Multiple physical crosslinked highly adhesive and conductive hydrogels for human motion and electrophysiological signal monitoring.

Hydrogel-based flexible electronic devices serve as a next-generation bridge for human-machine interaction and find extensive applications in clinical therapy, military equipment, and wearable devices. However, the mechanical mismatch between hydrogels and human tissues, coupled with the failure of conformal interfaces, hinders the transmission of information between living organisms and flexible devices, which resulted in the instability and low fidelity of signals, especially in the acquisition of electromyographic (EMG) and electrocardiographic (ECG) signals. In this study, we designed an ion-conductive hydrogel (ICHgel) utilizing multiple physical interactions, successfully applied for human motion monitoring and the collection of epidermal physiological signals. By incorporating fumed silica (F-SiO2) nanoparticles and calcium chloride into an interpenetrating network (IPN) composed of polyvinyl alcohol (PVA) and polyacrylamide (AAm)/acrylic acid (AA) chains, the ICHgel exhibited exceptional tunable stretchability (>1450% strain) and conductivity (10.58 ± 0.85 S m-1). Additionally, the outstanding adhesion of the ICHgel proved to be a critical factor for effective communication between epidermal tissues and flexible devices. Demonstrating its capability to acquire stable electromechanical signals, the ICHgel was attached to different parts of the human body. More importantly, as a flexible electrode, the ICHgel outperformed commercial Ag/AgCl electrodes in the collection of ECG and EMG signals. In summary, the synthesized ICHgel with its outstanding conformal interface capabilities and mechanical adaptability paves the way for enhanced human-machine interaction, fostering the development of flexible electronic devices.

Highly coordinative molecular cobalt-phthalocyanine electrocatalyst on an oxidized single-walled carbon nanotube for efficient hydrogen peroxide production.

H2O2 production via the two-electron oxygen reduction reaction (2e- ORR) offers a potential alternative to the current anthraquinone method owing to its efficiency and environmental friendliness. However, it is necessary to determine the structures of electrocatalysts with cost-effectiveness and high efficiency for future industrialization demand. Herein, a supramolecular catalyst composed of cobalt-phthalocyanine on a near-monodispersed and oxidized single-walled carbon nanotube (CoPc/o-SWCNT) was synthesized via a solution self-assembly method for catalyzing the 2e- ORR for H2O2 electrosynthesis. Benefiting from the enhanced intermolecular interaction by introducing oxygen functional groups on o-SWCNTs, the oxidation states of single-atom Co sites were tuned via the formation of two extra Co-O bonds. Coupled with structural characterizations, density-functional theory (DFT) calculations reveal that the depressed d-band center of the Co site regulated by two axially-bridged O atoms gives rise to a suitable binding strength of oxygen intermediates (*OOH) to favor the 2e- ORR. Thus, the CoPc-6wt%/o-SWCNT-2 catalyst with optimized synthetic parameters delivers competitive 2e- ORR performance for H2O2 electrosynthesis in a neutral electrolyte (pH = 7), including enhanced H2O2 generation, satisfactory molar selectivity of ∼83-95% and long-period stability (75 h) in H-cell measurement. Moreover, it could also be boosted to show a high current of 45 mA cm-2, recorded turnover frequency of 25.3 ± 0.5 s-1 and maximum H2O2 production rate of 5.85 mol g-1 h-1 with a continuous H2O2 accumulation of 1.2 wt% in a flow-cell device, which outperformed most of the reported neutral-selective nonprecious metal single-atom catalysts.

Bimodal Intelligent Electronic Skin Based on Proximity and Tactile Interaction for Pressure and Configuration Perception.

