Charge Percolation Research Articles

Can 3D-printed flow electrode gaskets replace CNC-milled graphite current collectors in flow capacitive deionization?

As billions of people suffer from water scarcity, finding sustainable water resources is imperative. Flow capacitive deionization (FCDI) is a highly promising desalination process that can produce clean water from saline streams such as brackish and seawater. Conventional FCDI systems employ Computerised Numerical Control (CNC)-milled graphite plates that serve as current collectors and flow electrode channels. However, they have drawbacks such as high manufacturing costs, waste generation, and the difficulty of producing complex geometries required for efficient flow electrode mixing. Here, we successfully demonstrate that 3D-printed flow electrode gaskets, made of non-conductive polyethylene terephthalate glycol (PET-G) or a carbon black-infused conductive polylactic acid (PLA), are viable alternatives to traditional graphite plates. In specific cases, the desalination and energy efficiency in FCDI cells with 3D-printed conductive gaskets were even 25 % and 10 % higher, respectively, compared to traditional CNC-milled current collectors. The transition to 3D printing offers notable benefits, such as the competence to fabricate complex designs that enhance internal mixing and charge percolation. This innovation represents a change of paradigm in the way FCDI cells should be designed and manufactured, using additive manufacturing, which represents an efficient, scalable, and cost-effective substitute for the conventional approach, contributing therefore for the advancement of FCDI desalination technology.

An in-depth insight at the percolation model and charge transport mechanism in La0.7Ca0.1Pb0.2Mn1-2xAlxSnxO3 manganite prepared by sol–gel route

An in-depth insight at the percolation model and charge transport mechanism in La0.7Ca0.1Pb0.2Mn1-2xAlxSnxO3 manganite prepared by sol–gel route

Quasiclassical Anderson transition and thermally activated percolative charge transport in single-crystalline ScN

Quasiclassical Anderson transition and thermally activated percolative charge transport in single-crystalline ScN

Improved performance of flow-electrode capacitive mixing through N-doping of activated carbon

Flow electrodes, which are integral to flow-electrode capacitive mixing (F-CapMix), primarily consist of activated carbon (AC), conductive additive and an aqueous electrolyte with a salt. For the better performance of F-CapMix, the AC must have a high surface area and excellent electrical conductivity to facilitate efficient charge percolation and electron transport between the AC particles within the flow electrode. In this study, nitrogen-doped activated carbon (N-doped AC) was synthesized through a straightforward process involving the heating of a mixture of raw AC and melamine in a covered container. The resulting N-doped AC powder exhibited an average of 20 % higher electrical conductivity than raw AC powder without sacrificing the surface area (AC: 2284.7 m2/g vs N-doped AC: 2125.6 m2/g) owing to the incorporation of graphitic nitrogen and oxidized nitrogen into the raw AC surface. The surface characteristics of N-doped AC were found to be similar to those of raw AC. Electrochemical impedance spectroscopy analysis of F-CapMix utilizing N-doped AC in the flow electrode revealed reduced resistance and increased capacitance, leading to an enhancement in power density from 0.706 to 0.828 W/m2. Consequently, integrating N-doped AC into the flow electrode can contribute to the improved performance of F-CapMix.

Double-sided semitransparent titania photoelectrode with enhanced light harvesting

In this work, unique semitransparent electrodes were prepared by the anodization of titanium layers (540 nm thick) initially deposited on the both sides of glass substrates employing indium-tin oxide interface layers serving as a current collector for the induced photocurrent. The anodization strategy used in this study enables fabrication of semitransparent titanium dioxide nanotube arrays with either aligned or spaced architecture on the two sides of the planar substrate. This study aims to perform a detailed investigation of this novel photoelectrode system (crystal structure, morphology and optical properties) to reveal their photoelectrochemical features. It was found that the photoelectrode exhibits enhanced photocurrent density about 1.9 times higher (4.6 μAcm−2 at +0.5 V) for aligned nanotubes compared to a substrate overgrown symmetrically by separated nanotubes (2.4 μAcm−2 at +0.5 V). This can be effectively explained by the higher tube density in the case of aligned nanostructures, which provide more channels for charge percolation. In addition, both the high donor concentration (6.4 × 1020 cm−3) together with the low charge transfer resistance of the semitransparent electrode of the aligned nanotubes make the material promising for application in photoelectrochemical systems and smart light management.

