Improved Power Density Research Articles

Improving the performance and long-term durability of high-temperature PEMFCs: A polyvinylpyrrolidone grafting modification strategy of polybenzimidazole membrane

This study introduces an innovative approach to graft Polyvinylpyrrolidone (PVP) onto Polybenzimidazole (PBI) to synthesise Proton Exchange Membranes (PEMs) with high performance and durability. As a widely used hydrophilic polymer in industry, PVP can add numerous nitrogen-containing functional groups to the membrane to enhance its phosphoric acid (PA) binding ability. In this work, Polybenzimidazole-graft-polyvinylpyrrolidone (PVP-g-PBI) polymers with varying grafting degrees were synthesized and tested to investigate the impact of the grafting modification on the membrane's proton conductivity, thermal properties, and electrochemical performance. With the introduction of PVP side chains, the fuel cell showed enhanced PA uptake and substantial improvements in peak power density. Notably, PBI-g-PVP membranes with a grafting degree of 22.4 % achieved a peak power density enhancement up to 1312 mW cm⁻2 at 160 °C, a 59.6 % increase over pristine PBI membranes. Due to the increased PA binding sites in the membrane, the PBI-g-PVP PEMs exhibit better PA adsorption ability and long-term durability than pristine membranes. The accelerated stress test (AST) demonstrated that the PBI-g-PVP membranes maintain a peak power density of 1105 mW cm⁻2 after a 70-h test, equivalent to 183.9 % of the pristine PBI membrane. The improved fuel cell performance and durability of PBI-g-PVP PEMs underscore the potential of this grafting strategy.

Numerical investigation on designs and performances of multi-dimensional forced convection flow field design of proton exchange membrane fuel cell

The geometric modification of the flow field is validated as an effective measure for improving proton exchange membrane fuel cell (PEMFC) performance and reactant mass transfer ability. In this paper, a parallel flow channel with X-structure connecting two adjacent channels is established. The multi-dimensional forced convection is formed by adding the stepped shape with three connecting flow fields to increase the performance and mass transfer capacity. Six cases based on the flow field of the X shaped channels are proposed to assess the impact of different designs. The results indicate that the X-structure design improves the uniformity of oxygen distribution and drainage capacity. A stepped design with gradually increasing height improves power density and generates a large area of localized gas vertical velocity. The addition of connecting channels results in different flow behaviors at the nodes, such as slight backflow, increased flow velocity, decreased water content, and temperature rise. With a power density improvement of up to 6.9 % compared to the initial flow field, cell performance improves as the order of step height rises and the diamond structure connection channels set. The innovative flow fields are supplied as a reference for future flow field design.

Porphyrin-enhanced microbial fuel cell with PCN-600 electrocatalyst for efficient oxygen reduction reaction and eco-friendly energy generation

Microbial fuel cells (MFCs) stand as a sustainable alternative for wastewater treatment and the production of clean energy. The effectiveness of this technology is intricately linked to the cathodic oxygen reduction reaction (ORR). The exceptional tunability of metal–organic frameworks (MOFs) offers a distinctive platform for customizing their inherent properties, making them promising candidates as new electrocatalysts. In this study, metalloporphyrin MOF (PCN-600) with 1D channels and micro/mesoporous structure was prepared utilizing the preassembled [Fe3O(OOCCH3)6] building blocks. Electrochemical measurements demonstrated the superior ORR performance of PCN-600 compared to bare graphite electrodes, with higher onset and half-wave potentials and enhanced electron transfer rates. PCN-600 exhibited a remarkable 52.72 % improvement in power density (179.43 mW m−2) compared to the control group (MFC-Ctrl, 88.41 mW m−2). Additionally, the chemical oxygen demand (COD) removal efficiency was enhanced, with MFC-PCN-600 achieving 82.58 % COD removal compared to 59.87 % in MFC-Ctrl. The electron-withdrawing N and M−N structure of PCN-600 guarantees an outperforming ORR catalyst toward bioelectricity generation during MFCs performance.