The flexible bimodal e-skin exhibits significant promise for integration into the next iteration of human-computer interactions, owing to the integration of tactile and proximity perception. However, those challenges, such as low tactile sensitivity, complex fabrication processes, and incompatibility with bimodal interactions, have restricted the widespread adoption of bimodal e-skin. Herein, a bimodal capacitive e-skin capable of simultaneous tactile and proximity sensing has been developed. The entire process eliminates intricate fabrication techniques, employing DLP-3D printing for the electrode layers and sacrificial templating for the dielectric layers, conferring high tactile sensitivity (1.672 kPa-1) and rapid response capability (∼30 ms) to the bimodal e-skin. Moreover, exploiting the "fringing electric field" effect inherent in parallel-plate capacitors has facilitated touchless sensing, thereby enabling static distance recognition and dynamic gesture recognition of varying materials. Interestingly, an e-skin sensing array was created to identify the positions and pressure levels of various objects of different masses. Furthermore, with the aid of machine learning techniques, an artificial neural network has been established to possess intelligent object recognition capabilities, facilitating the identification, classification, and training of various object configurations. The advantages of the bimodal e-skin render it highly promising for extensive applications in the field of next-generation human-machine interaction.

Dimension Evolution of Self-Assembled Organic Microcrystal for Laser and Polarization-Rotation Function.

Multidimensional integrated micro/nanostructures are vitally important for the implementation of versatile photonic functionalities, whereas current material structures still suffer undesired surface defects and contaminations in either multistep micro/nanofabrications or extreme synthetic conditions. Herein, the dimension evolution of organic self-assembled structures 2D microrings and 3D microhelixes for multidimensional photonic devices is realized via a protic/aprotic solvent-directed molecular assembly method based on a multiaxial confined-assisted growth mechanism. The 2D microrings with consummate circle boundaries and molecular-smooth surfaces function as high-quality whispering-gallery-mode microcavities for dual-wavelength energy-influence-dependent switchable lasing. Moreover, the 3D microhelixes with smooth surfaces and natural twistable characteristics act as active photon-transport materials and polarization rotators. These results will broaden the horizon of constructing multidimensional microstructures for integrated photonic circuits.

Physiological sensing system integrated with vibration sensor and frequency gel dampers inspired by spider.

Recent advances in bioelectronics in mechanical and electrophysiological signal detection are remarkable, but there are still limitations because they are inevitably affected by environmental noise and motion artifacts. Thus, we develop a gel damper-integrated crack sensor inspired by the vibration response of the viscoelastic cuticular pad and slit organs in a spider. Benefitting from the specific crack structure design, the sensor possesses excellent sensing behaviors, including a low detection limit (0.05% strain), ultrafast response ability (3.4 ms) and superior durability (>300 000 cycles). Such typical low-amplitude fast response properties allow the ability to accurately perceive vibration frequency and waveform. In addition, the gel damper exhibits frequency-dependent dynamic mechanical behavior that results in improved stability and reliability of signal acquisition by providing shock resistance and isolating external factors. They effectively attenuate external motion artifacts and low-frequency mechanical noise, resulting in cleaner and more reliable signal acquisition. When the gel damper is combined with the crack-based vibration sensor, the integrated sensor exhibits superior anti-interference capability and frequency selectivity, demonstrating its effectiveness in extracting genuine vocal vibration signals from raw voice recordings. The integration of damping materials with sensors offers an efficient approach to improving signal acquisition and signal quality in various applications.

Universal and Energy-Efficient Approach to Synthesize Pt-Rare Earth Metal Alloys for Proton Exchange Membrane Fuel Cell.

Traditional synthesis methods of platinum-rare earth metal (Pt-RE) alloys usually involve harsh conditions and high energy consumption because of the low standard reduction potentials and high oxophilicity of RE metals. In this work, a one-step strategy is developed by rapid Joule thermal-shock (RJTS) to synthesize Pt-RE alloys within tens of seconds. The method can not only realize the regulation of alloy size, but also a universal method for the preparation of a family of Pt-RE alloys (RE = Ce, La, Gd, Sm, Tb, Y). In addition, the energy consumption of the Pt-RE alloy preparation is only 0.052 kW h, which is 2-3 orders of magnitude lower than other reported methods. This method allows individual Pt-RE alloy to be embedded in the carbon substrate, endowing the alloy catalyst excellent durability for oxygen reduction reaction (ORR). The performance of alloy catalyst shows negligible decay after 20k accelerated durability testing (ADT) cycles. This strategy offers a new route to synthesize noble/non-noble metal alloys with diversified applications besides ORR.

Surface oxidation of commercial activated carbon with enriching carboxyl groups for high-yield electrocatalytic H2O2production.

