Fiber Electrodes Research Articles

A Mediator-Free Multi-Ply Biofuel Cell Using an Interfacial Assembly between Hydrophilic Enzymes and Hydrophobic Conductive Oxide Nanoparticles with Pointed Apexes.

Biofuel cells (BFCs) based on enzymatic electrodes hold great promise as power sources for biomedical devices. However, their practical use is hindered by low electron transfer efficiency and poor operational stability of enzymatic electrodes. Here, a novel mediator-free multi-ply BFC that overcomes these limitations and exhibits both substantially high-power output and long-term operational stability is presented. The approach involves the utilization of interfacial interaction-induced assembly between hydrophilic glucose oxidase (GOx) and hydrophobic conductive indium tin oxide nanoparticles (ITO NPs) with distinctive shapes, along with a multi-ply electrode system. For the preparation of the anode, GOx and oleylamine-stabilized ITO NPs with bipod/tripod type are covalently assembled onto the host fiber electrode composed of multi-walled carbon nanotubes and gold (Au)NPs. Remarkably, despite the contrasting hydrophilic and hydrophobic properties, this interfacial assembly approach allows for the formation of nanoblended GOx/ITO NP film, enabling efficient electron transfer within the anode. Additionally, the cathode is prepared by sputtering Pt onto the host electrode. Furthermore, the multi-ply fiber electrode system exhibits unprecedented high-power output (≈10.4mW cm-2 ) and excellent operational stability (2.1mW cm-2 , ≈49% after 60 days of continuous operation). The approach can provide a basis for the development of high-performance BFCs.

CuO@NiCo-LDH core-shell structure for flexible fiber-shaped supercapacitor electrode material

Metal fiber electrodes are of great interest for their excellent electrical conductivity and flexibility, however the limited surface area is unfavorable for the electrochemical performance. Herein, CuO nanowires in-situ growth on one dimensional (1D) Cu wire were obtained by wet chemistry and annealing method, and NiCo-LDH nanoplates were further growth on CuO nanowires by hydrothermal method to fabricate CuO@NiCo-LDH. The combination of CuO nanowires and NiCo-LDH nanoplates creates a three-dimensional (3D) core-shell structure, which improves the specific surface area and the electrochemical properties. In addition, there is a synergistic effect between the highly reactive of NiCo-LDH and the well-conducting of CuO/Cu. The composite presents a high specific capacitance of 1220.4 mF cm−2 at 1 mA cm−2. Moreover, the CuO@NiCo-LDH//activated carbon paper (ACP) asymmetric supercapacitor exhibits an excellent energy density of 20.1 μWh cm−2 at the power density of 556.3 μW cm−2, outstanding cycling stability with specific capacitance retention of 87.1 % after 6000 cycles and good bending performance. This paper provides a novel idea for the reasonable construction of electrode material structure.

Electrospinning of Magnetite-Polyacrylonitrile Composites for the Production of Oxygen Reduction Reaction Catalysts.

In this study, electrospun carbon fiber electrodes were prepared by the carbonization of PAN-Fe3O4 electrospun fibers at 800 °C for their use as catalysts in the oxygen reduction reaction in an alkaline electrolyte. Magnetic nanofiber mats were fabricated using a needle-free electrospinning method by incorporating magnetic nanoparticles into a polymer solution. Electrochemical tests revealed that the oxygen reduction reaction (ORR) activity is optimized at an intermediate magnetite loading of 30% wt. These catalysts not only show better performance compared to their counterparts but also achieve high selectivity to water at low potentials. The onset and half-wave potentials of 0.92 and 0.76 V shown by these samples are only slightly behind those of the commercial Pt 20%-carbon black ORR catalyst. The obtained results point out that the electrospinning of PAN-Fe3O4 solutions allows the preparation of advanced N-Fe ORR catalysts in fibrillar morphology.