Manipulating cathode composition to enhance performance of proton-conducting solid oxide fuel cells through indium doping

One current research direction in proton-conducting solid oxide fuel cells (H–SOFCs) focuses on developing triple-phase conducting cathodes. By optimizing the cerium and indium ratio and adjusting the phase composition of barium ferrate cathode materials, improved power density is achieved in single cells with BaCe0.21Fe0.64In0.15O3-δ (BCFI15) as the cathode, reaching a peak power density of 1473 mW cm−2 at 700 °C. Density functional theory calculations (DFT) further support that the incorporation of indium through doping effectively reduces the energy barrier for proton transition, thereby enhancing proton absorption capability and electrochemical reactivity.

Effects of porosity and porosity distribution in gas diffusion layer on the performances of proton exchange membrane fuel cell

The transmission capability of the gas diffusion layer directly impacts electrochemical reaction and water drainage, consequently, the comprehensive performance and lifetime of the proton exchange membrane fuel cell. The gas diffusion layer's porosity and distribution must be designed effectively as a porous component. This study focuses on experimentally validated models to investigate the effects of porosity and distribution in the gas diffusion layer using three-dimensional numerical simulation. A porosity of 0.6, with a unitary distribution, provides comprehensive improvements in power density while minimizing pressure drops. Additionally, four different distribution patterns of porosity (28 cases) are studied while maintaining an overall porosity of 0.6. The linear porosity distribution (along the flow path) with positive slopes outperforms the alternant distribution due to the cumulative effects on the micro-subsection of the gas diffusion layer. The stepped and/or the sinusoidal distribution can also improve the performances, but just when the step gradient and/or the amplitude are sufficiently small. The adverse effects on the uniformity of current density cause the sinusoidal distribution to be inferior to linear and stepped distribution patterns. The transmission of oxygen significantly affects the dynamic performances, with the distribution patterns of porosity critically influencing sensitivity.

Transformerless Partial Power AC-Link Step-Down Converter

DC–DC power converters are essential for various applications, including photovoltaic systems, green hydrogen production, battery charging, and DC microgrids. Partial Power Converters (PPC) are notable for their efficiency, processing only a fraction of total power and reducing conversion losses, but this performance is overshadowed by the high cost of its construction, associated with high-frequency transformers (HFT). This paper introduces a transformerless partial power AC-link step-down converter, eliminating the need for an HFT and reducing costs while improving power density. An experimental validation using a reduced-scale prototype demonstrates the converter’s operation with a peak efficiency of 93.2% and overall efficiency above 92%, demonstrating the experimental viability of the converter. The proposed AC-link seen as a two-port network is shown to be very attractive for DC–DC step-down operations, and as a possible replacement of traditional PPC.

Nitrogen and Sulfur Co-doped Biomass-Derived Porous Carbon Electrodes for Ultra-High-Performance All-Aqueous Thermally Regenerative Flow Batteries.

Developing high-performance electrodes for the all-aqueous thermally regenerative ammonia battery (ATRB) system, serving as superior substitutes for commercial carbon cloth electrodes, is anticipated to enhance performance, yet it lacks effective guidance and research. In this work, theoretical analysis is initially used to evaluate the effective conversion and adsorption capacity of nitrogen and sulfur co-doped carbon with respect to copper ion by density functional theory calculation. On the basis of this concept, the nitrogen and sulfur co-doped biomass-derived porous carbon electrode (DGC) is prepared using natural porous carbon materials and thiourea. Compared with commercial carbon cloth electrodes, ATRB with DGC achieves a significant improvement in maximum power density of 49.2%. Via optimization of the doping conditions, the active sites can be effectively regulated to boost charge transfer at the reaction interface. Furthermore, the rapid charge transfer can match the excellent mass transfer performance, generating an impressive net power density of 847.5 W/m2.

Structural and electrochemical evaluation of symmetrical and fuel flexible perovskite electrode for low temperature solid oxide fuel cell

