Cell Performance Tests Research Articles

A novel proton-exchange porous silicon membrane production method for μDMFCs.

This study introduces a new production method to use as a porous silicon-based proton exchange membrane for μDMFCs. In this respect, EIS, fuel crossover test, and fuel cell performance test at the μDMFC sample cell are performed at room temperature on a porous silicon-based membrane that was produced for passive mode μDMFC as a proton exchange membrane. The reason for performing the fuel crossover test is to ensure the silicon opened pores along the silicon wafer and to examine the fuel permeability of the membrane. The fuel crossover test shows that the fuel cell provides energy for about 60 min with a 50 mL fuel. EIS reveals proton permeability of proton exchange membrane. The calculated value of the conductivity of the membrane is 0.0016 S/cm. OCV of the system is 0.4V, whereas values (with highest power density is 0.1 mW/cm²and with the highest current density is 0.39 mA/cm²) are low. However, porous silicon is not a natural proton conductor. Hence, these values can be increased by different ways such as porous silicon functionalized, or serial connection of fuel cells. On the other hand, the value of OCV is consistent with the previous studies. In sum, this study presents a simple, cost-effective, and short time-consuming method for the production of porous silicon as proton-conducting membrane behavior.

Small-angle neutron scattering studies on the distribution of polytetrafluoroethylene within microporous layers for polymer electrolyte fuel cells

The performance of polymer electrolyte fuel cells depends on the nanostructure of the polymer composites in their components. The microporous layer within the cells, which generally comprises a composite of carbon black and polytetrafluoroethylene (PTFE), is a key component that prevents mass-transport losses in electrochemical reactions of the cells; therefore, we studied the distribution of PTFE within microporous layers using contrast-variation small-angle neutron scattering. By performing annealing above the PTFE melting point, its self-aggregations were reduced, and this effect was explained via the surface energies of PTFE and carbon black. Moreover, fuel cell performance testing demonstrated that better mass-transport properties were achieved when there were fewer PTFE self-aggregations within the microporous layers. Our findings suggest that an optimal PTFE distribution within fuel cell microporous layers can be achieved by engineering the surface energies of carbon black.

Polybenzimidazole-modified carbon nanotubes as a support material for platinum-based high-temperature proton exchange membrane fuel cell electrocatalysts

We fabricate polybenzimidazole (PBI) wrapped carbon nanotubes (MWCNTs) as support material for platinum-based fuel cell electrocatalyst. With the aid of microwave-assisted polyol reduction, we obtain very fine platinum (Pt) nanoparticles on PBI/MWCNT support while reducing the amount of Pt waste during synthesis. Cyclic voltammetry (CV) concludes that Pt-PBI/MWCNT has 43.0 m2 g−1 of electrochemically active surface area (ECSA) to catalyze hydrogen oxidation. Furthermore, after the 1000th cycle, Pt-PBI/MWCNT preserves almost 80% of its maximum ECSA, meaning that Pt-PBI/MWCNT is much more durable than the Pt/MWCNT and commercial Pt/C. High-temperature proton exchange membrane fuel cell (HT-PEMFC) performance tests are conducted under H2/Air conditions at the temperatures ranging from 150 °C to 180 °C. Nevertheless, tests conclude that the maximum power density values of the Pt-PBI/MWCNT are found inferior to the Pt/C at all temperatures (e.g., 47 vs. 62 mW cm−2 at 180 °C), suggesting that some balance between durability and performance has to be taken into consideration.

Controllable synthesis of Fe–N4 species for acidic oxygen reduction

AbstractControllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction (ORR) in fuel cells. However, the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge. In this study, we developed a facile and scalable method for fabricating highly efficient ORR electrocatalysts with sole atomic Fe–N4 species as the active site. Herein, the use of cost‐effective highly porous carbon as the support not only could avoid the aggregation of the atomic Fe species but also a feasible approach to reduce the catalyst cost. The obtained atomic Fe–N4 in activated carbon (aFe@AC) shows excellent ORR activity. Its half‐wave potential is 59 mV more negative but 47 mV more positive than that of the commercial Pt/C in acidic and alkaline electrolytes, respectively. The full cell performance test results show that the aFe@AC sample is a promising candidate for direct methanol fuel cells. This study provides a general method to prepare catalysts with a certain type of active site and definite numbers.

