Charge Diffusion Research Articles

Chitosan Supports Boosting NiCo2O4 for Catalyzed Urea Electrochemical Removal Application.

Currently, wastewater containing high urea levels poses a significant risk to human health. Else, electrocatalytic methodologies have the potential to transform urea present in urea-rich wastewater into hydrogen, thereby contributing towards environmental conservation and facilitating the production of sustainable energy. The characterization of the NiCo2O4@chitosan catalyst was performed by various analytical techniques, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Furthermore, the activity of electrodes toward urea removal was investigated by several electrochemical techniques. As a function of current density, the performance of the modified NiCo2O4@chitosan surface was employed to remove urea using electrochemical oxidation. Consequently, the current density measurement was 43 mA cm-2 in a solution of 1.0 M urea and 1.0 M KOH. Different kinetic characteristics were investigated, including charge transfer coefficient (α), Tafel slope (29 mV dec-1), diffusion coefficient (1.87 × 10-5 cm2 s-1), and surface coverage 4.29 × 10-9 mol cm-2. The electrode showed high stability whereas it lost 10.4% of its initial current after 5 h of urea oxidation.

Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings.

We present low-temperature magnetotransport measurements on selectively grown Sb2Te3-based topological insulator ring structures. These devices display clear Aharonov-Bohm oscillations in the conductance originating from phase-coherent transport around the ring. The temperature dependence of the oscillation amplitude indicates that the Aharonov-Bohm oscillations originate from ballistic transport along the ring arms. We attribute these oscillations to the topological surface states. Further insight into the phase coherence is gained by comparing with similar Aharonov-Bohm-type oscillations in topological insulator nanoribbons exposed to an axial magnetic field. Here, quasi-ballistic phase-coherent transport is confirmed for closed-loop topological surface states in the transverse direction enclosing the nanoribbon. In contrast, the appearance of universal conductance fluctuations indicates phase-coherent transport in the diffusive regime, which is attributed to bulk carrier transport. Thus, it appears that even in the presence of diffusive p-type charge carriers in Aharonov-Bohm ring structures, phase-coherent quasi-ballistic transport of topological surface states is maintained over long distances.

Hetero-structural and hetero-interfacial engineering of MXene@Bi2S3/Mo7S8 hybrid for advanced sodium/potassium-ion batteries

Herein, heterogeneous bimetallic sulfides Bi2S3/Mo7S8 nanoparticles anchored on MXene (Ti3C2Tx) nanosheets (MXene@Bi2S3/Mo7S8) were prepared through a solvothermal process and subsequent chemical vapor deposition process. Benefiting from the heterogeneous structure between Bi2S3 and Mo7S8 and the high conductivity of the Ti3C2Tx nanosheets, the Na+ diffusion barrier and charge transfer resistance of this electrode are effectively decreased. Simultaneously, the hierarchical architectures of Bi2S3/Mo7S8 and Ti3C2Tx not only effectively inhibit the re-stacking of MXene and the agglomeration of bimetallic sulfides nanoparticles, but also dramatically relieve the volume expansion during the periodic charge/discharge processes. As a result, the MXene@Bi2S3/Mo7S8 heterostructure demonstrated remarkable rate capability (474.9 mAh/g at 5.0 A/g) and outstanding cycling stability (427.3 mAh/g after 1400 cycles at 1.0 A/g) for sodium ion battery. The Na+ storage mechanism and the multiple-step phase transition in the heterostructures are further clarified by the ex-situ XRD and XPS characterizations. This study paves a new way to design and exploit conversion/alloying type anodes of sodium ion batteries with hierarchical heterogeneous architecture and high-performance electrochemical properties.