Various disadvantages such as indolent oxidation/reduction and carbon-hydrogen (C–H) activation has hindered the commercialization of solid oxide fuel cells (SOFCs) operated with multi fuels at low temperatures (i.e. 400-700)°C. Extensive efforts have been made for the efficient performance of SOFCs by utilizing safe and cheap hydrocarbon fuels at low temperatures. In the current investigation, electrochemical performance of novel anode and cathode material SrMo0.5Fe0.5O3-δ (SMFO) is evaluated in the presence of multi-fuels such as hydrogen (gaseous), ethanol (liquid) and sub-bituminous coal (solid) at low temperature ∼ 700 °C. SMFO (synthesized through solid state reaction route) is thoroughly investigated via X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The average particle size measured is in the range from (60–90) nm. The electrical conductivity and power density is obtained between (190–389) S/cm and (994–1796) × 10−3 W/cm2 respectively among the various fuels. SMFO nanomaterial exhibits greater electrical conduction ∼390Scm−1 and power density ∼1687 × 10−3W/cm2 with ethanol to be utilized as fuel. The activation energies for SMFO are found to be (1.06, 0.65, 0.56) eV in the presence of hydrogen, ethanol and coal respectively. The active conduction and improved power densities make the fabricated nanomaterial well suited for SOFCs (at low temperature) both as cathode and anode with multi-fuel consumption.

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

In this study, pillar shaped yttria-stabilized zirconia (YSZ) 3D microstructures with ∼60 to 90 μm diameter and 12 to 20 μm height are fabricated by 3D inkjet printing to improve the topology of the electrolyte/cathode interface. The microstructures increase the surface area of the cell by ∼2.4% to 4.0% and enhance the connection between the dense YSZ electrolyte and mixed YSZ-lanthanum strontium manganite (LSM) cathode. The morphology and microstructure of the YSZ interface are characterized with scanning electron microscopy. Polarization curves confirm that the power density improves by 47% to 107% at 0.55 V, depending on the dimensions of the microstructures, in comparison to a flat interface. The non-linear improvement in power density with the size of microstructures is confirmed by calculating the uncertainty with repeated tests. Based on electrochemical impedance spectroscopy and distribution of relaxation times analysis, the performance improvement is attributed to changes in the oxygen surface exchange kinetics and O2− diffusivity in the cathode.

A pendulum based frequency-up conversion mechanism for vibrational energy harvesting in low-speed rotary structures

Motivated to run a self-powering monitoring sensor on a wind turbine blade, this paper proposes a pendulum based frequency-up converter that effectively captures a low-speed mechanical rotation into high-frequency vibration of a piezoelectric cantilever beam. A system of governing equations for the proposed concept is developed to describe the motion of the pendulum, the vibration of the beam, and the voltage output of the harvester. Design optimization is performed to improve the power generation performance, and the simulation results are verified experimentally. We demonstrate the improved power density from the proposed concept compared to the disk driven frequency-up converters.

Design and Analysis of an Interior Permanent Magnet Synchronous Motor for a Traction Drive Using Multiobjective Optimization

With the development of new energy industries, the demand for the driving range and power quality of electric vehicle (EV) drive systems is growing rapidly. The drive motor is faced with the challenge of continuously improving power density and performance. This paper proposes a multiobjective optimization method for an interior permanent magnet synchronous motor for a traction drive (IPMSMTD). Based on the flat wire winding technology, the multiobjective optimization design of the IPMSMTD is carried out to improve the motor power density and high-efficiency range, reduce the torque ripple, and suppress the electromagnetic vibration and noise. The structure and size equation of the IPMSMTD are described. The mathematical model considering iron losses is established, and the optimization objectives are determined. Based on the genetic algorithm, a multiobjective optimization mechanism of the magnetic pole structure is established. The operation performance of the motor is analyzed by the finite element simulation and efficiency map. In order to ensure the comprehensive operation index of the IPMSMTD, the vibration noise and modal analysis are carried out, which verifies the rationality of the designed motor and the optimization method.

A High Step-Down SiC-Based T-Type LLC Resonant Converter for Spacecraft Power Processing Unit

A spacecraft power processing unit (PPU) is utilized to convert power from solar arrays or electric batteries to the payload, including electric propulsion, communication equipment, and scientific instruments. Currently, a high-voltage converter is widely applied to the spacecraft PPU to improve power density and save launch weight. However, the high voltage level poses challenges such as high step-down ratios and high power losses. To achieve less conduction loss, a SiC-based T-type three-level (TL) LLC resonant converter is proposed. To further broaden the gain range and achieve high step-down ratios, a variable frequency and adjustable phase-shift (VFAPS) modulation scheme is proposed. Meanwhile, the steady-state time-domain model is established to elaborate the operation principles and boundary conditions for soft switching. Furthermore, the optimal resonant element design considerations have been elaborated to achieve wider gain range and facilitate easier soft switching. Furthermore, the numerical solutions for switching frequency and phase shift (PS) angle under each specific input could be figured out. Finally, the effectiveness of this theoretical analysis is demonstrated via a 500-W experimental prototype with 650∼950-V input and constant output of 48-V/11-A.

