Medium Current Density Research Articles

Numerical simulation of the effect of current density and cathode inlet humidity on the PEMFC with anode self-humidifying circulating

Abstract The use of circulating gas self-humidification for fuel cell anodes will reduce the use of external humidifiers, thus reducing the cost and layout space, so most fuel cells use the anode self-humidification cycle mode. However, there is little research on the 3D simulation of PEMFC considering the anodic self-humidification cycle. In this paper, a three-dimensional PEMFC model considering the anode self-humidification cycle was established to explore the effects of working current density and cathode inlet humidity on the fuel cell performance of the anode self-humidification cycle. The results show that in anode cycling mode, higher working current density has advantages, but the advantages of high cathode inlet humidity are not obvious, and the performance of low cathode inlet humidity is not bad in anode cycling mode. In anode cycling mode, it is recommended to use high current density between medium and high current density. Between medium and high cathode intake humidity, a medium cathode intake humidity is recommended.

Near-in-situ investigation of surface crack healing and strengthening mechanism of Ti-43.5Al-4Nb-1Mo-0.1B alloy by novel electroshock treatment

The Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy is prone to emerge surface cracks and other defects during processing and service, which will deteriorate the mechanical properties and fatigue life of the materials. In this work, a novel electroshock treatment (EST) for the surface crack repair and strengthening process has been proposed. Combined with near-in-situ experiments and theoretical analysis, the influence law and healing mechanism of different current densities and EST modes on the healing of surface cracks in the alloy were investigated. The scanning electron microscopy (SEM) near-in-situ observation reveals that the main factors influencing the healing of surface cracks relate to the time of energization, the current density, and the cracking angle. Meanwhile, the crack tip and locally bulging deflected positions are more likely to be healed in a short time under continuous EST mode and medium current density (75 A/mm2). The surface crack width at the calibration position decreases from 0.47 μm and 2.23 μm to 0 μm and 0.03 μm, respectively. The electron back scattered diffraction (EBSD) results show that the dislocation density increases around the surface crack healing area, and the dislocation density at the crack tip and away from the healing region is decreased and uniformly distributed after EST, which can further suppress the generation and propagation of the crack, resulting in a 20.1 % increase in tensile strength and a 40.3 % increase in fracture strain. Considering the coupling influence of the thermal and non-thermal effects of EST, a two-stage progressive atomic diffusion of thermal compressive stresses and crack bonding interfaces has been proposed to describe the evolution process of surface crack healing during EST.

Integrating natural tourmaline with energy conversion ability to magnetically assembled electrode: Boosted electrochemical oxidation wastewater treatment performance

Novel anodes are desirable in the development of electrochemical oxidation wastewater treatment (EOWT). Magnetically assembled electrode (MAE) is a novel modular electrode format that physically adsorbs magnetic particles (auxiliary electrodes, AEs) onto the main electrode (ME) by magnetic force which realizes an effective and sustainable EWOT process but puts a new requirement on AEs polarization. Therefore, tourmaline (Tml), a natural mineral with ferroelectricity, pyroelectricity, and piezoelectricity, was introduced into the MAE in this study. Tml particles were expected to utilize waste heat or mechanical energies in electrolysis (e.g., Joule heat, bubble strike) and give extra electricity to the stacked AEs (Fe3O4/Sb-SnO2 granules herein) to fully active MAE. Tml’s effects were investigated via different MEs (Ti/IrO2-Ta2O5, graphite, Ti/Sb-SnO2), different wastewater, different Tml sizes, loading amounts, and different conditions (e.g., current density). Results show that all these conditions could affect the buffering of Acid red G degradation, Tml could offer a 10∼40% buff. Medium Tml size and loading as well as low or medium current density (e.g., 2 mA·cm−2 or 20 mA·cm−2) are appropriate. For real wastewater degradation, Tml facilitates macromolecule destruction. This study may start a new application route of abundant natural energy-converting materials in the EOWT area.