Coupled optical-electric monitoring of charge percolation events in carbon flow-electrodes

The industrial application of electrochemical processes is limited by a variety of challenges, such as catalyst stability and selectivity. However, the question of how to efficiently exploit the entire reactor volume for the process is also essential for a viable implementation. Flow electrodes, which consist of conductive particles suspended in the electrolyte, are promising for increasing the active electrode area without increasing the reactor footprint. They are currently being used for different applications, such as energy storage or desalination. However, especially the charge transport mechanisms in flow electrodes remain unclear because the occurring phenomena are fast and highly complex. In this work, we introduce a methodology that combines electrical measurements with high-speed recording of particle movements in flow electrodes, simultaneously. Our algorithm evaluates the video sequences and calculates the detected particle area in the channel. This allows the electrical current to be correlated with the actual amount of particles in the channel. The results reveal that only an aqueous electrolyte can result in a substantial increase in conductivity because of the particles present in the fluid channel. Furthermore, the conductivity increases with the number of particles, regardless of the observed particle–electrode contact. When the particle flow was hydrodynamically forced toward the electrode, we found that the particle–electrode contact increased the conductivity even more strongly than that of isolated particle clusters in an unfocused flow. However, the greatest effect on the electrical conductivity relates to the formation of particle bridges resulting from the electrical percolation networks between the electrodes.

Three-dimensional titanium mesh-based flow electrode capacitive deionization for salt separation and enrichment in high salinity water

Flow electrode capacitive deionization (FCDI) is a highly promising desalination technique known for its exceptional electrosorption capacity, making it suitable for efficient salt separation in high salinity water. However, the unsatisfactory charge transfer process between the flow electrode and current collector severely curtails the salt separation and enrichment performance of the FCDI device. To address this issue, three-dimensional titanium mesh (3D-TM) was proposed as a novel current collector for FCDI device, which significantly amplifies the charge transfer area and exhibits excellent salt separation performance. The 3D-TM current collector promotes the electron transfer, charge percolation, and ion migration processes through the electroconvection generated by the turbulence effect on the flow electrode. In the specific case of the 20-mesh 3D-TM, which is composed of 12 stacking layers of titanium mesh, the remarkable average salt removal rate and charge efficiency were achieved 5.06 μmol cm−2 min−1 and 92.9 % under an appropriate applied voltage of 2.0 V, respectively. Dramatically, the desalination performance maintained above 76.4 % over 100 desalination cycles at 2.0 V, demonstrating the exceptional cyclic stability of the 3D-TM FCDI cell. In the seawater desalination, the 3D-TM FCDI cell exhibited an impressive salt removal efficiency of 97.5 % (from 34.2 g L−1 to 0.84 g L−1) for 1 L East China seawater at 2.0 V for 24 h. For lithium-ion enrichment, the FCDI continuous desalting system achieved an astonishing concentration of 17.3 g L−1 for Li+ ions enrichment from an initial concentration of 1.30 g L−1, obtaining the average salt treating rate of 23.6 g m−2h−1 and charge efficiency of 80.0 %. Moreover, the lithium-sodium ions and lithium-magnesium ions enrichments were both conducted, yielding an enriched concentration of 10.4 g L−1 and 7.30 g L−1 for Li+ ions, respectively. These findings highlight the enormous potential of FCDI technology in industrial engineering applications, further establishing it as a highly viable solution.

Simultaneous Optical and Electrical Monitoring of Charge Percolation in Flow Electrodes

Electrochemical reactions are limited to the surface of the electrode, which makes the construction and intensification of electrochemical processes challenging. To increase the space-time yield of electrochemical cells, the electrochemically active surface area has to be enlarged. This can be achieved by either increasing the surface of a fixed electrode (e.g., porous electrodes) or by so-called flow electrodes. Flow electrodes consist of conductive particles suspended in the electrolyte. They have the advantage of increasing the active surface area of the electrode and also enabling continuous recycling and exchange of the active electrode material. They have been successfully applied, for example, for energy storage in redox flow batteries and desalination in flow-electrode capacitive deionization (FCDI).In flow electrodes the conductive particles dynamically increase the active area of the electrode by collision with the electrode; however, the exact mechanism of charge transport in such suspensions, also called charge percolation, is not completely understood. Yet, the successful implementation of flow electrodes in electrochemical processes requires a deeper understanding of how these particles interact within the electrochemical system. Charge percolation in flow electrodes is highly dynamic, and the conductivity of the suspensions depends on multiple factors like the amount and position of the particles, the shape and accessibility of the current collector, and especially the contact between particles and current collector. Literature presents different approaches which deal with charge transport in conductive suspensions, either by analyzing the electrical properties of flow electrodes in flow or by examining the structure and position of the particles visually in static conditions. We combine visual and electrical in-situ monitoring of charge percolation events in a single experimental setup. We developed a transparent electrochemical flow cell, made of transparent polydimethylsiloxane (PDMS), allowing for in-situ measurements. A constant voltage is applied to the current collector by a potentiostat. The resulting electrical current is measured simultaneously by recoding the particle movements using an optical microscope and a high-speed camera. The design of the electrochemical cell enables different positions of the particles within the channel in different flow modes: Contact between particles and the current collector can be either prevented or enforced. A motion-tracking algorithm analyses the videos to determine the area of particles in the electric field and the area of particles contacting the current collector. This allows for the correlation of particle behavior and electrical current.We investigated the influence of electrolyte, particle fraction, and the contact probability of particles and current collector on charge transport. Our results show that contact between particles and the current collector is a main contributor to charge transport in flow electrodes. But particles cluster can also increase the current, even if they do not touch the current collectors. The highest increase in current was achieved for large particle fraction short circuiting both current collectors. These results show that the way the particle suspension interacts with the electrode and by guiding the flow the electrochemical processes can be improved dramatically.

