High Power Density Operation Research Articles

Engineered Porous Transport Electrode for Proton Exchange Membrane Water Electrolysers

Proton Exchange Membrane Water Electrolysers (PEMWEs) is among the most promising approaches for green hydrogen production due to its rapid response times and high-power density operation, which make this electrolysis technology well-suited to harvest the intermittent power from wind and solar plants. Nevertheless, the commercial breakthrough of PEMWE technology continues to face barriers due to its costs [1]. The porous transport layer (PTL) is one of the PEMWE components that facilitates the transport of incoming water to the catalyst layer and the removal of the product gases, hence it is very important for good electrolyser performance. The state-of-the-art PTLs are manufactured by high temperature sintering of titanium fibers or powders, which can generate oxidized surfaces that will reduce PEMWE performance. Furthermore, titanium is listed by the European Union as a critical raw material since 2020 [2], so it is advisable to reduce the amounts of its use to produce PTLs. Additionally, the (micro)structure of state-of-the-art PTLs is not optimized for efficient liquid and gas transport in electrolysis. The manufacturing process plays a key role in achieving PTLs with optimized liquid and gas transport as well as reducing the usage of titanium.In this work, we used lithography to manufacture PTLs in which the (micro-)structure can be optimized and the usage of titanium metal can be significantly reduced. The lithography manufactured PTLs were used as substrates to produce catalyst-coated electrodes (CCE) with (ultra-)low loadings of iridium and the PEMWE performance was evaluated, respect to CCEs manufactured on commercial PTLs. We demonstrate similar performance of the CCEs manufactured with the engineered PTL, with the advantage of using less titanium and being able to tune the (micro-)structure of the component.

Enhancing Proton Exchange Membrane Fuel Cell Durability By Using Porous Carbon-Supported Cathode Catalysts with Various Pt-Particle Sizes

Nowadays, proton exchange membrane fuel cells (PEMFCs) are envisioned for heavy-duty vehicles (HDVs) such as trucks and buses, due to their high power density, low emissions, and quiet operation.1 However, to be viable for HDVs, PEMFCs require cathode catalyst materials that are highly stable and durable in order to maintain performance over at least 30,000 hours of operation. One well-known challenge is that voltage cycling of the cathode leads to significant losses in the electrochemically active surface area (ECSA) due to Pt-dissolution and subsequent growth via Ostwald ripening or particle coalescence, as well as Pt loss into the ionomer/membrane phase.2 While larger Pt particles are less prone to dissolution due to their lower surface free energy,3 depositing Pt particles within the internal pores of primary porous carbon particles has been shown to effectively mitigate particle coalescence.4 Therefore, combining larger particles with locating them internally of the carbon pores shows promise for significantly reducing Pt surface area loss.In this study, voltage cycling-based accelerated stress tests (ASTs) were performed using 5 cm2 membrane electrode assemblies (MEAs) with 0.1 mgPt cmMEA -2 loaded Pt-based cathode catalysts supported on porous Ketjenblack carbon (TEC10E20E, TKK, referred to as “pristine” Pt/KB). To increase the Pt-particle size, the catalyst was subjected to a heat-treatment under an reductive atmosphere (5% H2/Ar mixture) at 900 °C for 1 h (referred to as “HT-900°C/1h”), while a subsequent treatment under oxidative atmosphere (under air/Ar mixture) at 250 °C for 12 h (referred to as “ox-HT-900°C/1h”) was also included to enhance catalyst accessibility by inducing a Pt-catalyzed local carbon support oxidation of the bottleneck pore entrances, as described by Lazaridis et al.5 A full MEA characterization was carried out, encompassing determination of the ECSA by CO-stripping, of the H2/air and H2/O2 performance, and of the O2 and H+ transport resistances in the cathode by limiting current measurements and electrochemical impedance spectroscopy, respectively.We found that the HT-900°C/1h cathode exhibited significantly improved ECSA retention compared to the pristine Pt/KB, primarily due to its larger Pt particle size (~5 vs. ~2.5 nm), which reduces Pt dissolution. However, it was also observed that these catalysts had a much lower beginning-of-life (BoL) H2/air performance, as evidenced by comparing the rightmost data points in Fig. 1 for the pristine (gray squares) and the HT-900°C/1h (blue triangles) catalysts. These performance losses are attributed to the reduced roughness factor (rf), i.e., the lower available Pt surface area per electrode area, which was demonstrated to affect various voltage loss terms.6 Especially at higher current densities, an increased impact of the local oxygen transport resistance is observed, due to its inverse proportionality to the cathode rf. To address these challenges, it was demonstrated that enhancing catalyst accessibility substantially improves H2/air performance at higher current densities, so that the ox-HT-900°C/1h catalyst surpasses the initial performance of the pristine Pt/KB (compare rightmost green circles). Thus, combining heat treatment of a Pt/KB catalyst under both reductive and oxidative atmosphere enhances cathode catalyst durability and concomitantly high current density H2/air performance.