Selective Electrophoretic Deposition of Silicon Nanoparticles onto PAN‐Based Carbon Fiber as a Prospective Anode for Structural Li‐Ion Batteries

AbstractThe demand for revolutionizing the lightweight design of Li‐ion batteries has become inevitable due to the ever‐increasing development of electric transportation modes. Integration of structural and energy storage functionalities into a single structural battery device can be a smart way to improve the overall performance of electric vehicles. In this study, we propose a facile and cost‐effective approach to develop a prospective anode for structural Li‐ion batteries through electrophoretic deposition of silicon (Si) particles onto polyacrylonitrile (PAN)‐based carbon fiber. The synthesis method is able to selectively deposit small‐sized silicon particles on the surface of carbon fiber, producing a thin, continuous, and porous coating of silicon nanoparticles on commercial PAN‐based carbon fiber. The synthesized Si/PAN‐based carbon fiber electrode exhibits remarkable mechanical properties, delivering a tensile strength of 2.57 GPa and a tensile modulus of 118.2 GPa. Benefitting from the morphology of the deposited silicon, the discharge capacity of silicon/PAN‐based carbon fiber anode can reach 565 mAh g−1 with 81 % capacity retention after 50 cycles. This work highlights the potential of silicon‐modified carbon fiber electrodes obtained via a simple and cost‐effective deposition method for structural Li‐ion battery applications.

All-Fabric Capacitive Pressure Sensors with Piezoelectric Nanofibers for Wearable Electronics and Robotic Sensing.

Flexible pressure sensors are increasingly sought after for applications ranging from physiological signal monitoring to robotic sensing; however, the challenges associated with fabricating highly sensitive, comfortable, and cost-effective sensors remain formidable. This study presents a high-performance, all-fabric capacitive pressure sensor (AFCPS) that incorporates piezoelectric nanofibers. Through the meticulous optimization of conductive fiber electrodes and P(VDF-TrFE) nanofiber dielectric layers, the AFCPS exhibits exceptional attributes such as high sensitivity (4.05 kPa-1), an ultralow detection limit (0.6 Pa), an extensive detection range (∼100 kPa), rapid response time (<26 ms), and robust stability (>14,000 cycles). The sensor's porous structure enhances its compressibility, while its piezoelectric properties expedite charge separation, thereby increasing the interface capacitance and augmenting overall performance. These features are elucidated further through multiphysical field-coupling simulations and experimental testing. Owing to its comprehensive superior performance, the AFCPS has demonstrated its efficacy in monitoring human activity and physiological signals, as well as in discerning soft robotic grasping movements. Additionally, we have successfully implemented multiple AFCPS units as pressure sensor arrays to ascertain spatial pressure distribution and enable intelligent robotic gripping. Our research underscores the promising potential of the AFCPS device in wearable electronics and robotic sensing, thereby contributing significantly to the advancement of high-performance fabric-based sensors.

Simulation Study on the Motion Characteristics and Influencing Factors of Fiber Impurity Particles in Oil Flow in a Typical Distributed Electric Field

There have been many studies on the motion and aggregation characteristics of fiber impurities in insulation oil under static conditions. However, there are few studies on the motion characteristics of fiber impurities in insulation oil under flow conditions. In large power transformers, insulation oil is constantly in a state of flow. As a result, the motion characteristics of fiber impurities suspended in the insulation oil are even more complex due to the effects of oil flow. This study constructed a multi-physics field model for single-particle fibrous impurities in solid-liquid two-phase flow and systematically analyzed its motion characteristics. The study shows that the collision frequency between fiber impurity particles and electrodes with the same effective area is negatively correlated with the degree of electric field distortion. The maximum particle velocity and collision frequency of fibrous impurities in both uniform and slightly non-uniform electric fields show an almost linear relationship with the particle size radius. Additionally, the slope of the relationship decreases gradually with an increase in oil flow rate. With the increase of particle size, under the same flow velocity, an increase in the maximum velocity of the fibrous particles and the number of collisions with the electrodes. thereby increasing the probability of fibrous impurities transferring charge between the electrodes. Compared to the motion characteristics of fibrous impurity particles under static conditions, oil flow mainly affects the collision frequency between fibrous impurity particles and electrodes, reducing the probability of particle transfer.