State-of-the-Art Lightweight Implementation Methods in Electrical Machines

The demand for high-power density motors has been increasing due to their remarkable output capability and compact construction. To achieve a significant improvement in motor power density, lightweight design methods have been recognized as an effective enabler. Therefore, extensive investigations have been conducted to reduce motor mass and achieve lightweight configurations through the exploration of lightweight materials, structures and manufacturing techniques. This article provides a comprehensive review and summary of state-of-the-art lightweight implementation methods for electrical machines, including the utilization of lightweight materials, structural lightweight design, and incorporation of advanced manufacturing technologies, such as additive manufacturing techniques. The advantages and limitations of each approach are also discussed in this paper. Furthermore, some comments and forecasts on potential future methodologies for motor lightweighting are also provided.

Light-Field Optimization of Deep-Ultraviolet LED Modules for Efficient Microbial Inactivation

Public awareness of preventing pathogenic microorganisms has significantly increased. Among numerous microbial prevention methods, the deep-ultraviolet (DUV) disinfection technology has received wide attention by using the nitride-based light-emitting diode (LED). However, the light extraction efficiency of DUV LEDs and the utilization rate of emitted DUV light are relatively low at the current stage. In this study, a light distribution design (referred to as the reflective system) was explored to enhance the utilization of emitted DUV from LEDs, leading to successful and efficient surface and air disinfection. Optical power measurements and microbial inactivation tests demonstrated an approximately 79% improvement in average radiation power density achieved by the reflective system when measured at a 5 cm distance from the irradiation surface. Moreover, a statistically significant enhancement in local surface disinfection was observed with low electric power consumption. The reflective system was integrated into an air purifier and underwent air disinfection testing, effectively disinfecting a 3 m3 space within ten minutes. Additionally, a fluorine resin film at the nanolevel was developed to protect the light module from oxidation, validated through a 1200 h accelerated aging test under humid conditions. This research offers valuable guidance for efficient and energy-saving DUV disinfection applications.

LTspice Modeling for GaN-GIT HEMT Including Cryogenic Temperature

Highly efficient electrically driven avionics have led to a renewed interest in cryogenic propulsion systems with the goal of reducing carbon emission footprint. Although cryogenic converters promise better efficiency and improved power density, the successful design is incumbent upon the appropriate switching device selection and simulation-based analyses prior to initial prototyping. In this work, a datasheet-driven compact model for a gallium nitride (GaN) Gate Injection Transistor (GIT) has been proposed and implemented in LTspice, a versatile, high performance, and free circuit simulator in order to investigate the merit of the chosen device in a power electronic system.

Green moisture-electric generator based on supramolecular hydrogel with tens of milliamp electricity toward practical applications.

Moisture-electric generators (MEGs) has emerged as promising green technology to achieve carbon neutrality in next-generation energy suppliers, especially combined with ecofriendly materials. Hitherto, challenges remain for MEGs as direct power source in practical applications due to low and intermittent electric output. Here we design a green MEG with high direct-current electricity by introducing polyvinyl alcohol-sodium alginate-based supramolecular hydrogel as active material. A single unit can generate an improved power density of ca. 0.11 mW cm-2, a milliamp-scale short-circuit current density of ca. 1.31 mA cm-2 and an open-circuit voltage of ca. 1.30 V. Such excellent electricity is mainly attributed to enhanced moisture absorption and remained water gradient to initiate ample ions transport within hydrogel by theoretical calculation and experiments. Notably, an enlarged current of ca. 65 mA is achieved by a parallel-integrated MEG bank. The scalable MEGs can directly power many commercial electronics in real-life scenarios, such as charging smart watch, illuminating a household bulb, driving a digital clock for one month. This work provides new insight into constructing green, high-performance and scalable energy source for Internet-of-Things and wearable applications.