(Invited) Electrochemical Construction of 3-D Catalyst Layer on Ordered Liquid-Gas Diffusion Electrode for Highly Stable and Cost-Efficient PEM Water Electrolyser

Proton exchange membrane (PEM) water electrolyser is an ideal way to produce green hydrogen with intermittent renewable energy. The high cost of noble metal in membrane electrode assembly is one of the key problems to be solved for its commercial applications. Developing 3-D electrode with high utilization of noble metal and prominent performance of mass diffusion is a promising solution.In this work, titanium foil with ordered openings is applied as liquid-gas diffusion layer (LGDL) for anode by photolithography. And 3-Dimensional structural catalyst layer (CL) is coated by controlled pulse electrodeposition. By adjusting the concentration of electrolyte, current density and pulse parameter, catalyst layer with structure of nanowires, nano-urchin and nano-flower can be obtained. With medium current density of 5 mA/cm2, a structure variation from nanowire to nano-urchin could be observed by prolonging the electrodepositing time. While high current density of 20 mA/cm2 was applied, catalyst layer with nano-flower structure was formed. However, similar morphology could not be observed when a flat titanium foil was used as substrate. The controlling mechanism would be studied with scanning electrochemical microscopy to unveil the key controlling issue, such as distribution of local current and steric effect of released gas. The single cell performance with nano-urchin CL coated ordered LGDL as anode electrode was studied. Though coverage of anode electrocatalyst on PEM is only 45% as the porosity of order LGDL is 55%, the single cell performs excellent activity and stability due to the high surface area, enhanced mass diffusion and structural stability of 3-D CL. With optimized loading of 0.25 mgIr /cm2, initial performance of 1.795 V@ 1 A/cm2 can be obtained. And a prominent performance on stability with decay rate of 4.17 μV/h is shown after 4000h running under 1A/cm2 at 80 ℃. It is predictable that, by further adjusting the pore diameter and porosity of order LGDL to optimize the area of electrocatalyst/membrane interface and mass diffusion, the performance could be further improved to fulfill long-term operation under high current density (＞2A/cm2). Figure 1

High-Entropy Composite Coating Based on AlCrFeCoNi as an Anode Material for Li-Ion Batteries

In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g−1. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g−1, an incredible discharge capacity of 543 mAh g−1 was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries.

The influence of current density dependent Li2CO3 properties on the discharge and charge reactions of Li-CO2/O2 battery

As a promising energy storage technology, Li-CO2/O2 batteries not only deliver ultrahigh discharge capacity but also capture and convert CO2 into renewable energy. The exploration into the deposition and decomposition kinetics of discharge product (Li2CO3) is urgent for the high thermodynamic stability. Herein, the influence of current density on the essential characteristics of Li2CO3 has been explored. The results show that the Li2CO3 with poor crystallinity and elliptical disk morphology can be obtained at medium current density, corresponding to the excellent electrochemical performance including ultrahigh capacity of 5800 mA h/g, lower discharge-charge gap of 1.15 V, and long-term cycle life of 80 cycles. In addition, the morphology and crystallinity of Li2CO3 are tailored by the relative energy barriers for electron migration and O2- generation. At a medium current density (500 mA/g), the accelerated electron migration can realize the nucleation rate equivalent to growth one of Li2CO3. At this time, Li2CO3 will uniformly deposit on the cathode surface, forming elliptical disk morphology with poor crystallinity. Obviously, this work provides new sights for promoting the development of Li-CO2/O2 battery through rational design of catalysts to accelerate the deposition and decomposition processes of Li2CO3.

