Uniform Current Distribution Research Articles

Far-zone analytical expressions for electromagnetic waves produced by a uniform-current loop placed in a uniaxial dielectric-magnetic material

We investigate the radiation generated by a current loop situated within an unbounded uniaxial dielectric-magnetic material characterized by a uniform current distribution. We employ dyadic Green functions in the frequency domain to derive closed-form expressions for the far-field radiation. Our analytical findings distinguish between two scenarios: one in which the loop’s axis aligns parallel to the optic axis and another where it is perpendicular to the optic axis. In cases where the loop’s axis parallel’s the optic axis, only magnetically extraordinary wave is emitted as a consequence. However, when the loop’s axis is perpendicular to the optic axis, both electrically and magnetically extraordinary waves are emitted. Our results demonstrate a pronounced dependence of the radiation pattern on the loop’s size, as observed for various loop radii.

Resistance bias estimation of a liquid column in a cylindrical conductivity cell with lateral liquid supply

The article shows a physical model of a cylindrical two-electrode conductivity cell with inlet and outlet holes for filling located perpendicular to the cell axis. Based on the finite element method (FEM), the non-uniformity of the current density distribution inside the cell was determined. For a range of geometrical parameters of the cell, the resistance biases of the liquid column with respect to the idealized model—a cell with a uniform current density distribution (without holes) are calculated. A mathematical expression is given that describes calculating the electrolytic conductivity value using the geometrical parameters of a conductivity cell, taking into account the field distortion caused by holes for filling. It has also been found that at the ratio of the cell diameter to the hole diameter D/d ≥ 5, the entire field distortion inside the cell is provided by a liquid column in the holes with a length of only (h ≤ d) mm. Theoretical estimates and mathematical models covered in this article were used to create the primary differential conductivity cell. Structurally, such a cell consists of two tubes of the same diameter but of different lengths, at the edges of which platinized electrodes are placed.

Development of Membrane Electrode Assembly with Double-Catalytic Layer for Micro Direct Methanol Fuel Cell

This paper presents a membrane electrode assembly (MEA) with a double-catalytic layered structure to improve the performance of the micro direct methanol fuel cell. The inner and outer parts of the double-catalytic layer comprise an unsupported and carbon-supported catalyst, respectively. A two-dimensional two-phase model of mass transport and electrochemical reaction is established and simulated to analyze the superiority of the double-catalytic layered structure. Simulation results show that this structure has a more uniform current density distribution and less over-potential across the catalyst layer. Methanol crossover is also reduced. Experimental results confirm that the MEA with the double-catalytic layered structure exhibits better performance than the traditional MEA. The adoption of a gas diffusion electrode as the outer catalytic layer and a catalyst-coated membrane as the inner layer of the double-catalytic layered structure can further improve the performance of the MEA. Both simulation and experimental results show the existence of an optimum number of metal loadings of the inner and outer parts of the double-catalytic layer.

Investigating the transient electrical behaviors in PEM fuel cells under various platinum distributions within cathode catalyst layers

The spatial distribution of platinum (Pt) within the cathode catalyst layer (CCL) is vital for the electrochemical reactions and mass transport in fuel cells. Though important, the transient effects of these distributions are seldom explored. This study examines the impact of Pt distribution on transient electrical behaviors, including voltage and local current distribution (LCD) uniformity, using a transient, two-dimensional, two-phase, non-isothermal fuel cell model that incorporates catalyst agglomerate. Three Pt distribution types are investigated: uniform, MPL-side biased, and PEM-side biased. Results indicate a voltage undershoot occurs during current loading. Compared to the homogeneous CCL, PEM-side bias reduces this undershoot by 12.5% due to shortened proton transfer paths and decreased ohmic loss, while MPL-side bias increases it by 18.8% due to the inverse effect. Additionally, Pt distribution affects both oxygen transport and reaction resistance within the agglomerate, influencing LCD uniformity. Under loading conditions, gradient CCLs show inferior LCD uniformity than homogeneous ones. Peak non-uniformity values of 0.22, 0.59, and 0.71 are observed for homogeneous, MPL-biased, and PEM-biased CCLs, respectively. From the perspective of voltage and LCD uniformity, the MPL-side biased CCL is not found to enhance dynamic characteristics, whereas the PEM-side bias improves voltage undershoot but at the cost of LCD uniformity. This study provides a novel perspective on fuel cell dynamics, emphasizing the transient effects of Pt distribution and their potential for optimizing dynamic performance by adjusting the Pt gradient.