Boosting the Lithium Storage Properties of a Flexible Li4Ti5O12/Graphene Fiber Anode via a 3D Printing Assembly Strategy

Traditional lithium-ion batteries cannot meet the high flexibility and bendability requirements of modern flexible electronic devices due to the limitations of the electrode material. Therefore, the development of high-performance flexible energy storage devices is of great significance for promoting flexible electronics. In recent years, one-dimensional flexible fiber lithium-ion batteries have been rapidly developed due to their advantages of high flexibility and bendability. However, it remains highly challenging to realize 1D flexible fiber lithium-ion batteries with excellent electrochemical properties and good mechanical performance. In this work, a reduced graphene oxide-based printing ink is proposed for the fabrication of flexible Li4Ti5O12/graphene fiber electrodes using a 3D printing assembly strategy. It is noteworthy that the green reducing agent vitamin C was used to reduce the graphene oxide in one step, which improved the conductivity of the fiber electrode. Furthermore, a 3D conductive network was constructed inside the fiber electrodes due to the high specific surface area of the reduced graphene oxide, which enhanced the electronic conductivity and ion mobility. The fiber electrode not only exhibits good mechanical performance, but also has excellent electrochemical properties. Equally importantly, the method is simple and efficient, and the working environment is flexible. It can precisely control the shape, size and structure of the one-dimensional fiber flexible electrode, which is of great significance for the development of future flexible electronic devices.

A braided flexible Zn–MnO2 yarn battery based on cobweb-like carbonized polypyrrole modified carbon fiber electrodes

Flexible zinc ion batteries (ZIBs) are promising candidates for energy storage devices because of high safety and low cost. Carbon fibers (CFs) are ideal current collectors for ZIBs due to their good flexibility, electrical conductivity and corrosion resistance. Herein, a novel CFs-based current collector is proposed. At first, the inertness and non-polarity of CFs were significantly modified by activating and etching to obtain a multi-layered porous structure. Thereafter, carbonized polypyrrole (CPPy) nanowire conductive networks were built up on etched carbon fibers (ECFs) by electrochemical in situ growth and carbonization. Based on the CPPy network, MnO2 nanoflowers were grown firmly by the hydrothermal method to construct multi-layer MnO2@CPPy@ECFs composite electrode. The multi-layered 3D CPPy conductive network is rooted in MnO2, providing a dedicated transmission path for both electrons and ions during electrochemical redox reactions. The MnO2@CPPy@ECFs electrode had an initial capacity of 346.1 mA h·g−1 at 0.1 A g−1 and 252.8 mA h·g−1 after 800 cycles. In addition, the integrated flexible Zn–MnO2 2D fabric battery with MnO2@CPPy@ECFs fabric cathode shows a specific capacity of 254.7 mA h·g−1 at 0.1 A g−1. Finally, a flexible Zn–MnO2 yarn battery with high flexibility, shape adaptability, structural integrity and good mechanical stability was fabricated by the 2D braid method. The initial specific capacity of the flexible Zn–MnO2 yarn battery is 111.7 mA h·g−1 at 0.1C, which also presents a remarkable volumetric energy density of 30.5 mW h cm−3. This work opens up a new pathway for the rational design of flexible electrodes for wearable ZIBs.

Nano zero-valent iron-based fiber electrode for efficient electro-Fenton treatment of pharmaceutical wastewater: Mechanism of degradation and sterilization