Studies on Non-Destructive State-of-Health Estimation for Lithium-Ion Batteries

IntroductionRecently, lithium-ion batteries (LIBs) have been used as an energy storage technology for electric vehicles and energy storage systems due to their high energy, power density and wide operating temperature range. However, degradation inevitably causes capacity and power decay. For the safer use of LIBs, state of health (SOH), which describes the condition of a battery compared to its initial condition, needs to be monitored to avoid electrolyte leakage and micro-short circuiting that lead to battery failure. In general, SOH can be estimated by identifying changes of parameters such as voltage, capacity, and impedance. Also, thickness swelling caused by side reactions such as SEI growth, lithium plating, or gas generation can be used as a degradation parameter to estimate SOH.[1] Applying mechanical pressure to LIB cells, which could externally modify the contribution of the side reactions, is a well-known effective approach to decrease irreversible thickness swelling.[1] On the other hand, the impact of electrolyte additives, which could internally modify the contribution of the side reactions, on the swelling behaviors has not been well-understood.In this study, non-destructive techniques including electrochemical impedance spectroscopy (EIS) combined with thickness measurement were employed to investigate the effects of electrolyte additives on the degradation behaviors of the cycled LIBs, which could be related with the SOH. Also, post-mortem analysis of the cycled LIBs was performed to further investigate the degradation degree of positive/negative electrodes separately.ExperimentalLaminated LIB cells with nominal capacity of 380 mAh were used for accelerated degradation tests. The positive and negative electrodes were LiNi0.5Co0.2Mn0.3O2 (NCM) and graphite, and the electrolyte was 1 mol dm−3 LiPF6/ethylene carbonate–diethyl carbonate (EC–DEC, 3:7 by volume) containing vinylene carbonate–fluoroethylene carbonate (VC–FEC, 1 wt% each), or without additive. At the beginning, low-rate charge–discharge cycles at a current density of 76 mA were performed at 25 ℃. EIS with a frequency range from 1 MHz to 1 mHz was carried out, followed by the measurement of the cell thickness. Then, high-rate charge–discharge cycles at a current density of 760 mA were performed at 60 ℃. Low-rate capacities of the degraded cells were measured every 100 cycles of high-rate charge–discharge.Results and discussionThe discharge capacities of the LIB cells roughly showed a decrease with charge–discharge cycles and dropped to around 80-85% of their initial value after 512 cycles. Compared with the LIB cells without additives, those with VC + FEC exhibited better high-rate and low-rate durability.In figure 1, Nyquist plots of the fresh full cell had two semicircles. The one at lower frequency was dependent upon temperature and voltage which was corresponded to charge transfer resistance.[2] From results of the symmetric cells, the semicircle at higher frequency should be assigned to the contact resistance between the current collector and the NCM electrode. There was also a semicircle of SEI resistance observed in graphite symmetric cells after degradation cycles, although it overlapped with the larger contact resistance in the full cell due to their similar time constants.With the increased number of the high-rate charge–discharge cycles, the semicircle at higher frequency which mainly came from the contact resistance increased, indicating the degradation of the LIB cells. This value significantly increased with the decrease in the low-rate discharge capacity, suggesting that the high-frequency semicircle could be used as a parameter for SOH estimation. Also, the increasing behavior of the contact resistance was suppressed with the presence of VC + FEC additives, indicating that suitable additive could suppress the increase of the contact resistance at the positive electrode and/or could be important for the formation of robust SEI at the negative electrode.

Next Generation Cathode Catalyst Layer Design with High Oxygen Permeable Ionomer – Benefits, Challenges, and Prospects for Heavy Duty Fuel Cell Applications

