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Paper-based self-pumping microfluidic fuel cells (PMFCs) typically exploit the wicking effects in porous papers to enable passive reactant delivery and co-laminar flow, eliminating micro pumps and physical membranes. PMFCs have been regarded as promising micro-power sources for next-generation paper-based electrochemical microfluidic assays for biomedical applications. However, the PMFC performance is fundamentally limited by the low capillary flow velocity and ineffective diffusive fuel transport. In this study, a novel PMFC with an anodic wedge-shaped channel is developed. The anodic wedge-shaped channel enables reactant convection at improved fuel flow velocity. Visualization experiments suggest that the fuel flow velocity can be improved by about 23 times in this anodic wedge-shaped channel configuration as compared to that in conventional single-layer paper-based flow channel. In addition, favorable features like localized enhancement of fuel transport and reduced fuel crossover are also observed in this novel configuration. Due to enhanced convective-diffusive fuel transport, the cell performance can be improved 245.8 % as compared to the single-layer case. The peak power density reaches 59.9 mW cm−2 and the limiting current density achieves 305.9 mA cm−2, outperforming most of the previous PMFCs. This anodic wedge-shaped channel configuration can also be potentially used in paper-based assays to enhance reactant delivery. • Wedge-shaped channel is formed by inserting anode between two-layer flow channel. • The anodic wedge-shaped channel can significantly increase fuel flow velocity. • The anodic wedge-shaped channel also helps to reduce fuel crossover. • Anodic fuel transport is enhanced by convection and diffusion. • The peak power density is increased 245.8 % by using wedge-shaped channel. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the microporous layer (MPL) and wet proofing on the MacMullin number has been evaluated for a custom series of Toray TGP-H-060 carbon paper gas diffusion layer (GDL). Complementary characterizations for these GDLs were performed by using scanning electron microscopy (SEM) images, pore size distribution (PSD) and fuel cell performance. The GDLs were customized by the addition of a microporous layer (MPL) and the treatment of, either or both, the substrate and MPL with 10% and 40% hydrophobic agent. SEM images correlated very well with the data shown for PSD. Distinction between the substrate layer and the MPL were clearly shown as two different slopes in the integral distribution and two different peaks in the differential distribution. The MacMullin number increased with increase in wet proofing but decreased with the addition of the MPL. The MacMullin number is a key parameter that contains the missing information for the path length in GDLs, which is generally approximated with the Bruggeman expression. The results provided an overview for the interpretation of the combined effect of the substrate and MPL properties as well as the cell operating conditions. [Copyright &y& Elsevier]

This paper presents a novel design and operation of microbial fuel cells (ΜFCs), which contain monolayer paper-based substrate/electrodes and microchannels with co-laminar flow. The electrodes with multi-wall carbon nanotubes are fabricated by the screen-printing method and the microchannels are patterned using photo-lithography. A double-inlet and diverging channel design is incorporated in the fuel cell configuration and demonstrated significantly improved performance. The fluid flows of electrolytes through the porous paper media are simulated using steady-state and transient computational fluid dynamics The best performance is achieved under the following conditions: an electroactive microbial (S. oneidensis) concentration of OD 600 1.5, 50 mM electron donor (lactate), and direct immobilized of the inoculum on the anode surface. The developed MFCs achieves a peak power density of 19.4 ± 0.23 μW cm−2 and maximum current density of 190.4 ± 1.39 μA cm−2, surpassing the performance of all previously reported paper-based single MFCs that utilize paper-based electrodes. In addition, hybrid-type MFCs that containing enzymatic air-breathing cathodes are investigated to enhance their performance. The novel paper based self-pumping MFC has the potential to make lab-on-a-chip type portable medical diagnosis devices with integrated power sources practical and feasible. [Display omitted] • A paper-based membraneless co-laminar flow microbial fuel cell was developed. • Microfluidic fuel cell was micromachined as a monolayer structure in paper substrate. • Co-laminar flow of the electrolyte through paper was simulated using CFD analysis. • Inoculation method, anolyte type, and cell configuration were tested and optimized. • A hybrid microbial-enzymatic fuel cell was also examined for performance improvement. [ABSTRACT FROM AUTHOR]

Abstract: While carbon fiber paper (CFP) has been widely used in batteries, fuel cells, and supercapacitors, its effect on device performance can be rather complicated. In this study, we examined the effect of CFP from different batches on the performance of a CFP-supported MnOx hybrid supercapacitor (CFP/MnOx). It is found that the contribution of the MnOx to the capacitance is dominating if the MnOx coating on CFP is dense and conformal, but becomes much less significant if the MnOx coating on CFP is porous or non-conformal. This is because annealing CFP/MnOx at 400 °C in air is necessary to obtain proper MnOx phases for high capacitance; the annealing process may increase the specific surface area of CFP if it is not fully covered by MnOx. Also, the etching of carbon surface weakens the attachment of MnOx to CFP and worsens the electrical connection of MnOx to CFP, further reducing the contribution of MnOx to capacitance. Finally, much to our surprise, it is found that the properties of the CFP varied from batches to batches, which critically influence the MnOx coating morphology/density. These factors in turn greatly affect the contribution of each component to the capacitance of the CFP/MnOx hybrid supercapacitors. [Copyright &y& Elsevier]

The gas diffusion layer (GDL) is considered one of the most significant components in the proton exchange membrane fuel cell (PEMFC). Its electrical impedance is crucial to the performance of power generation for PEMFC. The study of the conduction mechanism of the GDL substrate-carbon fiber paper(CFP) treated with PTFE is still a considerable challenge. This work reveals that the type and number of contact points are direct factors that affect CFP through-plane resistance. The CFP resistance along the through-plane direction is a function of the contact point density inside CFP, rather than traditional loading pressure. Based on the structural characteristics of CFP, a graph theory model that can express the complex three-dimensional structure and anisotropy of CFP is constructed instead of the finite element model or formula model—using the characterization of the distribution of PTFE in the CFP section. The accuracy of model prediction for the CFP resistance of 0 wt% and 20 wt% PTFE can reach 95% and 90%, respectively. This study provides a fundamental basis for the design and processing of CFP with lower electrical loss and is of great significance for further improving the power generation efficiency of PEMFC. Image 1 • A mechanism to explain the essential effect of PTFE on the conduction is proposed. • PTFE affects electrical resistance by changing the contact state of carbon fibers. • Graph theory model can be well used to simulate the conductivity of carbon paper. • There is huge potential for the reduction of electrical resistance in carbon paper. [ABSTRACT FROM AUTHOR]

