Biometric-Tuned E-Skin Sensor with Real Fingerprints Provides Insights on Tactile Perception: Rosa Parks Had Better Surface Vibrational Sensation than Richard Nixon.

The dense mechanoreceptors in human fingertips enable texture discrimination. Recent advances in flexible electronics have created tactile sensors that effectively replicate slowly adapting (SA) and rapidly adapting (RA) mechanoreceptors. However, the influence of dermatoglyphic structures on tactile signal transmission, such as the effect of fingerprint ridge filtering on friction-induced vibration frequencies, remains unexplored. A novel multi-layer flexible sensor with an artificially synthesized skin surface capable of replicating arbitrary fingerprints is developed. This sensor simultaneously detects pressure (SA response) and vibration (RA response), enabling texture recognition. Fingerprint ridge patterns from notable historical figures - Rosa Parks, Richard Nixon, Martin Luther King Jr., and Ronald Reagan - are fabricated on the sensor surface. Vibration frequency responses to assorted fabric textures are measured and compared between fingerprint replicas. Results demonstrate that fingerprint topography substantially impacts skin-surface vibrational transmission. Specifically, Parks' fingerprint structure conveyed higher frequencies more clearly than those of Nixon, King, or Reagan. This work suggests individual fingerprint ridge morphological variation influences tactile perception and can confer adaptive advantages for fine texture discrimination. The flexible bioinspired sensor provides new insights into human vibrotactile processing by modeling fingerprint-filtered mechanical signals at the finger-object interface.

Natural Antioxidant Vitamin C Improves Photovoltaic Performance of Tin-Lead Mixed Perovskite Solar Cells.

The oxidation of Sn2+ can occur even after the completion of the perovskite crystallization in a low oxygen environment. Concerning this, the natural antioxidant vitamin C (VC) is introduced to the surface of Sn-Pb mixed perovskite using a postprocessing method to achieve the purpose of inhibiting Sn2+ oxidation and enhancing perovskite solar cells performance. The results indicate that the VC could effectively inhibit Sn2+ oxidation and heal the vacancy defects of the annealed perovskite film. Meanwhile, the introduction of VC significantly improves the morphology and crystalline quality of the perovskite films. After optimization, the highest power conversion efficiency of the VC-treated Sn-Pb mixed device increased to 20.44%. Moreover, the VC-treated unencapsulated device shows excellent long-term stability, retaining 75.3% of its initial efficiency after 800 h of aging in a N2 atmosphere, which is much higher than the 20.1% of the control device.

N-P covalent bond regulation of mesoporous carbon-based catalyst for lowered oxygen reduction overpotential and enhanced zinc-air battery performance.

Developing sustainable metal-free carbon-based electrocatalysts is essential for the deployment of metal-air batteries such as zinc-air batteries (ZABs), among which doping of heteroatoms has attracted tremendous interest over the past decade. However, the effect of the heteroatom covalent bonds in carbon matrix on catalysis was neglected in most studies. Here, an efficient metal-free oxygen reduction reaction (ORR) catalyst is demonstrated by the N-P bonds anchored carbon (termed N,P-C-1000). The N,P-C-1000 catalyst exhibits superior specific surface area of 1362 m2 g-1 and ORR activity with a half-wave potential of 0.83 V, close to that of 20 wt% Pt/C. Theoretical computations reveal that the p-band center for C-2p orbit in N,P-C-1000 has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. The N,P-C-1000 assembled primary ZAB can attain a large peak power density of 121.9 mW cm-2 and a steady discharge platform of ∼1.20 V throughout 120 h. Besides, when served as the cathodic catalyst in a solid-state ZAB, the battery shows flexibility, conspicuous open circuit potential (1.423 V), and high peak power density (85.8 mW cm-2). Our findings offer a strategy to tune the intrinsic structure of carbon-based catalysts for improved electrocatalytic performance and shed light on future catalysts design for energy storage technologies beyond batteries.

Surfactant Self-Assembly Enhances Tribopositivity of Stretchable Ionic Conductors for Wearable Energy Harvesting and Motion Sensing.