Proton Exchange Membrane Fuel Cell (PEMFC) has a growing demand to power zero emission fuel cell applications. Ballard is the fuel cell industry leader, developing the next generation core technology to fulfill such demand and giving continuous efforts on cost reduction. Key requirements in fuel cell market applications include high power density and long-life operation, while maintaining high efficiencies and reducing costs. This places a high demand on improving catalyst performance and electrode layer transport, which can be sustained over the duration of the product lifetime. To reduce fuel cell membrane electrode assembly (MEA) cost, the push for high performance catalyst layers (CLs) with low platinum (Pt) loadings results in new challenges for the cathode material selection and electrode design. The increased oxygen transport resistance that occurs at lower catalyst loadings with reduced available catalyst electrochemical active surface area (ECSA), causes two very closely related challenges: 1) greater performance losses at high current density increases the difficulty to achieve the power requirements for the heavy duty market, and 2) the loss of catalyst ECSA via platinum dissolution over time puts additional demands on the design to achieve the end of life (EOL) performance requirement. Therefore, a combination of material solution, design choice and processing parameters are the key to optimize next generation cathode design for fuel cell applications1.One material solution to achieve high performance while reducing catalyst loadings is the development of high oxygen permeable ionomer (HOPI) that mitigates oxygen transport limitations at the Pt surface. Chemours has developed a HOPI with a bulky, sterically rigid monomer group in the ionomer backbone, which disrupts the packing density, improving oxygen permeability on the catalyst surface2. One of the key challenges of HOPI integration and the scale-able fabrication of the catalyst layer is high crack density of CL due to the rigid nature of the ionomer. Ballard has integrated HOPI in the cathode CL overcoming scale-able fabrication challenges through appropriate process parameter selection and evaluated CL performance. The use of accelerated testing and modeling approach developed by numerous product iteration, has been applied for lifetime estimation for HOPI technology introduction. In this talk, we will discuss details about benefit of High Oxygen Permeable Ionomer (HOPI) in next generation cathode CL design.Recently, key requirements in heavy-duty market applications are placing more importance on high efficiency rather than high power density to reduce fuel cost rather catalyst cost. Reaching the target lifetime, catalyst overloading to 0.45 mg/cm2 total Pt in anode and cathode, and 44% active membrane area oversizing are suggested3. Therefore, to achieve high efficiency target, high catalyst activity is more desired. Interestingly, HOPI also showed high specific activity due to the mitigation of catalyst poisoning by sulfonate anion groups4. We will also discuss the catalyst layer design prospect with HOPI for such transition on heavy duty market application.Acknowledgement: US Department of Energy (DOE) funded heavy duty MEA development project (DE-EE0008822).References M. Dutta, A. Young, V. Colbow, J. Bellerive and S. Knights 2020 Examining Catalyst Layer Design Strategies for Improved Fuel Cell Performance and Durability. ECS PRiME 2020S. Litster et al. 2020 Durable High-Power Density Fuel Cell Cathodes for Heavy-Duty Vehicle. DOE AMR 2020K. Ahluwalia and X. Wang 2024 Performance and Durability of Hybrid Fuel Cell Systems for Class-8 Long Haul Trucks. J. Electrochem. Soc. 171 034507R. Jinnouchi, K. Kudo and K. Kodama 2021 The role of oxygen-permeable ionomer for polymer electrolyte fuel cells. Nat Commun 12, 4956.

Novel Mesoporous Carbon Supporting PGM As an Effective ORR Catalyst in PEM Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells convert the chemical energy of hydrogen and oxygen into electrical energy through a proton-conducting polymer membrane. These cells are highly valued in compact applications such as electric vehicles and portable power systems for their high power density and low operating temperatures. The catalyst support plays a crucial role, not only anchoring the catalyst nanoparticles but also enhancing Oxygen Reduction Reaction (ORR) activity through heteroatom doping, facilitating mass transfer via microchannels, and improving conductivity.1 Mesoporous carbon, merging electrochemical and high surface area properties, serves as an ideal catalyst support. Its mesoscopic structures enable high dispersion of electrocatalysts, and although mesopores contribute relatively less to surface area compared to micropores, they are more effective for mass transport. 2-3 We employ Metal Organic Frameworks (MOFs)-derived porous carbon, synthesized through pyrolysis, to provide structurally optimized mesoporous support that enhances surface area and electrochemical stability. MIL-101 is a highly porous, crystalline MOF known for its exceptional surface area and potential in gas storage, separation, and catalysis.4 Our research details the production of a series of mesoporous carbon C-X-MIL-101 (X = NH2, CH3, NO2, OMe) through carbonization of X-MIL-101 MOFs at 1100 °C followed by acid etching to remove residual aluminum oxides, resulting in high-surface-area, controlled-mesoporosity carbon materials. Platinum nanoparticles are subsequently embedded using a solvent impregnation method to produce Pt@C-X-MIL-101, optimizing platinum use and preventing surface deposition. The resulting Pt@C-X-MIL-101 catalysts have been tested in fuel cell and comprehensive findings will be presented at the conference. Zaman, S., Wang, M., Liu, H., Sun, F., Yu, Y., Shui, J., ... & Wang, H. (2022). Trends in Chemistry, 4(10), 886-906.Chang, H., Joo, S. H., & Pak, C. (2007). Journal of Materials Chemistry, 17(30), 3078-3088.Xu, J. B., & Zhao, T. S. (2013). RSC Advances, 3(1), 16-24.Zorainy, M. Y., Alalm, M. G., Kaliaguine, S., & Boffito, D. C. (2021). Journal of Materials Chemistry A, 9(39), 22159-22217.