A paper-based membraneless single-compartment hydrogen peroxide power source prepared by micro-electromechanical systems (MEMS) technology is reported. The cell utilizes hydrogen peroxide as both fuel and oxidant in a low volume cell fabricated on paper. The fabrication method used is a simple method where precise, small-sized patterns are produced which include the hydrophilic paper bounded by hydrophobic resin. Open circuit potentials of 0.61 V and 0.32 V are achieved for the cells fabricated with Prussian Blue as the cathode and aluminium/nickel as the anode materials, respectively. The power produced by the cells is 0.81 mW cm −2 at 0.26 V and 0.38 mW cm −2 at 0.14 V, respectively, even after the cell is bent or distorted. Such a fuel cell provides an easily fabricated, environmentally friendly, flexible and cost saving power source. The cell may be integrated within a self-sustained diagnostic system to provide the on-demand power for future bio-sensing applications. [ABSTRACT FROM AUTHOR]

Easily disposable low cost fuel cells as power sources are environmentally benign alternates to batteries for powering micro-analytical systems. In this regard, for the first time, an ethanol-dichromate fuel-oxidant microfluidic fuel cell is implemented on a paper scaffold. In this cell, a proton conducting poly (4-styrenesulfonate) based gel electrolyte enables proton transport from the anode to the cathode. Hydrothermally synthesized molybdenum oxide nanorods catalyze dichromate reduction and ethanol oxidation at the respective electrodes. A peak power density of 6.32 mWcm −2 is achieved with the catalyst. However, the cell without catalyst delivers a maximum power density of only 2.74 mWcm −2 . The compositions of the catholyte and anolyte streams and molybdenum oxide loadings are optimized. A stack of two cells connected in series illuminates a 3 mm red light emitting diode for over 40 min. This real time demonstration showcases the potential of this cell as an alternative to batteries for powering micro-analytical devices. [ABSTRACT FROM AUTHOR]

A paper microfluidic fuel cell was developed that is powered by urea and compares favorably to recent literature reports of paper microfluidic fuel cells. During fuel cell testing, we found the maximum power density to be as high as 0.91 mW cm −2 and the maximum current density to be as high as 4.3 mA cm -2  at room temperature using 0.3 M urea as fuel. Under continuous reactant flow, the fuel cell voltage is stable for at least 1 h. Under stopped flow conditions, the voltage was stable for up to 20 min. When 3 fuel cells (using Ni anode) were connected in series, sufficient energy was produced to power the LCD screen of a paper-based, over-the-counter pregnancy test for at least 30 min. Since this fuel cell is constructed on paper, it does not require continuous flow of reactants as a micro-channeled microfluidic fuel cell would. Hence, it could be possible with this chemistry to integrate energy production with urinalysis on paper since human urine contains both urea (fuel) and hormones (analyte) to provide power and analyte simultaneously. [ABSTRACT FROM AUTHOR]

With emerging stability issues in fuel cell technology, a non-conventional catalyst not supported on carbon materials has been highlighted because it can avoid negative influences of carbon support materials on the stability, such as carbon corrosion. The nanostructured thin film catalyst is representative of non-conventional catalysts, which shows improved stability, enhanced mass specific activity, and fast mass transfer at high current densities. However, the nanostructured thin film catalyst usually requires multi-step processes for fabrication, making its mass production complex and irreproducible. We introduce a Pt-Cu alloy nanostructured thin film catalyst, which can be simply prepared by electrodeposition. By using hydrogen bubbles as a template, a three-dimensional free-standing foam of Cu was electrodeposited directly on the micro-porous layer/carbon paper and it was then displaced with Pt by simple immersion. The structure characterization revealed that a porous thin Pt-Cu alloy catalyst layer was successfully formed on the micro-porous layer/carbon paper. The synthesized Pt-Cu alloy catalyst exhibited superior durability compared to a conventional Pt/C in single cell test. [ABSTRACT FROM AUTHOR]

Abstract: The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) with multi-reflection solid boundary conditions is used to study anisotropic permeabilities of a carbon paper gas diffusion layer (GDL) in a fuel cell. The carbon paper is reconstructed using the stochastic method, in which various porosities and microstructures are achieved to simulate different samples. The simulated permeability and tortuosity show anisotropic characteristics of the reconstructed carbon papers with in-plane permeability higher than through-plane, and in-plane tortuosity lower than through-plane. The calculated permeabilities are in good agreement with existing measurements. The relationship between the permeability and the porosity is fitted with empirical relations and some fitting constants are determined. Furthermore, the obtained relationship of tortuosity and porosity is used in a fractal model for permeabilities. The results indicate that the fractal model and the Kozeny–Carman equation provide similar predictions on the through-plane permeability of the carbon paper GDL. [Copyright &y& Elsevier]

The printable paper-based enzymatic biofuel cell (PBFC) to directly power small devices is an important objective for realizing cost-effective and disposable energy harvesting devices. In the present study, a screen-printed circular-type PBFC, composed of a series of 5 individual cells, was constructed. The PBFC exhibited the open circuit potential of 2.65 V and maximum power of 350 μW at 1.55 V, which were sufficient to illuminate an LED without requiring a booster circuit. The output voltage of this PBFC can also be easily adjusted as required. [ABSTRACT FROM AUTHOR]

This work demonstrates a stand-alone power source that integrates a paper-based hydrogen fuel cell with a customized chemical heater that produces hydrogen in-situ upon the addition of a liquid. The presented approach operates by capillary action and takes advantage of the hydrogen released as a by-product of an exothermic reaction used in point-of-care diagnostics. The paper-based fuel cell produces a maximum power of 25.8 mW (103.2 mW cm −2 ), which is suitable for powering a diversity of electrical devices such as commercially available digital pregnancy tests and glucometers. While device shape and dimensions can be customized, here it is shown that the fuel cell can be designed in a compact form factor and footprint comparable to a lateral flow test while providing a remarkable power output. This approach holds great promise for powering portable diagnostics, as the generated electric power could enable device functionalities required for advanced assays, such as device timing, actuation, and signal quantification. Part of the same liquid sample that is to be analyzed (urine, saliva, water, etc) could be used to trigger the hydrogen generation and start the fuel cell operation. [ABSTRACT FROM AUTHOR]

Abstract: This study employed fuel cell gas diffusion layers (GDLs) consisting of carbon fiber paper made from carbon fiber felt with different yard weights in proton exchange membrane fuel cells (PEMFCs), and investigated the relationship between the yard weight of the carbon fiber paper and the fuel cell performance and thickness of the gasket. In this paper we discuss the relationship between carbon fiber felt with different yard weights and fuel cell performance and also explore the effect of carbon fiber paper thickness, air permeability, surface resistivity, and structural study. We focused on the material used for the gas diffusion layer in this study. Carbon fiber paper made in-house in this study contained 10wt% (all percentages are by weight unless otherwise noted) phenolic resin. When the tested area was 25cm2, the test temperature was 40°C, the gasket thickness was 0.06mm, and the yard weight 70gm−2, fuel cell current density was 1968mAcm−2 at a load 0.3V. When the gasket thickness was 0.36mm and yard weight was 190gm−2, fuel current density was 1710mAcm−2 at a load of 0.3V. [Copyright &y& Elsevier]