Two-electron oxygen reduction reaction (2e-ORR) for H2O2production is regarded as a more ecologically friendly substitute to the anthraquinone method. However, the search of selective and cheap catalysts is still challenging. Herein, we developed a neutral-selective and efficient nonprecious electrocatalyst that was prepared from a commercial activated carbon (AC) by simply microwave-assisted ash impurity elimination and hydrogen peroxide oxidation for surface functional sites optimization. The oxygen configuration can be tuned with enriching carboxyl group up to 6.65 at.% by the dosage of hydrogen peroxide (mass ratio of H2O2/C = ∼0-8.3). Chemical titration experiments identified the carbonyl groups as the most potential active sites, with selectivity boosted by the additional carboxyl groups. The microwave-assisted moderate-oxidized activated carbon (MW-AC5.0) demonstrated optimal 2e-ORR activity and selectivity in neutral electrolyte (0.1 M K2SO4), with H2O2selectivity reaching ∼75%-97%, a maximum H2O2production rate (1.90 mol·gcatal-1·h-1@0.1 V) and satisfying faradaic efficiency (∼85%) in gas-diffusion-electrode. When coupled with Fenton reaction, it can degrade a model organic pollutant (methylene blue [MB], 50 ppm) to colorless in a short time of 20 min, indicating the potential applications in the environmental remediation.

Self-Powered Integrated System with a Flexible Strain Sensor and a Zinc-Air Battery.

At present, self-powered, lightweight, and flexible sensors are widely applied, especially in the fields of wearable devices and human health monitoring. Nevertheless, conventional self-powered flexible sensor systems rely on power supply components such as supercapacitors, nanofriction generators, and solar cells, which present certain limitations, such as high dependence on external environmental factors and the inability to provide long-term stable energy supply. Thus, a paramount exigency emerges for the development of wearable sensors endowed with enduring battery life to enable continuous monitoring of human motion for extended periods. In our academic study, we present an innovative self-powered sensing system that seamlessly combines a pliable zinc-air battery with a strain sensor. This approach offers a stable output signal over extended periods without an external energy device, which is crucial for long-term, continuous human motion monitoring. Through the incorporation of various carbon materials, we realized the multifunction of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) dual network hydrogels and prepared zinc-air battery electrolytes and strain sensors. Notably, the batteries exhibit impressive power density (82.5 mW cm-2), high open-circuit voltage (1.42 V), and remarkable environmental stability. Even when subjected to puncture and breakage, the batteries remain operational without suffering from electrolyte leakage. Similarly, our strain sensor boasts a broad working range spanning from 0 to 1400%, coupled with a remarkable sensitivity (GF = 2.99) and exceptional capacity to accurately detect various mechanical deformations. When integrated into a single system, the integrated system can monitor human movement for up to 10 h, which has broad prospects in wearable sensor applications.

Nitrogen-doped hollow mesoporous carbon spheres for efficient oxygen reduction.

Extensive investigations have been devoted to nitrogen-doped carbon materials as catalysts for the oxygen reduction reaction (ORR) in various conversion technologies. In this study, we introduce nitrogen-doped carbon materials with hollow spherical structures. These materials demonstrate significant potential in ORR activity within alkaline media, showing a half-wave potential of 0.87 V versus the reversible hydrogen electrode (RHE). Nitrogen-doped hollow carbon spheres (N-CHS) exhibit unique characteristics such as a thin carbon shell layer, hollow structure, large surface area, and distinct pore features. These features collectively create an optimal environment for facilitating the diffusion of reactants, thereby enhancing the exposure of active sites and improving catalytic performance. Building upon the promising qualities of N-CHS as a catalyst support, we employ heme chloride (1 wt%) as the source of iron for Fe doping. Through the carbonization process, Fe-N active sites are effectively formed, displaying a half-wave potential of 0.9 V versus RHE. Notably, when implemented as a cathode catalyst in zinc-air batteries, this catalyst exhibits an impressive power density of 162.6 mW cm-2.

A liquid-free conducting ionoelastomer for 3D printable multifunctional self-healing electronic skin with tactile sensing capabilities.