Combined effect of channel to rib width ratio and gas diffusion layer deformation on high temperature – Polymer electrolyte membrane fuel cell performance

The present study investigates the combined influence of Channel to Rib Width (CRW) ratio and clamping pressure on the structure and performance of High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) using a three-dimensional numerical model developed previously. It also considers the impact of interfacial contact resistance between the Gas Diffusion Layer (GDL) and Bipolar Plate (BPP). The structural analysis of the single straight channel HT-PEMFC geometry shows that the von-Mises stress greatly increases in the GDL under the ribs as the CRW ratio increases resulting in considerably high deformation. The cell performance analysis depicts the significance of ohmic resistance and concentration polarization for different CRW ratios, particularly at higher operating current densities. However, in low to medium current density regions, the CRW ratio has little influence on cell performance. A substantial impact on the species, overpotential, and current distributions is observed. The findings also reveal that the CRW ratio significantly affects the temperature distribution in the cell.

Three-Dimensional Numerical Study of the inlet Temperature Effects on the Performance of Planar PEMFCs

In the present study, a CFD (computational fluid dynamics) three-dimensional model is performed to investigate the effects of the inlet temperature on the power density, pressure and local transport phenomena of a single cell PEMFC (proton exchange membrane fuel cell) with straight channels. Deferent inlet temperatures of the reactants (333, 343 and 353 K) have been investigated using ANSYS-FLUENT. The interest of our work is focused on obtaining I-P and I-V curves as well as the pressure, hydrogen, oxygen and water mass fraction profiles to analyze the effect of the oxygen and hydrogen inlet temperature on the current, voltage and power densities of the studied PEMFC. From the results obtained its appears that the variation in the inlet temperature values of the PEMFC has a significant influence on the cell performances at medium and higher current density. Therefore, the results analysis of the three-dimensional and single-phase model indicates that the increase in the reactants’ inlet temperature of the studied PEMFC shows a negative impact on the generated power densities, which have an inversely proportional effect.

Numerical investigation of design and operating parameter effects on permeability-differentiated alkaline fuel cell with metal foam flow field

• Effect of design and operating parameters are investigated and optimized numerically. • Temperature and pressure have different effect in different current density regions. • Anode metal foam thickness has significant effect while cathode is negligible. • Lower anode and higher cathode permeability lead to better performance. • Permeability-differentiated layout of metal foam flow fields is originally proposed. Metal foam (MF) material is recognized as an attractive flow field for the alkaline anion exchange membrane fuel cell (AAEMFC). In this paper, the effect of design parameters (MF thickness and permeability) and operating parameters (operating temperature and back pressure) are investigated and optimized through the numerical study. The maximum temperature of the AAEMFC with MF flow field is lower and temperature distribution is more uniform compared to that of AAEMFC with serpentine flow field. In general, the higher operating temperature decreases the cell performance slightly in the low current density region but enhances the cell performance obviously in the medium and high current density regions. The higher back pressure promotes the cell performance in the low current density region but decreases the cell performance in the high current density region. The anode MF thickness has the significant effect on the cell performance, and the thinner anode MF thickness benefits the cell performance. However, the effect of cathode MF thickness is relatively negligible. The lower permeability of the anode MF and higher permeability of cathode MF lead to the better performance. The permeability-differentiated layout of MFs in anode and cathode sides is proposed for the first time, and it is proven to improve the cell performance effectively due to the enhanced hydraulic permeation and membrane hydration. Electrochemical kinetics, thermal and water transport characteristics (including pressure drop, liquid water transport, membrane water distribution and ohmic loss) are analyzed in detail to explain the cell performance improvement.