Enhanced rate and specific capacity in nanorod-like core-shell crystalline NiMoO4@amorphous cobalt boride materials enabled by Mott-Schottky heterostructure as positive electrode for hybrid supercapacitors

The supercapacitor electrode materials suffer from structure pulverization and sluggish electrode kinetics under high current rates. Herein, a unique NiMoO4@Co-B heterostructure composed of highly conductive Co-B nanoflakes and a semiconductive NiMoO4 nanorod is designed as an electrode material to exert the energy storage effect on supercapacitors. The formed Mott-Schottky heterostructure is helpful to overcome the ion diffusion barrier and charge transfer resistance during charging and discharging. Moreover, this crystalline-amorphous heterogeneous phase could provide additional ion storage sites and better strain adaptability. Remarkably, the optimized NiMoO4@Co-B hierarchical nanorods (the mass ratio of NiMoO4/Co-B is 3:1) present greatly enhanced electrochemical characteristics compared with other components, and show superior specific capacity of 236.2 mA h g−1 at the current density of 0.5 A g−1, as well as remarked rate capability. The present work broadens the horizons of advanced electrode design with distinct heterogeneous interface in other energy storage and conversion field.

Titanium dioxide (TiO2) and gel-polymer solar cells

This research focuses on the study of semiconductor-based solar cells utilizing titanium dioxide (TiO2) and gel-polymer electrolytes. The technology for preparing the electrolytes used in these solar cells has been developed, encompassing both liquid and gel polymer electrolyte compositions. The electrochemical impedance method is employed to determine important parameters such as diffusion coefficient, mobility, and charge carrier concentration in both liquid and gel-polymer electrolytes. Experimental results are compared with theoretical calculations utilizing the electrochemical impedance spectroscopy graph. Moreover, the photon-to-current conversion efficiency of the semiconductor-based solar cells is determined using the Incident Photon to Current Conversion Efficiency (IPCE) method, covering a wavelength range of 300 nm to 900 nm.

First Study of a HEXITEC Detector for Secondary Particle Characterisation during Proton Beam Therapy

Online proton range verification is a rapidly emerging field characterised by its ability to reduce the error margins during proton beam therapy, as it is patient-specific and in vivo. In particular, secondary prompt gamma detection is a promising tool to monitor the dose delivery. The present research evaluates the capability of a HEXITEC detector to identify the prompt gammas produced during proton beam therapy, and assesses its potential for online range verification. To achieve this, the detector is placed at one side of a water phantom, which is irradiated at different proton energies in the University College London Hospital Proton Centre. For further analysis, Monte Carlo simulations are performed using Geant4 and the same geometry as the experiment. The results show that HEXITEC has the potential to be part of a detection system that could identify secondary prompt gammas within the secondary field produced inside the target, allowing for the in-detector discrimination of these particles via cluster size analysis. The comparison between data sets shows that there is a high level of accuracy between the model and the experimental measurements in terms of secondary flux and charge diffusion inside the detector, which poses the model as a fundamental tool for future optimisation studies.

Eu(III) and Am(III) adsorption on aluminum (hydr)oxide minerals: surface complexation modeling

Americium is a highly radioactive actinide element found in used nuclear fuel. Its adsorption on aluminum (hydr)oxide minerals is important to study for at least two reasons: (i) aluminum (hydr)oxide minerals are ubiquitous in the subsurface environment and (ii) bentonite clays, which are proposed engineered barriers for the geologic disposal of used nuclear fuel, have the same ≡AlOH sites as aluminum (hydr)oxide minerals. Surface complexation modeling is widely used to interpret the adsorption behavior of heavy metals on mineral surfaces. While americium sorption is understudied, multiple adsorption studies for europium, a chemical analog, are available. In this study we compiled data describing Eu(III) adsorption on three aluminum (hydr)oxide minerals—corundum (α-Al2O3), γ-alumina (γ-Al2O3) and gibbsite (γ-Al(OH)3)—and developed surface complexation models for Eu(III) adsorption on these minerals by employing diffuse double layer (DDL) and charge distribution multisite complexation (CD-MUSIC) electrostatic frameworks. We also developed surface complexation models for Am(III) adsorption on corundum (α-Al2O3) and γ-alumina (γ-Al2O3) by employing a limited number of Am(III) adsorption data sourced from literature. For corundum and γ-alumina, two different adsorbed Eu(III) species, one each for strong and weak sites, were found to be important regardless of which electrostatic framework was used. The formation constant of the weak site species was almost 10,000 times weaker than the formation constant for the corresponding strong site species. For gibbsite, two different adsorbed Eu(III) species formed on the single available site type and were important for the DDL model, whereas the best-fit CD-MUSIC model for Eu(III)-gibbsite system required only one Eu(III) surface species. The Am(III)-corundum model based on the CD-MUSIC framework had the same set of surface species as the Eu(III)-corundum model. However, the log K values of the surface reactions were different. The best-fit Am(III)-corundum model based on the DDL framework had only one site type. Both the CD-MUSIC and the DDL model developed for Am(III)-γ-alumina system only comprised of one site type and the formation constant of the corresponding surface species was ~ 500 times stronger and ~ 700 times weaker than the corresponding Eu(III) species on the weak and the strong sites, respectively. The CD-MUSIC model for corundum and both the DDL and the CD-MUSIC models for γ-alumina predicted the Am(III) adsorption data very well, whereas the DDL model for corundum overpredicted the Am(III) adsorption data. The root mean square of errors of the DDL and CD-MUSIC models developed in this study were smaller than those of two previously-published models describing Am(III)-γ-alumina system, indicating the better predictive capacity of our models. Overall, our results suggest that using Eu(III) as an analog for Am(III) is practical approach for predicting Am(III) adsorption onto well-characterized minerals.Graphical

