Maximum Power Density Of Cell Research Articles

Investigation of A-site deficient Ba0.9Co0.7Fe0.2Nb0.1O3−δ cathode for proton conducting electrolyte based solid oxide fuel cells

A novel cathode material for proton conducting electrolyte based solid oxide fuel cells (SOFCs) of A-site deficient Ba0.9Co0.7Fe0.2Nb0.1O3−δ (BCFN) has been synthesized and characterized. The A-site deficient BCFN has demonstrated a thermal expansion coefficient (TEC) similar to that of BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, enhanced oxygen reduction activity and chemical stability. The application of BCFN in proton-conducting electrolyte-based SOFCs has been investigated, and the SOFCs with Ni-BZCY|BZCY|BCFN configuration demonstrate maximum cell power outputs of 180, 240 and 300 mW cm−2 at 600, 650 and 700 °C, respectively. The cell polarization resistance is as low as 0.951, 0.387 and 0.201 Ω cm2 under open circuit voltage (OCV) at 600, 650 and 700 °C, respectively. The cell maximum power density increases from 300 to 356 mW cm−2 at 700 °C after over 118 h operating under a constant current of 300 mA cm−2.

Performance of Solid Oxide Fuel Cell With La and Cr Co-Doped SrTiO3 as Anode

The La0.3Sr0.55Ti0.9Cr0.1O3-δ (LSTC10) anode material was synthesized by citric acid-nitrate process. The yttria-stabilized zirconia (YSZ) electrolyte-supported cell was fabricated by screen printing method using LSTC10 as anode and (La0.75Sr0.25)0.95MnO3-δ (LSM) as cathode. The electrochemical performance of cell was tested by using dry hydrogen as fuel and air as oxidant in the temperature range of 800-900 °C. At 900 °C, the open circuit voltage (OCV) and the maximum power density of cell are 1.08 V and 13.0 mW·cm-2, respectively. The microstructures of cell after performance testing were investigated by scanning electron microscope (SEM). The results show that the anode and cathode films are porous and closely attached to the YSZ electrolyte. LSTC10 is believed to be a kind of potential solid oxide fuel cell (SOFC) anode material.

Transition metal-doped lanthanum germanate apatites as electrolyte materials of solid oxide fuel cells

In this study, the effects of Fe, Mn, Ni, and Ti dopants on the densification, phase structure, microstructure, and electrical conductivity of the La 9.5 Ge 6.0 O 26.25 ceramics were examined. After sintering, the La 9.5 Ge 5.5 Mn 0.5 O 26 and La 9.5 Ge 5.5 Ti 0.5 O 26.25 ceramics displayed hexagonal symmetry while the La 9.5 Ge 5.5 Ni 0.5 O 25.75 and La 9.5 Ge 5.5 Fe 0.5 O 26 ceramics produced triclinic lattice. The La 9.5 Ge 5.5 Fe 0.5 O 26 ceramic sintered at 1400 °C showed the best electrical conductivity of 0.033 Scm − 1 and the lowest densification temperature among the apatite ceramics evaluated, and the calculated thermal expansion coefficient of this system emerged to be 10.5 × 10 − 6 K −1 , compatible with those of the common adjacent materials used in solid oxide fuel cells (SOFCs). Single cells of NiO-SDC/La 9.5 Ge 5.5 Fe 0.5 O 26 /LSCF-SDC were built and evaluated. The open circuit voltages of the single cell read 0.96 and 1.01 V respectively at 950 and 800 °C, both in accord with the redicted theoretical values and verifying the pure ionic conduction in apatites. The maximum power densities (MPDs) of the single cell were 0.384, 0.280, 0.201, and 0.125 Wcm − 2 respectively at the measurement temperatures of 950, 900, 850, and 800 °C. The MPDs of the single cell with the La 9.5 Ge 5.5 Fe 0.5 O 26 electrolyte are superior to those of the SOFCs with apatite ceramics as electrolyte previously reported in the literature, thereby testifying to the potential of the La 9.5 Ge 5.5 Fe 0.5 O 26 ceramic as a promising electrolyte material for SOFCs. • Characteristics of Fe 3 + , Mn 3 + , Ni 2 + , and Ti 4 + doped La 9.5 Ge 6 O 26 ± δ were examined. • SOFC cells of NiO-SDC/La 9.5 Ge 5.5 Fe 0.5 O 26 /LSCF-SDC were built and characterized. • MPD of the cell with La 9.5 Ge 5.5 Fe 0.5 O 26 (0.39 mm) read 0.201 Wcm − 2 Wcm − 2 at 850 °C. • The results verified the potential of La 9.5 Ge 5.5 Fe 0.5 O 26 ceramic for use in SOFCs.