Modeling of PEMFC and Analysis of Multiple Influencing Factors on Output Characteristics

The output characteristics of the Proton-Exchange Membrane Fuel Cells (PEMFCs) are affected by multiple factors, but quantitatively describing the relationships is challenging. In this paper, a semi-empirical dynamic model of PEMFC is established firstly. The influence of a single factor on the output characteristics of PEMFC is analyzed longitudinally. Then, a derivative significance weight analysis based on support vector regression (SVR-DSWA) algorithm is proposed to analyze the influence weights of multi-factors on the output characteristics, and the optimal parameters combinations in different current density regions are obtained by maximizing the output voltage values based on formulated SVR model. The Root-Mean-Square Error (RMSE) of output voltage prediction results based on the SVR algorithm is less than 0.0458, and the accuracy of weight analysis results by using the SVR-DSWA algorithm and the optimal parameters combinations analysis method are verified by 4-factor 3-level orthogonal experiments in low, medium, and high current density regions. The SVR-DSWA algorithm and optimal parameters combinations analysis method can replace the orthogonal experiment to analyze the influence weights and optimal combinations of input factors on the output characteristics within the full current density range rapidly, and has much higher efficiency than the orthogonal experiment. The analysis results can provide theoretical support for improving fuel cell performance and formulating a control strategy.

A new zinc-ion battery cathode with high-performance: Loofah-like lanthanum manganese perovskite

Due to high safety and excellent rate performance, the aqueous Zn-ion battery is a promising energy storage battery for practical application. However, most manganese-based compounds suffer from poor cycling and rate performance. Herein, a new concept of Zn-ions battery is assembled with the loofah-like LaMnO3 perovskite as a novel cathode, achieving fast ion kinetics through the co-intercalation of Zn2+ and H+ cations. In this work, the Ni-doping strategy is adopted to improve the electrochemical performance of LaMnO3 perovskite as a cathode material for Zn-ion batteries. The resultant LaNixMn1-xO3 (x = 0.2) exhibits a superior capacity of 226 mAh g−1 after 80 cycles at 100 mA g−1 and high working voltages at 1.4 V and 1.26 V vs. Zn2+/Zn in the electrolyte of 2 M ZnSO4 + 0.2 M MnSO4. Even at 500 mA g−1, the new Zn/LaNixMn1-xO3 battery still delivers a discharge capacity of 113 mAh g−1 after 1000 cycles. At medium current density, the electrochemical process of the LaNixMn1-xO3 (x = 0.2) electrode is co-controlled by the solid diffusive and surface-capacitive process with a fast ion diffusion rate. The lanthanum manganese perovskite is a potential cathode material for Zn-ion batteries with long cycle performance and high rate cyclability. This work significantly opens up the way of perovskite materials as new cathodes for high-rate ZIBs.

Effect of Electrochemical and Mechanical Properties of SEI on Dendritic Growth during Lithium Deposition on Lithium Metal Electrode