In this study, a novel metal–organic framework (MOF) derived fiber electrode (NZVIF-800) was successfully fabricated by a novel electrostatic spinning and pyrolysis procedure. The NZVIF-800 electrode exhibited great catalytic activity in a heterogeneous electro-Fenton (EF) system for organic degradation, in which the secnidazole (SCZ) was completely degraded within 60 min with excellent stability (no significant change after eight cycles). Importantly, the NZVIF-800 electrode was also highly effective for decontaminating actual pharmaceutical wastewater, in which the TOC and COD removal reached 38% and 47%, respectively, after 4 h EF reaction. Based on experimental analysis, microstructure characterization, and theoretical calculations, the detailed reaction mechanism of the NZVIF-800 electrode was revealed. The impressive EF performance was mainly attributed to the in situ generation of active nano-zero-valent iron (NZVI) derived from the MOF pyrolysis and the confinement effect of the encased carbon layer that could effectively inhibit the loss and inactivation of Fe active sites. The degradation pathways of organic pollutants in simulated and real wastewater were proposed in detail. Significantly, the EF system with NZVIF-800 electrode exhibited strong sterilization ability for the wastewater matrix as evidenced by the colony condition, OD600 values, and Illumina MiSeq sequencing platform analysis (up to 95% sterilization efficiency within 4 h), expanding its application scope for actual wastewater treatment.

Three Dimensional Low-Tortuosity Carbon Fibers Enable High-Areal-Capacity and Long-Durability Battery

Increasing the thickness of lithium-ion battery electrodes enables significant improvement in energy density and reducing the manufacturing cost. However, the existing barriers such as manufacturing challenges, performance issues, and scalability impede the development of fabricating thick electrodes. Here, we demonstrate a three dimension, low-tortuosity, and metal current collector free carbon fiber (CF) electrode which works as an integrated host substrate for LiNi0.5Mn0.3Co0.2O2 (NMC 532) cathode materials, similarly, the paired anode. The low tortuosity (~ 1.7) aligned microchannels of CF provide a good electron conductivity (~ 0.23 S cm-1), low Li+ diffusion resistance (~ 22 Ω), and high reversibility (91% over 500 cycles at C/3) compared to ~ 0.01 S cm-1, ~ 34 Ω, and 50% over 50 cycles for 100 µm slurry-casting graphite electrode with tortuosity of 2.9, respectively. The large porosity (~ 60%) enables CF a high mass loading capability of NMC 532 (> 70 mg cm-2) which provides a theoretical areal capacity ~ 14 mAh cm-2. The practical design of NMC 532/CF versus CF thick cells, with NMC 532 mass loading 32 mg cm-2, and theoretical areal capacity ~ 5.5 mAh cm-2 show an initial discharge areal capacity 4.1 mAh cm-2 at C/3 (1.5 mA cm-2), a capacity retention of 90.4% (500 cycles), 78.1% (1000 cycles), and 65.5% (1500 cycles). Furthermore, the post-analysis of long-term cycled NMC 532 particles, with consistent morphology of pristine particles, demonstrates lessen thermal stress across the electrodes. Our work presents a well-aligned microstructure for thick lithium-ion electrodes with practical level, scalable manufacturing, high areal capacity, and long-term electrochemical durability.

Electric field forward osmosis (EFFO) fouling mitigation in algae harvesting

Efficient microalgae harvesting is crucial for sustainable biofuel production. Forward osmosis (FO) membranes offer a cost-effective solution for algae separation but are prone to membrane fouling. To address this, a bench-scale FO membrane unit was created, utilizing an aquaporin thin film composite FO membrane. The unit was combined with an electric field in both continuous and pulsing modes, employing stainless steel (SS) meshes to mitigate fouling during Chlorella vulgaris dewatering. Generally, applying higher electric potentials in continuous mode demonstrated improved water flux and flux recovery. The electric field forward osmosis (EFFO) configuration achieved significantly higher fluxes at applied potentials of −0.1, −0.4, and −1.0 V compared to the control. An electric potential as high as −10 V effectively removed fouling by inducing H2 gas formation on the SS cathode. Additionally, the application of high electric potential led to increased settling velocity, possibly due to electrocoagulation and the release of metals. Conversely, carbon fiber electrodes had no impact on algal cell morphology. Both higher salinity levels and increased potential enhanced lipid contents in algal biomass. Overall, EFFO technology in algae harvesting offers improved efficiency by reducing membrane fouling and increasing water flux, enabling cost-effective and sustainable biofuel production from microalgae.

