Flexible Electrodes and Electrolytes for Energy Storage

Metal and heteroatoms co-doped fluorescent carbon dots for highly selective and sensitive detection of Mg2+ ions in aqueous media: Applications in test strips, pharmaceutical, real samples and bioimaging

In this study, we successfully synthesized fluorescent carbon dots (CDs) through a one-pot hydrothermal method, utilizing tartaric acid, cysteine, and nickel chloride as precursors. This approach allowed for the incorporation of metal ion (nickel) as well as nitrogen and sulfur heteroatoms into the carbon dot structure, resulting in nickel-doped, nitrogen, and sulfur-co-doped CDs (Ni/NS-CDs). A comprehensive characterization of the Ni/NS-CDs was conducted using FT-IR, XRD, Raman, XPS, and HR-TEM analysis confirmed the successful doping of nickel, nitrogen, and sulfur into the Ni/NS-CDs. HR-TEM analysis showed that the synthesized Ni/NS-CDs were spherical with a well-monodispersed average particle size of 2.1 ± 0.2 nm. The Ni/NS-CDs displayed strong fluorescence with excitation-dependent emission behavior and a high quantum yield of 23.60 %. When excited at 480 nm, the Ni/NS-CDs exhibited bright green emission at 524 nm, showcasing their excellent fluorescent characteristics. Additionally, the Ni/NS-CDs demonstrated remarkable stability across a broad pH range and high salt ionic strengths, further enhancing their practical applicability in diverse environments. The Ni/NS-CDs showed high sensitivity and selectivity towards Mg2+ ions, with an impressively low limit of detection (LOD) of 19.38 nM within a wider range of 0-50 µM. Beyond sensing applications, the bright and stable fluorescence of the Ni/NS-CDs enabled clear cell imaging, making them promising candidates for use in biomedical research and diagnostics. Moreover, the practical utility of the Ni/NS-CDs were successfully applied for detecting Mg2+ ions in environmental samples, illustrating their potential for ecological monitoring and water quality assessment. This broad applicability underscores the multifunctionality of the synthesized Ni/NS-CDs, positioning them as valuable nanomaterials in fields such as pharmaceuticals, bio-imaging, environmental science, and analytical chemistry.

Exploring the Impact of Minor Water Content on Polymer Electrolytes with Molecular Dynamics

Solid-state polymer electrolytes (SPEs) are increasingly favored over liquid electrolytes for emerging energy storage devices due to their safety features, enhanced stability, and multifunctionality. Minor solvents (such as water) are often introduced unintentionally or intentionally into SPEs. Although it can significantly affect SPEs' electrochemical and mechanical properties, the fundamental role of such solvent content has rarely been studied. Here, we investigate the effects of minor water content on two representative SPEs through molecular dynamics simulations. Focusing on SPEs composed of different base polymers, namely, poly(ethylene oxide) (PEO) and poly(lactic acid) (PLA), and the same salt, lithium perchlorate (LiClO4), our simulations reveal that slight hydration facilitates an increase in ionic conductivity while preserving the mechanical integrity of the SPEs. Notably, these water contents appear to affect ionic conductivity more effectively in certain systems than others, which is attributed to the unique interactions among ions, water, and the polymer matrix. Moreover, small amounts of water can maintain the stiffness of SPEs rather than reducing it. Such results suggest a facile approach to developing SPEs with balanced ionic conductivity and mechanical properties, suitable for a range of energy storage applications.

Piezoelectric Behaviour in Biodegradable Carrageenan and Iron (III) Oxide Based Sensor

This paper is dedicated to the research of phenomena noticed during tests of biodegradable carrageenan-based force and pressure sensors. Peculiar voltage characteristics were noticed during the impact tests. Therefore, the sensors' responses to impact were researched more thoroughly, defining time-dependent sensor output signals from calibrated energy impact. The research was performed using experimental methods when a free-falling steel ball impacted the sensor material to create relatively definable impact energy. The sensor's output signal, which is analogue voltage, was registered using an oscilloscope and transmitted to the PC for further analysis. The obtained results showed a very interesting outcome, where the sensor, which was intended to be piezoresistive, demonstrated a combination of behaviour typical for galvanic cells and piezoelectric material. It provides a stable DC output that is sensitive to the applied statical pressure, and in case of a sudden impact, like a hit, it demonstrates piezoelectric behaviour with some particular effects, which are described in the paper as proton transfer in the sensor-sensitive material. Such phenomena and sensor design are a matter of further development and research.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Machine learning guided microwave-assisted quantum dot synthesis and an indication of residual H2O2 in human teeth