Improvement of current crowding effect in VCSEL arrays with non-uniform oxidation aperture design

A compact electro-opto-thermal model of 2-D vertical cavity surface emitting laser (VCSEL) arrays considering the current crowding effect in each array cell is established to study the impact of oxidation aperture on the device performance. Simulated results shows that increasing oxidation aperture of array cell is helpful to improve the uniformity of current density distribution. With careful design of non-uniform oxidation aperture layout, both the uniformity of the temperature distribution and the current distribution is improved by 36.52% and 42.08%, respectively. Furthermore, 3×3 VCSEL arrays with uniform oxidation aperture (array-1) and non-uniform oxidation aperture (array-2) are fabricated and the L-I-V curves of two types of VCSEL arrays at different biases are also measured. The peak output optical power of array-2 is enhanced to 1.83mW with an improvement of 8.91% when compared with that of array-1. Moreover, the total optical output power of array-2 is always superior to that of array-1 over a wide bias current range.

A numerical study of fuel recirculation in ammonia-fueled solid oxide fuel cell stacks

Fuel recirculation is a system configuration designed to improve the fuel utilization of fuel cells by recirculating the unreacted fuels at the outlet to the fuel inflow stream. In this study, fuel recirculation of a solid oxide fuel cell (SOFC) operated with ammonia is investigated. Recirculation operation results in a notable elevation of nitrogen content within the cell, originating from the decomposition of ammonia within the cell and subsequently reintroduced into the inflow stream. Therefore, the fuel flow rate needs to be increased to maintain the fuel utilization level the same as the base operation, which is an ammonia-fueled operation without recirculation. A multiscale model of an SOFC stack is used to compare the base operation and saturated level of the recirculation operation cases based on their polarization curves and distributions of ammonia, hydrogen, current density, temperature, first principal stress, and nitriding in the fuel electrode. The results show that overall stack performance, as reflected in the polarization curves, remains comparable between the base and recirculation operation cases. The power densities exhibit a difference of less than 2% between the base and recirculation operation cases. Moreover, it is indicated that the recirculation operation cases lead to more uniform hydrogen and current density distributions, lower temperature gradients, and lower thermal stresses. The results demonstrate that the recirculation operation cases lead to a reduction of up to 38% in the maximum tensile stresses within the fuel support layer. Nevertheless, these recirculation operation cases also induce nitriding across a larger portion of the active area. But as shown here this is a challenge that can effectively be addressed by applying nickel coatings to the inlet headers.

A novel in-tube reformer for solid oxide fuel cell for performance improvement and efficient thermal management: A numerical study based on artificial neural network and genetic algorithm

The pursuit of higher power density and compact structure presents a critical challenge to the thermal management of solid oxide fuel cell. In this study, a novel in-tube reformer is proposed and a Multi-physics simulation-Artificial neural network-Multi-objective genetic algorism based optimization framework is developed to improve the output performance and reduce the internal temperature difference in solid oxide fuel cell. First, a validated multi-physics model is developed for parametric simulation and generating dataset. Afterwards, a surrogate model is obtained by training an artificial neural network to predict the output performance and internal temperature field of solid oxide fuel cell. Finally, multi-objective genetic algorithm optimizations based on the surrogate model are performed to maximize the output performance and minimize the internal temperature difference under different operation strategies. It is found that compared to the conventional configuration (without in-tube reformer), the use of in-tube reformer can effectively promote the electrochemical reactions, increase the fuel utilization (up to 34.2%) and current density (up to 14.5%) while significantly reducing the maximum temperature difference (up to 85.5%) in the cell, resulting in a uniform current density and temperature distribution along the cell. The proposed novel in-tube reformer and optimization framework are demonstrated to be highly powerful and can be easily applied to other fuel cell/electrolyzer systems to effectively improve system performance and realize efficient thermal management under actual demands.