Boosting stretchability and electric output is critical for high-performance wearable triboelectric nanogenerators (TENG). Herein, for the first time, a new approach for tuning the composition of surface functional groups through surfactant self-assembly to improve the tribopositivity, where the assembly increases the transferred charge density and the relative permittivity of water polyurethane (WPU). Incorporating bis(trifluoromethanesulfonyl)imide (TFSI-) and alkali metal ions into a mixture of WPU and the surfactant forms a stretchable film that simultaneously functions as positive tribolayer and electrode, preventing the conventional detachment of tribolayer and electrode in long term usage. Further, the conductivity of the crosslinked film reaches 3.3 × 10-3 mS cm-1 while the elongation at break reaches 362%. Moreover, the surfactant self-assembly impedes the adverse impact of the fluorine-containing groups on tribopositivity. Consequently, the charge density reaches 155 µC m-2, being the highest recorded for WPU and stretchable ionic conductor based TENG. This work introduces a novel approach for boosting the output charge density while avoiding the adverse effect of ionic salts in solid conductors through a universal surfactant self-assembly strategy, which can be extended to other materials. Further, the device is used to monitor and harvest the kinetic energy of human body motion.

Effect of the Photoreduction Process on the Self-Cleaning and Antibacterial Activity of Au-Doped TiO2 Colloids on Cotton Fabric.

This study aims at understanding the effect of the photoreduction process during the synthesis of gold (Au)-doped TiO2 colloids on the conferred functionalities on cotton fabrics. TiO2/Au and TiO2/Au/SiO2 colloids were synthesized through the sol-gel method with and without undergoing the photoreduction step based on different molar ratios of Au:Ti (0.001 and 0.01) and TiO2/SiO2 (1:1 and 1:2.3). The colloids were applied to cotton fabrics, and the obtained photocatalytic self-cleaning, wet photocatalytic activity, UV protection, and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were investigated. The obtained results demonstrated that the photoreduction of Au weakened the self-cleaning effect and reduced the photocatalytic activity of coated fabrics. Also, an excess amount of Au deteriorated the photocatalytic activity under both UV and visible light. The most efficient self-cleaning effect was obtained on fabrics coated with a ternary TiO2/Au/SiO2 colloid containing ionic Au, where it decomposed coffee and red-wine stains after 3 h of illumination. Adding silica (SiO2) made the fabrics superhydrophilic and led to greater methylene blue (MB) dye adsorption, a faster dye degradation pace, and more efficient stain removal. Moreover, the photoreduction process affected the size of Au nanoparticles (NPs), weakened the antibacterial activity of fabrics against both types of tested bacteria, and modestly increased the UV protection. In general, the photoactivity of Au-doped colloids was influenced by the synthesis method, the ionic and metallic states of the Au dopant, the concentration of the Au dopant, and the presence and concentration of silica.

AI-Enabled Soft Sensing Array for Simultaneous Detection of Muscle Deformation and Mechanomyography for Metaverse Somatosensory Interaction.

Motion recognition (MR)-based somatosensory interaction technology, which interprets user movements as input instructions, presents a natural approach for promoting human-computer interaction, a critical element for advancing metaverse applications. Herein, this work introduces a non-intrusive muscle-sensing wearable device, that in conjunction with machine learning, enables motion-control-based somatosensory interaction with metaverse avatars. To facilitate MR, the proposed device simultaneously detects muscle mechanical activities, including dynamic muscle shape changes and vibrational mechanomyogram signals, utilizing a flexible 16-channel pressure sensor array (weighing ≈0.38 g). Leveraging the rich information from multiple channels, a recognition accuracy of ≈96.06% is achieved by classifying ten lower-limb motions executed by ten human subjects. In addition, this work demonstrates the practical application of muscle-sensing-based somatosensory interaction, using the proposed wearable device, for enabling the real-time control of avatars in a virtual space. This study provides an alternative approach to traditional rigid inertial measurement units and electromyography-based methods for achieving accurate human motion capture, which can further broaden the applications of motion-interactive wearable devices for the coming metaverse age.