The current preparation methods of carbon quantum dots (CDs) involve many reaction parameters, which leads to many possibilities in the synthesis processes and high uncertainty of the resultant production performance. Recently, machine learning (ML) methods have shown great potential in correlating the selected features in many applications, which can help understand the relevant structure-function relationships of CDs and discover better synthesis recipes as well. In this work, we employ the ML approach to guide the blue CD synthesis in microwave systems. After optimizing the synthesis parameters and conditions, the quantum yield (QY) increases to about 200% higher than the average value of the prepared samples without ML guidance. The obtained CDs are applied as fluorescent probes to monitor hydrogen peroxide (H₂O₂) in human teeth. The CD probe exhibits a linear relationship with the concentration of H₂O₂ ranging from 0 to 1.1 M with a lower detection limit of 0.12 M, which can effectively detect the residual H₂O₂ after bleaching teeth. This work shows that the adopted ML methods have considerable advantages in guiding the synthesis of high-quality CDs, which could accelerate the development of other novel functional materials in energy, biomedical, and environmental remediation applications.

A Strategic Review on Carbon Quantum Dots for Cancer-Diagnostics and Treatment

The understanding of the genesis of life-threatening cancer and its invasion calls for urgent development of novel technologies for real-time observations, early diagnosis, and treatment. Quantum dots (QDs) grabbed the spotlight in oncology owing to their excellent photostability, bright fluorescence, high biocompatibility, good electrical and chemical stability with minimum invasiveness. Recently, carbon QDs (CQDs) have become popular over toxic inorganic QDs in the area of bioimaging, biosensing, and drug delivery. Further, CQDs derived from natural sources like biomolecules and medicinal plants have drawn attention because of their one-pot, low-cost and ease of synthesis, along with remarkable tunable optical properties and biocompatibility. This review introduces the synthesis and properties of CQDs derived from natural sources, focusing on the applicability of CQD-based technologies as nano-theranostics for the diagnosis and treatment of cancer. Furthermore, the current issues and future directions for the transformation of CQDs-based nanotechnologies to clinical applications are highlighted.

One-Pot Hydrothermal Synthesis of Solution-Processable MoS2/PEDOT:PSS Composites for High-Performance Supercapacitors

It is challenging to hydrothermally synthesize solution-processable MoS₂, as the strong van der Waals force between MoS₂ nanosheets induces self-assembly of agglomerates. Here, we introduce poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into the precursor to impede aggregate formation in the hydrothermal process. A hybrid MoS₂/PEDOT:PSS (MP) hydrogel is formed due to the electrostatic interactions between the negatively charged MoS₂ and positively charged PEDOT chains. This hydrogel can be easily dispersed in water for subsequent solution processing such as vacuum filtration to form free-standing flexible films or extrusion 3D printing to create novel patterns. The MP film with a fracture strength of 18.59 MPa displays excellent electrochemical performance in both aqueous Na₂SO₄ electrolyte (474 mF cm^-2) and solid-state PVA-H₃PO₄ electrolyte (360 mF cm^-2). Flexibility and robustness can be evidenced by high capacitance retention rates of 94 and 89% after being repeatedly bent to 180° for 5000 cycles in aqueous and solid-state electrolytes, respectively.

Fabric based printed-distributed battery for wearable e-textiles: a review

Wearable power supply devices and systems are important necessities for the emerging textile electronic applications. Current energy supply devices usually need more space than the device they power, and are often based on rigid and bulky materials, making them difficult to wear. Fabric-based batteries without any rigid electrical components are therefore ideal candidates to solve the problem of powering these devices. Printing technologies have greater potential in manufacturing lightweight and low-cost batteries with high areal capacity and generating high voltages which are crucial for electronic textile (e-textile) applications. In this review, we present various printing techniques, and battery chemistries applied for smart fabrics, and give a comparison between them in terms of their potential to power the next generation of electronic textiles. Series combinations of many of these printed and distributed battery cells, using electrically conducting threads, have demonstrated their ability to power different electronic devices with a specific voltage and current requirements. Therefore, the present review summarizes the chemistries and material components of several flexible and textile-based batteries, and provides an outlook for the future development of fabric-based printed batteries for wearable and electronic textile applications with enhanced level of DC voltage and current for long periods of time.