Fluorocarbon Surfactant‐Assisted Large‐Area Uniform and Water‐Resistant Perovskite Films for Efficient Photovoltaics

Formamidinium (FA)‐based lead triiodide perovskites are suitable light‐absorbing materials for solar cells due to their narrow bandgap, long‐range charge diffusion length, and excellent thermal stability. However, large‐area uniformity and phase purity are still challenging issues in the two‐step solution processed perovskite films because of the incomplete spreading/reacting of the organic amine salt solution. Herein, a novel multifunctional nonionic fluorocarbon surfactant (FS) is introduced to improve the crystallization of perovskites via the strategy of reducing the surface tension of the organic amine salt solution and facilitating the adequate binding of the organic amine salts with PbI2. Moreover, the FS additives effectively reduce residual PbI2; passivate the surface and interfacial defects of perovskites. The FS modified perovskite solar cells (PSCs) exhibit a champion power conversion efficiency (PCE) of 21.72% (0.16 cm2) with an enhanced stability, and the unencapsulated device maintains about 80% of the initial PCE even after 1000 h of storage. In addition, the larger PSCs with the active area of 1.00 cm2 deliver a peak PCE of 19.19%. Eventually, FS impedes moisture intrusion and effectively mitigates the decomposition of perovskite film. This work opens the way to explore large‐area PSCs with high performance and long‐term stability.

Calculating of square-wave voltammograms—a practical on-line simulation platform

Square-wave voltammetry (SWV) is a widely used technique for getting insight into mechanistic and kinetic aspects of various electrochemical reactions. To date, this pulse-voltammetric technique has been utilized in numerous electrochemical studies and it remains one of the most sophisticated electrochemical methods available. As a result of its higher sensitivity and its potential to provide insights similar to cyclic voltammetry for electrode mechanisms characterization, the SWV is increasingly being included in undergraduate electrochemistry laboratory curriculums. The features of experimental SW voltammograms are affected by various factors, such as kinetics of charge transfer, diffusion, adsorption phenomena, and chemical reactions coupled to electron transfer step. To understand some of the physical and chemical phenomena hidden in a single experimental SW voltammogram, it is inevitable to get a help of computer simulations. The purpose of this article is to offer a basic introduction to SWV written in a simple language, intended to engage students and familiarize them with the fundamentals of this technique. The ultimate objective is to provide the aspiring young electrochemists with a simulation procedure using the MATHCAD software, which can be employed to compute SW voltammograms following a rather easy simulation approach. A detailed tutorial on simulating SW voltammograms with MATHCAD software is presented. The simple tutorial offers a step-by-step breakdown of the simulation process of a square-wave voltammogram. Additionally, a MATHCAD ready-to-use file for simulation of a common electrode mechanism is provided. The current work aims to assist undergraduate students in learning about electrochemical simulations that serve as a corner stone to more advanced studies in SWV.

