Mechanical metamaterials have unprecedented properties that contribute to the development of science and technology. However, once the mechanical metamaterials are fabricated, the single configuration will limit their application, especially in areas requiring rich programmability and efficient shape reconfigurability, etc. To break through this limitation and explore more potential of mechanical metamaterials, this work proposes a novel design strategy for 4D printed metamaterials with programmable stiffness. Deriving from the origami concept, the stiffness of the structure can be adjusted not only by changing the geometric parameters but also by changing the geometric configuration utilizing the shape memory property. Through numerical simulation, theoretical analysis and experimental tests, the design strategy is verified in the 4D printed mechanical metamaterials. With this strategy, the stiffness of the structure can be adjusted, and the mechanical programmability, shape reconfigurability and adaptability can be significantly improved. Utilizing excellent energy absorption performance, we design and fabricate a kind of shoe sole. By integrating the sensor function of the Triboelectric Nanogenerator (TENG) into the sole, gait monitoring is successfully realized. The 4D printed shape memory metamaterials show extraordinary potential in the field of programmable shock absorption and intelligent monitoring.

Accurate and effective observation of ocean waves is critical for many applications including weather forecasting, marine resources development, etc. In marine environments where electrical power supply is limited, the self-powered ocean-wave sensors are highly demanded. Herein, we propose an innovative solution to achieve self-powered ocean-wave sensing using triboelectric nanogenerators (TENGs) embedded with overrunning clutches. The ocean wave spectrum is obtained through the pulsed electrical output of two TENGs converting the up-and-down wave motion into rotary frictions, where the rise and fall of waves is distinguished by the combination of a rectifier bridge and a developed intelligent mechanical structure, one-way overrunning clutch embedded with a brake. The ocean wave observation capability of the developed sensor was demonstrated, where the wave height and period were revealed with the accuracy of 90.20% and 99.16%. The proposed sensor can easily achieve centimeter to meter level monitoring, which is 10 times higher than that of previous work. This significant advantage makes the proposed sensor highly suitable for practical applications in ocean wave height observations, where the wave height is usually larger than 100 cm. This work paves a new way to solve the energy-harvesting and information sensing issues for the ocean observation system in the meantime.

This report provides a proof of concept for the realization of an organic pyroelectric nanogenerator which encompasses the fabrication and study of charge driven π-conjugated hetero-system by pyrophototronic effect. A rectifying junction is created with polycrystalline graphene-based material, and crystalline polyaniline-rubrene thin-film which belongs to the aromatic class of organic materials where light-induced change in surface layer polarization helps the device to achieve pyroelectric behavior. The fabricated device is self-sustainable and can generate current as well as voltage in self-powered mode. Overall, this work reveals the viable alternatives and new perspectives for harnessing power from organic materials to realize an organic pyroelectric nanogenerator.

As a kind of micro-nano energy collection device, triboelectric nanogenerator (TENG) converts low-frequency mechanical energy into electrical energy, paving the way to micro-nano power sources, self-powered sensors and blue energy. The mechanism of TENG has been incisive explored through vast investigations to enhance their power density and decrease impedance. The external output voltage/current of the TENG results from the opposite charge generated by its electrode layer induced dielectric layer. The addition of doped materials with high dielectric constant enhances the capacitance of the dielectric layer, resulting in an increase in the amount of opposite charge induced by the electrode layer. Consequently, as a method with simple process and high cost-performance, dielectric layer doping technology makes it possible to improve the performance and large-scale application of TENG. This review provides a detailed analysis of the impact mechanism of various doped materials (metal, inorganic non-metal, organic polymer and two-dimensional materials) embedded in dielectric layers on TENG output performance, based on TENG and dielectric layer doping theory. Moreover, the extension of dielectric layer doping methods to TENG functionalization or application is also discussed, and the existing and potential dielectric layer doping methods are summarized. Finally, we analyze the emerging challenges and opportunities in dielectric layer doping from multiple perspectives.

Triboelectricity and mechanoluminescence (ML) arise from the same physical processes of charge separation and recombination within the material. By measuring both phenomena simultaneously, researchers can gain insights into the nature and extent of charge separation and recombination, as well as the correlation between mechanical stress and light emission. This work shows that a composite based on polydimethylsiloxane (PDMS)/ ZnS:Cu particles possess the ideal ML and can also generate electric output by contact electrification. Using mechanoluminescent materials in wearable devices offers a non-invasive and reliable way to measure mechanical deformation and stress, generating crucial data for a wide range of applications. The single-electrode mode-based triboelectric nanogenerator (TENG) was developed to realize the simultaneous ML and TENG output. During pressing motion, the PDMS/ ZnS: Cu-based TENG device delivered an electrical output of 210 V and 800 nA. Furthermore, the bending motion was then utilized to demonstrate the simultaneous ML and TENG output during various self-powered applications, such as the monitoring of bent body parts, finger joints, and harnessing wind flow.