Potassium β–alanine – A promising agent for reducing carbon capture cost via electrochemically mediated amine regeneration

Electrochemically mediated amine regeneration (EMAR) for CO2 capture is a promising substitute for traditional organic amine–based CO2 capture by replacing the thermal process with electricity. To avoid problems such as oxidative degradation, toxicity, volatilization, and precipitation of organic amine absorbent, potassium β–alanine was suggested as an absorbent using EMAR process for the first time in this study. The CO2 absorption performance under different copper loading and chemical reactions were studied, and cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry and the Taffel extrapolation method were used to study the electrochemical characterization. Compared to the benchmark monoethanolamine (MEA) system, a smaller potential difference between oxidation and reduction peak was acquired in the potassium β–alanine system, of which the energy consumption was only 44.1% of the MEA system at the current of 100 A/m2. The cathode Faraday efficiency in the potassium β–alanine system was 101.9% higher than that in the MEA system at the current density of 25 A/m2. Furthermore, the result of scanning electron microscope of the electrode surface after desorption showed that potassium β–alanine absorbent improved the inhomogeneity of the electrode surface and was in favor of uniform current distribution. Overall, potassium β–alanine can be used as a more environmentally friendly absorbent in the EMAR system and has great potential to further reduce the actual energy consumption and improve the Faraday efficiency and cycling performance.

Evaluation of performance and mass transfer characteristics by applying oblique fin flow field to air-cooled PEMFCs under different ambient conditions

The choice of a suitable cathode flow field under varying ambient conditions (humidity and temperature) is essential for restraining mass transfer resistance and preventing localized overheating in air-cooled proton exchange membrane fuel cells (PEMFCs). To achieve this objective, this study recommends adopting a modified design that integrates tapered oblique fin (OF) channels into the ribs of the conventional parallel flow field. Subsequently, the superiorities of the modified design in terms of mass transfer capabilities and performance improvements under various ambient conditions are assessed compared to the conventional design through numerical analysis. The results show significant enhancements in mass transfer and cell performance with the modified design at higher humidity levels (e.g., 60 %-90 %). Besides, the modified design also achieves better performance in low air temperatures (e.g., 281.15 K-302.15 K). At an air temperature of 281.15 K, a maximum performance improvement of 9.34 % can be obtained. Air temperature and humidity both non-linearly affect current density distribution uniformity in the cathode CL. This is attributed to the complex interplay between water accumulation and oxygen transport under the ribs, coupled with convection phenomena within the OF channels. Moreover, the modified design more effectively enhances the temperature uniformity within porous electrodes at lower air temperatures.

Quantitative Field Emission Imaging for Studying the Doping-Dependent Emission Behavior of Silicon Field Emitter Arrays.

Field emitter arrays (FEAs) are a promising component for novel vacuum micro- and nanoelectronic devices, such as microwave power amplifiers or fast-switching X-ray sources. However, the interrelated mechanisms responsible for FEA degradation and failure are not fully understood. Therefore, we present a measurement method for quantitative observation of individual emission sites during integral operation using a low-cost, commercially available CMOS imaging sensor. The emission and degradation behavior of three differently doped FEAs is investigated in current-regulated operation. The measurements reveal that the limited current of the p-doped emitters leads to an activation of up to 55% of the individual tips in the array, while the activation of the n-type FEA stopped at around 30%. This enhanced activation results in a more continuous and uniform current distribution for the p-type FEA. An analysis of the individual emitter characteristics before and after a constant current measurement provides novel perspectives on degradation behavior. A burn-in process that trims the emitting tips to an integral current-specific ideal field enhancement factor is observed. In this process, blunt tips are sharpened while sharp tips are dulled, resulting in homogenization within the FEA. The methodology is described in detail, making it easily adaptable for other groups to apply in the further development of promising FEAs.