In the past three decades, lithium-ion batteries experienced a long series of successful improvements, which nowadays make them a widespread technology. Intercalation electrodes, like graphite in the negative electrode, drove large part of this success. On the other hand, they constitute a limit in terms of energy density, which makes them unlikely to match the increasing demands set by renewable energies and especially electric mobility. Thus, it becomes fundamental to investigate new materials that overcome these limits. Lithium metal represents the optimal candidate for the negative electrode, due to its high theoretical capacity (3860 mAh.g-1) and low potential (-3.04 V SHE). On the other hand, the major drawback of this technology is the formation of dendrites, which are lithium structures that form during its deposition. They can cause thermal runaway and internal short-circuits, potentially leading to explosion. Moreover, during lithium stripping, some parts of the lithium electrode tend to be isolated in the electrolyte. This phenomenon causes a reduction of the electroactive lithium quantity thus a limited lifetime of the cell. Therefore, a deeper comprehension of the interfacial phenomena involved during lithium deposition and stripping is necessary to make lithium metal a viable and competitive option as a negative electrode, fostering the transition towards the next generations of batteries.The proposed model starts from the stability analysis of the electrode interface proposed by Newman and Monroe [1] that considers the effect of the mechanical properties on the lithium deposition. Different from it, the presented model studies a time-dependent variation of the surface and it includes a pseudo-2D representation of the Solid Electrolyte Interface (SEI) component. The approach to model the SEI is based on the work of Liu and Lu [2]; and it includes both SEI creation, due to deposition side reactions, and SEI thickness deformation due to the change in geometry of the underlying electrode. In addition, the model considers the effect of the mechanical properties of the SEI on the surface evolution of the electrode. Therefore, starting from the initial surface geometry and the electrochemical and mechanical properties of the components, the model is able to predict the conditions that favors dendritic growth. The figure shows lithium electrodeposition, starting from the same surface defect, on the lithium metal electrode in a liquid electrolyte. After the same quantity of lithium is deposited, it is possible to distinguish different patterns of surface evolution, due to the difference in magnitude of the current density applied: a quasi-uniform growth at low current density (left), a mossy behavior at medium current density (center) and a branching pattern at high current density (right). The difference in dendritic regime is strictly connected to the local change in the SEI thickness, as shown in the figure, which confirms the importance of this component, often neglected in the literature of dendrites models.Since SEI has a major impact on dendritic growth, a consistent set of experiments has been designed to provide its parameters to the model. Electrochemical Impedance Spectroscopy (EIS) was applied to find the electrochemical parameters of the SEI (e.g. SEI diffusion coefficient, SEI resistivity), while Atomic Force Microscopy (AFM) was conducted to find its mechanical properties (e.g. SEI Young’s modulus). The proposed model has the goal of guiding the experiments in finding ways to avoid or curtail dendrites formation, being able to simulate the effects on dendrites growth of operative conditions, SEI and electrolyte compositions, electrode surface defects and coatings. Starting from the model, innovative ways to increase the lifetime of the lithium metal anodes will be analyzed during the presentation; including coatings, surface morphology modification and pulse charging.[1] C. Monroe, J. Newman, Journal of the Electrochemical Society 151(6), A880-A886 (2004)[2] G. Liu, W. Lu, Journal of the Electrochemical Society 164(9), A1826-A1833 (2017) Figure 1

Accessing a high‐voltage nonaqueous hybrid flow battery with a sodium‐methylphenothiazine chemistry and a sodium‐ion solid electrolyte

AbstractThe development of redox flow batteries (RFBs) with nonaqueous electrolytes offers the possibility of accessing a high cell‐operation voltage (no restrain of hydrogen evolution and oxygen evolution potentials) and a low operation temperature (can be operated below the freezing point of water). Therefore, nonaqueous RFBs have recently garnered increasing attention. However, the cross‐mixing of liquid electrode/electrolyte materials has been plaguing the progress of the nonaqueous RFBs. Herein, we present a crossover‐free, high voltage nonaqueous hybrid flow battery (HFB) with a novel sodium‐methylphenothiazine (MPT) chemistry and a single‐ion solid‐electrolyte separator. The Na‐MPT redox couple delivers a high voltage of ~2.6 V when the cell was operated at a medium current density. A NASICON‐type solid electrolyte membrane (Na3Zr2Si2PO12) could circumvent the crossover of the liquids between the positive and negative electrodes, and meanwhile could maintain a single‐ion (Na+‐ion) conduction between the two electrodes to sustain the electrochemical reactions. Under such an electrochemical mechanism, the nonaqueous Na‐MPT HFB shows remarkable cycling performance.

Effect of Electrode Material on the Removal of Industrial Oil and Soap Wastewater Using Electrocoagulation Process

Treatment of oil and soap industrial wastewater using aluminum and iron electrode material has been investigated in this study to compare for each electrode, the performance of the electrocoagulation process. The effectiveness of relevant industrial wastewater characteristics such as the chemical oxygen demand (COD) and oil-grease removal effects of major operating parameters such as medium pH value, electrode material, and current density, and running time and energy consumption were studied. All experiments were done in an electrocoagulation cell with an effective volume of 500 mg/ liters. Under the same operating conditions, it was observed that aluminum electrodes have higher efficiency of removal than iron electrodes. COD and O&G removal efficiencies of 94.93%, 90.20% and 27.49%, 13.27% were observed for aluminum and iron electrode in a special case with optimum initial pH value, maximum current density, time, and initial COD concentration equal to 3, 73.33 A/m2, 30 min, 19750 mg/l, respectively. The electrode energy consumptions for each electrode material have been calculated to be 1.68, 3.04 KWh/kg COD for Aluminum and iron respectively at 15 volts. It can be concluded that the electrocoagulation process using aluminum electrodes is efficient for COD and O&G removal from industrial wastewater