(Invited) integration of Microneedles and Electrochemical Sensors for Medical Applications

Microneedles are small-scale devices that may be used for access to interstitial fluid and/or capillary blood for transdermal monitoring of chemicals [1]. In this presentation, the integration of several types of electrochemical sensors with hollow microneedles will be considered. For example, carbon fiber electrodes have been integrated with digital micromirror device-produced microneedles; ascorbic acid and hydrogen peroxide were detected with these devices [2]. Carbon paste electrodes have also been integrated with digital micromirror device-produced microneedles; electrodes made from rhodium-dispersed carbon paste were used for hydrogen peroxide sensing [3]. In addition, lactate oxidase-modified rhodium-dispersed carbon paste electrodes were demonstrated for lactate sensing, including in the presence of interferents such as ascorbic acid, uric acid, and acetaminophen. A multiplexed microneedle array containing digital micromirror device-produced microneedles was subsequently used for amperometric detection of glucose, lactate, and pH; detection of these analytes in complex media was shown [4]. More recently, digital micromirror device-produced hollow microneedles were modified with a working sensor, which was prepared with graphene ink and 4 (3-Butyl-1-imidazolio)-1-butanesulfonate) ionic liquid. Direct oxidation of fentanyl via square-wave voltammetry was shown; a detection limit of 27.8 μM was demonstrated using this approach [5]. Two photon polymerization has also been used to create hollow microneedles for biosensing; a porous carbon electrode created using interference lithography was used for potassium ion sensing in the presence of interfering sodium ions [6]. In another study, nitrogen-incorporated ultrananocrystalline diamond coatings were deposited on Ti –6Al–4V alloy microneedles using microwave plasma enhanced chemical vapor deposition; dopamine and uric acid were electrochemically detected in an in vitro study [7]. These studies indicate that microneedles may have utility for minimally invasive detection of analytes in a real time manner. Benefits and disadvantages of the microneedle-based sensing approach as well as efforts needed for clinical translation of microneedle-based sensing technology will be considered.

Development of an all‐electrospun high‐performance textile supercapacitor for wearable device applications

AbstractThis paper reports the synthesis and electrochemical performance of electrospun polyaniline (PANI) nanofiber membranes that work as high‐performance electrodes in an all‐textile supercapacitor (SC). The electrospun separator membrane consists of a mix of polyacrylonitrile (PAN) and poly (ethylene sulfonate) (PES). The all‐textile SC consists of a PES‐PAN membrane, previously soaked in an electrolyte, stacked between two PANI fiber electrodes. Scanning electron microscopy and Fourier‐transform infrared spectroscopy are carried out to characterize the morphology and chemical structure of the PANI and PES‐PAN fiber membranes. Cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy are carried out to characterize the electrochemical properties of the SCs. The all‐textile SC shows very competitive specific capacitances of 275 F/g at 0.25 A/g and a maximum specific power of 1350 Wkg−1. These all‐electrospun SCs show higher performance than the SCs using PANI films and commercial cellulose as separators. Finally, we report a flexible all‐electrospun and all‐solid‐state SC was fabricated using flexible substrates and a gel‐type electrolyte. Flexible SC has a specific capacitance of 270 F/g, confirming that the performance of all‐electrospun SCs is a promising approach for future textile energy storage devices for its potential use in wearable devices.

Computational modeling of a thread-based microfluidic fuel cell with carbon fiber electrodes

Thread-based microfluidic fuel cells are promising micro power sources for portable and wearable electronic devices. In this study, a three-dimensional computational model is developed for a thread-based microfluidic fuel cell with carbon fiber electrodes. The interaction of fluid flow, species transport and electrochemical reactions is elucidated. The cell polarization curve obtained from modeling is validated by the experimental data. Moreover, effects of operational parameters and structural parameters on the cell performance and mass transport are further investigated. Results demonstrate that the presence of the intermediate flow channel can effectively prevent the reactant crossover and the parasitic current density is negligible. Appropriate increase in the reactant concentration is beneficial to yield uniform concentration distribution and enhance the mass transfer. Besides, the peak power density is only increased by 0.7% when the flow rate of anolyte and catholyte is increased by four times. Additionally, lowering the electrode spacing and the electrode porosity result in the superior cell performance. With the electrode spacing of 3 mm and the electrode porosity of 0.6, the peak power density of 34.6 mW cm−2 and the maximum current density of 112.5 mA cm−2 are achieved. This work provides theoretical guidance for future development and optimization for thread-based microfluidic fuel cells.