Lanthanum modified nickel-based anode of SOFCs

The effects of adding lanthanum to the nickel-based anode on the cell performances were studied. Because lanthanum can react with nickel and zirconium, it can hinder the sintering of nickel and yttrium stabilized zirconium (YSZ) and improve the interfacial contact between Ni and YSZ on the anode. When 10% (mol) lanthanum was added to the anode, the particles in the anode became smaller and better interfacial contact and the distribution was more uniform than Ni-YSZ anode, which led to a great decrease of the polarization resistance and a great increase of the activity for electrochemical oxidation of hydrogen. When the content of lanthanum added to NiO was 10 mol %, the cell maximum power density increased to 1.61W/cm2 from 1.33 W/cm2 of the Ni-YSZ anode cell at 800 oC. When the lanthanum content increased to 20% (mol), a large amount of La2Zr2O7 was formed, which led to both the decrease of the electronic conductivity of anode and the decrease of the cell performance.

Optimization of physical parameters of solid oxide fuel cell electrode using electrochemical model

To enhance the performance of anode-supported solid oxide fuel cell (SOFC), an electrochemical model has been developed in this study. The Butler-Volmer equation, Ohm’s law and dusty-gas model are incorporated to predict the activation, ohmic and concentration overpotentials, respectively. The optimal cell microstructure and operating parameters for the best current-voltage (J-V) characteristics have been sought from the information of the exchange current density and gas diffusion coefficients. As the cell temperature rises, the activation and ohmic overpotentials decrease, whereas the concentration overpotential increases due to the considerable reduction of gas density at the elevated temperature despite the increased diffusion coefficient. Also, increasing the hydrogen molar fraction and operating pressure can further augment the maximum cell output. Since there exists an optimum electrode pore size and porosity for maximum cell power density, the graded electrode has newly been designed to effectively reduce both the activation and concentration overpotentials. The results exhibit 70% improved cell performance than the case with a non-graded electrode. This electrochemical model will be useful to simply understand overpotential features and devise the strategy for optimal cell design in SOFC systems.

Aerosol Jet Printing and Microstructure of SOFC Electrolyte and Cathode Layers

We report the cathode layer optimization efforts undertaken to improve the cell performance of a previously reported (10) aerosol jet printed SOFC with strontium doped lanthanum manganate (LSM) based cathode. The cathode current collection layer, LSM with different thicknesses, solids loading in printing ink, and sintering temperature was examined. These parameters were observed to have a significant impact on the cell performance, changing the maximum power density of cells from 200 - 460 mW/cm2 at 850 ºC, depending on the processing conditions. Low voltage scanning electron microscopy was used to clearly distinguish the different phases of the composite LSM/YSZ layer. This method was used as a diagnostic tool to qualitatively assess the feasibility of "on the fly mixing" of the individually aerosolized inks. Cells with printed gadolinia doped ceria (GDC)-lanthanum strontium cobalt ferrite (LSCF) cathodes showed a performance, about twice that of cells with LSM cathodes.

Low Temperature Operating Micro Solid Oxide Fuel Cells with Perovskite Type Proton Conductors

We fabricated micro solid oxide fuel cells with perovskite type proton conductors on silicon substrates, and evaluated their electrical properties using electrochemical impedance spectroscopy (EIS). The cells with 15mol% yttrium-doped BaZrO3 and Pt-Pd electrodes could resist several thermal cycles from room temperature to 317oC, and they showed sufficient open circuit voltage over 1V around 300oC, if physical gas leakage was properly prevented. Maximum power density of cells reached 8.4mW / cm2 at 270oC. This value was quite promising for low temperature operation. But, the results of power generation test were so different each other and difference was sometimes over two orders of magnitude. EIS results indicated the contribution of electrolyte resistance to total resistance was small and those differences were due to the difference of electrode reaction components.

Nitrogen-doped carbon nanotubes as air cathode catalysts in zinc-air battery

Nitrogen-doped carbon nanotubes (N-CNTs) derived from ethylenediamine precursor have been used as air cathode catalyst for zinc-air batteries (ZABs) in half cell and single cell. Investigation of N-CNTs employed a rotating disc electrode system revealed excellent catalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolyte. The influence of alkaline electrolyte concentration on single cell performance of ZABs has also been explored. The highest cell performance was achieved at an electrolyte concentration of 6M KOH, which resulted in a maximum cell power density of 69.5mWcm−2.