Abstract: This study uses fuel cell gas diffusion layers (GDLs) made from carbon fiber paper containing carbon black in proton exchange membrane fuel cells (PEMFCs) in order to determine the relationship between carbon black content and fuel cell performance. The connection between fuel cell performance and the carbon black content of the carbon fiber paper is discussed, and the effects of carbon black on the carbon fiber paper''s thickness, density, and surface resistivity are investigated. When a carbon fiber paper GDL contains 10wt% phenolic resin and 2% carbon black, and reaction area was 25cm2 and operating temperature 40°C, tests show that a carbon electrode fuel cell could achieve 1026.4mAcm−2 and maximum power of 612.8mWcm−2 under a 0.5V load. [Copyright &y& Elsevier]

A general mathematical model is developed for electrochemical energy conversion in paper-based, capillary-driven, microfluidic flow cells. A two-dimensional version of the model is implemented to simulate a novel flow cell of this kind called PowerPAD. The methodology developed is validated against experimental data for this particular cell under both steady and unsteady modes of operation. It is shown that a 2D model can represent a 3D cell in unsteady flows provided that the Nernst-Planck equation is properly refined. The results are interpreted in terms of transient back-diffusion and crossover of the reactant species which are found to be the key factors controlling the electrochemical performance of this cell. The validated model is used to enhance the power output, runtime, and energy efficiency of this particular cell through altering its flow architecture and microstructure of electrodes and absorbent pad. The refined cell design is shown to roughly triple the power output and runtime of the device. The optimized design also outperforms the original design in terms of energy efficiency. The developed mathematical model, the fundamental understanding, and the proposed cell design may be utilized to develop new devices and concepts for capillary-based electrochemical systems, including biodegradable batteries, fuel cells, and electrolyzers. [Display omitted] • A dynamic mathematical model is developed for paper-based microfluidic flow cells. • A 2D model can represent a 3D cell subject to Nernst-Planck equation refinement. • The model reveals the unique working mechanism of imbibition and back-diffusion. • Crossover is identified as the key limiting factor for cell performance and runtime. • An optimized cell design is proposed with 3x performance improvement. [ABSTRACT FROM AUTHOR]

Under the dual pressure of energy consumption and environmental pollution, mankind hopes to develop clean and renewable alternative energy, and the rapid development of fuel cells meets people's demand for energy-efficient power systems. The emergence of portable micro energy systems represented by microfluidic fuel cells, such as paper-based microfluidic fuel cells, has greatly enriched the means of medical detection to better cope with the threat of disease transmission. In this work, the numerical simulation method is innovatively introduced to study the paper-based microfluidic fuel cells. Both transient and steady-state modes are employed to demonstrate the whole operation process of the paper-based microfluidic fuel cell. In addition, the different structural parameters, including electrode spacing, the distance between electrode and inlet, channel thickness, and electrode length, are also investigated their influence mechanisms on cell performance. Results show that the increase of most structural parameters decreases cell output power in different degrees. Even on the premise that increasing channel thickness has a positive impact on the output power, the fuel utilization still shows a downward trend. These conclusions provide theoretical support and reference for future optimization work and accelerate the development of microfluidic fuel cells. • Numerical simulation is employed to study paper-based microfluidic fuel cell. • The effects of structure parameters on cell performance are discussed. • Through fuel concentration distribution to reveal cell performance mechanism. • Fuel utilization is used to evaluate energy efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The porous carbon electrode in a fuel cell not only acts as an electrolyte and a catalyst support, but also allows the diffusion of hydrogen fuel through its fine porosity and serves as a current-carrying conductor. A suitable carbon paper electrode is developed and possesses the characteristics of high porosity, permeability and strength along with low electrical resistivity so that it can be effectively used in proton-exchange membrane and phosphoric acid fuel cells. The electrode is prepared through a combination of two important techniques, viz., paper-making technology by first forming a porous chopped carbon fibre preform, and composite technology using a thermosetting resin matrix. The study reveals an interdependence of one parameter on another and how judicious choice of the processing conditions are necessary to achieve the desired characteristics. The current–voltage performance of the electrode in a unit fuel cell matches that of a commercially-available material. [Copyright &y& Elsevier]

A microporous PTFE/carbon sublayer between the carbon paper and the catalyst layer played a crucial role in PEM fuel cells. Such a layer reduced the difference among different carbon paper types made by different manufacturers or by the same manufacturer at different times. When such a sublayer was present, the carbon paper seemed to function merely as a support that provided the mechanical strength for the sublayer. A sublayer was extremely useful if the carbon paper was prone to flooding. Sublayers of different thickness containing 24, 35 and 45% PTFE were tested. A four-cell stack could operate stably at a current density of 145 mA/cm2 using unhumidified air and hydrogen when sublayered carbon paper was employed. [Copyright &y& Elsevier]

The present work deals with a frugal paper-based microbial fuel cell (PMFC) that generates an average power of 25 μW per device using Shewanella putrefaciens. Bacteria colonized on the paper matrix can be activated by readily available nutrient sources leading to instant power generation. Current study translates this technology to energize a wireless Internet of Things (IoT) sensor. A well-designed stacking of multiple cells is adopted to boost the power output. The power profile characteristics of three 10-unit PMFC configurations namely series (C1), parallel (C2), and combination of both (C3) are investigated. Attempts to directly charge a supercapacitor using serially-connected PMFC stack results in voltage reversal (VR). Hence, to harvest this microbial energy prudently, a customized power management system consisting of integrated Maximum Power Point Tracking (MPPT) feature is deployed. This helps in interfacing the PMFCs to capture charge, boost the harvested voltage and to prevent voltage reversal (VR). Power harvested from PMFCs is stored into a supercapacitor in order to drive the wireless IoT sensor module, which in turn measures temperature and communicates the data to a smart phone. The current endeavours can pave the way for "bacteria powered IoT devices" by unlocking the potential of microbes through PMFCs. Image 1 • PMFCs serve as instant power generation sources. • Voltage reversal was observed in serially connected PMFC stacks. • A tailored energy harvesting scheme was proposed for PMFCs. • An IoT temperature sensor node was powered by PMFC stack. [ABSTRACT FROM AUTHOR]