Parametric Studies of Direct Methanol Fuel Cell under Different Modes of Operation

Direct methanol fuel cell (DMFC) performance tests were carried out in different modes of operation, namely, passive, active (air as oxidant) and active (oxygen as oxidant). Few parameters including methanol concentration (2 M, 4 M, 6 M, and 8 M) and methanol flow rate (1-4 mL min-1) were considered to investigate their effects on the DMFC performance. Fuel consumption was indicated by refractive index tests. Results showed that the performance of DMFC increased with the increase of methanol concentration and flow rate, until they reach certain values, i.e., 4-6 M and 2 mL min-1. Furthermore, for all parameters, the active mode with oxygen yielded the highest power density, followed by the active mode with air and passive DMFC system. The active mode with oxygen yielded the power density which peaks at 10.41 mW cm-2 during 6 M of methanol concentration and 2 mL min-1 rate of flowing methanol, followed by active mode with air at the cathode with 8.39 mW cm-2 and passive mode with 5.39 mW cm-2 respectively. It also records a better fuel consumption efficiency among all modes. These results indicate that investigating the level of fuel concentration and flow rate can lead to enhancement of mass transport and diffusion thus generating better performance of DMFC system.

Enhancement of alkaline conductivity and chemical stability of quaternized poly(2,6-dimethyl-1,4-phenylene oxide) alkaline electrolyte membrane by mild temperature benzyl bromination.

A series of quaternized polyphenylene oxide (QPPO) based alkaline electrolyte membranes with different degrees of quaternization were synthesized via a benzyl bromination method at mild temperature (75 °C). Quite a high hydroxide conductivity under the reduced water uptake and swelling was exhibited by this method. When the degree of bromination measured from 1H NMR analysis was 30%, the corresponding hydroxide ion conductivity was 0.021 S cm−1. The chemical stability of the QPPO membranes was excellent, showing only 3% weight loss in 3 M NaOH solution during 1 month. The fuel cell performance test under H2/O2 exhibited the power density of 77 mW cm−2 and the current density of 190 mA cm−2 at 70 °C. Such excellent properties of QPPO membranes resulted from the achievement of the quaternization at the benzyl position, specifically.

TiO2/Bi5O7I Composite Films for Dye-Sensitized Solar Cells

Bi5O7I is one of the bismuth oxyiodides family members which is commonly utilized for photocatalyst, but it has not been applied yet as a photovoltaic material. Herein, we study the effect of Bi5O7I addition to TiO2 for the photovoltaic device which worked based on the dye-sensitized solar cell (DSSC). A better photovoltaic performance was performed by using TiO2/Bi5O7I composite than the TiO2 based DSSC. The different ratios of Bi5O7I mixed with TiO2 resulted in the TiO2/Bi5O7I composite material films which were characterized on their structural, morphological, and optical properties. X-ray diffraction and scanning electron microscope analysis results displayed the crystal character and the morphology of Bi5O7I and TiO2 in our films. In addition, the existence of Bi5O7I in the films had an impact on the decreasing in the bandgap energy of composite materials. Moreover, the solar cell performance test with I−/I3− electrolyte solution, Pt-FTO counter electrode, and N719 dye was carried out to the composite cells. As a result, there was a slight increase in the current density and open-circuit voltage. Also, the cell efficiency could enhance up to 60% in comparison to the TiO2-DSSC in this report.

Investigation of the effects of SPEEK and its clay composite membranes on the performance of Direct Borohydride Fuel Cell