Electrochemical-Thermal Modeling of Large-Format, Thin-Film, Lithium-Ion Batteries with Cocurrent and Countercurrent Tab Connections Using a Reduced-Order Model

We derive and implement a new reduced-order model for the simulation of large-format, thin-film batteries with cocurrent and countercurrent tab connections. We employ the multi-site, multi-reaction (MSMR) framework to describe the solid phase thermodynamics as well as irreversible phenomena associated with diffusion and electrochemical reactions for a graphite negative and a spinel manganese oxide positive. The calculations are streamlined by using the reduced-order electrochemical model for a porous electrode derived by means of a perturbation analysis, which we term ROM1. For discharge rates less than 1 C, where the 1 C rate corresponds to the current needed to fully discharge the cell in 1 h, ROM1 yields accurate results for traction-battery electrodes. We employ ROM1 in the cell energy balance, with the overall results allowing one to clarify the current and temperature distributions within the cell during discharge and isolate and identify the different heat sources. The governing partial differential equations are coupled and nonlinear in part due to the temperature dependence of the physicochemical properties. We show how cocurrent tab locations yield higher cell energy densities, while countercurrent tab locations yield more uniform current and temperature distributions. Sensitivity analyses underscore the flexibility of the approach. Overall, the equation system and open-source (Python) software enables an efficient and rational tool for cell design and integration.

A 3D Lithiophilic Host for Dendrite-Free Lithium Metal Anode via One-Step Carbonization of an Energetic Metal-Organic Framework.

Low Coulombic efficiency (CE) and safety issues are huge problems that hinder the practical application of Li metal anodes. Constructing Li host structures decorated with functional species can restrain the growth of Li dendrites and alleviate the great volume change. Here, a 3D porous carbonaceous skeleton modified with rich lithiophilic groups (Zn, ZnO, and Zn(CN)2 ) is synthesized as a Li host via one-step carbonization of a triazole-containing metal-organic framework. The nano lithiophilic groups serve as preferred sites for Li nucleation and growth, regulating a uniform Li+ flux and uniform current density distribution. In addition, the 3D porous network functions as a Li reservoir that provides rich internal space to store Li, thus alleviating the volumetric expansion during Li plating/stripping process. Thanks to these component and structural merits, an ultra-low overpotential for Li deposition is achieved, together with high CE of over 99.5% for more than 500 cycles at 1mAcm-2 and 1mAhcm-2 in half cells. The symmetric cells exhibit a prolonged cycling of 900h at 1mAcm-2 . The full cells by coupling Zn/ZnO/Zn(CN)2 @C-Li anode with LiFePO4 cathode deliver a high capacity retention of 94.3% after 200 cycles at 1C.

Non-invasive current collectors for improved current-density distribution during CO2 electrolysis on super-hydrophobic electrodes

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.

Impact of Morphological Dimensions in Carbon‐Based Interlayers on Lithium Metal Anode Stabilization

AbstractLithium metal batteries (LMBs) offer high energy density and promise as a future technology. Yet, their adoption is hindered by safety concerns and cycle life stability, arising from Li dendrite formation, solid electrolyte interphase instability, and volume changes during cycling. In response to these challenges, carbon‐based materials have been utilized as an artificial interface layer for modifying the surface of copper current collector in LMBs. Among the diverse carbon‐based materials, 0D carbon, with its high specific surface area, is advantageous for enhancing Li ion transport rates and ensuring uniform current distribution. 1D carbon structures foster a network that facilitates Li ion diffusion, while 2D carbon establishes a protective layer, mitigating side reactions. 3D carbon structures promote Li deposition within their internal cavities, effectively controlling volume fluctuations. With this understanding, this review delves into the latest advancements in carbon‐based materials for modifying copper current collectors. It offers a detailed exploration of how each dimension of carbon‐based materials contributes to regulating Li deposition. Furthermore, the ongoing challenges and potential avenues in the development of carbon‐modified copper current collectors for LMBs are spotlighted, aiming to provide insightful guidance for the design of anode‐free Li metal batteries.