Research on the impact of inter-turn short circuit faults on the electromagnetic and thermal characteristics of closed oil-cooled back-wound high-speed permanent magnet generator

The oil-cooled back-wound high-speed permanent magnet generator (OBHPMG), is suitable for the aerospace field, gas turbines, and flywheel energy storage due to its high efficiency as well as high-power density. However, the high-power density operation of the generator inevitably results in a significant temperature rise, particularly when inter-turn short circuit faults (ISCFs) occur in the windings. In order to clarify the electromagnetic as well as thermal characteristics of the OBHPMG under the different ISCF degrees, it is of great significance to research the electromagnetic and temperature field variation characteristics of the generator at various inter-turn short circuit faults degrees. Firstly, the electromagnetic field of the 40 kW OBHPMG is investigated at normal operating in this paper, the rotor eddy current densities as well as stator core magnetic flux densities distribution is determined. Secondly, based on the model of the generator ISCF, the effects of the winding different ISCF degrees on the rotor eddy current densities and stator core magnetic flux densities are further explored in detail. The variation characteristics of the rotor current loss as well as stator core magnetic flux densities under the winding different ISCF degrees are revealed. Finally, the effect of the different ISCF degrees on the windings and permanent magnets temperature is analyzed in depth by combining the variation mechanism of the electromagnetic loss. The temperature variation characteristics of the OBHPMG with the different ISCF degrees are obtained, and the cooling effect of the OBHPMG under the ISCF is clarified. It provides a theoretical basis for clearly mastering the variations in the performance of the generator under the windings ISCF in this paper.

Covalent triazine frameworks crosslinked microporous polymer membranes with fast and selective ion transport for ultra-stable vanadium redox flow batteries

The vanadium redox flow batteries (VRFBs) are an essential pathway to long-duration energy storage with the merits of power and energy decoupling, long lifetime and safety. However, low coulombic efficiency stemming from vanadium crossover across the membrane together with notable ohmic loss originated from low proton conductivity of the membrane still limits high performance operation of the VRFBs. Herein, we proposed 2,2′-bipyridine-based covalent triazine frameworks (bipCTF) crosslinked sulfonated-poly (4,4′-diphenylether-5,5′-bibenzimidazole) (SOPBI) (bipCTF/SP-100) for use as the membrane in VRFBs, which synergistically prevents vanadium crossover and enhances proton conductivity. By delicately tuning the sulfonation degree and properly incorporate bipCTF, the bipCTF/SP-100 membrane is successfully synthesized based on OPBI polymers, which delivers a reduced area resistance of 0.3 Ω cm2 and a low VO2+ permeability of 19.05 × 10−9 cm2 s−1, affording an excellent trade-off between proton conductivity and ion selectivity. Theoretical calculation further corroborates that the high proton conductivity of bipCTF/SP-100 is attributed to the ionic channels formed by bipCTF, while the superior ion selectivity is assigned to protonated imidazole and pyridine. Benefiting from microporous bipCTF/SP-100 membrane, the VRFB exhibits a high CE of 99.8 % and an excellent EE of 78.3 % at 250 mA cm−2 and meanwhile yields a high capacity retention of 94.8 % after 200 cycles at 200 mA cm−2, which shows enormous potential for high power density operation of the VRFBs.

Hierarchical porous carbon with abundant N/O doping as an anode for zinc ion hybrid supercapacitors

Aqueous zinc-ion hybrid supercapacitors (ZISCs) known for their affordability, stability, and high energy density represent innovative energy storage devices. Porous carbon is usually used as the cathode material of ZISCs, and its structure significantly affects the dual performance of high power density and energy density of ZISCs. Herein, a one-pot carbonization strategy is proposed, eliminating the need for templates, additional heteroatom compounds, and activation processes. By precisely controlling the temperature to optimize the structure and electrochemical performance of carbon materials, we successfully synthesized hierarchical porous carbon materials (NOPC-800) with a high specific surface area of 1545.7 mg, featuring dual doping of 12.3 at% nitrogen and 13.35 at% oxygen. The self-doping of abundant nitrogen and oxygen atoms facilitates the chemical adsorption of ions and accelerates pseudocapacitive reaction kinetics. Leveraging these advantages, ZISCs were assembled using NOPC-800 as the positive electrode and zinc as the negative electrode, showcasing remarkable performance: a specific capacity of up to 121.9 mAh g, an energy density of 97.5 Wh kg, and a power density of up to 16000 W kg. Remarkably, NOPC-800 maintained an excellent capacity retention of 94.9% after 10,000 cycles at a current density of 10 A g. This research paves an innovative and feasible path for the design and advancement of novel heteroatom-rich carbon cathodes.