Abstract: Solid oxide fuel cells using non-glass sealants have become increasingly common. In this paper, fumed silica infiltrated ceramic fiber paper with pre-compression was compared with plain and pre-compressed at 10MPa hybrid mica as compressive seals. Leakage tests were measured under a 0.1–1.0MPa compressive load with the pressure gradient varying from 2 to 15kPa. The results demonstrated that the leakage rate of infiltrated fiber paper was 0.04sccmcm−1 for a 10kPa gradient, under 1.0MPa compressive load, while for mica it was 0.60 and 0.63sccmcm−1 which indicated that the infiltrated ceramic fiber paper showed a much lower leakage than mica. Long-term thermal cycling tests demonstrated that although the leakage of fumed silica infiltrated fiber paper was slightly higher than that of hybrid mica, it remained stable after 20 thermal cycles and no interlayer was needed. The mass loss of the fiber paper was 1.7×10−2 mgcm−2 h−1 in a hydrogen environment at 1073K for 200h. The leakage of infiltrated fiber paper remained about 0.06sccmcm−1 after reduction. [Copyright &y& Elsevier]

Paper-based microfluidic fuel cells are prominent in flexible electronics, including wearable and disposable devices, such as smart packages and point-of-care diagnostics. However, the performance is generally low, and the long-term durability is questionable. In this work, we propose a flexible paper-based fuel cell with a novel cell architecture that adopts a single flow for the delivery of both the fuel and the supporting electrolyte. During cell operation, the anode is immersed in a liquid fuel with a supporting electrolyte, while the cathode is exposed to the ambient air. The performance of this cell is increased by one order of magnitude compared to the conventional co-flow cell architecture due to the enhanced mass transfer. A maximum power density of ~20 mW/cm2 and a maximum current density of 122.9 mA/cm2 are achieved, which are the highest among all reported paper-based direct formate fuel cells. Furthermore, this cell can steadily discharge at 5 mA cm−2 for more than 10 days continuously, while the morphology of the anode and the cathode before and after cell operation remains unchanged. Finally, this paper-based fuel cell can be efficiently fabricated by 3D printing, which is simple, low cost, and advantageous for paper-based fuel cell fabrication. • An innovative architecture for a single-flow paper-based fuel cell (PBFC) is proposed. • The air-breathing PBFC uses formate as fuel, which can be efficiently fabricated by printing. • A peak power density of 20 mW/cm2 and a cut-off current density of 123 mA/cm2 are achieved. • The PBFC can discharge at 5 mA cm−2 for more than 10 days continuously until fuel depletion. • The PBFC can be re-activated by refueling. [ABSTRACT FROM AUTHOR]

Abstract: This article reports two routes, microwave-assisted synthesis and thermal reduction, to deposit silver nanoparticles on oxidized carbon paper (CP) electrodes. In comparison, as-grown Ag particles, prepared by the microwave-assisted route, exhibit uniform particle size and well-dispersion over the CP substrate. Electrochemical behavior of Ag–CP electrodes is characterized by cyclic voltammetry and AC impedance spectroscopy, incorporated with equivalent circuit. Both the catalyst electrodes display redox reversibility within the potential region of 0–0.5V vs. saturated calomel electrode (SCE) in 1M NaOH. According to the Randles–Sevcik plot, the diffusion coefficient under voltammetric regime ranges from 9.06×10−10 to 3.33×10−10 cm2 s−1. These differences of diffusion coefficient and capacitance are ascribed to the resulting Ag nanocatalysts with small particle size and no aggregation. On the basis of the results, the microwave-assisted approach for depositing nano sized Ag catalysts on CP electrodes shows the potential in application of alkaline fuel cells because of its fast synthesis, high activity, and simplicity. [Copyright &y& Elsevier]

Macroscopic continuum models are an essential tool to understand the complex transport phenomena that take place in gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs). Previous work has shown that macroscopic models require effective properties obtained under uniform saturation conditions to get a consistent physical formulation. This issue, mostly unappreciated in the open literature, is addressed in detail in this work. To this end, lattice Boltzmann simulations were performed on tomographic images of dry and water-invaded carbon-paper GDL subsamples with nearly uniform porosity and saturation distributions. The computed effective diffusivity shows an anisotropic dependence on local porosity similar to that reported for morphologically analogous GDLs. In contrast, the dependence on local saturation is rather isotropic, following a nearly quadratic power law. The capability of the local correlations to recover the layer-scale properties obtained from inhomogeneous GDLs is checked by global averaging. Good agreement is found between the upscaled results and the diffusivity data of the GDL from which the present subsamples were taken, as well as other global data presented in the literature. A higher blockage effect of local saturation is, however, expected for the under-the-rib region in operating PEFCs. [ABSTRACT FROM AUTHOR]

Paper-based vanadium membraneless co-laminar flow fuel cells with graphene paste electrodes are developed to enhance the power density. The developed fuel cells are precisely microfabricated utilizing photolithography and screen printing methods for flow channel patterning and electrode forming, respectively. The measured fuel cell performances change with varying concentrations of fuel/oxidant (0.5–2.0 M V2+/VO 2 +) and a support electrolyte (0.5–4.0 M H 2 SO 4). The maximum power density (15.09 ± 1.05 mW cm−2) and maximum current density (30 ± 0.62 mA cm−2) are the highest for concentrations of 2.0 M vanadium redox couple and 2.0 M sulfuric acid. The performance of the proposed fuel cell is also affected by contact with air. Regardless of air contact, the prototype paper-based vanadium fuel cell shows higher performance than those of previously reported paper-based co-laminar flow fuel cells. This novel proof-of-concept fuel cell is important for achieving the required power density for practical use of paper-based microfluidic fuel cells. • Vanadium redox couple is proposed for both fuel and oxidant in the paper-based fuel cell. • Micromachining is used to make precise and reproducible paper-based fuel cells. • Vanadium-based fuel cell shows better performance than other fuel-based fuel cells. • Contact with air adversely affects paper-based vanadium co-laminar flow fuel cells. • The performance depends on the concentration of fuel, oxidant, and electrolyte. [ABSTRACT FROM AUTHOR]

A novel photocatalyst is designed by surface modification and cocatalyst loading of graphitic carbon nitride (g-C 3 N 4) with ammonium hydroxide and silver nanocubes (AgNCs), respectively. The synergistic effect of the modification in the intralayer of g-C 3 N 4 and surface plasmon resonance (SPR) bands of AgNCs significantly enhances the migration and separation efficiency of photo-induced charge carriers. A nickel mesh coated with photocatalyst and the carbon paper loaded with pristine g–C 3 N 4 –mixed iron phthalocyanine (FeIIPc) used as the photoanode and cathode, respectively, are constructed for the self-powered photoelectrochemical cell, which exhibits the maximum power density of 0.74 mW cm−2. The AHCN/AgNCs-based cell reveals approximately a 3.1-times enhancement in maximum power density compared with the pristine g–C 3 N 4 –based cell. In addition, the photocatalytically generated H 2 O 2 (chemical energy) can be stored in water, and then used as fuel by the connection of two electrodes in the dark. After the fuel cell is operated for 12 h, the specific capacitance retention rate still maintains as high as 57.2 %, which is the greatest retention rate in comparison with the previously reported H 2 O 2 fuel cell systems. Our work offers a feasible opinion on how to improve the visible light utilization of semiconductors by tuning the intralayer properties and loading plasmonic metal. • A novel composite photocatalyst (AHCN/AgNCs) is applied in the H 2 O 2 fuel cell. • The metal-semiconductor heterojunction facilitate the photocatalytic H 2 O 2 production. • The AHCN/AgNCs produces 0.045 M H 2 O 2 under light irradiation for 2.5 h. • The specific capacitance keeps 57.2 % of initial value after 12 h of cell operation. [ABSTRACT FROM AUTHOR]