Scalable Solution Processing MoS2 Powders with Liquid Crystalline Graphene Oxide for Flexible Freestanding Films with High Areal Lithium Storage Capacity

Freestanding flexible electrodes with high areal mass loading are required for the development of flexible high-performance lithium-ion batteries (LIBs). Currently they face the challenge of low mass loading due to the limited concentrations attainable in processable dispersions. Here, we report a simple low-temperature hydrothermal route to fabricate flexible layered molybdenum disulfide (MoS₂)/reduced graphene oxide (MSG) films offering high areal capacity and good lithium storage performance. This is achieved using a self-assembly process facilitated by the use of liquid crystalline graphene oxide (LCGO) and commercial MoS₂ powders at a low temperature of 70 °C. The amphiphilic properties of ultralarge LCGO nanosheets facilitates the processability of large-size MoS₂ powders, which is otherwise nondispersible in water. The resultant film with an areal mass of 8.2 mg cm^-2 delivers a high areal capacity of 5.80 mAh cm^-2 (706 mAh g^-1) at 0.1 A g^-1. This simple method can be adapted to similar nondispersible commercial battery materials for films fabrication or production of more complicated constructs via advanced fabrication technologies.

Flexible Hydrogel Electrolyte with Superior Mechanical Properties Based on Poly(vinyl alcohol) and Bacterial Cellulose for the Solid-State Zinc-Air Batteries

Flexible solid-state zinc-air batteries are promising energy technologies with low cost, superior performance and safety. However, flexible electrolytes are severely limited by their poor mechanical properties. Here, we introduce flexible bacterial cellulose (BC)/poly(vinyl alcohol) (PVA) composite hydrogel electrolytes (BPCE) based on bacterial cellulose (BC) microfibers and poly(vinyl alcohol) (PVA) by an in situ synthesis. Originating from the hydrogen bonds among BC microfibers and PVA matrix, these composites form load-bearing percolating dual network and their mechanical strength is increased 9 times (from 0.102 MPa of pristine PVA to 0.951 MPa of 6-BPCE). 6-BPCE shows extremely high ionic conductivities (80.8 mS cm^-1). In addition, the solid-state zinc-air batteries can stably cycle over 440 h without large discharge and charge polarizations equipped with zinc anode and Co₃O₄@Ni cathode. Moreover, flexible solid-state zinc-air batteries can cycle well at any bending angle. As flexible electrolytes, they open up a new opportunity for the development of superior-performance, flexible, rechargeable, zinc-air batteries.

A "Tandem" Strategy to Fabricate Flexible Graphene/Polypyrrole Nanofiber Film Using the Surfactant-Exfoliated Graphene for Supercapacitors

The surfactant-assisted liquid-phase exfoliation of expanded graphite can produce graphene sheets in large quantities with minimal defects. However, it is difficult to completely remove the surfactant from the final product, thus affecting the electrochemical properties of the produced graphene. In this article, a novel approach to fabricate flexible graphene/polypyrrole film was developed: using surfactant cetyltrimethylammonium bromide as a template for growth of polypyrrole nanofibers (PPyNFs) instead of removal after the exfoliation process; followed by a simple filtration method. The introduction of PPyNF not only increases the electrochemical performance, but also ensures flexibility. This composite film electrode offers a capacitance up to 161 F g^-1 along with a capacitance retention rate of over 80% after 5000 cycles.

The effect of SiO2 additives on solid hydroxide ion-conducting polymer electrolytes: a Raman microscopy study

Effect of SiO₂ and particle size on hydroxide ion-conduction in an alkaline polymer electrolyte correlated to structure and chemistry.