In this study, composite cation exchange membranes (CEM) were developed. With the experience from widely studied proton exchange membrane fuel cells (PEMFC), sulfonated polyether ether ketone (SPEEK) was prepared to be a more effective and cheaper ionomer alternative to the industry standard Nafion ®. SPEEK polymer membrane can reach sufficient ionic conductivities but have some mechanical and chemical stability problems (at a high degree of sulfonations (DS)). Therefore, in order to optimize the membrane, composite mixing with a well-known organic/inorganic clays called Cloisite® 15A, Cloisite ® 30B and MMT were used. Test cells for both single-cell and conductivity were designed and constructed. The ionic conductivity cell was different than the ones used in most studies, measuring conductivity in-plane with 4 probes using EIS. The membranes were characterized for their proton conductivity with electrochemical impedance spectroscopy (EIS), for DS with H NMR, water uptake, and fuel cell performance tests. First results showed that the acidic sulfonic groups of SPEEK interacted with organic/inorganic clays and as a result of partial barrier the ionic conductivity was decreased but power densities were increased. SPEEK-Cloisite® 30B composite membrane has given 40 mW/cm2 power density value which is higher than pure SPEEK membrane (35 mW/cm2). The proton conductivities of the final composite membranes were close to bare SPEEK membranes which are 0,065 and 0,075 S/cm for SPEEK-Cloisite ® 30B and pristine SPEEK, respectively.

Lattice Boltzmann modelling of the coupling between charge transport and electrochemical reactions in a solid oxide fuel cell with a patterned anode

A fundamental understanding of the electrochemical reactions and the associated transport processes in electrodes of solid oxide fuel cells (SOFCs) is critical to the development of new electrode materials. To date, however, our understanding of the electrode processes is still very limited due to the lack of well-designed experiments and carefully-validated predictive models. To facilitate studies in this area, we have developed a numerical model that has taken into consideration of the coupling between the transport of mobile charged species (e.g., ions and electrons) in conducting phases and the electrochemical reactions at the three phase boundaries of an SOFC anode. The validity of this model has been confirmed by the electrochemical performance of test cells with a patterned anode consisting of well-defined electronic and ionic conducting phases. The model is then applied to quantifying the factors that critically influence the performance of a patterned anode, resulting in three key dimensionless parameters governing the coupling of transport and reactions in the anode: the ratio of electronic-to-ionic conductivity (σel/σion), the dimensionless exchange current density (iex/i0), and the dimensionless electric potential (Fϕ0/RT). In particular, it is found that only iex/i0 and Fϕ0/RT play a significant role under typical SOFC operating conditions: anode performance increases with the increase in iex/i0 and Fϕ0/RT. Accordingly, we have constructed a phase map to demonstrate the combined effect of iex/i0 and Fϕ0/RT, which is helpful for rational design and operation of SOFC patterned electrodes of different materials and geometries. More importantly, our present model is also applicable to the study of actual porous SOFC electrodes with known 3D microstructures.

Amino acid clusters supported by cellulose nanofibers for proton exchange membranes

Inspired by the structure of amino acid residues chain in transmembrane proteins, amino acid molecules are immobilized onto cellulose nanofibers to form clusters as quasi-one dimensional proton-conducting pathways for nanofiber hybrid proton exchange membranes. The structure of conducting clusters and properties of the hybrid proton exchange membranes are examined. The results show that the amino acid clusters enhance the proton conductivity, and the proton exchange membrane with Ser-clusters shows the highest proton conductivity of 0.264 S/cm at 80 °C under 100% humidity and temperature. Diffusion coefficients and mean square displacements of hydronium ion are then calculated using Density-Functional Tight-Binding method to better understand the proton-conducting mechanism of amino acid clusters, and the results of molecular dynamics simulation are in good agreement with the experiments. Besides, the structure of three-dimensional hydrophilic network of nanofibers exhibits significant effect on the performance of water uptake, dimensional stability, methanol permeability and thermal stability of the hybrid proton exchange membranes. Fuel cell performance test confirms that these membranes are suitable for direct methanol fuel cells.

Ionic conduction mechanism of a nanostructured BCY electrolyte for low-temperature SOFC

