the excellent TE performances and the high flexibility.The results provide a new avenue for the fabrication of solution-processable and flexible TE hybrid films and will speed up the applications of flexible electronics and energy conversion.

Numerical Evaluation of Residual Water Content after Freezing during the Lyophilization of Platelets

Pre-freezing is an important stage in freeze-drying processes.For the lyophilization of a cell,freezing not only plays a role for primary dehydration,but it also determines the amount of residual(intracellular or extracellular)water,which in turn can influence the solution properties and the choice of operation parameters.The freezing of human platelets in lyoprotectant solution is theoretically investigated here.A two-parameter model and an Arrhenius expression are used to describe cell membrane permeability and its temperature dependency.It is assumed that the intracellular solution is composed of four components:sodium chloride,trehalose,serum protein and water,while the extracellular solution consists of three components.Non-ideal solution behaviors are predicted using measured data.The concentration of maximally freeze-concentrated solution is estimated on the basis of an assumption of solute hydration.The impacts of lyoprotectant composition and extracellular sub-cooling on intracellular supercooling and residual water content in the cell are analyzed.The values of activation energy of hydraulic permeability at low temperatures are tested to study their impact on the critical cooling rate.As the mass fraction extracellular lyoprotectant(trehalose+bovineserum albumin)increases from 5 wt%to 20 wt%,the intracellular water content at the end of freezing does not change,but the intracellular solution undergoes much higher super-cooling degree.Increasing the mass ratio of trehalose to bovine serum albumin does not change the intracellular water content,but can mitigate intracellular super-cooling.While 0.05 mol/kg trehalose is loaded into platelet,the total quantity of residual water at the end of freezing may raise by 4.93%.The inclusion of dimethyl sulfoxide(Me2SO)in protectant may bring negative impacts to the drying stage by increasing the residual water content and lowering the drying temperature.

Self-assembled aerogel sheet electrodes of thermocells for low-grade heat harvest

Efficiently harvesting low-grade heat is crucial for sustainable energy management. Thermocells(TECs), inducing heat-toelectricity conversion via the thermogalvanic effect, have thus drawn tremendous attention in recent years. This study introduces a self-assembly approach for fabricating aerogel sheet electrodes(ASEs) tailored for TECs. The crafted ASEs retain a remarkable porous architecture with approximately 95% porosity, even with their slimmed-down thickness. Results reveal that the electrode composition has minimal influence on the thermopower of TECs. Notably, the porous ASE with tunned composition demonstrates an optimal effective surface area for the thermogalvanic effect, resulting in enhanced output current density. This balances the desirable traits of electrode compactness with abundant redox active sites, positioning it favorably against conventional bulky electrode designs. The TECs utilizing the optimized ASE achieve a peak output power of 22.10 μW cm^(-2)under a temperature difference of 30 K. Furthermore, a tubular TEC device is readily assembled and specially designed for harvesting heat energy from hot fluids. These findings underscore the potential of composite electrodes in the realm of low-grade heat harvest, paving the way for broader applications in sustainable energy solutions.

Development of Wheel-Legged Biped Robots:A Review

The wheel-legged biped robot is a typical ground-based mobile robot that can combine the high velocity and high efficiency pertaining to wheeled motion and the strong,obstacle-crossing performance associated with legged motion.These robots have gradually exhibited satisfactory application potential in various harsh scenarios such as rubble rescue,military operations,and wilderness exploration.Wheel-legged biped robots are divided into four categories according to the open–close chain structure forms and operation task modes,and the latest technology research status is summarized in this paper.The hardware control system,control method,and application are analyzed,and the dynamic balance control for the two-wheel,biomimetic jumping control for the legs and whole-body control for integrating the wheels and legs are analyzed.In summary,it is observed that the current research exhibits problems,such as the insufficient application of novel materials and a rigid–flexible coupling design;the limited application of the advanced,intelligent control methods;the inadequate understanding of the bionic jumping mechanisms in robot legs;and the insufficient coordination ability of the multi-modal motion,which do not exhibit practical application for the wheel-legged biped robots.Finally,this study discusses the key research directions and development trends for the wheel-legged biped robots.