Investigation of the current density’s non-uniform distribution in dead-end PEMFC with multi-zone measurement methods

Uneven current density distribution in a proton exchange membrane fuel cell (PEMFC) can decrease the reactant and catalyst utilization, reduce the energy conversion efficiency of the whole fuel cell, and even lead to a shortened cell life. Therefore, studying current density distribution has a critical role in the research and development of PEMFC. To investigate the distribution of the proton exchange membrane fuel cells' local current density under different operating conditions, a single cell using the segmented cell technique consisting of 36 zones was designed. The results show that the maximum current density first appears at the outlet and then moves to the inlet. In addition, when the cell output is stable, the most negligible current density appears in the cell's middle area. The current density distribution was improved when the cell temperature was 50 °C. Compared with other operation temperatures (without cooling, 40 °C, 60 °C), the current density is decreased by 14.0 %, 9.8 %, and 40.6 %, respectively. At the same time, the cell voltage is increased by 10 %, 6.45 % and 22.22 %, respectively. Higher gas pressure is more favourable to improving cell performance and the uniformity of current density distribution. However, when the cathode gas pressure exceeds that of the anode, the reverse inverse current is pronounced in the middle of the cell at the starting process. The reverse duration of the 50 °C cell is reduced by 30 s (25.4 %) compared to the cell without cooling.

Quaternary AlInGaN/AlInGaN Polarization-Engineered Green Lights-Emitting Diodes by Using Inverted Trapezoidal Quantum Barriers

In this paper, a structure design using grading quaternary AlInGaN as inverted trapezoidal multiple quantum barriers is shown. This paper proposes an inverted trapezoidal structure in quantum barriers to decelerate the transmission of the electron which will enhance efficient carrier injection into the quantum wells and get a more uniform distribution of carriers. The polarization-matched AlInGaN/AlInGaN structures have less polarization and increase the overlap of electron and hole wave function, effectively improving the internal quantum efficiency and wall-plug efficiency, and making the In composition adjustable. The results show that the Inverted trapezoidal polarization-matched AlInGaN structure significantly improves the phenomenon of “green gap” and “green droop.” As a result, the new structure mitigates the droop ratio from 25.5% to 7%, and the LED power is increased from 59.95 mW to 109.68 mW at 200 mA. Finally, the device exhibits a uniform current distribution and greater radiative recombination while reducing resistance.

Surface modified by SnI2 boosts Dendrite-Free all-solid-state lithium metal batteries

Lithium metal is the most promising next-generation anode due to its extremely high theoretical specific capacity and lowest operation potential. However, the high reactivity of lithium brings about a series of side reactions and fast capacity decay. Moreover, the inevitably growth of lithium dendrite will cause short circuit or other safety issues. Here, an artificial mixed ionic/electronic SEI (solid electrolyte interphase) is designed by treating the lithium anode with SnI2 solution in a simple drop coating method. The artificial SEI can inhibit the dendrite growth by forming nuclear agent sites and enable uniform current distribution. Solid state electrolyte is further utilized to improve the safety of battery. The symmetrical cells can cycle for > 750 h at 0.2 mA cm−2. Notably, all-solid-state LiFePO4 (LFP)/Li battery can deliver excellent capacity remains 120.6 mAh g−1 after 1000 cycles at 1C with a higher Coulombic efficiency at 99.8%. These results may be also useful for the developing of high energy and high safety lithium metal batteries.

New biometric flow slab designed in proton exchange membrane fuel cell

The flow slab design is an important factor in the Proton Exchange Membrane Fuel Cells (PEMFCs) because of its significant impact on the system performance along with the manufacturing cost, as crucial for commercial applications. Therefore, the flow slab with a low-pressure drop, high uniformity, and excellent power performance is a topic of concern. In this study, a new biometric flow slab with an elbow and baffle is designed and compared with the conventional flow slabs under a series of studied cases. The results show that the power performance of the biometric flow slab is better than the conventional types of flow slabs. Here, the power density of 6182.43 W/m2 is obtained by the new biometric type of BFS2 and up to 37.36% of ratio to the type of parallel flow slab. That is to say, the new type of biometric flow slab has effectively avoided the sharp drops issue of the power density appearing in the type of parallel flow slab. Similarly, a lower pressure drop in the biometric type has been observed when compared to the serpentine flow slab. The results have also indicated a positive correlation between the oxygen diffusion flux and the current density distribution. It has also been observed that the more uniform oxygen diffusion flux distribution was supported, the more uniform current density distribution was obtained. The net power performance of the biometric flow slab at a working Vcell = 0.4 V has been increased up to 36.98% when compared to the parallel flow slab. Finally, the new type of biometric flow slab BFS2 seemed to be the better choice for its significant overall performance because of the reduced power loss and certified flow visualization. These findings could be useful for the improvement of the flow field design in PEMFC when applied in commercialization in the future.