A solid oxide fuel cell with 1.2 mm thick nanocrystalline BCY (BaCe0.9Y0.1O3) electrolyte was prepared by the copressing method, and its electrochemical performance was tested in H2/air conditions. The maximum power density of the nanocrystalline electrolyte cell prepared with BCY powders calcined at 1000 °C and operated at 550 °C in H2 is 405.2 mW cm−2. The carriers of nanocrystalline BCY electrolyte were studied by using double-layer electrolyte cells with pure oxygen ion conductor GDC (Gd0.1Ce0.9O2) and proton conductor SCY (SrCe0.95Y0.05O3), sintered at high temperatures as proton and oxygen ion filters. It is found that nanocrystalline BCY is a mixed conductor of oxygen ions and protons. The results of hydrogen and oxygen concentration cells show that the transference number of oxygen ions in the nanocrystalline BCY prepared in this study is higher than that of protons. XPS and HRTEM results of BCY particles before and after performance testing showed that an amorphous layer containing a high concentration of oxygen vacancies and suspected carbonate was formed on the surface of BCY particles after fuel cell performance testing. We believe that the amorphous layer should be a high-speed ion conduction channel for nanocrystalline BCY electrolyte during performance testing.

Improved performance and durability of sulfonated polyether ether ketone/cerium phosphate composite membrane for proton exchange membrane fuel cells

In this study, a new cerium phosphate (CePO4)-doped sulfonated polyether ether ketone (SPEEK) composite membranes were synthesized by using solution casting method with different CePO4 loading. Their performance and durability were investigated for proton exchange membranes fuel cells. Different techniques, namely Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), dynamic mechanical tests (DMA), and electrochemical impedance spectroscopy (EIS) analyses were used to characterize the synthesized membranes. Water uptake (WU) and swelling properties as well as ion exchange capacities (IEC) of synthesized membranes were also determined. Fuel cell performance, durability, and Fenton tests for oxidative stability of the synthesized membranes were also investigated. Experimental results showed that addition of CePO4 up to 10% by weight improved the membrane properties. 10 wt% CePO4-doped membrane possessed a good proton conductivity of 0.242 S/cm at 80 °C. Current and power densities of this membrane were obtained as 790 mA/cm2 and 474 mW/cm2, respectively, at 0.6 V cell potential and 80 °C fuel cell temperature. OCV decrement value of this membrane was 5.93%. When the performance and durability properties of 10% CePO4-doped membrane is compared to commercial Nafion membrane, it could be a good alternative for proton exchange membrane fuel cells.

Poly(ether ketone) composite membranes by electrospinning for fuel cell applications

This work is dedicated to preparation of the composite membranes to control the water absorption and dimensional stability of a highly sulfonated poly(ether ketone) matrix. To achieve this goal, the non-sulfonated poly(ether ketone) fibers are prepared by electrospinning process and then fibers are impregnated by highly sulfonated poly(ether ketone). Both highly sulfonated and non-sulfonated polymers are synthesized by condensation polymerization reaction and are characterized by spectroscopic methods. The water absorption measurements indicate that introducing 20 and 30 wt% of non-sulfonated fibers lead to the water absorption of 31 and 25% respectively, in comparison to water absorption of highly sulfonated matrix that is 54%. The presence of fibers also improves the mechanical strength of membranes. Tensile strength reaches from 27 to 81 MPa by addition of 30 wt% electrospun fibers. Moreover, in H2/O2 fuel cell performance test, the composite membranes show current density in the range of 700–1090 mA cm−1 at different cell temperatures and backpressure amounts. Also proton conductivity of the samples is examined by electrochemical impedance spectroscopy and the values are between 0.05 and 0.16 S cm−1. Morphology of the fibers and membranes is studied by scanning electron microscopy as well.

Estudo do desempenho térmico de células-teste enterrada e semienterrada

Uma alternativa construtiva vernacular dos grupos indígenas na região sul do Brasil baseava-se no enterramento da edificação com o provimento de cobertura leve. O presente estudo tem por objetivo avaliar o desempenho térmico de células-teste enterradas e semienterradas quando comparadas a uma célula controle térrea visando uma arquitetura bioclimática que utilize métodos passivos. O método é baseado na comparação das variações de temperatura medida no interior de células-teste quanto à temperatura externa e do solo medidos em Curitiba, PR, durante o período de inverno. As células testes foram confeccionadas em escala reduzida, todas com as mesmas dimensões e especificações de materiais. Para a avaliação de desempenho foram analisados a amplitude térmica, o atraso térmico, as diferenças de temperaturas e amplitudes de sensores superficiais e os índices de conforto de cada célula-teste. A análise de dados constatou que a célula-teste enterrada apresentou menor amplitude térmica e maior atraso térmico. No que tange à somatória dos graus-hora fora da faixa de temperatura de conforto, a célula-teste enterrada obteve o menor tempo em desconforto durante o período de inverno. Foi possível verificar também que quanto maior a área em contato com o solo, melhores as condições de conforto observadas.