Conductive elastomers with both softness and conductivity are widely used in the field of flexible electronics. Nonetheless, conductive elastomers typically exhibit prominent problems such as solvent volatilization and leakage, and poor mechanical and conductive properties, which limit their applications in electronic skin (e-skin). In this work, a liquid-free conductive ionogel (LFCIg) with excellent performance was fabricated by utilizing the innovative double network design approach based on a deep eutectic solvent (DES). The double-network LFCIg is cross-linked by dynamic non-covalent bonds, which exhibit excellent mechanical properties (2100% strain while sustaining a fracture strength of 1.23 MPa) and >90% self-healing efficiency, and a superb electrical conductivity of 23.3 mS m-1 and 3D printability. Moreover, the conductive elastomer based on LFCIg has been developed into a stretchable strain sensor that achieves accurate response recognition, classification, and identification of different robot gestures. More impressively, an e-skin with tactile sensing functions is produced by in situ 3D printing of sensor arrays on flexible electrodes to detect light weight objects and recognize the resulting spatial pressure variations. Collectively, the results demonstrate that the designed LFCIg has unparalleled advantages and presents wide application potential in flexible robotics, e-skin and physiological signal monitoring.

Tough and Robust Mechanically Interlocked Gel-Elastomer Hybrid Electrode for Soft Strain Gauge.

Soft strain gauges provide a flexible and versatile alternative to traditional rigid and inextensible gauges, overcoming issues such as impedance mismatch, the limited sensing range, and fatigue/fracture. Although several materials and structural designs are used to fabricate soft strain gauges, achieving multi-functionality for applications remains a significant challenge. Herein, a mechanically interlocked gel-elastomer hybrid material is exploited for soft strain gauge. Such a material design provides exceptional fracture energy of 59.6 kJ m-2 and a fatigue threshold of 3300 J m-2 , along with impressive strength and stretchability. The hybrid material electrode possesses excellent sensing performances under both static and dynamic loading conditions. It boasts a tiny detection limit of 0.05% strain, ultrafast time resolution of 0.495 ms, and high linearity. This hybrid material electrode can accurately detect full-range human-related frequency vibrations ranging from 0.5 to 1000 Hz, enabling the measurement of physiological parameters. Additionally, the patterned soft strain gauge, created through lithography, demonstrates superior signal-noise rate and electromechanical robustness against deformation. By integrating a multiple-channel device, an intelligent motion detection system is developed, which can classify six typical human body movements with the assistance of machine learning. This innovation is expected to drive advancements in wearable device technology.

Dense-Packed RuO2 Nanorods with In Situ Generated Metal Vacancies Loaded on SnO2 Nanocubes for Proton Exchange Membrane Water Electrolyzer with Ultra-Low Noble Metal Loading.

Proton exchange membrane water electrolyzer (PEMWE) is a green hydrogen production technology that can be coupled with intermittent power sources such as wind and photoelectric power. To achieve cost-effective operations, low noble metal loading on the anode catalyst layer is desired. In this study, a catalyst with RuO2 nanorods coated outside SnO2 nanocubes is designed, which forms continuous networks and provides high conductivity. This allows for the reduction of Ru contents in catalysts. Furthermore, the structure evolutions on the RuO2 surface are carefully investigated. The etched RuO2 surfaces are seen as the consequence of Co leaching, and theoretical calculations demonstrate that it is more effective in driving oxygen evolution. For electrochemical tests, the catalysts with 23 wt% Ru exhibit an overpotential of 178 mV at 10 mA cm-2 , which is much higher than most state-of-art oxygen evolution catalysts. In a practical PEMWE, the noble metal Ru loading on the anode side is only 0.3 mg cm-2 . The cell achieves 1.61 V at 1 A cm-2 and proper stability at 500 mA cm-2 , demonstrating the effectiveness of the designed catalyst.

Tough hydrogel with high water content and ordered fibrous structures as an artificial human ligament.

Natural biological tissues such as ligaments, due to their anisotropic across scale structure, have high water content, while still maintaining high strength and flexibility. Hydrogels are ideal artificial materials like human ligaments. However, conventional gel materials fail to exhibit high strength or fatigue resistance at high water content in human tissues. To address this challenge, we propose a simple integrated strategy to prepare an anisotropic hierarchical hydrogel architecture for artificial ligaments by combining freeze-casting assisted compression annealing and salting-out treatments. The hybrid polyvinyl alcohol hydrogels are of water content up to 79.5 wt%. Enhanced by the added carbon nanotubes, the hydrogels exhibit high strength of 4.5 MPa and a fatigue threshold of 1467 J m-2, as well as excellent stress sensitivity. The outstanding durability of the artificial ligament provides an all-around solution for biomedical applications.