Triboelectric nanogenerator (TENG), a device that can convert mechanical energy into electricity based on the principle of triboelectrification, has gained tremendous attention since its first discovery in 2012. Although TENG has versatile applications in energy harvesting and self-powered sensing, its commercialization is still limited by the low power output. Recently, metal-organic frameworks (MOFs), with their large surface area and excellent tunability, have been explored to enhance the electrical performance of TENG. Herein, we synthesized nanoparticles of hydrophobic zeolitic imidazolate framework ZIF-71 (RHO topology) and its non-porous counterpart ZIF-72 (LCS topology), which were subsequently incorporated in a polydimethylsiloxane (PDMS) matrix as filler materials. By modifying the topology of ZIF nanofillers, we found the dielectric constant and surface adhesion of composites are both enhanced, thereby generating significantly higher triboelectric output. Moreover, we show the resultant ZIF/PDMS nanocomposite films exhibit enhanced triboelectric properties and long-term stability under cyclic mechanical loading. After integrating the prepared nanocomposite films into TENG devices, we accomplished the peak output voltage and current of 578 V and 19 μA for thin films (3 ×3 cm2, thickness ∼0.33 mm), respectively, by embedding 1 wt % of ZIF-72 nanoparticles into PDMS matrix, with an instantaneous maximum power density of ∼5 W m−2. In this study, the mechanism of improved TENG performance by incorporating MOF nanoparticles has, for the first time, been revealed through nanoscale-resolved mechanical and chemical studies. Furthermore, the practicality of MOF-based TENG was demonstrated by harvesting energy from oscillatory motions, for powering up commercial microelectronics, transmitting electrical signals remotely, and functioning as a self-powered Morse code generator.

There are numerous magnetic field sensors available, but no simple, robust, sensitive sensor for biomedical applications that does not require cryogenic cooling or shielding has yet been developed. In this contribution, a new approach for building a magnetoelectric field sensor is presented, which has the potential to fill this gap. The sensor is based on a resonant cantilever with a piezoelectric readout layer and a pair of opposing permanent magnets. One is attached to the cantilever, and the other one is fixed to a sample holder below. This new concept can be deduced from the most basic composite-based sensor [1], where the magnets interact analog to two particles in a polymer matrix. The bias-free, empirical measurements show a limit-of-detection of 46 pT/√Hz with a sensitivity of 2170 V/T using the sensor’s resonance frequency of 223.5 Hz under ambient conditions. The sensor fabrication is based on low resolution silicon technology, which promises high compatibility and the possibility to be integrated into MEMS devices. The design of this new sensor can be easily altered and adjusted according to the requirements of the specific sensor application. For example, tuning of the operating resonance frequency cannot solely be modified in the production of the cantilever but also by the arrangement of the permanent magnets. In addition, the concept can also be applied to energy harvesters. Beside possible mechanical excitation, the presence of a magnetic stray field alone allows the sensor to convert 20 µT into a power of 1.31 µW/cm³∙Oe². The fact that the device does not require any DC bias field makes it very attractive for energy harvesting applications since this allows a purely passive operation. In this manuscript, the sensor assembly, measurements of directional sensitivity, noise level, limit-of-detection, evaluation for energy harvesting applications from magnetic fields and a quantitative sensor model are presented.

Piezo-electrocatalytic CO2 reduction reaction (PECRR) technique has been verified as an effective CO2-to-fuel conversion strategy by exploiting and utilizing the widely distributed mechanical energy in nature, e.g., blue energy. The facile large-scale preparation of high-performance and low-cost piezo-electrocatalysts is therefore highly desired but challenging. Herein, a method of physical mixing of piezo-electrocatalysts and earth-abundant carbon-based materials is proposed to address the above issue, and we verified this method with typical piezoelectric BaTiO3 and graphene oxide (GO) as a demonstration. With an optimized GO concentration, the BaTiO3 shows a CO yield of 134.4 μmol·g-1·h-1 which is about 45.3% higher than that of pristine BaTiO3. The mechanisms for the enhancement are revealed via boosted piezo-carrier dynamics and charge transfer from BaTiO3 to GO as well as enhanced intrinsic activity. Furthermore, physical mixing of GO is extended to other piezo-electrocatalysts (MoS2, ZnO, ZnS, CdS, Bi2WO6), from which it is found that their performance is improved compared to the counterpart of those without GO. This work suggests that the physical mixing GO is a universal method to improve PECRR performance and may be a decent candidate approach for large-scale preparation of high-performance and low-cost piezo-electrocatalysts in future.