Performance comparison of portable direct methanol fuel cell mini-stacks based on a low-cost fluorine-free polymer electrolyte and Nafion membrane

A low-cost fluorine-free proton conducting polymer electrolyte was investigated for application in direct methanol fuel cell (DMFC) mini-stacks. The membrane consisted of a sulfonated polystyrene grafted onto a polyethylene backbone. DMFC operating conditions specifically addressing portable applications, i.e. passive mode, air breathing, high methanol concentration, room temperature, were selected. The device consisted of a passive DMFC monopolar three-cell stack. Two designs for flow-fields/current collectors based on open-flow or grid-like geometry were investigated. An optimization of the mini-stack structure was necessary to improve utilization of the fluorine-free membrane. Titanium-grid current collectors with proper mechanical stiffness allowed a significant increase of the performance by reducing contact resistance even in the case of significant swelling. A single cell maximum power density of about 18 mW cm −2 was achieved with the fluorine-free membrane at room temperature under passive mode. As a comparison, the performance obtained with Nafion 117 membrane and Ti grids was 31 mW cm −2. Despite the lower performance, the fluorine-free membrane showed good characteristics for application in portable DMFCs especially with regard to the perspectives of significant cost reduction.

Cu 1− xPd x/CeO 2-impregnated cermet anodes for direct oxidation of methane in LaGaO 3-electrolyte solid oxide fuel cells

A series of ceramic–metal composite anodes containing 1.0 wt.% Cu 1− x Pd x alloys (where x = 0, 0.15, 0.25, 0.4, 0.5, 0.75 and 1.0) were prepared by impregnation of the respective metal salts and 5.0 wt.% CeO 2 into a porous La 0.4Ce 0.6O 2− σ anode skeleton. The performance of these anodes was evaluated in both dry H 2 and CH 4 in the temperature range of 700–800 °C using the 300-μm thick La 0.8Sr 0.2Ga 0.83Mg 0.17O 3− σ (LSGM) electrolyte-supported solid oxide fuel cells (SOFCs). The addition of Pd to Cu significantly increased the performance of the single cells in dry CH 4, with the cell maximum power density changed from 66 mW cm −2 for Cu 1.0Pd 0.0 to 345 mW cm −2 for Cu 0.0Pd 1.0 at 800 °C. In H 2, however, the performance improvement was not as significant compared to that in CH 4. In addition, carbon formation was greatly suppressed in the Cu–Pd alloy-impregnated anodes compared to that with pure Pd after exposure to dry CH 4 at 800 °C, which led to different performance stability behaviors for these cells operating with dry CH 4.

Novel proton-exchange membrane based on single-step preparation of functionalized ceramic powder containing surface-anchored sulfonic acid

A novel approach to the synthesis of a low-cost proton-exchange membrane (PEM) based on the single-step preparation of a functionalized ceramic powder containing surface-anchored sulfonic acid (SASA) and a polymer binder, is presented for the first time. The added value of this technique, compared with earlier work published by our group, is the adoption of a direct, single-step synthesis, as opposed to a multiple-step synthesis. The latter requires an oxidation step, in order to convert the thiol group into a sulfonic group. SASA powders of different compositions have been prepared and characterized by means of Brunaur–Emmet–Teller (BET), thermogravimetric analysis–differential thermal analysis (TGA–DTG), differential scanning calorimeter (DSC), Fourier transformation infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and electrochemical techniques. The lowest equivalent weight measured for SASA powders is 1281gequiv.−1. The ionic conductivity of a 100-μm-thick membrane is measured ex situ at room temperature (25±3°C) and the highest proton conductivity is 48mScm−1. The typical pore size, for the SASA powders is less than 10nm and ranges from 2 to 50nm for the SASA-based membranes. The membranes are thermally stable up to 250°C.Direct methanol fuel cells (DMFCs) are assembled with some of the membranes. Preliminary tests showed that the cell resistance for a ∼100-μm-thick membrane ranges between 0.29 and 0.19Ωcm2 from 80 to 130°C, respectively, and that the maximum cell power density with a 1M methanol solution is 127, 208 and 290mWcm−2 at 80, 110 and 130°C, respectively, while the corresponding methanol crossover current density is 0.093, 0.238 and 0.281Acm−2.

Improvement of cathode–electrolyte interfaces of tubular solid oxide fuel cells by fabricating dense YSZ electrolyte membranes with indented surfaces

To improve cathode–electrolyte interfaces of solid oxide fuel cells (SOFCs), dense YSZ electrolyte membranes with indented surfaces were fabricated on tubular NiO/YSZ anode supports by two comparable methods. Electrochemistry impedance spectroscopy (EIS) and current–voltage tests of the cells were carried out to characterize the cathode–electrolyte interfaces. Results showed that the electrode polarization resistances of the modified cells were reduced by 52% and 35% at 700 °C, and the maximum power densities of cells were remarkably increased, even by 146.6% and 117.8% at lower temperature (700 °C), respectively. The indented surfaces extended the active zone of cathode and enhanced interfacial adhesion, which led to the major improvement in the cell performance.