Three-dimensional multi-phase simulation of cooling patterns for proton exchange membrane fuel cell based on a modified Bruggeman equation

A three-dimensional multi-phase non-isothermal model of proton exchange membrane fuel cell (PEMFC) is developed based on a modified Bruggeman equation. The developed model is validated with experimental results and it shows the modified model can more accurately simulate actual working conditions of PEMFC at medium and high current density. The influences of different cooling patterns on the performances of PEMFC are explored. Results reveal that different gas flow patterns have roughly the same effect on the temperature distribution of the membrane in the case of the cooling water counter-current flowing. Under the counter-current gas flow pattern, pattern 3 is the best cooling pattern, that is to keep the cooling water flow direction consistent with the cathode gas flow direction. Under the co-current gas flow pattern, pattern 6 is the best cooling pattern, that is to keep the cooling water flow direction consistent with the gas flow direction. Meanwhile, the temperature distribution of the cathode and the anode is basically symmetrical at the interface of the cathode gas diffusion layer and the cathode catalyst layer. Additionally, the optimal cooling patterns need to ensure the cooling water co-current flowing, and it has obvious advantages of system integration and cost reduction.

Dynamic modeling and parameter analysis study on reversible solid oxide cells during mode switching transient processes

Reversible solid-oxide cells (SOCs) are a promising technology for mitigating the fluctuation of power from renewable sources. Mode switching between electrolysis and fuel cells occurs frequently and is necessary for an SOC stack. Herein, a dynamic SOC-stack model was developed and validated against experimental data. Subsequently, we extensively studied the stack temperature (Ts), voltage (Vs), and reversible efficiency (ηre) with different designing and operating parameters, including stack heat capacity (Cs), inlet hydrogen fraction (xH2), stack operational pressure (p), inlet work medium temperature (Tin), current density (I), and mode switching frequency (f). For an actual SOC plant, the stack may work in a nearly adiabatic environment. Our calculation results show that with xH2 increasing from 0.2 to 0.6, the variation in ΔTs decreases by 25%, Vs increases by 10%, and ηre increases by 2.9%. With fourfold increasing in CS and p, ΔTs decreases by 75% and 25% and ηre increases by 0.47% and 1.8%, respectively, whereas, Vs is nearly unaffected. ΔTs and ΔVs almost proportionally increase with I. In relation to Tin or f, ΔTs is unaffected, ΔVs decreases, and ηre slightly increases. Overall, this work identified the most critical stack designing and operating factors affecting the transient behavior of an SOC stack during mode switching processes. The results can serve as guidelines for SOC-stack design and operation-strategy optimization.

3D investigation of the channel cross-section configuration effect on the power delivered by PEMFCs with straight channels

In the present study, a three-dimensional (CFD) model is performed to investigate the effects of the channel cross-section shape on power density, pressure drop and local transport phenomena of the single straight channel PEMFC. 30 forms of channel cross-section including 5 well-known and 25 new innovative channel cross-section configurations have been investigated using ANSYS-FLUENT. The carried out experimental and numerical validations to verify the present model accuracy have shown a good agreement. The channel cross-section shapes have a significant influence on the power density at medium and higher current density. The best performance is reported by the channel cross-section configuration that has a trapezoidal bottom shape and an inverted trapezoidal top form. Whereas, the worst performance is obtained by the channel cross-section configuration that has an inverted half elliptical bottom shape and an inverted trapezoidal top form. A bad choice of the channel cross-section configuration can lead to a power density loss of 4.65%. The largest pressure drop is obtained from the triangular channel cross-section form whereas; the smallest pressure drop is reported by the rectangular channel cross-section shape.