Understanding the oxygen reduction reaction of one-dimensional Ca3Co2O6 cathodes for SOFC

Understanding the processes of different cathode materials is part of the journey toward the development of intermediate-temperature solid oxide fuel cells. In this work, the one-dimensional Ca3Co2O6 (C326) electrode and its composite with Ce0.9Gd0.1O2-δ (CGO) are systematically investigated as a function of sintering temperature using a symmetrical cell test. For both batches of samples, the optimum sintering temperature is 1000 °C. Interpretation of the impedance spectra reveals that this optimization is associated with improvements in the processes of surface diffusion and interfacial charge transfer due to the higher effective reaction area for ionic transfer at the electrode/electrolyte interface and better connectivity between the electrode grains. The temperature dependence of the individual processes indicates that the addition of CGO significantly improves the steps of dissociative oxygen adsorption and diffusion, which should occur first on its surface, with the charge transfer of oxygen species at the CGO/C326 boundary being the rate-limiting step.

Transient Nyquist Diagram for Fuel Cells

Transient Nyquist diagrams were calculated by significantly changing the load current of polymer electrolyte fuel cells (PEFCs) while a perturbation current of a constant amplitude of ±2 A (±0.04 A cm−2) was simultaneously applied to the load current. The frequencies used for the calculation ranged from approx. 0.38 Hz to approx. 10 kHz, the number of noise-reduced impedance points was 255, and the measurement time was approx. 2.6 s. Fast Fourier Transform (FFT) electrochemical impedance spectroscopy (EIS) was used to calculate the impedance, and the ergodic hypothesis was used for noise reduction. Instead of a time-averaged impedance, this method uses an ensemble average of impedances with different frequencies (quasi-ensemble-median). The load current was changed in the form of a step or ramp, or in a form equivalent to the US06 drive cycle. The obtained transient Nyquist diagrams were arc-shaped, similar to those obtained by the usual FRA method, and altering RH did not change their shape. For the step response and US06 drive cycle, a local increase in impedance was observed when the load current increased sharply. This is believed to be caused by an increase in gas diffusion resistance or charge transfer resistance.

2D Fluid Modeling of Light Pumped Na Containing Plasma to Develop a Prototype of a Photo Electromotive Force Converter

The development of innovative technologies for direct solar energy conversion is one of the main trends of modernity. The use of solar semiconductor panels is well-known in solar photovoltaics. As an alternative to this, the use of gas photoplasma can be promising. However, research in this direction is still very fragmentary so far. This paper shows the results of a systematic study of photoplasma in mixtures of sodium and inert gases to obtain photo-EMF in a gas cell. A fluid modeling considering detailed plasma chemistry, radiation transfer, and charge diffusion processes and 2D simulation were fulfilled and main plasma parameters were obtained and analyzed. In particular, non-trivial dependence of EMF in a two-chamber gas cell containing sodium and argon on the pressure of the inert gas was obtained, reaching up to 1.3 eV by absolute value at 100 Torr of Ar and changing its sign near 5 Torr at the decrease of the pressure.

A fast numerical method with non-iterative source term for pseudo-two-dimension lithium-ion battery model

In this work, a fast numerical method with non-iterative volumetric source for pseudo-two-dimensional (P2D) model is proposed for lithium-ion batteries and has been implemented in the open-source software OpenFOAM. The direct determination of the precise potential distribution is enabled by correct boundary conditions derived from the Butler-Volmer equation and charge conservation, due to the mathematical characteristic of the Laplace equation and the small grid scale involved. This method eliminates repeated iterations to obtain the accurate volumetric source distribution for each step required by the sequential full-order model (SFOM) method. The numerical solving boundary conditions coincide with those of the conventional P2D model in terms of physical meaning. Nevertheless, some innovations were introduced to render it more computationally efficient. We integrated this method into OpenFOAM, and applied it to typical examples with the same parameters as COMSOL Multiphysics, the output results were found to match almost completely with the latter. This method holds tremendous promise for practical application in battery design. It accurately represents chemical processes within the battery, including mass and charge transfer, migration and diffusion. Additionally, it improves efficiency over the full-order P2D model.