Decoupling Activation and Transport by Electron-Regulated Atomic-Bi Harnessed Surface-to-Pore Interface for Vanadium Redox Flow Battery.

Vanadium redox flow battery (VRFB) promises a route to low-cost and grid-scale electricity storage using renewable energy resources. However, the interplay of mass transport and activation processes of high-loading catalysts makes it challenging to drive high-performance density VRFB. Herein, a surface-to-pore interface design that unlocks the potential of atomic-Bi-exposed catalytic surface via decoupling activation and transport is reported. The functional interface accommodates electron-regulated atomic-Bi catalyst in an asymmetric Bi─O─Mn structure that expedites the V3+ /V2+ conversion, and a mesoporous Mn3 O4 sub-scaffold for rapid shuttling of redox-active species, whereby the site accessibility is maximized, contrary to conventional transport-limited catalysts. By in situ grafting this interface onto micron-porous carbon felt (Bi1 -sMn3 O4 -CF), a high-performance flow battery is achieved, yielding a record high energy efficiency of 76.72% even at a high current density of 400 mA cm-2 and a peak power density of 1.503 W cm-2 , outdoing the battery with sMn3 O4 -CF (62.60%, 0.978 W cm-2 ) without Bi catalyst. Moreover, this battery renders extraordinary durability of over 1500 cycles, bespeaking a crucial breakthrough toward sustainable redox flow batteries (RFBs).

Asymmetric Chemical Potential Activated Nanointerfacial Electric Field for Efficient Vanadium Redox Flow Batteries.

Constructing active sites with enhanced intrinsic activity and accessibility in a confined microenvironment is critical for simultaneously upgrading the round-trip efficiency and lifespan of all-vanadium redox flow battery (VRFB) yet remains under-explored. Here, we present nanointerfacial electric fields (E-fields) featuring outstanding intrinsic activity embodied by binary Mo2C-Mo2N sublattice. The asymmetric chemical potential on both sides of the reconstructed heterogeneous interface imposes the charge movement and accumulation near the atomic-scale N-Mo-C binding region, eliciting the configuration of an accelerator-like E-field from Mo2N to Mo2C sublattice. Supported with theoretical calculations and intrinsic activity tests, the improved vanadium ion adsorption behavior and charge-transfer process at the nanointerfacial sites were further substantiated, hence expediting the electrochemical kinetics. Accordingly, the pronounced promotion is achieved in the resultant flow battery, yielding an energy efficiency of 77.7% and an extended lifespan of 1000 cycles at 300 mA cm-2, outperforming flow cells with conventional single catalysts in most previous reports.

A Stretchable Solid Ionic Electrode-Based Triboelectric Nanogenerator for Biomechanical Energy Harvesting and Self-Powered Sensors.

Stretchable power devices and self-powered sensors have become increasingly desired for wearable electronics and artificial intelligence. In this study, an all-solid-state triboelectric nanogenerator (TENG) is reported, whose one solid-state structure prevents delamination during stretch and release cycles and increasing the patch adhesive force (3.5 N) and strain (586% elongation at break). Through the synergetic virtues of stretchability, ionic conductivity, and excellent adhesion to the tribo-layer, reproducible open-circuit voltage (VOC ) of 84 V, charge (QSC ) of 27.5 nC, and short-circuit current (ISC ) of 3.1 µA after drying at 60°C or 20,000 contact-separation cycles are obtained. Apart from contact-separation, this device shows unprecedented electricity generation through stretch-release of solid materials leading to a linear relationship between VOC and strain. For the first time, this work provides a clear explanation of the working mechanism of contact-free stretching-releasing and investigates the relationships of exerted force, strain, thickness of the device, and electric output. Benefitting from the one solid-state structure, this contact-free device remains stable even after repeated stretch-release cycling, maintaining 100% of its VOC after 2500 stretch-release cycles. These findings provide a strategy toward highly conductive and stretchable electrodes for harvesting mechanical energy and health monitoring.