Modulating Charge Percolation in Biocompatible Norbornene Redox-Active Polymers Obtained Via ROMP

Organic redox-active materials are actively being developed as next-generation energy storage systems. These materials have multiple advantages, including superior chemical and physical properties, and excellent electrochemical storage performance compared to metal-based inorganic materials. Specifically, redox-active and conductive polymers have been used over organic single molecules due to the advantages that polymeric materials offer such as good stability, excellent processability, and simple device fabrication. Furthermore, we can adjust the synthetic process to obtain a wide range of desirable properties and can incorporate conductive and redox-active polymers into biological entities to carry out bio-inspired functions such as shuttling electrons through wastewater mediated processes or sensing of heavy metals in wastewater. By leveraging natural processes, our goal is to engineer resistant and sustainable energy storage technologies using conductive and redox-active polymers. To that end, we present the synthesis and characterization, including material and electrochemical characterizations, of biocompatible norbornene redox-active polymers in which we modulated charge percolation by copolymerizing with a water-soluble polymer for potential applications in bio-inspired redox-flow batteries.

Effect of Charging Protocol on the Performance of LiNi0.6Co0.2Mn0.2O2 Lithium Slurry Batteries

With flowable slurry electrode architecture, lithium slurry battery (LSB) has the advantages of high energy density and independent energy and power, which can be used as an excellent energy storage device. However, its practical application is still hindered by multiple factors, including prolonged ion/electron passage, serious interfacial parasitic reactions, low energy efficiency, et al. The special electrode structure can influence the charge percolation pathway, reduce the apparent Li+ diffusion coefficient (), and further impact the battery performances. Herein, a special six‐stage constant current (SS‐CC) charging protocol for LSB is developed based on under different state of charges, that is, higher charging rate at larger . Comparing with other charging protocols commonly used in lithium‐ion batteries such as constant current‐constant voltage, the LSB charged by SS‐CC protocol not only shows higher energy efficiency, but also enhanced cycle stability. This is attributed to the better synergy between lithium desertion and plating, which kinetically reduces the parasitic reactions such as solid–electrolyte interphase accumulation, dead lithium, or dendrite generation. It is believed that this charging protocol design strategy can also be applied in other LSB systems.

Percolative Charge Transport on Electrified Surface of Polytetrafluoroethylene

Percolative Charge Transport on Electrified Surface of Polytetrafluoroethylene

Impact of Molecular Weight on the Ionic and Electronic Transport of Self‐Doped Conjugated Polyelectrolytes Relevant to Organic Electrochemical Transistors

AbstractOrganic electrochemical transistors (OECTs) have gained considerable attention due to their potential applications in emerging biosensor platforms. The use of conjugated polyelectrolytes (CPEs) as active materials in OECTs is particularly advantageous owing to their functional, water‐processable, and biocompatible nature, as well as their tunable electronic and ionic transport properties. However, there exists a lack of systematic studies of the structure‐property relationships of these materials with respect to OECT performance. This study shows how by tuning the molecular weight of self‐doped CPE (CPE‐K) it is possible to fabricate OECTs with a µC* value of 14.7 F cm−1 V−1 s−1, one order of magnitude higher than previously reported CPE‐based devices. Furthermore, OECTs with a transconductance of 120 mS are demonstrated via device engineering. While CPE‐K batches with different molecular weights show good doping behavior and high volumetric capacitance, as confirmed by spectroelectrochemistry and electrochemical impedance spectroscopy, the medium molecular weight possesses the highest carrier mobility of ≈0.1 cm2 V−1 s−1 leading to the highest transconductance. The enhanced charge transport is due to a favorable charge percolation pathway, as revealed by the combination of X‐ray analysis and conductive atomic force microscope. These insights provide guidelines for further improving the performance of CPE‐based OECTs.