Wheel-legged In-pipe Robot with a Bioinspired Hook and Dry Adhesive Attachment Device

In-pipe robots have been widely used in pipes-with smooth inner walls.However,current in-pipe robots face challenges in terms of moving past obstacles and climbing in marine-vessel pipeline systems,which are affected by marine biofouling and electrochemical corrosion.This paper takes inspiration from the dual-hook structure of Trypoxylus dichotomus’s feet and gecko‑like dry adhesives,proposing an in-pipe robot that is capable of climbing on rough and smooth pipe inwalls.The combination of the bioinspired hook and dry adhesives allows the robot to stably attach to rough or smooth pipe inwalls,while the wheel-leg hybrid mechanism provides better conditions for obstacle traversal.The paper explores the attachment and obstacle-surmounting mechanisms of the robot.Moreover,motion strategies for the robot are devised based on different pipe structural features.The experiments showed that this robot can adapt to both smooth and rough pipe environments simultaneously,and its motion performance is superior to conventional driving mechanisms.The robot’s active turning actuators also enable it to navigate through horizontally or vertically oriented 90°bends.

An Aerial–Wall Robotic Insect That Can Land, Climb, and Take Off from Vertical Surfaces

Insects that can perform flapping-wing flight,climb on a wall,and switch smoothly between the 2 locomotion regimes provide us with excellent biomimetic models.However,very few biomimetic robots can perform complex locomotion tasks that combine the 2 abilities of climbing and flying.Here,we describe an aerial–wall amphibious robot that is self-contained for flying and climbing,and that can seamlessly move between the air and wall.It adopts a flapping/rotor hybrid power layout,which realizes not only efficient and controllable flight in the air but also attachment to,and climbing on,the vertical wall through a synergistic combination of the aerodynamic negative pressure adsorption of the rotor power and a climbing mechanism with bionic adhesion performance.On the basis of the attachment mechanism of insect foot pads,the prepared biomimetic adhesive materials of the robot can be applied to various types of wall surfaces to achieve stable climbing.The longitudinal axis layout design of the rotor dynamics and control strategy realize a unique cross-domain movement during the flying–climbing transition,which has important implications in understanding the takeoff and landing of insects.Moreover,it enables the robot to cross the air–wall boundary in 0.4 s(landing),and cross the wall–air boundary in 0.7 s(taking off).The aerial–wall amphibious robot expands the working space of traditional flying and climbing robots,which can pave the way for future robots that can perform autonomous visual monitoring,human search and rescue,and tracking tasks in complex air–wall environments.

Design of an Active Flexible Spine for Wall Climbing Robot Using Pneumatic Soft Actuators

Wall climbing robots can be used to undertake missions in many unstructured environments.However,current wall climbing robots have mobility difficulties such as in the turning or accelarating.One of the main reasons for the limitations is the poor flexibility of the spines.Soft robotic technology can actively enable structure deformation and stiffness varations,which provides a solution for the design of active flexible spines.This research utilizes pneumatic soft actuators to design a flexible spine with the abilities of actively bending and twisting by each joint.Using bending and torsion moment equilibriums,respectively,from air pressure to material deformations,the bending and twisting models for a single actuator with respect to different pressure are obtained.The theoretical models are verified by finite-element method simulations and experimental tests.In addition,the bending and twisiting motions of single joint and whole spine are analytically modeled.The results show that the bionic spine can perform desired deformations in accordance with the applied pressure on specified chambers.The variations of the stiffness are also numerically assessed.Finally,the effectiveness of the bionic flexible spine for actively producing sequenced motions as biological spine is experimentally validated.This work demonstrated that the peneumatic spine is potential to improve the spine flexibility of wall climbing robot.