PtM/C (M = Sn, Ru, Pd, W) based anode direct ethanol–PEMFCs: Structural characteristics and cell performance

In the present work, the role of the structural characteristics of Pt-based catalysts on the single direct ethanol proton exchange membrane fuel cell (PEMFC) performance is examined. Several PtM/C (M = Sn, Ru, Pd, W) catalysts were characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) and then evaluated as anode catalysts in single direct ethanol fuel cells. XRD spectra showed that Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. According to the obtained experimental results, PtSn catalysts presented better electrocatalytic activity towards ethanol electro-oxidation. Based on these results, PtSn/C catalysts with different Pt/Sn atomic ratio were tested and compared. The maximum power density values obtained were correlated with the structural characteristics of the catalysts. A volcano type behaviour between the fuel cell maximum power density and the corresponding atomic percentage of Sn (Sn%) was observed. It was also observed that Sn% affects almost linearly the Pt x Sn y catalysts’ lattice parameter.

Novel composite proton-exchange membrane based on silica-anchored sulfonic acid (SASA)

A new approach to the synthesis of a low-cost proton-exchange composite membrane (C-PEM) based on PVDF and silica with surface-anchored sulfonic acid (SASA) groups, is presented for the first time. SASA membranes of different compositions have been prepared and characterized with the use of SEM, DSC, TGA, BET and electrochemical techniques. The room-temperature conductivity of SASA-based C-PEMs, is in the range of 2.0–50 mS cm −1. The equivalent weight of two SASA powders, SASA3(A) and SASA4(A) are 1600 and 2500 g equiv. −1 respectively. The typical pore size as measured by BET is about 4 nm. The membrane is thermally stable up to 250 °C. Direct methanol fuel cells (DMFCs) have been assembled with some of the membranes. Preliminary tests show that the cell resistance with a non-optimized membrane is in the range of 3 Ω cm −2, therefore the maximum cell power density achieved so far does not exceed 32 mW cm −2 at 70 °C. The crossover-current density for a 100 μm-thick membrane DMFC measured in 1 M methanol at 80 °C is 110 mA cm −2.

Direct ethanol fuel cells based on PtSn anodes: the effect of Sn content on the fuel cell performance

In the present work, several carbon supported PtSn catalysts with different Pt/Sn atomic ratios were synthesized and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Both the results of TEM and XRD showed that all in-house prepared carbon supported Pt and PtSn catalysts had nanosized particles with narrow size distribution. According to the primary analysis of XPS results, it was confirmed that the main part of Pt of the as-prepared catalysts is in metallic state while the main part of Sn is in oxidized state. The performances of single direct ethanol fuel cells were different from each other with different anode catalysts and at different temperatures. It was found that, the single DEFC employing Pt 3Sn 2/C showed better performance at 60 °C while the direct ethanol fuel cells with Pt 2Sn 1/C and Pt 3Sn 2/C exhibited similar performances at 75 °C. Furthermore, at 90 °C, Pt 2Sn 1/C was identified as a more suitable anode catalyst for direct ethanol fuel cells in terms of the fuel cell maximum power density. Surface oxygen-containing species, lattice parameters and ohmic effects, which are related to the Sn content, are thought as the main factors influencing the catalyst activity and consequently the performance of single direct ethanol fuel cells.

Increasing Power Density of LSGM-Based Solid Oxide Fuel Cells Using New Anode Materials

Chemical reactions between the superior perovskite oxide-ion conductor Sr- and Mg-doped (LSGM), and NiO have been studied by powder X-ray diffraction. The results showed that an extensive reactivity occurs as a result of La migration driven by a gradient of La chemical activity. La migration across the LSGM/electrode interfaces in a fuel cell leads to the formation of resistive phases at the interface, either or Use of 40 mol % -doped as an interlayer between anode and electrolyte as well as in the NiO-containing anode prevents all reactions found. Consequently, the air- cell maximum power density was increased to nearly 900 mW/cm2 at 800°C with a 600 μm thick LSGM electrolyte. No sign of degradation was observed at 800°C over 2 weeks for an interlayered cell under a loading current density of 250 mA/cm2. © 2001 The Electrochemical Society. All rights reserved.