Near-infrared (NIR) organic photodetectors (OPDs) play significant roles in night vision, optical communication and bio-imaging for low cost, easy fabrication and flexibility. However, their development is facing a serious challenge that efforts on suppressing typically high dark current density (JD) generally encounter photoresponse loss because of accompanying with less exciton generation or poorer carrier extraction. Here, novel structure and mechanism are pioneered to overcome that challenge: forming a reverse-distribution phase featured gradient heterojunction (RP-GHJ) to build an effective charge transport channel. In such structure, increased barriers are established to prevent unfavorable charge injection for suppressing JD. Additionally, photogenerated carriers are wrapped by anti-recombination region in reverse phase for efficient charge extraction. Therefore, RP-GHJ suppresses JD of NIR-OPDs to 8.48 × 10−9 A cm−2 which is far superior to 1.81 × 10−6 A cm−2 of traditional BHJ one (bias of −1 V) and simultaneously keeps high photoresponse. Consequently, RP-GHJ makes NIR-OPD realize stable-high detectivity over 1013 Jones at bias region from 0 to − 0.5 V and when the bias increases from − 0.5 to − 1 V, decrease of specific detectivity is slight (under 830 nm). And more importantly, a very large linear dynamic range of nearly 160 dB is obtained under 0 V bias. The structure is proven to be universally effective in NIR-OPDs and a highly sensitive arterial pulse monitoring is developed. The novel structure and mechanism provide a universal strategy for realizing high-performance NIR-OPDs and their real applications.

Data-driven technologies, like Internet-of-Everything, which enables intelligence, rely on photoelectric elements, electronics, and communications. The conventional framework possesses optics, signal-processing, power supplies, and redundancies, which are riddles in its utilization. Optical wireless communication (OWC) can liberate such constraints, empowering widespread deployment to assemble information from surrounding objects and their energy efficiency. This study proposes a transparent photovoltaic (TPV) window that generates onsite-power and is suitable for indoor illumination for machine-learning. A TPV framework exhibited bifacial performance, including fast photoresponse and spectral responsivity, suitable for indoor illumination. For OWC, the spike-induced photoresponse is examined for pyroelectric ZnO and silver nanowire-embedded TPV devices, resulting in a notable binarization scheme and superior reliability of the optical signal. Owing to an ultrafast spike in the current, which flips from negative to positive current values and vice-versa upon optical signaling, preprocessing-free decoding of Morse-code is enabled to ensure the data-reliability of the optical signal of the 420 nm wavelength. In contrast to the Si device, the TPV device decodes a fast Morse-code carrying an optical signal >10,000 Hz with greater reliability. The results obtained for the TPV device with machine learning features provide a guiding significance for the development of high-performance, and reliable informatics.

Food safety is of constant major concern worldwide. Each year, hundreds of millions of people fall ill due to consuming contaminated food, and the resulting economic loss runs into hundreds of billions of dollars. To mitigate these issues, we developed Tribo-sanitizer, which utilizes a freestanding rotational triboelectric nanogenerator (FSR-TENG) to convert mechanical energy into sustainable, low-cost or free electricity that powers an ultraviolet-C (UVC) lamp for food-safety applications. Thanks to the air gap in its circuit – a design inspired by a natural phenomenon, lightning, which can lead to electrical breakdown of air – the optimal FSR-TENG can generate a high voltage output of 4 kV. This high electrical output, in turn, enables brighter illumination of the UVC lamp. Tribo-sanitizer’s decontamination efficacy was evaluated against a gram-positive bacterial strain (Listeria monocytogenes) and a gram-negative one (Escherichia coli O157:H7) inoculated in a liquid buffer, a polymer widely used in the food-packaging industry, and two types of fresh produce. Tribo-sanitizer achieved a 5.03-log reduction and a 5.95-log reduction for E. coli O157:H7 in buffer solution and on polyethylene terephthalate (PET), respectively, in line with the 5-log reduction recommended in government guidelines for microbial control. The log reductions for L. monocytogenes in buffer solution and on PET were 4.36 and 3.81, respectively. Lesser effectiveness was observed with the apples and romaine lettuce, likely due to these fresh produce samples’ greater surface roughness as compared to PET, one of the most widely used polymers for the construction of food packaging and drinks bottles. Our results also demonstrate that biomechanical motions can provide Tribo-sanitizer with sufficient power to achieve bacterial inactivation, demonstrating its excellent potential for use in low-resource settings. With further improvements, it could help mitigate severe food-safety problems around the world, leading to a more secure and sustainable food system.