Flexible nanocomposite electrodes with optimized hybrid structure for improved low-grade heat harvest via thermocells

Thermal energy is ubiquitous and constantly generated in nature and society.Thermocells(TECs)represent a promising energyconversion technology that can directly translate thermal energy into electricity with a large thermopower,thus having attracted considerable attention in recent years.Nevertheless,the use of noble platinum electrodes in TECs has substantially limited their widespread applications,as the scarcity of platinum element increases the cost of materials,and its intrinsic rigidity is not conducive to flexible and wearable applications under heat sources with complex surface geometry.Herein,we propose a facile hybridizing route to constructing flexible electrodes with optimized nanostructures.The flexible composite electrode is fabricated by decorating a single-walled carbon nanotube network with conducting polypyrrole nanospheres through controlled electrochemical deposition.With refined interfacial nanostructures,the resultant composite film can facilitate carrier transport/transfer at the electrolyte-electrode interface,and thereby shows superior overall thermoelectrochemical performance to noble platinum electrode.The TEC employing the flexible composite electrodes yields a maximum output power of 2.555μW under the temperature difference of 30 K,and a device comprising 6 TEC units is assembled to efficiently utilize waste heat and human body heat,revealing the high potential of low-grade heat harvesting.

Design and Theoretical Research on Aerial-Aquatic Vehicles:A Review

With the rapid development of unmanned aerial and underwater vehicles,various tasks,such as biodiversity monitoring,surveying,and mapping,as well as,search and rescue can now be completed in a single medium,either underwater or in the air.By systematically examining the water–air cross-medium locomotion of organisms,there has been growing interest in the development of aerial-aquatic vehicles.The goal of this review is to provide a detailed outline of the design and cross-medium theoretical research of the existing aerial-aquatic vehicles based on the research on the organisms capable of transiting between water and air.Although these designs and theoretical frameworks have been validated in many aerial-aquatic vehicles,there are still many problems that need to be addressed,such as inflexible underwater motion and unstable medium conversion.As a result,supplementation of the existing cross-medium biomimetic research,vehicle design,power selection,and cross-medium theory is urgently required to optimize the key technologies in detail.Therefore,by summarizing the existing designs and theoretical approaches on aerial-aquatic vehicles,including biomimetic research on water–air cross-medium locomotion in nature,different power selections,and cross-medium theoretical research,the relative problems and development trends on aerial-aquatic vehicles were thoroughly explored,providing significant help for the subsequent research process.

A Bio-inspired Climbing Robot with Flexible Pads and Claws

Many animals exhibit strong mechanical interlocking in order to achieve efficient climbing against rough surfaces by using their claws in the pads. To maximally use the mechanical interlocking, an innovative robot which utilizes flexible pad with claws is designed. The mechanism for attachments of the claws against rough surfaces is further revealed according to the theoretical analysis. Moreover, the effects of the key parameters on the performances of the climbing robots are obtained. It indicates that decreasing the size of the tip of the claws while maintaining its stiffness unchanged can effectively improve the attachment ability. Furthermore, the structure of robot body and two foot trajectories are proposed and the new robot is presented. Using experimental tests, it demonstrates that this robot has high stability and adaptability while climbing on vertical rough surfaces up to a speed of 4.6 cm.s^-1.

Annular flexible thermoelectric devices with integrated-module architecture

Organic and composite thermoelectric(TE)materials have witnessed explosive developments in recent years.Design strategy of their flexible devices is vital to achieve high performance and suit various application environments.Here,we propose a design strategy of annular flexible TE devices with integrated-module architecture,where the independent modules made up of alternatively connected p-n couples are connected in series,and then rounded head-to-tail into annular configuration.The achieved devices can not only save plenty of space owing to their highly integrated structure design,but also be directly mounted on cylindrical objects(like pipes)to suit versatile applications.More importantly,the annular TE devices display excellent performances,superior to most previous work and the traditional serial single-layer film structure.For example,the annular device with eight modules consisting of three p-n couples reveals an output power of 12.37μW at a temperature gradient of 18 K,much higher than that of the corresponding single-layer film structure(1.74μW).The integration process is simple and easy to scale up.This architecture design strategy will greatly speed up the TE applications and benefit the research of organic and composite TE materials.