Scalable, flexible carbon fiber electrode thread arrays for three-dimensional probing of neurochemical activity in deep brain structures of rodents

We developed a flexible “electrode-thread” array for recording dopamine neurochemicals from a lateral distribution of subcortical targets (up to 16) transverse to the axis of insertion. Ultrathin (∼10 μm diameter) carbon fiber (CF) electrode-threads (CFETs) are clustered into a tight bundle to introduce them into the brain from a single-entry point. The individual CFETs splay laterally in deep brain tissue during insertion due to their innate flexibility. This spatial redistribution allows navigation of the CFETs towards deep brain targets spreading horizontally from the axis of insertion. Commercial “linear” arrays provide single-entry insertion but only allow measurements along the axis of insertion. Horizontally configured arrays inflict separate penetrations for each individual channel. We tested functional performance of our CFET arrays in vivo for recording dopamine and for providing lateral spread to multiple distributed sites in the rat striatum. Spatial spread was further characterized in agar brain phantoms as a function of insertion depth. We also developed protocols to slice the embedded CFETs within fixed brain tissue using standard histology. This method allowed extraction of the precise spatial coordinates of the implanted CFETs and their recording sites as integrated with immunohistochemical staining for surrounding anatomical, cytological, and protein expression labels. Our CFET array has the potential to unlock a wide range of applications, from uncovering the role of neuromodulators in synaptic plasticity, to addressing critical safety barriers in clinical translation towards diagnostic and adaptive treatment in Parkinson’s disease and major mood disorders.

Oxidative chemical vapor deposition of polypyrrole onto carbon fabric for flexible supercapacitive electrode material

Polypyrrole has been a promising conjugated polymer for application in electrochemical energy storage devices. One primary feature is its pseudocapacitive behavior, which makes it suitable for hybridization with traditional carbon-based electrical double layer capacitive materials. The processing condition for such a hybridization is a critical aspect for the electrode performance in long term. Oxidative chemical vapor deposition was used to deposit polypyrrole onto 3D carbon fiber fabric. This allowed uniform and conformal deposition of polypyrrole on individual fibers as well as a control over its thickness depending on the reaction time. The obtained composite was characterized for electrochemical energy storage application using cyclic voltammetry and galvanostatic charge discharge measurements. Additionally, the stability of the polypyrrole-carbon fiber electrode was tested using microscopy and energy dispersive spectroscopy in order to obtain insights into physical and chemical degradation of polypyrrole during electrochemical aging. Results showed thickness-dependence of electrode stability, tuning of which in the correct voltage window is necessary for optimal long-term performance.

Combining voltage-sensitive dye, carbon fiber array, and extracellular nerve electrodes using a 3-D printed recording chamber and manipulators

BackgroundThe analyses of neuronal circuits require high-throughput technologies for stimulating and recording many neurons simultaneously with single-neuron precision. Voltage-sensitive dyes (VSDs) have enabled the monitoring of membrane potentials of many (10–100 s) neurons simultaneously. Carbon fiber electrode (CFE) arrays allow for stimulation and recording of many neurons simultaneously, including intracellularly. New methodCombining CFE with VSD leverages the advantages of both technologies, allowing for stimulation of single neurons while recording the activity of the entire network. 3-D printing technology was used to develop a chamber to simultaneously perform VSD imaging, CFE array recording, and extracellular recording from individual glass electrodes. ResultsAplysia buccal ganglia were stained with VSD and imaged while also recording using a CFE array and extracellular nerve electrodes. Coincident spiking activity was recorded by VSD, CFE, and extracellular nerve electrodes. Current injection with CFE electrodes could activate and inhibit individual neurons as detected by VSD and nerve recordings. Comparison to existing methodsThe large size of traditional manipulators limits the number of electrodes used and the number of neurons recorded during an experiment. Here we present a method to build a 3-D printed recording chamber that includes a 3-axis micromanipulator to position a CFE array and eight 2-axis manipulators to position eight extracellular electrodes. Conclusions3-D printing technology can be used to build a custom recording chamber and micromanipulators. Combining these technologies allows for the direct modulation of the activity of neurons while recording the activity of 100 s of neurons simultaneously.