High-Throughput Synthesis and Characterization of PGM-Free PEFC Cathode Catalysts

The high cost of platinum, widely used in the electrode of polymer electrolyte fuel cells (PEFCs), is one of main barriers to the widespread use of fuel cell vehicles. Many studies have focused on reducing the excessive production cost of the fuel cell stack by either decreasing the platinum loading using more active Pt-based catalysts and nanostructured alloys or developing platinum group metal-free (PGM-free) catalysts based on low-cost transition metals (e.g., iron and cobalt), carbon, and nitrogen. This presentation will describe high-throughput techniques for synthesis, physical and chemical characterization, hydrodynamic activity screening, electrode fabrication, and fuel cell performance testing of PGM-free catalysts under the auspices of the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Offices’ Electrocatalysis Consortium (ElectroCat) [1]. Argonne’s robotic systems have been utilized to rapidly synthesize unique iron and transition metal-nitrogen-carbon (TM-N-C) catalysts exploring a large number of variables such as nitrogen content, ZIF-8 content, Fe content, TM dopant, and Fe precursor. These variables have been shown to be important factors in determining the activity and stability of the resulting catalysts. The catalysts were synthesized using multi-port ball-milling and multi-sample heat treatment. The ORR activity of synthesized materials was characterized using a newly-developed multichannel flow double electrode cell (m-CFDE), allowing the aqueous hydrodynamic measurement of multiple samples simultaneously and using removable electrode plugs to facilitate the quick change of catalyst [2]. A custom-designed system was utilized to deposit the catalyst-ionomer inks onto the glassy carbon electrodes of the m-CFDE electrode plugs. This system is equipped with a nano-liter injector with exchangeable micro-tips and a computer-controlled XY table mount for the electrode plug to uniformly distribute the ink across the 3 mm x 1 mm glassy carbon electrodes. The ORR activity is correlated with catalyst Fe speciation, as determined using Fe K-edge X-ray absorption spectroscopy (XAFS) and also with catalyst BET and electrochemically-determined surface areas. A segmented 25-electrode array cell was used for the high-throughput performance testing of 25 different types of catalyst in a single membrane-electrode assembly (MEA). The automated electrode deposition system has been used in combination with a custom-designed heated vacuum table and a multi-channel peristatic pump to deposit 25 circular electrodes onto the membrane in the pattern required by the NuVant Systems Inc. array fuel cell hardware [3]. This automated ink dispensing system can be used for precise and even catalyst ink deposition across the small circular array electrodes while minimizing the amount of material required to form those uniform electrodes. This presentation will correlate the performance of the catalysts in the MEA with the catalysts’ ORR activity, physical and chemical properties, and synthesis parameters. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357.

Novel Electrospun Gas Diffusion Layers with Spatially Graded Pore Sizes for Polymer Electrolyte Membrane Fuel Cells