Nano-sphere RuO2 embedded in MOF-derived carbon arrays as a dual-matrix anode for cost-effective electrochemical wastewater treatment.

The electrodes' activity, surface area and cost hinder the deployment of electrochemical wastewater treatment. Using an economical microfiber-based carbon felt (CF) substrate, we design RuO2 nanospheres confined by CoxO cooperated carbon nanoarrays (RuO2-CoxO@TCF) to augment noble metal utilization and thus reduce the catalyst cost. RuO2-CoxO@TCF anode with vertical diffusion channels exhibits rapid generation ability of oxidizing species particularity in the presence of Cl- ions, which play a crucial role in azo bond cleavage and benzene ring chlorination of methyl orange. As a result, the catalyst shows 99.5 % color removal and ∼ 70 % mineralization efficiency at a concentration of 60 ppm. In synthetic dyeing wastewater, RuO2-CoxO@TCF delivers a stable total organic carbon (TOC) removal throughout ten cycling tests. Moreover, the electricity consumption of RuO2-CoxO@TCF is far below the reference anode, showing great promise for dye degradation and remediation of industrial wastewater.

Wide-Bandwidth Nanocomposite-Sensor Integrated Smart Mask for Tracking Multiphase Respiratory Activities.

Wearing masks has been a recommended protective measure due to the risks of coronavirus disease 2019 (COVID-19) even in its coming endemic phase. Therefore, deploying a "smart mask" to monitor human physiological signals is highly beneficial for personal and public health. This work presents a smart mask integrating an ultrathin nanocomposite sponge structure-based soundwave sensor (≈400 µm), which allows the high sensitivity in a wide-bandwidth dynamic pressure range, i.e., capable of detecting various respiratory sounds of breathing, speaking, and coughing. Thirty-one subjects test the smart mask in recording their respiratory activities. Machine/deep learning methods, i.e., support vector machine and convolutional neural networks, are used to recognize these activities, which show average macro-recalls of ≈95% in both individual and generalized models. With rich high-frequency (≈4000 Hz) information recorded, the two-/tri-phase coughs can be mapped while speaking words can be identified, demonstrating that the smart mask can be applicable as a daily wearable Internet of Things (IoT) device for respiratory disease identification, voice interaction tool, etc. in the future. This work bridges the technological gap between ultra-lightweight but high-frequency response sensor material fabrication, signal transduction and processing, and machining/deep learning to demonstrate a wearable device for potential applications in continual health monitoring in daily life.

Biotechnology of Plastic Waste Degradation, Recycling, and Valorization: Current Advances and Future Perspectives.

Invited for this month's cover is the collaborative group of Dr. Carol Sze Ki Lin and Dr. Xiang Wang. The image illustrates the biodegradation of plastics and the potential for plastic waste recycling and valorization to address the plastic waste dilemma. The Minireview itself is available at 10.1002/cssc.202100752.

Biotechnology of Plastic Waste Degradation, Recycling, and Valorization: Current Advances and Future Perspectives.

Although fossil-based plastic products have many attractive characteristics, their production has led to severe environmental burdens that require immediate solutions. Despite these plastics being non-natural chemical compounds, they can be degraded and metabolized by some microorganisms, which suggests the potential application of biotechnologies based on the mechanism of plastic biodegradation. In this context, microbe-based strategies for the degradation, recycling, and valorization of plastic waste offer a feasible approach for alleviating environmental challenges created by the accumulation of plastic waste. This Minireview highlights recent advances in the biotechnology-based biodegradation of both traditional polymers and bio-based plastics, focusing on the mechanisms of biodegradation. From an application perspective, this Minireview also summarizes recent progress in the recycling and valorization of plastic waste, which are feasible solutions for tackling the plastic waste dilemma.

Carboxymethyl cellulose-chitosan composite hydrogel: Modelling and experimental study of the effect of composition on microstructure and swelling response.