To harvest low-grade heat energy from human body, flexible thermoelectric generators (TEGs) are highly necessitated and have attracted significant interests. However, developing novel thermoelectric materials with high stretchability and Seebeck coefficient is still challenging. Here we report a tellurium-nanowire-doped (Te-NW-doped) PEDOT:PSS/polyvinyl alcohol (TPP) hydrogel with excellent mechanical and thermoelectric characteristics. The effect of Te-NWs doping on the thermoelectric characteristics has been systematically investigated and the optimized TPP hydrogel exhibits a high Seebeck coefficient value of 787 μV K−1, a low thermal conductivity of 0.468 W m−1 K−1, and a high tensile strain value of ⁓ 400%. Furthermore, a wearable thermoelectric module with a staggered Z-shaped structure is developed to achieve a voltage output of 138 mV when it is applied on the human arm. After being integrated with a power management unit, the TPP TEG module enables the operation of electronic devices like a commercial calculator and a white LED, which exhibits great potential for applications in human heat energy harvesting and wearable electronics.

Ru-based materials have regarded as ideal alternatives to Pt-based catalysts for hydrogen evolution reaction (HER), however, strong adsorption of H intermediate for Ru-based catalysts results in an unsatisfactory HER activity. Herein, we perform a high-throughput computational screening of different Ru clusters that supported on a carbon substrate embedded with various non-precious metals by comparing their structure stability and adsorption energy of H intermediate. Guided by the computational predictions, a unique 3D catalyst of Ru cluster with a size of < 2 nm anchored on spherical carbon shell confining Ni particles (Ru/Ni@C) is developed. Owing to the strong metal-substrate interaction and optimized electronic structure, Ru/Ni@C exhibits an outstanding HER performance with an ultra-low overpotential of 309 mV at 1.0 A cm−2, outperformed commercial Pt/C and Ru/C catalysts. Experimental observations and theoretical calculations demonstrate the efficient electron transfer from anchored Ru cluster to core Ni particles via carbon layer, which leads to the formation of electron-deficient Ru site, beneficial to adjust the ability of H adsorption and eventually promotes the whole HER process.

The stretchable conductive materials with adjustable electromagnetic interference (EMI) shielding performance and other multifunctional integrated applications are remarkably desirable and challenging in flexible electronics. However, the existing stretchable materials often suffer from the decay of EMI shielding performance during the stretching process, which limits their practical applications. Meanwhile, it remains a great challenge to construct materials with ordered porous frameworks as integrated shielding devices. Incorporating porous structure will generate abundant interior surfaces/interfaces, facilitating multiple reflections of incident electromagnetic waves (EMWs). Herein, we employ ultrasound method to modify liquid metal (LM) with carbon nanotubes (CNTs), and further utilize an UV in-situ polymerization method to fabricate CNT@LM/polyacrylamide/gelatin (LMCPG) dual network hydrogel elastomer. The LMCPG hydrogel elastomer possesses high strength and durability, and its tensile strength reaches 117 kPa at 1033% strain owing to the high strength of the rigid network and the beneficial deformation ability of the flexible network. Deformable CNT@LM droplets elongate randomly during stretching process, which facilitates establishing more conductive paths. The EMI shielding capacity of the stretched elastomer can be controlled, achieving an intelligent on-off behavior, which exhibits a 211% increase at 200% strain in EMI shielding effectiveness (SE) compared with the undeformed state. Moreover, the LMCPG elastomer shows a significant triboelectric performance, which can provide power supply for flexible electronic devices, achieving an uninterrupted monitoring of the human body motion by devices. Therefore, as a flexible electronic material, it can offer a facile solution to achieve intelligent multifunctional integrated EMI shielding materials.

Built-in electric field (BIEF) has recently emerged as a promising strategy for promoting charge transfer by supplying additional coulomb forces. However, the challenge lies in the intelligent control over the thickness and intensity of BIEF to augment these Coulomb forces, thereby enhancing charge transfer in bulk electrodes. Here we deliberately engineer a graded MnO@Mn3O4 junction characterized by a spatially intensified BIEF to accelerate charge transfer over an extended atom layer thickness. This graded MnO@Mn3O4 junction exhibits a phase transition gradient, characterized by a steady decline in Mn valence and work function from shell to core, giving rise to an intense BIEF across the junction. The enhanced BIEF should be ascribed to the spatially accumulated polarization, resulting in an increase in electron delocalization and a decrease in the energy barrier for ion transfer. As a result, the MnO@Mn3O4 manifests improved capacity and rate performance. This work highlights the significance of modulating the BIEF’s thickness and intensity to facilitate charge transfer, thereby pushing the boundaries of electrochemical energy storage.