High current density performance of a polymer electrolyte membrane (PEM) fuel cell is severely limited by the accumulation of liquid water in the gas diffusion layer (GDL) of the cell. The accumulation of water blocks pathways for oxygen transport and leads to reduced cell performance. Graded GDL properties, such as increasing porosity and decreasing hydrophobicity are strategies for expelling excess water and improving cell performance [1,2]. A powerful tool to manufacture GDL materials with tailored, graded properties is electrospinning [3]. In this study, novel electrospun, nano-fibrous, graphitic, and hydrophobic GDLs with increasing pore-sizes from the catalyst layer (CL) to the flow fields were designed and fabricated to improve the high current density performance of PEM fuel cells. The fiber diameters, pore-sizes, material composition, and electrical conductivity of the novel materials where quantified using a combination of scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and 4-point probe measurements. The effects of the electrospun GDLs (eGDLs) with graded pore-sizes on cell performance were evaluated via fuel cell performance testing and electrochemical impedance spectroscopy (EIS). A solution of polyacrylonitrile (PAN) and N,N-dimethylformamide was used to electrospin nano-fibrous polymer substrates. Higher PAN concentrations in the polymer solution led to larger fibre diameters and pore sizes. Graded pore structures were manufactured by spinning subsequent layers with increasing PAN concentrations. The electrospun substrates were converted to graphitic carbon substrates via heat treatment at 1400 oC and rendered hydrophobic without structural morphological alterations via an oxygen plasma and trichloro(1H,1H,2H,2H-perfluorooctyl)silane treatment. Two uniform eGDLs were manufactured for base line comparison, and two graded eGDLs were manufactured to test the effect of graded pore-sizes on cell performance. The two uniform eGDLs were called s-eGDL and l-eGDL and comprised of small fibres and large fibres, respectively. The two graded structures were called the Bi-Layer eGDL and Tri-Layer eGDL and had increasing fibre diameters and pore-sizes from the catalyst layer to the flow fields. The fuel cell tests were conducted at 60oC and 50, 75,and 100% RH conditions. The graded eGDL materials led to improved high current density performance compared to the uniform eGDLs at all test conditions with the most significant improvements at 100% RH (≥ 27% increase in peak power output). EIS measurements at 2.0 A/cm2 and 100% RH indicated a substantial decrease (≥ 23%) in mass transport resistance for the graded eGDLs compared to the uniform eGDLs. The reduction in mass transport losses is attributed to enhanced liquid water removal due to the graded structures. The increasing pore-sizes from the CL to the flow fields leads to a capillary pressure gradient favourable for liquid water removal which leads to improved oxygen transport. Additionally, the high frequency resistance (HFR) of the cell at 100% RH did not vary significantly between the s-eGDL and the graded eGDL materials at 2.0 A/cm2 (≤ 8%). However, the l-eGDL material, which had relatively larger pores at the CL compared to the other three materials, had a significantly higher measured HFR value compared to the s-eGDL (31% increase) at the same conditions. The higher HFR value for the l-eGDL material may be attributed to reduced diffusion of water from the CL towards the membrane due to the larger pore-sizes, leading to reduced membrane hydration and increased ohmic losses. In this study, novel electrospun GDLs with graded pore sizes were manufactured for PEM fuel cells. The results provide valuable insight into the effects of GDL pore structure and material properties on cell performance. The work presented can aid in the design of the next generation of GDL materials for improved PEM fuel cell performance. REFERENCES Kitahara, T., Nakajima, H., Inamoto, M., Shinto, K. (2014). Triple microporous layer coated gas diffusion layer for performance enhancement of polymer electrolyte fuel cells under both low and high humidity conditions. Journal of Power Sources, Vol. 248, 1256-1263. doi:https://doi.org/10.1016/j.jpowsour.2013.10.066Ko, D., Doh, S., Park, H. S., Kim, M. H. (2018). The effect of through plane pore gradient GDL on the water distribution of PEMFC. International Journal of Hydrogen Energy, Vol. 42, 2369-2380. doi: https://doi.org/10.1016/j.ijhydene.2017.12.007Chevalier, S., Lavielle, N., Hatton, B. D., Bazylak, A. (2017). Novel electrospun gas diffusion layers for polymer electrolyte membrane fuel cells: Part I. Fabrication, morphological characterization, and in situ performance. Journal of Power Sources, Vol. 352, 272–280. doi: http://dx.doi.org/10.1016/j.jpowsour.2017.03.098

Polytetrafluoroethylene content in standalone microporous layers: Tradeoff between membrane hydration and mass transport losses in polymer electrolyte membrane fuel cells

Fuel cell performance testing and in operando synchrotron radiography were used to investigate the effect of polytetrafluoroethylene (PTFE) in standalone microporous layers (MPLs) on mass transport and membrane hydration. Two standalone MPLs with 20 wt% and 30 wt% PTFE were fabricated and tested with inlet gas relative humidity (RH) between 50 and 100%. This study demonstrates that the performance of a fuel cell using a standalone MPL with 30 wt% PTFE decreases when the RH of the inlet gases is increased from 50% to 100%, whereas the performance of a fuel cell using a standalone MPL with 20 wt% PTFE remains stable over the same relative humidity range. Furthermore, this study demonstrates that a tradeoff between membrane hydration and mass transport losses must be considered when increasing the PTFE content within the MPL. Higher PTFE content led to greater liquid water accumulation adjacent to the catalyst layer. The greater liquid water accumulation adjacent to the catalyst layer improved membrane hydration and proton conductivity but also led to an increase in mass transport resistance. Standalone MPLs with higher PTFE content did not support high current density operation because the mass transport limitations outweighed the benefits of improved membrane hydration.