High-Density CoSe2 Sites Embedded within 2D Porous N-Doped Carbon for High-Performance Oxygen Reduction Reaction Electrocatalysis.

Designing and fabricating efficient and stable nonprecious metal-based oxygen reduction reaction (ORR) electrocatalysts is a pressing and challenging task for the pursuit of sustainable new energy devices. Herein, porous P-CoSe2@NC electrocatalysts with high-density carbon-coated CoSe2 sites were successfully fabricated based on a pyridyl-porphyrinic metal-organic framework (Co-TPyP MOF) via a molten salt-assisted synthesis method. The hierarchical pore and N-doping carbon substrate of P-CoSe2@NC promotes mass transfer and electron-transfer efficiency, which is beneficial to maximize CoSe2 site utilization. Well-designed P-CoSe2@NC exhibits efficient ORR catalytic activity with a high half-wave potential of 0.863 V and excellent catalytic stability. Meanwhile, rechargeable aqueous primary/quasi-solid-state ZABs based on a P-CoSe2@NC air cathode show a high peak power density and exceptional operating stability, catering to the demands of practical applications. The qualified performance and structure stability of the electrocatalytic system may be mainly attributed to the protection of the CoSe2 nanoparticle by the coated carbon layer. Given the rational design of the structure and the component of the electrocatalyst with enhanced ORR activity, we believe that this work has provided a reliable pathway to the development of high-performance transition-metal chalcogenides for energy-storage and -conversion devices.

The method of gain parameterizing measurement data and parameter estimation for a proton exchange membrane fuel cell model

Abstract Proton exchange membrane fuel cells (PEMFCs) are a technology that produces clean energy, with promising prospects in wide applications because of their high power density and low operating temperature. Experiments conducted to develop the PEMFC are both time-consuming and costly. Through modeling and simulation, performance development and analysis can be done more efficiently. This paper presents a simulation model for PEMFC based on mathematical equations developed using MATLAB/Simulink. To fully grasp and reproduce PEMFC characteristics, empirical parameter estimation using the genetic algorithm (GA) is implemented. The parameters estimated from the loss equations have not been previously utilized. A script connecting Simulink and the GA was developed to estimate these parameters. Validation is conducted by comparing the polarization curve simulation results with experimental data for both single-cell and stack-type PEMFCs. Comparisons with various other estimation methods were conducted to assess the reliability of the employed method. The model that utilizes estimated parameters exhibits agreement with experimental data showcasing an error value <3%. Furthermore, the method's superiority is evident from the polarization curve as well as the objective value. Observing the reaction conditions in each PEMFC loss region with the obtained parameter values becomes easier and more accessible.

Influence of Ethanol Decomposition on Dispersion of PEFC Catalyst Ink

To achieve high power density operation of polymer electrolyte fuel cells (PEFCs), it is required to realize high-performance catalyst layer with low oxygen transport resistance, high proton and electron conductivities, and high electrochemical surface area (ECSA) with low Platinum loading. Because dispersion structure of catalyst ink strongly affects porous structure of the catalyst layer, it is crucial for realization of high-performance catalyst layer to understand the dispersion mechanism of the catalyst ink. Our group has reported that decomposition of ethanol, as a solvent, by platinum catalyst significantly affects aggregation of the catalyst ink. [1, 2] But, the mechanism of the catalyst ink aggregation was not fully understood. In this study, effect of ethanol decomposition on the aggregation of the catalyst ink was investigated.The catalyst ink was fabricated by mixing platinum-supported carbon (TEC10V30E, Tanaka Kikinzoku), ionomer (DE1021, Sigma-Aldrich), and water/ethanol solvent (water/ethanol: 60/40 wt%). Decomposition product of ethanol within the catalyst ink solvent was analyzed by GC/MS (GCMS-QP2020NX, SHIMADZU), and presence of acetaldehyde (C2H4O) and acetic acid (CH3COOH) was detected. In order to investigate the influence of these products on aggregation of the catalyst ink, acetaldehyde or acetic acid was added to the catalyst ink. The particle size distribution was evaluated by using laser diffraction type particle size distribution meter (LA-960V2, HORIBA) without dilution, and it was confirmed that the acetaldehyde-added catalyst ink showed larger particle size and the acetaldehyde caused the aggregation of the catalyst ink (Figure 1). In addition, dispersion of the catalyst ink was observed by using an optical microscopy, and aggregation of the catalyst ink by adding the acetaldehyde was clearly observed (Figure 2). To understand the aggregation mechanism by adding acetaldehyde, ionomer adsorption fraction on the platinum-supported carbon was measured by using centrifugation method, and the decrease in ionomer adsorption fraction by adding acetaldehyde was confirmed. From these results, it was confirmed that acetaldehyde generated by the decomposition of ethanol in the catalyst ink leads to a decrease in the ionomer adsorption fraction. It is reported that the ionomer promotes the dispersion of platinum-supported carbon due to electrostatic repulsion forces, and it is suggested that the decrease in ionomer adsorption fraction results in the aggregation of the catalyst ink. Therefore, to realize high-performance catalyst layer, influence of acetaldehyde should be minimized and further research is requested to understand it. Acknowledgement This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Interactions between Catalyst Layer Degradation and Liquid Water Distribution in Polymer Electrolyte Fuel Cells