Developing a fast diagnostic technology for membranes and accurately predicting the lifetime of membranes that can effectively reduce the manufacturing cost and overcome the technical barriers of proton exchange membrane fuel cell (PEMFC) lifetime. This paper focuses on developing an ex-situ accelerated chemical degradation method and investigating the impact of chemical degradation on membrane structure and fuel cell performance. The results show that voltage drop and hydrogen permeation current can detect the state online and predict the remaining lifetime of membrane electrode assembly (MEA). The aging rate is faster by three orders of magnitude than that of the published results by the established aging way. This study provides an additional decision for evaluating performance degradation and fuel cell system optimization, which could potentially lead to further improvements in the efficiency and durability of PEMFC systems. • The paper has developed an ex-situ accelerated chemical degradation method. • Voltage drop and hydrogen permeation current can predict the lifetime of the MEA. • The aging rate is three orders of magnitude faster than that of the published results. [ABSTRACT FROM AUTHOR]

This work presents the construction and evaluation of a membraneless nanofluidic fuel cell made with fiberglass using flow-through porous electrodes based on Toray paper, coupled with a microelectronic interface to supply energy to low-power demand applications. The device performance is optimized for different operating conditions related with flow rate, stoichiometry and concentration and employing formic acid as fuel. Evaluation tests were performed with a homemade testing station using a commercial varying resistance. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cells and the economics of unmanned aerial vehicles (UAVs) are gaining global attention. With higher energy densities, fuel cells can overcome the range limitations of lithium battery-powered aircraft. This paper is to address two important issues often overlooked in research on fuel cell UAVs. It innovatively quantified the ranges within which fuel cells remain a better option and originally focused on the impact of altitudes on the power demand. A detailed literature review was conducted to determine the flight profile. Environment models, power demand models, and other models were established using MATLAB to analyse the impact of altitude on performance. Some parameters were obtained through fluid field simulations using Ansys. The study shows that using air-cooled fuel cells in a 3.5 kW UAV is a superior solution compared to lithium batteries when the energy demand exceeds 2.8 kWh. Furthermore, the power demand increases by 3.5 % per kilometre in altitude, and the maximum flight altitude is reduced by approximately 266 m per kilogram of take-off mass. It also emphasizes that solely increasing the air stoichiometric ratio cannot always enhance performance. Through sensitivity analysis, it was found that improving the stack's power density has the highest relative gain. • A comprehensive UAV system model and a thorough system matching are made. • Energy density and endurance of fuel cell and lithium battery UAVs are compared. • The impact of altitude on power requirements and heat dissipation are analysed. • Sensitivity analysis, assessing the influence of eight parameters, is conducted. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cell (PEMFC) is characterized by environmental protection and energy saving, clean and pollution-free, which is consistent with the development background of the current era. At present, it has become the development direction of many countries. The short lifetime and poor durability of PEMFC are the main problems restricting their application and industrial development. Especially in the transportation field, there is still a big gap between PEMFC and internal combustion engine in terms of lifetime. State of health (SOH) monitoring and prediction is an important approach to improve the durability and reliability of PEMFCs. By analyzing the mechanism of fuel cell degradation, extracting the parameters that characterize the degradation process and monitoring them in real time can realize the SOH prediction of PEMFC, which can effectively avoid the damage and loss of life of the fuel cell. The improvement of the accuracy of SOH monitoring under dynamic operating conditions and the exploration of more efficient and comprehensive prediction models and methods are key challenges in SOH monitoring and prediction of PEMFC systems. This paper mainly summarizes the different monitoring and prediction methods applied in PEMFCs, and explores the strategies for evaluating the prediction results. • Short lifetime and poor durability of PEMFCs are the key problems in application. • SOH prediction is an important method to improve the reliability of PEMFC. • Degradation mechanisms of PEMFC and effects on system are investigated. • Feature parameters for SOH monitoring and prediction are presented. • SOH prediction methods and results evaluation methods are summarized. [ABSTRACT FROM AUTHOR]

Advancing protonic ceramic electrochemical cell (PCEC) technology offers promise for a variety of energy applications, including membrane reactors, fuel cells, and electrolyzers. Computational modeling of PCECs requires tracking the movement of three mobile charge carriers: protons, oxygen vacancies, and small polarons to adequately predict the cell operating characteristics. This paper develops an experimentally validated, quasi-2D (1＋ 1D), transient, dual-channel cell model based on a multiple-charged defect-conducting electrolyte. The new model advances predictive capabilities on a number of fronts. First, it reduces empiricism, simplifies integration of experimentally derived modeling parameters, and enables rapid model scale-up to large cell platforms. Additionally, it predicts the distribution of properties in the streamwise gas flow direction and cell faradaic efficiency over a wide range of operating cell conditions helping to establish the inlet gas conditions needed to produce a dry hydrogen product gas. Model simulation reveals that the evolution of steady-state, thermal-neutral voltages in a PCEC can significantly change from initial operating values due to a dynamic, complex interaction which arises from local decreases in faradaic efficiency. Insights from model-based performance predictions touch upon thermal management considerations and the means for regulating cell temperature when trying to achieve either adiabatic or quasi-isothermal PCEC operation. • Experimentally validated, quasi-2D, transient cell model with MCDC electrolyte. • Model reduces empiricism and enables numerical modeling scale-up to large cells. • PCEC transports protons (majority carrier), oxygen vacancies, small polarons. • Operating-conditions-dependent faradaic efficiency changes thermal-neutral voltage. • Adiabatic PCEC at theoretical thermal-neutral condition requires thermal management. [ABSTRACT FROM AUTHOR]