The impact of lithiated active binder on Li-ion battery charge–discharge and rate capability, Part II: Mesoscale modeling of LCO based Half-cell

Even though thick electrodes are essential to increasing the energy density of LIBs, high current rates cause them to lose power density due to high polarization and ion depletion in the pore spaces. Mixed active binders with lithiated bound charges can improve the battery capacity and voltage at high C-rates, even compared to similar high concentrated electrolyte. The lithiated binders also provide a more uniform spatial distribution of intercalation reaction current, electric potential, and open circuit potential. The LIB half cell is modeled at mesoscale by taking into account the diffusion–reaction physics of the bound charge mixed electrolyte in active carbon-binder-domain (CBD), that accounts the dissociation of anionic ligands. Electrolyte in separator and active CBD are coupled by Donnan theory at the interface, and the reaction interfaces are modeled by the standard Butler–Volmer equation. By means of a thermodynamically consistent model and its implementation in a FEM code, we investigate the impact of particle distribution, electrode thickness, and separator thickness for both standard binder and active binder mixed cathodes in terms of ion depletion, current density, and electric potential. This mathematical model can also be extended to the modeling of ion conducting polymer electrolytes, gel polymers, and other conductive materials for battery applications.

Numerical Study on the Influence of Variable Section-Enhanced Mass Transfer Flow Field Design on PEMFC Performance Based on Underrib Convection Flow

The optimal design of variable section is a flow field optimization method that changes the pressure of the reacting gas in the flow channel by setting up a contraction surface in the flow channel, which is effective in improving many aspects of the proton exchange membrane fuel cell (PEMFC) performance. However, there are also problems such as uneven oxygen distribution in some of the flow channels, and the current density and net output power are not significantly improved. To find a balance among gas transfer efficiency, drainage capacity, uniformity of current density distribution, and output performance, this paper investigates the design of a variable cross-section-enhanced mass transfer flow field for PEMFC flow channel contraction by establishing a three-dimensional numerical model, starting from the sidewall width direction and the bottom height direction of the flow channel cross-section dimensions, in order to assess the effects of variable cross-section contraction at the bottom and sidewalls of the flow channel on the cell performance. The polarization curves, mass transfer capacity, current density distribution, and net output power of the variable cross-section contraction flow field are analyzed and compared with the straight flow field. On this basis, the optimum size parameters and operating parameter combinations are determined. Variable cross-sectional contraction flow field improves PEMFC output performance. The contraction of the variable cross-section contraction flow field at the sidewalls effectively improves reactive gas transfer efficiency and drainage capacity, improves current density distribution, and increases the net output power of the PEMFC. In particular, the sidewall contraction flow field has a 9.0% increase in power density, a 6.45% increase in the effective mass transfer coefficient (EMTC), a 6.52% increase in uniformity of current density distribution, and a 6.05% net power increment compared to the straight flow field, respectively. The best output performance, the highest oxygen concentration, and the lowest water concentration are achieved with a combination of parameters: number of sidewall contractions N = 6 , length L f = 6 mm , and width W f = 1.2 mm . And a wide range of air stoichiometry ratios are applied when the contraction of the variable cross-section contraction flow field is located at the sidewalls. Increasing the cathode stoichiometry ratio from 10 to 50 increased the cell power density by 25.5% and from 50 to 90 increased the cell power density by 9.5%. The simulation results can provide theoretical basis for the application of variable section flow field design for practical PEMFC.