Managing liquid water distribution in PEFCs is critical to desirable high power density operation and cell durability [1–3]. Degradation modes such as carbon corrosion in the cathode catalyst layer (CCL) are believed to depend on local humidification [2,4], while the distribution of liquid water may also be influenced by performance drop associated with such degradation [3]. Although some studies have shown the influence of carbon corrosion on liquid water distribution [2,3], the possible reverse effect of liquid water distribution on the CCL degradation requires further investigation.The objective of the present work is to establish a deeper understanding of the cause-and-effect interactions between CCL degradation and liquid water distribution. This is achieved experimentally by carrying out voltage-cycling accelerated stress tests (ASTs) on fuel cells which differ only in the constituent gas diffusion layers (GDLs); namely, SGL 22 BB and a proprietary Avcarb. Three-dimensional X-ray microscopy is used to observe both degradation effects and liquid water distribution at different stages of the ASTs. A relatively rapid operando two-dimensional visualization technique [5] was also used to investigate the differences in liquid water distribution between the two GDLs. The fuel cells imaged are analyzed and exhibit different liquid water distributions, whereby the Avcarb exhibits a higher liquid water condensation close to the CCL, compared to the SGL. Supported by model results, this difference in liquid water distribution is shown to be attributable to the different transport properties of the GDLs. The degradation results, such as the CCL thickness (Fig. 1) show that the Avcarb cell experiences a faster CCL degradation than the SGL cell. Furthermore, the Avcarb liquid water distribution is seen to change with increasing AST cycles in a manner indicating higher vapour phase removal. These results provide insights for GDL design consideration, showing that GDL transport properties may influence liquid water distribution at the electrode with important implications for CCL durability. Acknowledgement Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada,Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund,and Canada Research Chairs.

Key operational parameters assessment for a chromium (VI)-reducing annular upflow microbial fuel cell

Development of upflow microbial fuel cells (MFCs) is of importance since these types of MFCs can be integrated in wastewater treatment plants for the provision of continuous treatment and energy recovery. In this study, key operational parameters were assessed for a hexavalent chromium [Cr(VI)] reducing annular upflow MFC (approximately 5 L total liquid volume). The optimized operational parameters were cathode and anode hydraulic retention times of 2 days, temperature of 34 °C, influent Cr(VI) concentration of 800 mg L−1, and anode and cathode pH of 7 and 4 respectively. This study demonstrated that a parallel configuration is advantageous since it leads to a high current and power density operation due to low internal resistance when compared to series configuration. The precipitation of Cr(III) over time was demonstrated to have a potential to reduce MFC performance and operating at high influent Cr(VI) pHs (7–10) should be avoided. The optimized peak output potential difference and maximum power density achieved under parallel configuration were 896 mV and 994 mW m−3 respectively, at a current density of 1191 mA m−3. This study provides a step into developing continuous metal reducing MFCs for use in simultaneous treatment of heavy metals in wastewater and energy recovery.

Power Electronics Revolutionized: A Comprehensive Analysis of Emerging Wide and Ultrawide Bandgap Devices.

This article provides a comprehensive review of wide and ultrawide bandgap power electronic semiconductor devices, comparing silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and the emerging device diamond technology. Key parameters examined include bandgap, critical electric field, electron mobility, voltage/current ratings, switching frequency, and device packaging. The historical evolution of each material is traced from early research devices to current commercial offerings. Significant focus is given to SiC and GaN as they are now actively competing with Si devices in the market, enabled by their higher bandgaps. The paper details advancements in material growth, device architectures, reliability, and manufacturing that have allowed SiC and GaN adoption in electric vehicles, renewable energy, aerospace, and other applications requiring high power density, efficiency, and frequency operation. Performance enhancements over Si are quantified. However, the challenges associated with the advancements of these devices are also elaborately described: material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference. Alongside the cost reduction through improved manufacturing, material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference are critical hurdles of this technology. The review analyzes these issues and emerging solutions using advanced packaging, circuit integration, novel cooling techniques, and modeling. Overall, the manuscript provides a timely, rigorous examination of the state of the art in wide bandgap power semiconductors. It balances theoretical potential and practical limitations while assessing commercial readiness and mapping trajectories for further innovation. This article will benefit researchers and professionals advancing power electronic systems.