Surface-enhanced fully nanofiber-based self-cleanable ultraviolet resistive triboelectric energy harvester for wearable smart garments

Wearable triboelectric nanogenerators (TENGs) with high electrical performance have recently prompted great expectations. However, charge diffusion and recombination affect the electric field strength, resulting in a weak electrostatic potential in the displacement region. Current research on film-type dielectric interlayers indicates that charge trapping can prevent charge recombination, although surface charge air breakdown has not been addressed, and becomes a crucial demand in wearable energy applications. In the present study, the surface charge density of poly(vinylidene fluoride) (PVDF) nanofibers is greatly improved by co-electrospraying PDMS-PVDF (PDPV) charge-trapping microbeads; this new approach prolongs the lifetime of surface charges. In particular, the PDPV beads prevent charge recombination, and the interlocking mechanism enhances the tensile property of the PVDF nanofibers. These result in a two-fold increase in the open-circuit voltage and peak power density to 305 V and 124.3 mW m−2, respectively. The device is successfully employed in portable electronic gadgets. Ag-nanoparticle-grafted styrene-butadiene-styrene (SBS) fiber is used as an electrode because it has favorable stretchability with low resistance and is antibacterial. The addition of TiO2/multiwalled carbon nanotube to PVDF nanofiber membrane shows excellent electricfield-induced photocatalyst and ultraviolet protection. Our surface-enhanced fully fiber-based TENG is a promising energy harvester for flexible smart garments applications.

Exciton diffusion in amorphous organic semiconductors: Reducing simulation overheads with machine learning.

Simulations of exciton and charge hopping in amorphous organic materials involve numerous physical parameters. Each of these parameters must be computed from costly abinitio calculations before the simulation can commence, resulting in a significant computational overhead for studying exciton diffusion, especially in large and complex material datasets. While the idea of using machine learning to quickly predict these parameters has been explored previously, typical machine learning models require long training times, which ultimately contribute to simulation overheads. In this paper, we present a new machine learning architecture for building predictive models for intermolecular exciton coupling parameters. Our architecture is designed in such a way that the total training time is reduced compared to ordinary Gaussian process regression or kernel ridge regression models. Based on this architecture, we build a predictive model and use it to estimate the coupling parameters which enter into an exciton hopping simulation in amorphous pentacene. We show that this hopping simulation is able to achieve excellent predictions for exciton diffusion tensor elements and other properties as compared to a simulation using coupling parameters computed entirely from density functional theory. This result, along with the short training times afforded by our architecture, shows how machine learning can be used to reduce the high computational overheads associated with exciton and charge diffusion simulations in amorphous organic materials.

Modeling and Analysis of Polarization Losses in Solid Oxide Fuel Cells with Linear Siloxane Contamination

In this study, the degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetra-siloxane (L4) contamination is examined. A model is developed for the polarization losses based on the charge transfer coefficient, α, and diffusion layer thickness, į, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. Ohmic losses are dominant in the anode due to much higher anode thickness (380 µm) compared to electrolyte thickness (13 µm). Activation losses vary with α, which decreases from 0.31 to 0.25. Mass transport losses vary with both į and α, with įincreasing from 28 µm to 45 µm. The results of the model indicate that the total polarization losses increase for each subsequent time interval, with a total increase of approximately 45% from 0 to 180 min. Activation losses dominate the polarization losses initially but decrease in their total contribution while mass transport losses increase.

A Comparative Study of the Performance and Electrode Processes of Solid Oxide H2O Electrolysis and CO2 Electrolysis

Solid oxide CO2 electrolysis was less studied compared with H2O electrolysis and the relevant reaction mechanism and electrode processes were poorly understood. This paper investigated the performance and electrode processes differences between CO2 electrolysis and H2O electrolysis. The shape of j-V curves, electrochemical impedance spectroscopy data and calculated distribution relaxation time results were analyzed. It was found that the performance of CO2 electrolysis degraded the most compared with that in SOFC mode and for H2O electrolysis after a 65 h’ operation. Meanwhile, j-V curve of CO2 electrolysis changed a lot and finally showed a convex total resistance pattern with applied current. It was also found that the characteristic frequency of charge transfer reaction and diffusion process for CO2 electrolysis was much lower than that of H2O electrolysis. A thermal activated peak at 10-100 Hz which was not noted for H2O electrolysis was considered to be CO2 adsorption and dissociation process in fuel electrode. Besides, diffusion process for H2O-H2 and CO2-CO mixture also differed. Finally, it was indicated that the different performance degradation may be due to different suppressed degree of charge transfer reaction in fuel electrode for H2O electrolysis and CO2 electrolysis and additional suppressed adsorption or dissociation process of CO2 for CO2 electrolysis.