Sulfonated hypercrosslinked polymer enhanced structural composite supercapacitors

Structural supercapacitors are multifunctional devices able to bear mechanical load while storing electrical energy. Carbon fibres can be used as a bifunctional component within structural supercapacitors, acting both as current collector and mechanical reinforcement. A promising route to such devices is to increase the surface area of carbon fibres, which can be achieved by the deposition of active materials, and embed them into a structural electrolyte. A highly sulfonated, high porosity hypercrosslinked polymer was deposited onto carbon fibres by electrophoretic deposition from an aqueous suspension. We investigated the effect of polymer and binder concentration in the deposition suspension on the electrochemical properties of the coated carbon fibre electrodes. Multifunctional structural composite supercapacitors had a fibre volume fraction of only 21% and possessed a tensile strength and Young's modulus of 495 MPa and 49 GPa, respectively. A specific capacitance of 1.2 F/g was reached, comparable to graphene coated carbon fibre electrodes. At room temperature and ambient humidity an energy density of 39 mWh/kg and a power density of 15 W/kg were measured. We demonstrate that moisture plays a major role in the energy storage mechanism in these SCs.

An Antifouling Redox Sensor with a Flexible Carbon Fiber Electrode for Machine Learning-Based Dissolved Oxygen Prediction in Severely Eutrophic Waters

Machine-learning-based models are used to predict dissolved oxygen (DO); however, acquiring continuous water quality data for input variables in harsh environments remains challenging. Herein, redox potential (ORP) determined by a thermo-treated flexible carbon fiber electrode was introduced as a single or preferential input variable for machine-learning-based DO prediction in a year-round eutrophic estuary. The novel ORP sensor was operated for 4 months, and DO was predicted from ORP and six water quality data sources using a long short-term memory (LSTM) neural network. ORP and DO concentration showed a linear correlation, but the first-order correlation slopes varied seasonally. The optimal LSTM hyperparameters were proposed, which depended on the prediction time step and predictor case. Simulation results showed higher seasonal DO dynamics reproduced using ORP alone (RMSE = 1.09) than that predicted using six other water quality parameters (RMSE = 1.32). In addition, ORP played a key role in DO prediction when combined with all water quality parameters (RMSE = 1.08). The feature importance of ORP as a predictor was evaluated from a random forest model. Overall, the highly selective redox sensor has a distinct response to DO concentration and offers a novel and cost-effective approach for monitoring or predicting DO in eutrophic waters.

High-performance carbon-fiber-based supercapacitors: Enhanced performance through the porosity modification of electrodes containing a redox mediator

Carbon-fiber-based supercapacitors (CFS) are emerging as a prospective option for innovative wearable energy storage devices by reason of their safety, environmental compatibility, and high power density. However, the limited practical application of CFS is attributed to its poor energy storage performance, which is caused by the carbon fiber electrode's limited specific surface area and low wetting ability. To address this, this study developed a CFS with micro-meso porous carbon fibers electrodes and a redox additive electrolyte (CFS-MMRE). The CFS-MMRE showed exceptional energy storage capaability, high specific capacitance of 876 mF cm−2 at 70 μA cm−2, respectively, cycling stability over 5,000 cycles with 70 % capacitance retention at 400 μA cm−2. Moreover, CFS-MMRE possesses mechanical pliability, high achievability, and remarkable energy storage performance, which make them a viable choice for wearable electronic devices.