Influence of Ethanol Decomposition on Dispersion of PEFC Catalyst Ink

To achieve high power density operation of polymer electrolyte fuel cells (PEFCs), it is required to realize higher performance catalyst layer. Because dispersion structure of catalyst ink strongly affects the catalyst layer structure, it is crucial to understand the dispersion mechanism of PEFC catalyst ink. Though water/ethanol solution is used as solvent of the catalyst ink, decomposition of ethanol by Platinum catalyst strongly affect dispersion of the catalyst ink. In this study, influence of ethanol decomposition on dispersion of catalyst inks were investigated. Among the decomposition byproducts of ethanol, results of rheology characteristics and direct observation by scanning electron assisted dielectric microscopy clearly showed that acetaldehyde has a significant impact on aggregation of catalyst ink. To reveal the mechanism of aggregation, particle size measurement and ionomer adsorption fraction measurement of the catalyst ink were carried out. The results suggested that the acetaldehyde impede adsorption of the ionomer on Platinum catalyst.

Comparative Analysis of Surface-Attached Cooling Structure for Efficient Thermal Management of SPMM-TW

Efficient thermal management is the essential precondition for electrical machines to achieve high power density and reliable operation. This paper presents a surface-attached cooling structure (SACS) for the thermal management of slotless permanent magnet motor (SPMM) with toroidal winding. The SACS consists of several channels attached to the surface of the toroidal winding, and the shorter heat path guarantees that the heat generated in the winding can be effectively extracted. Three-dimensional electromagnetic finite-element analysis and the computational fluid dynamics are used to evaluate the losses of the SPMM and obtain the accurate convective heat transfer coefficient (CHTC). For predicting the winding temperature accurately, the layered winding model is proposed to simulate the actual winding conditions. In addition, the influence of different channel materials on temperature rise is experimentally evaluated on the same prototype. The experimental results show that the layered winding model can well simulate and predict the actual temperature distribution of the winding, and the SACS can effectively reduce the temperature rise of the winding compared with the housing water jacket cooling, where the SPMM with the SACS can withstand a continuous current density of 17.2 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a peak current density of 28 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Numerical investigation and experimental validation of water condensation in the gas diffusion layer with different properties

Liquid water in porous media hinders the transport of reactant to catalyst layer, where the electrochemical reactions occur, which in turn, reduces performance and lifetime of a proton exchange membrane fuel cell (PEMFC). In this study, two types of gas diffusion layer (GDL) materials are used to study the two-phase saturation distribution in a PEMFC. The correlations between the effective and anisotropic transport properties and porosity of the two GDLs are solved by the pore scale model. In addition, the anisotropic liquid water permeability and the relationship between saturation pressure and capillary pressure is determined by using the Lattice-Boltzmann method. Fuel cell performance as well as liquid water distribution in the GDL using neutron radiography are obtained for validation. Under wet conditions, the cell with Freudenberg GDL performs better than that using Toray GDL, especially at high current densities. The results of the two-phase model simulation show that the peak water saturation for Toray GDL occurs in the catalyst layer and can reach 40%, while the peak water saturation for Freudenberg GDL occurs inside the GDL directly under the ribs and only reaches 25% saturation. The combined results provide key insights to enable high power density operation of a PEMFC through GDL material optimization.

PERFORMANCE ANALYSIS OF A BIPOLAR PLATE IN A FUEL CELL USING COMPUTER FLUID DYNAMICS STUDIES

Over the past ten years, proton exchange membrane (PEM) fuel cells have gained popularity as a potential energy source. PEM fuel cells are a high efficiency, environmentally friendly power source that are not constrained by Carnot efficiency. Due to its characteristics of zero emissions, high power density, rapid start-up, and low operating temperature, they are seen as one of the attractive options to be utilized for electric cars. In this project work, a fuel cell uses that a low cost bipolar plate material with a high fuel cell performance are important for the establishment of PEM fuel cells into the competitive market world are taken in consideration. The analysis is carried out for the selected materials like Aluminium, Copper and Stainless steel on considering the design and operational parametric conditions of the PEM fuel cell. The aluminium bipolar plate exhibits improved uniformity in the dispersion of hydrogen, oxygen, and water vapour, which will improve the ionic conductivity in the membrane. After analysing the data, we found that the aluminium bipolar plate material had the best temperature distribution in the fuel cell and the lowest pressure loss when compared to the copper and stainless steel materials. Therefore, due to its light weight and reasonably low price of material, aluminium serpentine bipolar plate material may be thought of as the ideal bipolar plate material, especially for portable applications.