Layer Structured Materials for Advanced Energy Storage and Conversion

Owing to the strong in-plane chemical bonds and weak van der Waals force between adjacent layers, investigations of layer structured materials have long been the hotspots in energy-related fields. The intrinsic large interlayer space endows them capabilities of guest ion intercalation, fast ion diffusion, and swift charge transfer along the channels. Meanwhile, the well-maintained in-plane integrity contributes to exceptional mechanical properties. This anisotropic structural feature is also conducive to effective chemical combination, exfoliation, or self-assembly into various nanoarchitectures, accompanied by the introduction of defects, lattice strains, and phase transformation. This review starts with a brief introduction of typical layered materials and their crystal structures, then the structural characteristics and structure oriented unique applications in batteries, capacitors, catalysis, flexible devices, etc., are highlighted. It is surprising to observe that layered materials possess: (1) high reactivity, high reversibility, and enhanced performance via forming additional chemical bonds in alkali-metal ion batteries; (2) facile phase modulation, great feasibility for in-plane/sandwich device design, and cation intercalation enabled high capacitance in supercapacitors; (3) promoted structural diversity, effective strain engineering, and capabilities to function as ideal supporting materials/templates in electrocatalysis field. Finally, the future prospects and challenges faced by layered materials are also outlined.

Skeleton/skin structured (RGO/CNTs)@PANI composite fiber electrodes with excellent mechanical and electrochemical performance for all-solid-state symmetric supercapacitors

Polyaniline coated reduced graphene oxide/carbon nanotube composite fibers ((RGO/CNTs)@PANI, RCP) with skeleton/skin structure are designed as fiber-shaped electrodes for high performance all-solid-state symmetric supercapacitor. The one-dimensional reduced graphene oxide/carbon nanotube composite fibers (RGO/CNTs, RC) are prepared via a simple in-situ reduction of graphene oxide in presence of carbon nanotubes in quartz glass pipes, which exhibit excellent mechanical performance of >193.4 MPa of tensile strength. Then polyaniline is coated onto the RC fibers by electrodepositing technique. The electrochemical properties of the RCP fiber-shaped electrodes are optimized by adjusting the feeding ratio of carbon nanotubes. The optimized one exhibits good electrochemical characteristic such as highest volumetric specific capacitance of 193.1 F cm^-3 at 1 A cm^-3, as well as excellent cyclic retention of 92.60% after 2000 cyclic voltammetry cycles. Furthermore, the all-solid-state symmetric supercapacitor, fabricated by using the final composite fiber as both positive and negative electrodes pre-coated with the poly(vinyl alcohol)/H₂SO₄ gel polyelectrolyte, possesses volumetric capacitance of 36.7 F cm^-3 at 0.2 A cm^-3 and could light up a red light-emitting diode easily. The excellent mechanical and electrochemical performances make the designed supercapacitor as promising high performance wearable energy storage device.

Comparative study on polyvinyl chloride film as flexible substrate for preparing free-standing polyaniline-based composite electrodes for supercapacitors

The free-standing polyaniline (PANI)-based composite film electrodes were prepared with polyvinyl chloride (PVC) and the aniline modified PVC (PVC-An) films as flexible substrates for supercapacitors, via facile in-situ chemical oxidative polymerization of aniline, with conventional chemical oxidative polymerization or rapid-mixing chemical oxidative polymerization technique. Owing to the grafting of PANI from the PVC-An film as substrate and the suppression of the secondary growth of the primary PANI particles in the rapid-mixing chemical oxidative polymerization, the PVC-g-PANI-2 composite film with loose surface possessed better comprehensive performance, accompanying the high specific capacitance (645.3F/g at a current density of 1A/g), good rate capacitance (retaining 63.2% of original value at a current density of 10A/g and 52.0% at a scan rate of 100mV/s), good cycle stability (retaining 83.1% after 1000 cycles) and the improved internal resistance. Besides its excellent flexibility, it could retain 61.2% of its original specific capacitance under the stress of 8.66MPa for 1h, demonstrating a good tensile-resistance.

Direct spinning of fiber supercapacitor

A direct wet spinning approach is demonstrated for facile and continuous fabrication of a whole fiber supercapacitor using a microfluidic spinneret. The resulting fiber supercapacitor shows good electrochemical properties and possesses high flexibility and mechanical stability. This strategy paves the way for large-scale continuous production of fiber supercapacitors for weavable electronics.

A facile approach for fabrication of mechanically strong graphene/polypyrrole films with large areal capacitance for supercapacitor applications

Mechanically strong and flexible graphene/polypyrrole composite films with hierarchical structures are fabricated. They demonstrate very high areal capacitances.