Molecular recognition is essential for the advancement of functional supramolecular natural polymer-based hydrogels. First, a series of carboxymethyl cellulose (CMC)-chitosan (CSN) hydrogels crosslinked with fumaric acid are studied, where the influence of composition on microstructure and swelling is investigated using mathematical modelling and experiment and the hydrolytic properties, microstructure parameters and physicochemical properties are examined. Second, best fit values for the responses are obtained using multiple linear regression and MATLAB R2020a curve fitting and predictive models are generated. Third, the optimum microstructure is loaded with polyethylene glycol (PEG) and bismuth telluride (Bi2Te3) and coated on fabric for imparting thermal sensitivity. The results show that (1) optimum microstructure (25.65 ± 1.86 nm mesh size, 116.25 ± 0.00 µmol/cm3 effective crosslinking-density, 348.03 ± 10.81% swelling, and 62.86 ± 1.11% gel fraction) is found at CMC:CSN = 1:3 for G3; (2) the model shows good agreement with experimental data demonstrating potential for estimating hydrogel swelling and microstructure; and (3) G3/PEG and G3/PEG/Bi2Te3 enhance thermal conductivity of fabric at ambient, body, and elevated temperatures. The study demonstrates the potential of the generated model in predicting CMC-CSN swelling and G3 as an ideal host matrix for wearable textiles/devices.

Tribo-charge enhanced hybrid air filter masks for efficient particulate matter capture with greatly extended service life.

Face masks have been an effective and indispensable personal protective measure against particulate matter pollutants and respiratory diseases, especially the novel Coronavirus disease recently. However, disposable surgical face masks suffer from low filtration efficiency for particles ranging from nano- to micro-size, and the limited service life of ~ 4 h. Here, a nano/micro fibrous hybrid air filter mask composing of electrospun nanofibrous network and poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) coated polypropylene (PP) is proposed. Furthermore, the resultant filter is supplied with tribo-charges by a freestanding sliding triboelectric nanogenerator. Through the enhanced synergistic effect of mechanical interception and electrostatic forces, the hybrid air filter demonstrates high filtration efficiency for particle size of 11.5 nm to 2.5 µm, with a 9.3-34.68% enhancement for particles of 0.3-2.5 µm compared to pristine PP, and 48-h stable filtration efficiency of 94% (0.3-0.4 µm) and 99% (1-2.5 µm) with a low pressure drop of ~110 Pa. In addition, sterilization ability of the tribo-charge enhanced air filter is demonstrated. This work provides a facile and cost-effective approach for state-of-the-art face masks toward high filtration performance of nano- to micro- particles with greatly extended service life.

Nanogap and Environmentally Stable Triboelectric Nanogenerators Based on Surface Self-Modified Sustainable Films.

The advancement of wearable electronics and environmental awareness requires a wearable triboelectric nanogenerator (TENG) to feature the concepts of sustainability and environmental suitability. While most wearable TENGs are developed based on complex surface modification approaches to avoid the necessity of a physical spacer, herein a nanogap TENG is fabricated based on surface self-modified sustainable polymer films. Compared with poly(lactic acid) (PLA)-based and polycaprolactone (PCL)-based TENGs, the polybutylene succinate (PBS)-based TENG shows the highest output performance, representing up to 3.5-fold that of the reported TENGs based on biodegradable materials with a 0-4 mm spacer, due to the higher content of the ester group and surface roughness resulting from the surface self-modification. The nanogap device is demonstrated as a pressure/angle sensor with acceptable sensitivity for use in health monitoring. More importantly, the environmental suitability of the triboelectric films in air, water, and phosphate buffered saline systems indicates their stability in natural water and saline environments. Moreover, the antibacterial property of the triboelectric films indicates future applications in wearable and implantable electronics. This work demonstrates the potential applications of a biocompatible and environmentally stable TENG in wearable electronics and biomedical systems.

Carbon Dot-Based Composite Films for Simultaneously Harvesting Raindrop Energy and Boosting Solar Energy Conversion Efficiency in Hybrid Cells.