Triboelectric nanogenerators (TENGs), offering self-powered actuation, grasping, and sensing capabilities without the need for an external power source, have the potential to revolutionize the field of self-powered robotic systems. TENGs can directly convert mechanical energy into electrical energy that can be used to power small electronics. This review explores the huge potential of TENGs' mechanisms and modes for various robotics actuation and sensing applications. Firstly, the improvements in efficiency and reliability of TENG-based actuation systems by self-powered actuation systems are discussed. Following that, TENG-based grippers having controlled gripping power and a distinctive ability to self-calibrate for precise and sharp object handling are enlightened. Additionally, the design and development of TENG-based pressure sensors incorporated into robotic grippers are further discussed. Self-powered multimode-sensing robotic devices, which can sense many stimuli such as temperature, applied force and its direction, and humidity, are briefly discussed. Integrating self-powered robotic systems with human-machine-interaction (HMI) technologies enables more sophisticated and intelligent robotic contact with its external environment, is also highlighted. Finally, we addressed the challenges and future improvements in this emerging field. In conclusion, TENGs can open up a wide range of opportunities for self-powered actuation, gripping, and sensing with exceptional efficiency and precision while being compatible with both soft and rigid robotic systems.

Abstract not available

Touch panels utilizing surface-capacitive mechanism are ubiquitous in our daily life. However, the need for an additional probe signal generator and receiver module to detect the resistance distribution and variation caused by finger touching adds complexity and energy consumption to the system. Herein, we propose a self-powered and high-precision tribo-touch-position sensor (TPS) that can operate without an external probe signal generator and receiver module. By detecting the contact electrification signal and extracting the signal ratio between the edges of a uniform resistance film, TPS exhibits precise touch position detection with minimal channels. The mechanism and feasibility of this sensor is systematically analyzed from theory and experiment. Moreover, the resistance range and parameters that affect the sensing performance are discussed in depth. Compared to traditional capacitive touch panels, TPS can function in high moisture conditions and is not limited to grounded objects. Finally, the designed TPS achieves spatial resolutions of 0.001 and 1 mm in touching space and size, and a prototype 2D touch panel is fabricated experimentally. The signals ratio of 2D touch panel changes more obviously in the middle than on the sides while the fingers touch various positions. This work provides an alternative platform for simple and diverse contact localization using triboelectric effect.

With the current intricate application environment, extended versatility is critical to the future development of phase change materials (PCMs). Herein, we prepared a series of phase change composites (PCCs) with excellent electromagnetic interference shielding effectiveness (EMI SE) and versatile thermal management. Specifically, the hybridized multi-stage porous biological carbon base with magnetic and electrical conductivity was prepared as the substrate material for encapsulating paraffin wax (PW) by carbonizing in situ growth ZIF-67 on waste agricultural. The synergy between the functions of the porous biological carbon and PW makes the PCCs have high-performance EMI SE (44.81 dB) and high enthalpy value (175.88–229.52 J/g) at the identical time. In which CC-ZIF-3 @PW has outstanding effect in storing and releasing thermal energy for photo-thermal, magnetic-thermal and electric-thermal conversion. Unsurprisingly, the PCCs breaks innovative ground for energy storage and conversion materials with potential value in various fields such as electronic protection, deicing and thermal energy utilization.

As the demand for environmental purification and energy harvesting continues to grow, research on maximizing the efficiency of catalysts is attracting great attention. The piezo-phototronic effect has emerged as an effective strategy to enhance the photocatalytic activity of semiconductors. While p-type semiconductors exhibit high photoresponsivity across a wide spectral range, their potential as piezo-photocatalysts has been limited due to their low carrier concentration and inferior carrier migration behavior. Therefore, it is hypothesized that overcoming these limitations would allow p-type semiconductors to achieve catalytic performance comparable to, or even surpassing, that of n-type systems. Here, we introduce two effective strategies into p-type trigonal selenium nanowires (Se NWs): electron-proton co-doping and localized surface plasmon resonance effect. These approaches improve the light absorption capacity, charge transport ability, and piezoelectricity, thereby significantly enhancing the piezo-photocatalytic performance. Under the influence of the piezo-phototronic effect, the post-treated Se NWs exhibit markedly enhanced evolution rates of reactive oxygen species compared to pure Se NWs. Consequently, the degradation efficiency of organic contaminants is increased up to 4-fold. This breakthrough opens up a new pathway for the development of p-type piezoelectric materials, which can potentially replace their n-type counterparts in catalytic applications.