Effects of discharge mode and fuel treating temperature on the fuel utilization of direct carbon solid oxide fuel cell

Direct carbon solid oxide fuel cells (DC-SOFCs) with the novel perovskite La0.3Sr0.7Fe0.7Ti0.3O3–δ (LSFT) electrodes are evaluated by using biochar derived from some one-time toothpicks made of wood as fuel in different discharging modes. The constant current (CC) mode and constant resistance (CR) mode are compared with same fuel cell configuration and fuel loading. The results show that the fuel discharged in CR mode possesses larger fuel utilization (39.7%) than that in CC mode (34.5%). The biochar fuels obtained from the wood pyrolysis in Ar atmosphere for 1 h at 400 °C, 500 °C, 600 °C and 700 °C present the efficiencies of fuel utilization are 26.3%, 34.1%, 38.6% and 39.6%, respectively. A special discharging mode is employed in this paper for DC-SOFC to test cell performance and improve fuel utilization simultaneously as well.

Sulfonated poly(ether ether ketone)-based hybrid membranes containing polydopamine-decorated multiwalled carbon nanotubes with acid-base pairs for all vanadium redox flow battery

Sulfonated poly(ether ether ketone) (SPEEK) hybrid membranes containing polydopamine-decorated multiwalled carbon nanotubes (MWCNTs@PDA) as the interfacial modifier have been fabricated. The membrane structure and physicochemical properties such as water uptake, swelling ratio, proton conductivity and vanadium ion permeability of SPEEK hybrid membranes are evaluated by XPS, TG, SEM, TEM and single-cell apparatus. The deposited mass percentage of PDA layer onto MWCNTs and the loaded contents of MWCNTs@PDA nanofillers into SPEEK membrane are detailed discussed. A 33 wt% PDA decorated MWCNTs offers a good membrane performance. In the single cell performance test, SPEEK/MWCNTs@PDA-1 hybrid membrane shows a higher coulombic efficiency (CE: 94.7%) and energy efficiency (EE: 85.9%), and a longer self-discharge time (55 h) against Nafion 117 membrane (23 h) is illustrated. A 100-time charging-discharging cycle indicates a good chemical stability of SPEEK/MWCNTs@PDA-1 hybrid membrane, which is ascribed to the formed acid-base interaction. The durability for SPEEK hybrid membranes need to be enhanced for VRB application.

An Examination of the Factors That Influence Primary Battery Longevity Performance Under Multiple-Cell Vs Single-Cell Testing Conditions

Primary alkaline batteries still account for the vast majority of battery sales in the US. According to the test standards the American National Standards Institute (ANSI), primary alkaline cell longevity performance is intended to be measured by discharging individual cells under specific load and duty cycle conditions to prescribed cutoff voltages. However, market research studies indicate that greater than 90% of battery-driven devices in the US require more than 1 cell, in electronic series configuration, to function. Thus, the analysis of primary alkaline battery performance in multiple-cell configuration will yield results that are far closer to the battery performance observed in actual devices and, therefore, is more consumer relevant. Focusing on AA size batteries, multiple cells discharged in series configuration demonstrated consistently lower cell performance (measured in service hours) vs single cells discharged under similar load and duty cycle conditions. The magnitude of decrease in performance for any battery design was highly related to the performance variability exhibited in single cell performance testing. Additional factors that influenced the lower performance observed in multiple-cell testing included the number of cells in series, discharge load magnitude, load type, endpoint voltage and battery design characteristics such as rate of increase of polarization during discharge. The relative importance of these factors to multiple-cell performance was quantified along with consideration of the deficiencies of reporting primary battery performance based on single-cell performance testing.