Toward improved trade-off between thermoelectric and mechanical performances in polycarbonate/single-walled carbon nanotube composite films

Polymer thermoelectric(TE)composites have witnessed explosive developments in recent years,arising from their promising prospect for lightweight flexible electronics and capability of harvesting waste-heat.In sharp contrast with intrinsically conducting polymers(CPs),the insulating thermoplastics have seldom been employed as the matrices for flexible TE composites despite their advantages of low costs,controllable melt-flowing behaviors and excellent mechanical properties.Here,we report flexible films of polycarbonate/single-walled carbon nanotube(PC/SWCNT)composites with improved trade-off between TE and mechanical performances.The SWCNTs with 1D nanostructure were dramatically aligned by PC melt-flowing under hot-pressing in the radial direction.The composite maximum power factor reaches 4.8±0.8μW m^(−1) K^(−2) at 10 wt%SWCNTs in the aligned direction,which is higher than most previously reported thermoplastics-based TE composites at the same SWCNT loading and even comparable to some intrinsically CPs and their composites.In addition,these composites display significantly higher tensile modulus and strength than CPs and their composites.This study paves an effective way to fabricate flexible films of polymer composites with simultaneously high TE and mechanical performances via judicious alignment of SWCNTs in thermoplastic polymers.

A Wavy-Structured Highly Stretchable Thermoelectric Generator with Stable Energy Output and Self-Rescuing Capability

Thermoelectric generators(TEGs)demonstrate great potential for flexible and wearable electronics due to the direct electrical energy harvested from waste heat.Good wearability requires high mechanical flexibility and preferable stretchability,while current TEGs are primarily developed with rigid or non-stretchable components,which do not conform well to human skin or accommodate human motions,thus hindering further applications.

Numerical simulation and experimental research on heat transfer and flow resistance characteristics of asymmetric plate heat exchangers

The asymmetric plate heat exchanger(APHE)has the possibility of achieving balanced pressure drops on both hot and cold sides for situations with unbalanced flow,which may in turn enhance the heat transfer.In this paper,the single-phase water flow and heat transfer of an APHE consisted of two types of plates are numerically(400≤Re≤12000)and experimentally(400≤Re≤3400)investigated.The numerical model is verified by the experimental results.Simulations are conducted to study the effects of,an asymmetric index proposed to describe the geometry of APHEs.The correlations of the Nusselt number and friction factor in the APHEs are determined by taking and working fluids into account.It is found that an optimal exists where the pressure drops are balanced and the heat transfer area reaches the minimum.The comparison between heat transfer and flow characteristics of the APHEs and the conventional plate heat exchanger(CPHE)is made under various flow rate ratios of the hot side and the cold side and different allowable pressure drops.The situations under which APHE may perform better are identified based on a comprehensive index.

Effect of Crystalline Microstructure Evolution on Thermoelectric Performance of PEDOT:PSS Films

Although organic polymer thermoelectric(TE)materials have witnessed explosive advances in the recent decade,the molecular mechanism of crystallization engineering of TE performance,even for the most successful polymer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS),is still far from clear.Here,we deepen the understanding of the role of annealing-induced crystalline microstructure evolution on TE performance of the PEDOT:PSS film with thickness of 10μm,which is usually more effective than thin ones in applications.Annealed at optimized temperature of 220°C,the film displays a power factor of 162.5 times of that of the pristine film before annealing.The enhanced TE performance is associated with the changes of crystallographic and morphologic microstructures,including increased crystallinity and crystal grain size,a domain morphology transformation from granular to crystalline nanofibril,and reduced insulating PSS in the skin layer.These variances facilitate the carrier transport by a transition from 3D to 1D hopping,reduce the activation energy,and improve the carrier mobility.The mechanism of crystallization engineering reported here can be conceptually extended to other TE polymers and guides the future rational design of preparation principles for organic and composite TE materials.