Self‐Sacrificial Template Synthesis of Fe‐N‐C Catalysts with Dense Active Sites Deposited on A Porous Carbon Network for High Performance in PEMFC

AbstractIron‐nitrogen‐carbon (Fe‐N‐C) single‐atom catalysts are promising sustainable alternatives to the costly and scarce platinum (Pt) to catalyze the oxygen reduction reactions (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). However, Fe‐N‐C cathodes for PEMFC are made thicker than Pt/C ones, in order to compensate for the lower intrinsic ORR activity and site density of Fe‐N‐C materials. The thick electrodes are bound with mass transport issues that limit their performance at high current densities, especially in H2/air PEMFCs. Practical Fe‐N‐C electrodes must combine high intrinsic ORR activity, high site density, and fast mass transport. Herein, it has achieved an improved combination of these properties with a Fe‐N‐C catalyst prepared via a two‐step synthesis approach, constructing first a porous zinc‐nitrogen‐carbon (Zn‐N‐C) substrate, followed by transmetallating Zn by Fe via chemical vapor deposition. A cathode comprising this Fe‐N‐C catalyst has exhibited a maximum power density of 0.53 W cm−2 in H2/air PEMFC at 80 °C. The improved power density is associated with the hierarchical porosity of the Zn‐N‐C substrate of this work, which is achieved by epitaxial growth of ZIF‐8 onto g‐C3N4, leading to a micro‐mesoporous substrate.

Structured mesh material with gradient surface wettability for high-power-density proton exchange membrane fuel cells

ABSTRACT A compact cell structure is highly desirable for next-generation high-power-density proton exchange membrane (PEM) fuel cell (>9.0 kW L−1). A novel integrated bipolar plate (BP) – gas diffusion layer (GDL) structure utilizing porous material is a promising configuration, which not only improves output power due to the reduced transport resistance but also reduces cell thickness. Herein, we propose a structured mesh material with gradient surface wettability for this cell structure, which is characterized by an ordered skeleton in the three-dimensional (3D) space with high structure design flexibility. It is experimentally found that the structured mesh material shows higher performance than serpentine and parallel flow fields. Meanwhile, 3D modeling work on an automobile fuel cell (cell area: 245.76 cm2) with the distribution zones of dot matrix structure for hydrogen, air and coolant flow, is conducted, and it is found that the structured mesh material effectively decreases the concentration and electric ohmic losses in comparison with the traditional “BP/flow field + GDL” structure, improving power density with uniform distribution characteristics. Moreover, the gradient wettability on the mesh surface helps promote the water detach the GDL and hold the residual liquid water in the top region, optimizing the water management.

Comparative Evaluation of Dual-Purpose Converters Suitable for Application in DC and AC Grids

This paper presents a comparative evaluation of several topological solutions to the universal power electronics interface for the dc or single-phase ac grids using the same terminals. The idea of a dual-purpose approach lies in the utilization of the same semiconductors in the dc-dc and in the dc-ac configuration, resulting in minimal redundancy. Particular focus is on the power density improvement and control. Out of the three solutions under investigation, the first is the buck-boost cell with unfolding circuit presented earlier. The second solution is a conventional voltage source inverter with an intermediate boost cell considered as one of obvious competitors. The third design is based on a phase-modular solution with buck-boost cells. The design example and experimental prototypes of the universal power electronics interface converter rated for 3.6 kVA power in the ac mode and more than 5 kW in the dc mode are presented. Our experimental results demonstrate the ability of operation in the ac or dc grids with main corresponding modes. Possible applications along with main benefits are addressed in the conclusions.

Tailoring the electron free path in an ultra-lightweight gas-solid composite insulation system for high dielectric strength

Reliable electric insulation is the premise for the application of high-voltage technologies, such as power transmission, emergent electrified transportations, and advanced propulsion systems. With the current insulation strategy, the credibility of insulation system depends on the sufficient insulation materials usage, suffering from bulky structure, expensive production costs and environmental pollution. Here, we propose a strategy that applies a lightweight multiple-barrier skeleton in gas insulation to tailor electron free path and restrain electron avalanche, thus realizing a high insulation strength with less material usage. This strategy is verified by the composite insulation of porous polyimide aerogel and various types of insulating gases. It achieves a comparable insulation strength to conventional polymers by less than 10% materials usage. With above insulation strategy, a 152.5% improvement in power density and a 54.6% weight reduction are acquired in the cable system for more or all electric aircraft. This strategy inspires the design of efficient insulation solution with both high breakdown strength and lightweight.