Abstract This paper devises an optimization framework for efficient energy management and components sizing of a plug-in fuel cell urban logistics vehicle. Based on the propulsion system structure, fuel cell system model, and convex battery health model, a convex programming problem is formulated to simultaneously optimize both the control decision and parameters of power sources, including a fuel cell pack and a battery pack. This paper seeks to minimize a summation of energy cost and power sources cost, while satisfying vehicle power demand and battery health requirements. Considering different drive cycles, the optimal parameters and energy cost are systematically investigated. As a result, the optimal battery rated power and energy capacity are about 54 kW and 29 kWh, respectively, which are not affected by different drive cycles, given an electric-only range between 40 km and 60 km. Finally, based on the developed convex programming control law and optimal parameters, we examine the power distribution of the plug-in fuel cell urban logistics vehicle with different hydrogen prices, which significantly influences the vehicle's fuel economy. Highlights • Convex optimization of power sources' dimensioning and control. • Convex battery health model and equivalent costs of power sources. • Financial analysis for sub-optimal fuel cell parameters in different drive cycles. • Impact analysis of the hydrogen price on energy management and fuel economy. [ABSTRACT FROM AUTHOR]

Abstract This is the second paper in a series of two that introduce our research on dynamic programming on new energy vehicles. In the first paper, we introduce the four main problems (the interpolation leakage problem, the dimension disaster problem, the standardization problem and the Markov problem) of dynamic programming on new energy vehicles, and put forward a unified dynamic programming model and its solution method for electric vehicles and hybrid electric vehicles. In this paper, we present a unified dynamic programming model and its solution method to solve these problems for fuel cell electric vehicles. Firstly, typical topologies of fuel cell electric vehicles are summarized, and two typical control strategies of fuel cell systems are studied. Then, based on the work mode of fuel cell vehicles, a unified dynamic programming model is established. To reduce the computation load, a unified solution framework that consists of a variety of methods is proposed based on the first paper and the work characteristics of fuel cell electric vehicles. To verify the proposed method, two case studies are given. The results demonstrate that the proposed method is much better than Basic Dynamic Programming and Level-Set Dynamic Programming in both calculation time and computation accuracy. Highlights • Work mode and FCS power are taken as state variables to solve the Markov problem. • A unified DP model for FCEVs is built to solve the standardization problem. • A combination method is put forward to solve the dimension disaster problem of DP. • The proposed method is compared with Basic DP and Level-Set DP in different cases. [ABSTRACT FROM AUTHOR]

In this study, porous g-C 3 N 4 with structural defects of oxygen atom and cyano group (COCN) prepared by thermal polymerization of directly calcinating the mixture of urea and ascorbic acid, is firstly applied in the H 2 O 2 fuel cell. By employing a nickel mesh coated with COCN as the photoanode and iron phthalocyanine (FeIIPc) mixed with g-C 3 N 4 on carbon paper as the cathode, this COCN-based cell exhibits a maximum power density of 0.298 mW·cm−2 in the water solution including 0.1 M HCl under AM 1.5G solar light at air atmosphere, which has an approximate 5.0 times enhancement compared with that of pristine g–C 3 N 4 –based one. The corresponding solar-to-electricity conversion efficiency (SECE) of above cell is estimated to be 0.248%. In addition, the photocatalytically produced H 2 O 2 (chemical energy) is stored in water with the electrodes disconnected under light irradiation for 3 h, and then is directly used as the fuel in an H 2 O 2 fuel cell by connecting the electrodes in the dark, yielding a specific capacitance of 5900 mF·cm−2. After 6 h of cell operation, the retention rate of specific capacitance is still as high as 76.9%. The primary results provide a facile strategy to introduce structural defects in g-C 3 N 4 for boosting H 2 O 2 fuel cell performance. [Display omitted] • Porous g-C 3 N 4 with structural defects (COCN) is applied in the H 2 O 2 fuel cell. • The structural defects in COCN facilitate the photocatalytic H 2 O 2 generation. • The COCN as the photoanode produces 0.036 M H 2 O 2 under light irradiation for 3 h. • The COCN-based cell converts solar energy to H 2 O 2 fuel for generating electricity. • The specific capacitance keeps 76.9% of initial value after 6 h of cell operation. [ABSTRACT FROM AUTHOR]

Control and monitoring systems are crucial for ensuring optimal performance, efficiency, and longevity of Solid Oxide Fuel Cells (SOFC). Developing a model to accurately capture the transient behavior of the SOFC under dynamic operation is essential for these applications. As electrochemical, mass-transfer, and thermal equations are involved in SOFCs' dynamic, physics-based approaches to capture all the complexity of SOFC systems are often too computationally expensive for real-time implementation. In this paper, an innovative multi-input neural network is developed to build an accurate model of SOFC that is computationally efficient. The proposed algorithm uses experimental data and is a modified nonlinear autoregressive exogenous (NARX) network. An optimal sequence of the most recent observations (output voltages) that characterize the SOFC dynamics is passed through stacked 1D convolutional layers (CNN) to extract latent spatial/temporal information. Then the output is concatenated with current and past exogenous inputs. The fusion of learned features, representing the internal dynamics and the effect of exogenous inputs, is then fed to a fully connected network for one-step ahead performance prediction. This hybrid structure, called HY-CNN-NARX, is capable of identifying the transient dynamics of the SOFCs by unrolling information from historical outputs and inputs within a feedforward framework. To evaluate the model performance, lab-scale tubular SOFCs are experimentally tested at 650–750 °C under various dynamic operations and initial conditions, and the transient and steady-state responses of the SOFC are collected. Once the model is validated using a wide operating range of data, the generalization and prediction performance of the proposed network is compared with a conventional NARX and a recurrent stacked Long short-term memory (LSTM) model. The comparative results demonstrate that the proposed HY-CNN-NARX model outperforms the NARX model on unseen data with an accuracy improvement of 59.2% for root mean square error and 53.7% for mean absolute percentage error. In addition, the prediction performance of the HY-CNN-NARX is comparable to its recurrent counterpart, the LSTM model, but with a 39.3% faster execution time. [Display omitted] • A novel hybrid neural network to capture the transient performance of SOFC. • Validation on extensive dynamic data from lab-scale fuel cells. • Comparing the prediction accuracy and computation speed with benchmarks. [ABSTRACT FROM AUTHOR]

Cathode recirculation provides a new solution to the accelerated degradation of proton exchange membrane fuel cells (PEMFCs) due to low humidity and high potential at low load conditions. Analyzing the internal impact mechanisms is basis for a more appropriate use of this technology. This paper presents a systematic investigation of the mechanisms by which key operating parameters of the cathode recirculation, including current density, cathode recirculation ratio, and stoichiometry of the fresh air path, affect the internal and external properties of PEMFCs. The voltage suppression effect and humidification effect under different cathode recirculation strategies are first analyzed. Then, as a novelty, the distribution of relaxation times (DRT) method is used to deconvolve electrochemical impedance spectra and qualitatively resolve the polarization impedance under different strategies. DRT is enabled to separate up to five polarization processes with different time constants and assign them to oxygen diffusion, oxygen reduction reaction and proton transport processes affected by the cathode recirculation. Finally, DRT quantified the change in ohmic impedance due to cathode recirculation and confirmed the effect of external humidity changes. This work provides a more in-depth insight into internal mechanisms of cathode recirculation in PEMFCs, and especially provides a comprehensive theoretical basis for the development of idle controllers for automotive PEMFCs in terms of improved durability. • A systematic study of cathode recirculation on PEMFC under low-load conditions. • The polarization process at various recirculation strategies are identified by DRT. • Cathode circulation has positive prospects in vehicle self-humidifying PEMFC system. [ABSTRACT FROM AUTHOR]