Mn-N-C catalysts derived from metal triazole framework with hierarchical porosity for efficient oxygen reduction.

Manganese and nitrogen co-doped porous carbon (Mn-N-C) are proposed as one of the most up-and-coming non-precious metal electrocatalysts to substitute Pt-based in the oxygen reduction reaction (ORR). Herein, we chose metal triazole frameworks as carbon substrate with hierarchical porosity for trapping and anchoring Mn-containing gaseous species by a mild one-step pyrolysis method. The optimized Mn-N-C electrocatalyst with a large metal content of 1.71 wt% and a volume ratio of 0.86 mesopores pore delivers a superior ORR activity with a half-wave potential (E1/2) of 0.92 V in 0.1 M KOH and 0.78 V in 0.1 M HClO4. Moreover, the modified Mn-N-C catalyst showed superior potential cyclic stability. TheE1/2remained unchanged in 0.1 M KOH and only lost 6 mV in 0.1 M HClO4after 5000 cycles. When applied as the cathode catalyst in Zn-air battery, it exhibited a maximum peak power density of 176 mW cm-2, demonstrating great potential as a usable ORR catalyst in practical devices.

Tensile-Strained RuO2 Loaded on Antimony-Tin Oxide by Fast Quenching for Proton-Exchange Membrane Water Electrolyzer.

Future energy demands for green hydrogen have fueled intensive research on proton-exchange membrane water electrolyzers (PEMWE). However, the sluggish oxygen evolution reaction (OER) and highly corrosive environment on the anode side narrow the catalysts to be expensive Ir-based materials. It is very challenging to develop cheap and effective OER catalysts. Herein, Co-hexamethylenetetramine metal-organic framework (Co-HMT) as the precursor and a fast-quenching method is employed to synthesize RuO2 nanorods loaded on antimony-tin oxide (ATO). Physical characterizations and theoretical calculations indicate that the ATO can increase the electrochemical surface areas of the catalysts, while the tensile strains incorporated by quenching can alter the electronic state of RuO2 . The optimized catalyst exhibits a small overpotential of 198 mV at 10 mA cm-2 for OER, and keeps almost unchanged after 150 h chronopotentiometry. When applied in a real PEMWE assembly, only 1.51 V is needed for the catalyst to reach a current density of 1 A cm-2 .

Optimizing graphene oxide membranes for effective removal of dyes by modulating the reduction degree and doped nitrogen.

The excellent mechanical and chemical characteristics of graphene oxide (GO) enable their potential application in the realm of membrane separation. However, the expansion and instability of GO nanosheets in water limit its application. In this work, nitrogen-doped GO (NGO) was obtained by a harmless hydrothermal reduction method. The obtained NGO films were attached to a polyvinylidene fluoride support membrane by vacuum filtration. By changing the hydrothermal reaction temperature, the reduction degree of GO and doping amount of nitrogen was adjusted to control the inter-layer structure and permeability of NGO. The defect of NGO nanosheets and the reduction of oxygen-containing functional groups could accelerate the transportation of water molecules through the inter-layer space of the hydrophobic graphene sheets. Significantly, the polarization and high adsorption energy of pyridine-N serve as a supplement to the exclusion mechanism of the inter-layer spacing. NGO membranes have better permeability than the initial GO membranes without sacrificing the rejection rate. The optimized NGO film has a significant rejection rate of above 99% for various dyes, such as methylene blue, Congo red and methyl blue.

High-performance manganese and nitrogen codoped carbon (Mn-N-C) oxygen reduction electrocatalyst from Mn2+coordinated sodium alginate.