Energy harvesting has drawn worldwide attention as a sustainable technology, while combining several approaches in a single device to maximize the overall energy output holds great promise to offer valuable technologies able to alleviate the energy crisis. Here, we present a hybrid cell composed of a silicon solar cell and a water-droplet-harvesting triboelectric nanogenerator (WH-TENG) with the capacity of harvesting both solar and raindrop energies. A transparent and solution processable carbon dot-based composite film is introduced as a dual-functional layer, acting as the transmittance enhancement layer of the solar cell as well as an ionic conductor of the WH-TENG. At an optimal loading of carbon dots in the composite, the significant enhancement of transmittance in visible spectral range increases the short-circuit current density of the solar cell, which results in an increase of its power conversion efficiency from 13.6% to 14.6%. In addition, the transparent WH-TENG consisting of fluorinated ethylene propylene as a triboelectrification layer can generate a maximum power of 13.9 µW by collecting raindrop energy. This study provides a promising strategy to boost the energy conversion through multiple sources with the aid of a dual-functional layer for enhancing solar cell performance as well as harvesting raindrop energy.

MOF-Derived Sulfide-Based Electrocatalyst and Scaffold for Boosted Hydrogen Production.

Metal-organic frameworks (MOFs) can act as precursors or templates to a myriad of nanostructured materials that are difficult to prepare. In this study, Co-MOF nanorods (NRs) were prepared at room temperature followed by a calcination and hydrothermal sulfurization strategy to transform the MOF into CoS NRs on carbon cloth (CoS/CC). Intriguingly, the resultant 3D sulfide NRs can serve as scaffolds to electrodeposit layered double hydroxides (LDHs) on the surfaces. Through combining the advantages of structure and composition, the as-fabricated CoS@CoNi-LDH/CC exhibits remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). An overpotential of 124 mV is needed to reach a current density of 10 mA cm-2 with a Tafel slope of only 89 mV dec-1, which is superior to that of pure CoS/CC (141 mV along with 103 mV dec-1) and other reported cobalt-based catalysts. Notably, after the chronopotentiometry test for 50 h, the overpotential of CoS@CoNi-LDH/CC increased by 17 mV only.

Seed-Assisted Growth for Low-Temperature-Processed All-Inorganic CsPbIBr2 Solar Cells with Efficiency over 10.

All-inorganic CsPbIBr2 perovskite has recently received growing attention due to its balanced band gap and excellent environmental stability. However, the requirement of high-temperature processing limits its application in flexible devices. Herein, a low-temperature seed-assisted growth (SAG) method for high-quality CsPbIBr2 perovskite films through reducing the crystallization temperature by introducing methylammonium halides (MAX, X = I, Br, Cl) is demonstrated. The mechanism is attributed to MA cation based perovskite seeds, which act as nuclei lowering the formation energy of CsPbIBr2 during the annealing treatment. It is found that methylammonium bromide treated perovskite (Pvsk-Br) film fabricated at low temperature (150 °C) shows micrometer-sized grains and superior charge dynamic properties, delivering a device with an efficiency of 10.47%. Furthermore, an efficiency of 11.1% is achieved for a device based on high-temperature (250 °C) processed Pvsk-Br film via the SAG method, which presents the highest reported efficiency for inorganic CsPbIBr2 solar cells thus far.

Mechanism of Water Effect on Enhancing the Photovoltaic Performance of Triple-Cation Hybrid Perovskite Solar Cells.

The water effect on the performance of perovskite solar cells has been intensively studied in recent years. However, the conflicting conclusions derived from different studies make it impossible to fully understand the mechanism involved. Besides, all studies have concentrated on single methylammonium cation perovskites. As a consequence, the effects of water on formamidinium and cesium perovskites are still unclear. Herein, we introduce water during the fabrication of triple-cation hybrid perovskites. By controlling the water content, we demonstrate that an optimal concentration of water contributes to a better crystallized and more uniform hybrid perovskite film without impurities, resulting in significant enhancement in power conversion efficiency and long-term stability. In addition, two forms of water (hydrate water and bulk water) are found in the hybrid perovskite film. Hydrate water induces a recrystallization process, whereas bulk water leads to decomposition of the perovskite. These distinct phases are considered to form the basic mechanism affecting the performance of the cells.