Localised electrochemical impedance spectroscopy investigation of polymer electrolyte membrane fuel cells using Print circuit board based interference-free system

Polymer electrolyte membrane fuel cells are promising power sources for vehicle and other portable applications due to their high energy efficiency and zero pollution emission during operation. To improve the performance and reliability of polymer electrolyte membrane fuel cells, effective and accurate diagnostic tools are urgently needed for polymer electrolyte membrane fuel cells practical applications. Different from the previous diagnostic methods that may damage the fuel cell structure, a novel interference-free diagnostic system based on the printed circuit board is proposed in this study. Fuel cell localised electrochemical impedance spectroscopy at different current density is observed. It is found that the activation impedance near inlet decreases sharply when current density increase. In addition, it is also found the flooding problem and the mass transport problem can occur at a medium current density due to the non-uniform behaviour of the polymer electrolyte membrane fuel cells. The proposed diagnostic system is demonstrated to be an effective tool to improve efficiency and robust of polymer electrolyte membrane fuel cells.

Effect of Anode Channel Depth on Cell Performance in Polymer Electrolyte Membrane Water Electrolyser

The Bipolar/Flow field plate is a vital component of Polymer Electrolyte Membrane Water Electrolysers (PEMWE) which enables electronic conduction, provide mechanical support to the cell and facilitates mass transport of liquid water and produced gases to and from the electrocatalyst surface. From a mass transport viewpoint, especially at high current density operation, optimizing the dimensions and configuration of the flow field plate is crucial to reducing mass transport limitation and achieve improved cell performance. This work investigates the effect of channel depth of the anode flow field plate on performance of a PEM Water Electrolyser using polarization curve and Electrochemical Impedance Spectroscopy technique. A single electrolyser cell with flow field plate having a single straight channel was employed having the channel depth varied from 3.0 mm to 8.0 mm and the cell performance was studied at current densities up to 2 A/cm2. The impedance spectroscopy results show that the effect of channel depth on cell performance is negligible at low and medium current densities, but significant at high current densities. The result indicate that the two-phase flow liquid/gas interactions in the flow channel and the flow regime of operation have a direct influence on mass transport losses and overall performance in the PEM Water Electrolyser. Furthermore, the impedance spectroscopy result at high current densities shows that, generally, deeper channels show better performance than shallower channels which suggests that the effective mass transfer area at the surface of the gas diffusion layer increases with increase in channel depth thus yielding improved mass transport. However, the best performance was observed at 4.5 mm depth which suggests that there exist an optimal channel depth where an increase or decrease in depth would lead to loss of performance. This is attributed to the trade-off between reduced liquid flow velocity and reduced surface coverage of gas bubble/slug in the channel with increasing channel depth in the PEMWE flow field. Fig 1: Effect of channel depth on cell performance at (a) low, (b) medium and (c) high current density at water flow rate of 40 mL/min and inlet water temperature of 80°C. Figure 1

Effect of via depth on the TSV filling process for different current densities

Through-silicon-via (TSV) filling with optimum electrodeposition parameters is still a challenge in the industry, especially for via with different depths. Herein, the effects of via depth on optimum current density and filling patterns were investigated. It was found that the deeper the via, the lower the optimum current density. At low current density (4 mA cm−2), the via depth only affects the size of the defect, but does not change the filling pattern. However, at medium current density (7 mA cm−2), the filling pattern changes from super-conformal filling to sub-conformal filling with the increase of via depth, the pinch-off position remaining constant at a depth of about 70 µm from the top surface. Simulations of the TSV filling process using COMSOL modeling software revealed that the local concentration of additives, which is affected by the via depth, determine the morphology of the electrodeposition, matching well the experimental results.