Biowaste-derived oxygen-self-doped three-dimensional interconnected porous carbon for electrochemical supercapacitor applications

ABSTRACT Biowaste for producing a biomaterial is an inexpensive, profuse, widely available, and viable natural source and has been extensively investigated and applied in a wide range of research fields. In this work, jackfruit leaf waste as a biowaste source was utilized to prepare a three-dimensional (3D) interconnected porous carbon framework self-doped with oxygen by KOH impregnation, carbonization, and activation under a CO2 atmosphere. The as-prepared porous carbon has a 3D interconnected porous framework with a rich oxygen content of 36.82%, and high BET surface area of 455.687 m2 g−1 with a pore volume of 0.522 cm3 g−1. The 3D interconnected porous framework exhibits a high specific capacitance of 199 F g−1 with a maximum energy density of 27.64 Wh kg−1 at a power density of 99.60 W kg−1 at a sweep rate of 1 mV s−1 in a two-electrode setup. The correlation between structure and great performance of electrode materials is deeply studied. The great capacitive performance of porous carbon materials can be assigned to its 3D interconnected porous framework, high specific surface area, suitable pore size distributions, and advantageous heteroatom-doping, resulting in the rapid ion diffusion and sufficient charge storage along with the contributed pseudocapacitance behavior. Hence, the exciting results reveal an efficient, cost-effective, time-saving, and facile method to prepare 3D interconnected porous carbon frameworks self-doped with oxygen derived from natural biowaste sources for developing supercapacitor devices.

126 A Laboratory Procedure and a Recording System for the Maintenance of Personal, Hand-Held and Benchtop Time-Resolved Aerosol Instruments

Abstract The HSE Science and Research Centre use time-resolved instruments to collect aerosol data for research and to support the sampling of aerosols in workplace environments. The performance of these instruments (traditional and low cost sensor devices) is dependent on regular maintenance and calibration. However, it can deteriorate within the recommended manufacturer calibration period, particularly if they have been exposed to high concentration of dust, or exposed for extended periods. This poster will describe the practical strategy developed at HSE for the maintenance of time-resolved devices and the lessons learnt. HSE owns a range of hand-held or compact time-resolved instruments, which are optical particle counters (OPCs), condensation particle counters (CPCs), diffusion chargers as well as photometers measuring particle number, surface area and mass concentrations. Some of the instruments are size-resolved devices. Photometers and OPCs were benchmarked using SPHERIGLASS ® A- 5000 in a calm-air chamber for a wide range of concentrations against a dedicated reference photometer or OPC, not necessarily of the same model or size range characteristic. For devices, measuring in the nanometre size range (CPCs and Diffusion Chargers), a salt nanoparticle aerosol was generated using a Collison nebulizer and a CPC used as the reference. Acceptable tolerances from the reference concentration were established for the CPCs and Diffusion Chargers. For each photometer model, an average ratio of the evaluated photometers concentrations by the reference photometers concentrations was calculated and a linearity plot of the photometer concentration versus the reference photometer concentration was established. © Crown Copyright (2022)

Bias Reconfigurable Photoresponse of an Infrared Nanocrystal Film Integrated into a Coupled Fabry-Perot Resonator

The coupling of a photonic structure to a nanocrystal film enables light focusing over a distance compatible with the charge diffusion length. This strategy has been implemented in infrared sensors based on nanocrystal films to maximize their absorption. Here, we demonstrate that the photonic structure can be further exploited to generate a bias-reconfigurable photoresponse. To reach this goal, we use a coupled Fabry-Perot structure that can be seen as a periodic grating with two different cavities per period. The two cavities are coupled and a resonance appears, increasing the effective absorption coefficient by a factor of 30 compared to standard interdigitated electrodes. When connected in the appropriate configuration, this device enables the turning-on and -off of part of the spectral response (over a factor of 25 in magnitude) simply by tuning the applied bias (<1 V). Finally, we also demonstrate that this resonator geometry is promising for integration at the focal plane array level since the resonance is maintained for a pixel size as small as 10 μm.