Realized potential as neutral pH flow batteries achieve high power densities

High power density operation of redox flow batteries (RFBs) is essential for lowering system costs, but until now, only acid-based chemistries have achieved such performance, primarily due to rapid membrane proton (H + ) transport. Here, we report a neutral pH RFB using the highly reducing Cr-(1,3-propylenediaminetetraacetate) (CrPDTA) complex that achieves acid-like power performance while utilizing potassium ion (K + ) transport. We investigate RFB resistance components and demonstrate the high and consistent K + conductivity of the Fumasep E-620(K) membrane. When combined with a robust bismuth electrocatalyst, this membrane enables constant voltage efficiency operation of a CrPDTA|Fe(CN) 6 RFB for 200 cycles. An optimized CrPDTA|Fe(CN) 6 RFB, which combines a high cell potential with a low area-specific resistance (0.46 Ω cm 2 ), demonstrates a maximum discharge power density of 1.63 W cm −2 and an average discharge power density over 500 mW cm −2 while maintaining 80% round-trip energy efficiency cycling, which are records for non-acid-based RFBs. • High-power flow battery operates at neutral pH with potassium membrane transport • Record discharge-power performance for a flow battery not using proton transport • Inexpensive membrane provides high conductivity and constant efficiency cycling • Chelated metal electrolyte enables high voltage battery and high-power operation High-power flow battery operation lowers system costs but has previously required proton transport. By combining high voltage with low resistance from a highly selective and conductive membrane, Robb et al. demonstrate an aqueous flow battery that achieves record non-acidic power performance while utilizing potassium membrane transport at neutral pH.

(Invited) Development of 3-inch AlN Single Crystal Substrates

Aluminum nitride (AlN) holds great promise as a substrate for electronic devices such as high-power switches, high power density, high frequency and high operating temperature devices for RF. This promise is largely due to its superior properties, for instance its ultra-wide bandgap (UWBG) of 6.2 eV, high thermal conductivity (> 290 W/m*K), high melting point (> 2800°C), relatively good chemical resistance, similarity of its lattice structure and parameters to that of Gallium nitride (GaN), high hardness value of about 12 GPa (at 1 N using Vickers indenter), etc. Presently AlN substrates are successfully used for fabrication of ultraviolet (UV) light emitting diodes (LEDs) operating at wavelengths shorter than 280 nm, i.e., in the UVC region of the spectrum. The AlN-based UVC LEDs are employed in water disinfection, surface cleaning, air purification, and environmental sensing. Several factors including substrate availability, size, production capacity, quality, and cost influence the commercialization of the aluminum nitride both as an UWBG and as an opto-electronic substrate. In this work we present the present and future outlook for the AlN substrates made using Physical Vapor Transport (PVT) growth technique.The PVT crystal growth method of aluminum nitride is carried out in a Tungsten crucible that accommodate the AlN source material as well as the (0001) oriented AlN seed. The thermal gradient is provided by an rf-heating plus appropriate shielding and insulation. In this setup, the sublimed source material is transported to the Al-polar face of the seed where it incorporates into a single crystal. The AlN crystals are then oriented, sliced, and polished. The resulting 2-inch substrates are tested to meet certain specification needed for further epitaxial growth and LED processing. The two-inch AlN wafer specification as well as number of physical properties and purity were previously reported [1].In addition to the 2-inch AlN crystal growth there is an ongoing effort to increase the substrate diameter. Large-diameter (e.g. 100 mm) AlN substrates are a practical requirement benefiting high power electronic devices. Again, PVT growth method is used to expand the crystal size and diameter. However, several challenges have yet to be resolved en route to 100 mm diameter crystals. These challenges are associated with increased thermally induced stress, the need for better control of the axial/radial thermal gradients, vendor ability to provide materials, maintaining crystal quality during expansion, etc.Our PVT growth technique demonstrates high crystal growth yield which allows to contain relatively low production cost. Furthermore, we have established a high-capacity process capable to produce many thousands of 2-inch AlN substrates per year. Our current crystal growth process also demonstrated greater than 3-inch diameter single-crystal AlN substrates; properties of such wafers will be reported. Robert T Bondokov et al 2021 ECS Trans. 104 37