The research on low-cost, high-performance non platinum group metal (PGM) oxygen reduction reaction (ORR) catalysts is of great significance for the rapid promotion of fuel cells' practical applications. In this work, Mn-N-C catalyst with outstanding activity was prepared through using hydrogel formed by coordination of sodium alginate (SA) and Mn2+as the precursor. During the preparation process, g-C3N4was added to improve the surface area enrich the pore structure of catalysts, as well as to function as the nitrogen source. Compare with commercial Pt/C catalyst, the optimum Mn-N-C catalyst possesses extraordinary ORR activity in alkaline electrolytes, with a half-wave potential (E1/2) of 0.90 V. In addition, the Mn-N-C catalyst also displays exceptional stability in alkaline and acidic electrolytes, much superior to Pt/C catalyst.

Bead-like carbon fibers consisting of abundantly exposed active sites for the oxygen reduction reaction.

Rational design is essential in the synthesis of electrocatalysts for the oxygen reduction reaction (ORR). Herein, we introduced zeolitic imidazolate framework-8 (ZIF-8) and polyvinyl pyrrolidone (PVP) into the electrospinning process of the polyacrylonitrile (PAN) and hemin to increase the active site loading and exposed active area of the final product with empty bead-like structures. In this method, ZIF-8 acts as a carbon skeleton to provide a rich microporous structure that can support active sites, and as a nitrogen dopant to improve nitrogen contents. PVP changes the properties of the spinning solution, adjusts the fiber morphology, and to increase the exposed area of active sites as a pore former. The obtained Fe-N-C ORR catalyst delivered a half-wave potential (E1/2) of 0.924 V in a 0.1 M KOH solution and 0.77 V in a 0.1 M HClO4solution. A homemade zinc air battery with power density of 236 mW cm-2demonstrated the excellent performance of the catalyst under working conditions.

A Partial Sulfuration Strategy Derived Multi-Yolk-Shell Structure for Ultra-Stable K/Na/Li-ion Storage.

Metal sulfides are attractive anodes for alkali metal ion batteries due to the high theoretical capacity, while their practical implementation is hampered by the inherent poor conductivity and vast volume variation during cycles. Approaching rational designed microstructures with good stability and fast charge transfer is of great importance in response to these issues. Herein, a partial sulfuration strategy for the rational construction of multi-yolk-shell (m-Y-S) structures, from which multiple Fe1- x S nanoparticles are confined within hollow carbon nanosheet with tunable interior void space is reported. As anode materials, the m-Y-S Fe1- x S@C composite can display high capacity and excellent rate capability (134, 365, and 447 mA h g-1 for K+ , Na+ , and Li+ storage at 20 A g-1 ). Remarkably, it exhibits ultra-stable potassium storage up to 1200, 6000, and 20 000 cycles under current densities of 0.1, 0.5, and 1 A g-1 , which is much superior to previous yolk-shell structures and metal-sulfide anodes. Based on comprehensive experimental analysis and theoretical calculations, the exceptional performance of m-Y-S structure can be ascribed to the optimized interior void space for good structure stability, as well as the multiple connection points and conductive carbon layer for superior electron/ion transportation.

Transforming C60 Molecules into Polyhedral Carbon Micro-Nano Shells for Electrochemically Producing H2O2 in Neutral Electrolytes.

The electrochemical production of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (ORR) can realize the customer-oriented onsite synthesis of H2O2 in a green and sustainable method. The ongoing challenge that needs to be solved is the fabrication of robust electrocatalysts of excellent performance. In this work, C60 was selected as a precursor due to its uniform structure and abundant pentagon rings. Thanks to the strong interaction between C60 and thiophene, after heteromolecule assembly in the liquid reaction and subsequent reconstruction of the carbon topological structure in solid calcination, C60 was successfully transformed into polyhedral carbon micro-nano shells (PCMNS) with an effective pore structure for the first time, which exhibited excellent capacity for production of H2O2 via two-electron ORR, especially in neutral media. In addition to the high onset potential (0.49 V vs reversible hydrogen electrode (RHE)) and low Tafel slope (72 mV dec-1), its selectivity reached >90% within the potential range of 0.30-0.45 V and maintained >80% after constant potential electrolysis for 10 h. The yield rate of H2O2 was 1102.5 mmol gcat-1 h-1, determined by an H-type electrolytic cell, which was one of the highest values of metal-free carbon-based ORR electrocatalysts ever reported. Such excellent two-electron ORR performance of PCMNS was attributed to its abundant accessible active sites and hierarchical pore structures.