Abstract: In this study, woven gas diffusion layers (GDLs) with varying weave type and tightness are investigated. Plain and twill weave patterns were manufactured in-house. The in-plane and through-plane air permeability of the woven samples were tested, and mercury intrusion porosimetry (MIP) tests were performed to study the pore structure. It was found that the twill weave has a higher permeability than the plain weave, which is consistent with literature. Like non-woven carbon papers, woven GDLs have higher in-plane permeability than through-plane permeability; however it has been shown that it is possible to manufacture a GDL with higher through-plane permeability than in-plane permeability. It was also concluded that the percentage of macropores in the weave is the driving factor in determining the through-plane air permeability. This work lays the groundwork for future studies to attempt to characterize the relationship between the weave structure and the air permeability in woven GDLs. [Copyright &y& Elsevier]

Amorphous films of mean composition Ni33Ta41C26 were prepared by deposition onto carbon paper using dc magnetron sputtering. The material showed low corrosion currents and significant electrocatalytic activity for hydrogen oxidation and oxygen reduction when polarised potentiostatically in 1.5 M H2SO4 at 20 and 70 °C. The results are interpreted in terms of the passivity of the tantalum component offering corrosion protection to the nickel electrocatalytic component in the aggressive acidic electrolyte. [Copyright &y& Elsevier]

Fuel cell- and battery-based public bus technologies are reviewed and compared for application in tropical urban areas. This paper scrutinizes the reported literature on fuel cell bus, fuel cell electric bus, battery electric bus, hybrid electric bus, internal combustion diesel bus and compressed natural gas bus. The comparison includes the capital and operating costs, fuel consumption and fuel cycle emissions. To the best of authors knowledge, this is the first study to holistically compare hydrogen and battery powered buses, which is the original contribution of this paper. Moreover, this is the first study to focus on supplying hydrogen and electricity from fossil resources, while including the associated emissions. The study shows that compressed natural gas and hybrid electric buses appear to be the cheapest options in terms of total cost of ownership, but they are unable to meet the EURO VI emissions' standard requirement. Only fuel cell based buses have the potential to achieve the emissions' standard when the fuel cycle based on fossil energy was considered. Fuel cell electric buses are identified as a technology allowing for the largest CO 2 emission reduction, making ∼61% decrease in annual emissions possible. [ABSTRACT FROM AUTHOR]

Deformable energy devices play a crucial role in flexible and wearable electronics. Currently, deformable energy storage devices demonstrate deficiencies, forcing flexible and wearable electronics to be unable to be further applied on a large scale. Flexible fuel cells are a powerful alternative to solve the low energy density of current flexible energy storage devices. However, flexible fuel cells still have considerable problems, such as low power density, fuel storage issues, etc. In this paper, primary strategies of configurations at the device level are reviewed that have been successfully employed to fabricate flexible and wearable fuel cells. Besides, their future applications are also discussed. This paper will contribute to developing flexible and wearable fuel cells by comprehensively understanding their current strategies and further research directions. [Display omitted] • A unique perspective to review flexible and wearable fuel cells. • The configuration covers layered, fiber-based, planar, and composite structures. • The application of flexible fuel cells in wearable systems and self-charge. [ABSTRACT FROM AUTHOR]

Various research are currently done about fuel cells. They can concern the application context, the fuel cell technology by itself or the socio-economic bolts. This paper deals with fuel cells stack testing and especially the accelerated stress testing. Long and expensive ageing tests are performed to study the behavior of the fuel cell with the aim of making it as robust as possible versus permanent degradation over time. Accelerated stress tests should provide results faster as classical ageing tests, thus inducing cost reduction. This paper reviews fuel cell component degradation, including degradation mechanisms, and the accelerated stress tests dedicated to all the constituting components (catalyst layer, membrane, gas diffusion layer and bipolar plates). Obviously, the harmonized accelerated stress tests given by the Department of Energy (DoE) are presented but all other recent accelerated test protocols proposed in the literature are also reviewed. In addition, several tables are given to detail operating conditions, specimen, characterization planning and a degradation rate that will be relevant and helpful to converge with an optimal AST solution. • Degradation mechanisms on polymer electrolyte membrane fuel cells are explained. • Harmonized or not accelerated stress test protocols at component level are reviewed. • A recent state of the art on durability key issues is provided. [ABSTRACT FROM AUTHOR]

The gas diffusion layer (GDL) is a thin porous layer sandwiched between a bipolar plate (BPP) and a catalyst coated membrane in a fuel cell. Besides providing passage for water and gas transport from and to the catalyst layer, it is responsible for electron and heat transfer from and to the BPP. In this paper, a method has been developed to measure the GDL bulk thermal conductivity and the contact resistance at the GDL/BPP interface under inhomogeneous compression occurring in an actual fuel cell assembly. Toray carbon paper GDL TGP-H-060 was tested under a range of compression pressure of 0.34 to 1.71 MPa. The results showed that the thermal contact resistance decreases non-linearly (from 3.8 × 10 −4 to 1.17 × 10 −4 Km 2 W −1 ) with increasing pressure due to increase in microscopic contact area between the GDL and BPP; while the effective bulk thermal conductivity increases (from 0.56 to 1.42 Wm −1 K −1 ) with increasing the compression pressure. The thermal contact resistance was found to be greater (by a factor of 1.6–2.8) than the effective bulk thermal resistance for all compression pressure ranges applied here. This measurement technique can be used to identify optimum GDL based on minimum bulk and contact resistances measured under inhomogeneous compression. [ABSTRACT FROM AUTHOR]

Based on constructal theory, the structure of a single tubular solid oxide fuel cell (TSOFC) is optimized in this paper. The maximum power output is chosen as the optimization objective. The optimal constructs of the TSOFC are obtained. The results show that the local power output P E,j and the local current density i j decrease along the flow direction. For the fixed anode, cathode and electrolyte volume fractions, there exist optimal anode, cathode and electrolyte thicknesses as well as the corresponding optimal fuel cell lengths which lead to the maximum power outputs of the TSOFC, respectively. For the fixed inner radius of the solid parts, there exist an optimal cathode thickness and an optimal fuel cell length which lead to the double maximum power output (the power output after twice maximization) of the TSOFC. The power output of the TSOFC after constructal optimization is increased by 18.20% compared to that of the TSOFC with cathode thickness t c = 2200 μm and fuel cell length L = 1.5 m. The performance of the TSOFC is evidently improved by adopting the optimal constructs obtained in this paper. [ABSTRACT FROM AUTHOR]