Enhancing charge transfer utilizing ternary composite slurry for high-efficient flow-electrode capacitive deionization

Weak contact between activated carbon (AC) particles results in a poor conductivity for the electrode slurry, which limits the improved desalination performance in flow-electrode capacitive deionization (FCDI). Based on the bridging and filling effects of nanoparticles, we report a ternary composite slurry with multi-dimensional sized carbon particles by introducing the carbon nanotubes (CNT) and carbon black (CB) into AC-based slurry, namely AC/(CB + CNT) slurry. Further enhanced electrical conductivity relative to conventional pure AC slurry. By comparison analysis, FCDI system with the ternary carbon composite slurry had a faster average salt removal rate (ASAR) of 1.89 μmol cm−2 min−1 under at 1.2 V in a feed salinity of 2.0 g L−1, which is 3.27 1.92 and 1.46 times that of pure AC, AC/CB and AC/CNT slurry. In long-term operation (1800 min, U = 1.6 V), the AC/(CB + CNT) slurry exhibited a stable ASAR of 4.41 μmol cm−2 min−1 and maintained a charging efficiency (CE) of around 96% and molar energy consumption (Em) of 0.043 kWh mol−1. Electrochemical analysis and computational fluid dynamics (CFD) simulation further confirms that AC/(CB + CNT) slurry enable system with a point-to-line-to-surface connection morphology, which generates a robust charge percolation network with diverse pathway and facilitates the charge transfer. In summary, this study developed a facile strategy for increasing the slurry conductivity to provide a feasible approach in efficient desalination application.

Structural-disorder-driven critical quantum fluctuation and localization in two-dimensional semiconductors

Quantum fluctuations of wavefunctions in disorder-driven quantum phase transitions (QPT) exhibit criticality, as evidenced by their multifractality and power law behavior. However, understanding the metal-insulator transition (MIT) as a continuous QPT in a disordered system has been challenging due to fundamental issues such as the lack of an apparent order parameter and its dynamical nature. Here, we elucidate the universal mechanism underlying the structural-disorder-driven MIT in 2D semiconductors through autocorrelation and multifractality of quantum fluctuations. The structural disorder causes curvature-induced band gap fluctuations, leading to charge localization and formation of band tails near band edges. As doping level increases, the localization-delocalization transition occurs when states above a critical energy become uniform due to unusual band bending by localized charge. Furthermore, curvature induces local variations in spin-orbit interactions, resulting in non-uniform ferromagnetic domains. Our findings demonstrate that the structural disorder in 2D materials is essential to understanding the intricate phenomena associated with localization-delocalization transition, charge percolation, and spin glass with both topological and magnetic disorders.

Revealing the Impact of Molecular Weight on Mixed Conduction in Glycolated Polythiophenes through Electrolyte Choice

Developing material design guidelines for organic mixed ionic–electronic conductors (OMIECs) is critical to enable high efficacy mixed transport within bioelectronics. One important feature which has yet to be thoroughly explored is the role of molecular weight on OMIEC performance. In this work, we examined a series of prototypical glycolated polythiophene materials (P3MEEET) with systematically increasing molecular weights within organic electrochemical transistors (OECTs)─a common testbed for investigating mixed transport. We find that there is improved performance beyond an intermediate molecular weight; however, this relationship is electrolyte dependent. Operando analysis suggests that the enhanced mobility at higher molecular weights may be negated by significant swelling when operated in NaCl due to disruption of intercrystallite charge percolation. The role of molecular weight is revealed through operation in KTFSI, as doping occurs through cation expulsion, preventing detrimental swelling and maintaining percolative pathways. These findings demonstrate the importance of both molecular weight and electrolyte composition to enhance the performance of OMIECs.

Random networks of disconnected nanoparticles in dielectric layers as a source of electric responsivity

Many efforts are currently focused on materials with responsive features for neural-inspired devices. Different approaches are followed, based on various mechanisms – from ferroelectric switching to structural phase changes, from magnetic tunnel junctions to metal filament formation. Here we analyze an alternative strategy based on an unconventional electrical response arising from percolative charge transport and charge trapping in discrete random networks of oxide nanostructures in a dielectric matrix. After an analysis of the mechanisms which can potentially be a source of a plastic response in this class of systems, we report evidence of this behavior in a system comprising an alkali-germanosilicate amorphous matrix with incorporated Ga-oxide nanostructures. The active material – consisting in a film 70 nm thick interfaced to p-type Si and Au electrodes – gives a responsive behavior to pulsed bias which is accompanied by bias dependent electric conduction, with resistivity changes of an order of magnitude by applying 2 V, as well as a dielectric response with hysteretic features, as expected by the model. The results represent a first proof of concept of an unexplored strategy for the design of responsive systems.