Proton ceramic electrolysis cells (PCECs), electrochemical devices that convert electrical energy into chemical energy, have attracted increasing interest; however, their development has been severely limited by the slow kinetics of the air electrodes. Therefore, this paper reports a novel Zn-doped Pr 1.8 Ba 0. 2 NiO 4+δ (PBN) air electrode material in terms of crystal structure, phases, surface chemistry, hydration and conduction behaviors, and electrochemical performance in PCECs. The results show that the optimal Zn doping amount is 0.1 mol replacing Ni (Pr 1.8 Ba 0. 2 Ni 0. 9 Zn 0. 1 O 4+δ , PBNZ1). The PBNZ1 cell achieves a maximum power density of 1.36 W cm−2 in fuel cell mode at 700 °C, while it exhibits an electrolysis current density of 2.95 A cm−2 at 700 °C and 1.3 V, which is 30% higher than that of the PBN cell. This improvement can be attributed to the acceleration of charge transfer processes in the air electrode through Zn doping. • Zn doping was used to modify Pr 1.8 Ba 0. 2 NiO 4+δ air electrode. • 2.95 A/cm2 at 700 °C is achieved on PCEC mode with Pr 1.8 Ba 0. 2 Ni 0. 9 Zn 0. 1 O 4+δ. • DRT methods are employed to interpret electrode processes. [ABSTRACT FROM AUTHOR]

The development of fuel cells highly depends on the reliable operation of fuel cells on test benches for testing purposes. Even though the test bench's control software contains an alarm module, it is only able to detect the most extreme failures due to the widespread operating parameter range of a fuel cell. This paper presents a novel machine learning based approach to monitor the operation of fuel cell stacks on a test bench and thereby ensuring the proper conduction of the tests. Methods for monitoring the operating conditions set by the test bench using clustering as well as methods to monitor the fuel cell's performance using digital twins are proposed. The developed methods are applied on real testing data to demonstrate their ability to detect even slight deviations that remained undiscovered to the state of the art monitoring system of the test bench. After automating, the proposed methods allow a more sensitive monitoring of the fuel cell operation on test benches leading to more usable data and clearer test results and thereby speeding up the development of fuel cells. • Lifelong performance monitoring of fuel cells. • Detecting anomalies using machine learning. • Using recurrent neural networks to predict fuel cell performance. • Neural network as digital twin. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a microgrid consisting of four fuel cell-battery hybrid Distributed Energy Resources (DERs) is devised for an industrial crusher–conveyor load. Each fuel cell was accompanied by a Li-ion battery to provide energy storage support under islanded condition of the microgrid since the fuel cells typically have poor transient response characteristics. After carrying out extensive modeling and analysis in MATLAB®, the battery utilization was found to vary significantly based on the DER's ‘electrical’ placement within the microgrid. This paper presents, under such conditions, a variety of battery life balancing solutions through the use of the new framework of Flexible Distribution of EneRgy and Storage Resources (FDERS). It is based on an in-situ reconfiguration approach through ‘virtual’ reactances that help in changing the ‘electrical’ position of each DER without physically displacing any component in the system. Several possible approaches toward balancing the battery utilization are compared in this paper taking advantage of the flexibility that FDERS offers. It was observed that the estimated battery life is dependent on factors such as cycling sequence, pattern, and occurrence. [Copyright &y& Elsevier]

Abstract: A unique requirement of underwater vehicles' power/energy systems is that they remain neutrally buoyant over the course of a mission. Previous work published in the Journal of Power Sources reported gross as opposed to neutrally-buoyant energy densities of an integrated solid oxide fuel cell/Rankine-cycle based power system based on the exothermic reaction of aluminum with seawater. This paper corrects this shortcoming by presenting a model for estimating system mass and using it to update the key findings of the original paper in the context of the neutral buoyancy requirement. It also presents an expanded sensitivity analysis to illustrate the influence of various design and modeling assumptions. While energy density is very sensitive to turbine efficiency (sensitivity coefficient in excess of 0.60), it is relatively insensitive to all other major design parameters (sensitivity coefficients < 0.15) like compressor efficiency, inlet water temperature, scaling methodology, etc. The neutral buoyancy requirement introduces a significant (∼15%) energy density penalty but overall the system still appears to offer factors of five to eight improvements in energy density (i.e., vehicle range/endurance) over present battery-based technologies. [Copyright &y& Elsevier]

The urgent need for green energy to curb environmental pollution and solve the energy crisis calls for the rapid development of clean power supplies. Besides proton exchange membrane fuel cells (PEMFCs), anion exchange membrane fuel cells (AEMFCs) are a promising technology which get rid of precious catalysts and harsh strong acid environments. The target of reducing cost and enabling widespread commercialization may be met in the near future. The influence of water transfer in AEMFCs determines their power density and efficiency. This paper reviews the literature associated with water transfer in the bipolar plates, gas diffusion layers, catalyst layers, and membranes, researching the key issues in high performance fuel cells development. Furthermore, studies concerning water transfer under various operational conditions are analyzed in-depth and the core mechanism of water transfer is uncovered. Moreover, via the experimental and simulation methods summarized in this paper, efficient strategies are proposed and AEMFC water management is optimized. This review not only explains the water management mechanism, but also contributes to the enhancement of AEMFCs power density and efficiency. • Water transfer limits performance of anion exchange membrane fuel cells (AEMFCs). • Key issues of water generation, consumption and transportation are summarized. • Experiments and simulations on water transfer in each component are discussed. • Strategies to optimize the water management of AEMFCs are outlined. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an innovative hybrid analytic-numerical approach to modelling species transport in fuel cells suitable for application on the system level. The core principle of this modelling approach is taking 1D numerical model for gas-flow and superimposing onto it a 2D analytic solution for concentration distribution in the plane perpendicular to the gas-flow together giving a 3D information on species concentration in the fuel cell. A hybrid analytic numerical model of a simple geometry isothermal fuel cell is presented and comparatively evaluated by benchmarking it against a professional full 3D CFD simulation tool. This evaluation shows very close agreement with the benchmarking 3D CFD simulation and computational times comparable to 1D models. This computational efficiency originates in the model''s analytic nature in the other two dimensions making it suitable for system level application. The paper features an extensive appendix with a comprehensive detailed mathematical derivation of the hybrid analytic-numerical model. [Copyright &y& Elsevier]