Numerical prediction of pressure drop and flow characteristics of activated carbon and salt-water for flow-electrode capacitive mixing (F-CapMix)

In flow-electrode capacitive mixing (F-CapMix), prediction of the flow characteristics and pressure drop of the flow-electrode is important as it pertains to both efficient charge percolation and electron transport of activated carbons in the flow-electrode, as well as the net power of F-CapMix. In this study, the flow characteristics and pressure drop of activated carbon and salt-water within the flow-electrode of F-CapMix are predicted by applying numerical simulations, when the channel depth for the flow-electrode is changed from 0.5 mm to 2.5 mm. The numerical simulation was validated by comparing the experimental results of pressure drop measurements of the flow-electrode. To analyze the variables related to electron transfer between the activated carbon and the current collector, the particle wall normal pressure was numerically calculated. As the channel depth for the flow-electrode decreased by 0.5 mm, the pressure exerted by the activated carbon particle on the wall increased by 32.92 % on average. Consequently, the power density of F-CapMix increased to 14.03 % owing to the elevated pressure at the wall. Predicting the behavior of activated carbon and the pressure drop through numerical simulation is a key step for the designing of the flow channel for the F-CapMix.

Percolative charge transport on electrified surface of polytetrafluoroethylene

The charge transport on the electrically charged surface of polytetrafluoroethylene (PTFE) films in the presence of the adsorption of an electrically conductive phase has been studied. The attenuation of the rate of displacement of the potential drop over the film surface, which limits the area of its expansion, has been found. An estimate has been made for the critical index of the correlation length of a percolation cluster that forms on an electrified PTFE surface at high humidity. It has been experimentally established that the leak of charge from an electrically charged surface is determined by percolation processes. Keywords: percolation, percolation threshold, adsorption, electrization.

Core–Shell Fe3O4@C Conductive Additives for Magnetic Flow-Electrode Capacitive Deionization: Reconstruction of Charge Percolation Networks

Flow-electrode capacitive deionization (FCDI) based on suspension or semisolid electrodes is a promising alternative for large-scale applications, yet precise control over their transport behavior has not yet been accomplished. Here, we report a general approach for remotely manipulating the transport of the hybrid suspension electrodes composed of core–shell Fe3O4@C nanoparticles and powdered activated carbon (AC) simply by employing a magnetic field. Benefiting from the reconfiguration of the charge percolation networks, the average salt removal rate (ASRR) of magnetic FCDI was increased by 61.7% compared to that of FCDI without the magnetic field. The mechanism of magnetic field-magnetic carbon (MC) coupling includes three main pathways: (i) increasing the local concentration of active electrodes on the current collector surface, (ii) increasing the contact sites available to the current collector, and (iii) shortening the ion transport distance. It was also demonstrated that MC could be used as a novel active electrode by further increasing the adsorption capacity of the carbon shell. Under a moderate magnetic flux (Φ = 45 mT), the ASRR and charge efficiency reached 0.16 μm cm–2 min–1 and 94.3%, respectively. In addition, MC is mechanically and chemically robust and can be recovered and reused in long-term operation by magnetic separation. In brief, our study introduces a general strategy to enhance charge transport in suspension electrodes and demonstrates the promising potential of magnetic FCDI for efficient and low-cost desalination.

Synergistic Charge Percolation in Conducting Polymers Enables High‐Performance In Vivo Sensing of Neurochemical and Neuroelectrical Signals

Challenges remain in establishing a universal method to precisely tune electrochemical properties of conducting polymers for multifunctional neurosensing with high selectivity and sensitivity. Here, we demonstrate a facile and general approach to achieving synergistic charge percolation in conducting polymers (i.e., poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) by incorporating conductive catalysts (i.e., carbon nanotubes, CNTs) and post-processing. The approach shows synergistic effects: (i) CNTs and post-processing together promote PEDOT ordered interconnection for highly efficient charge percolation that accelerates electrochemical kinetics; (ii) CNTs catalyze the electrooxidation of vitamin C for selective electrochemical sensing; (iii) CNTs enhance the charge storage/injection capacity of PEDOT:PSS. The prepared CNT-PEDOT:PSS fiber mechanically matches with neural tissues and is proved to be a biocompatible versatile microsensor capable of high-performance neurosensing in vivo.