Kinetic effect of the ionomer on the oxygen reduction in carbon-supported Pt electrocatalysts

The mechanism of the oxygen reduction reaction (ORR) on nanoparticulated Pt/C-Nafion electrodes prepared in one step has been studied to simulate the reaction in the cathode of a Polymer Electrolyte Fuel Cell (PEFC). The kinetic parameters have been obtained by hydrodynamic polarization in O₂-saturated 0.01–1.00 M H₂SO₄ and temperatures in the range 25.0–50.0 °C. The ORR current density was maximum and practically independent of the ionomer fraction in the rage 10–55 wt% Nafion. The poorer proton conductivity for lower Nafion fractions and the formation of catalyst areas completely surrounded by Nafion together with adsorption of Pt sites by sulfonate groups for higher Nafion fractions, explain the minor ORR activity in these conditions. The ionomer influence on the O₂ diffusion at high overpotentials for Pt/C-Nafion was negligible when the Nafion content was smaller than 20 wt%. The higher kinetic current density for Pt/C-Nafion (100 mA cm⁻²) with respect to smooth Pt-Nafion (40 mA cm⁻²), together with the smaller activation energy of the former (25 ± 4 kJ mol⁻¹) with respect to the latter (42 ± 5 kJ mol⁻¹) highlighted the better properties attained by the nanosize effect. A remarkable novel result is that the reaction order of H⁺ in HClO₄ is close to unity, whereas in sulfuric acid it is significantly smaller and changes with potential, what has been related to the sulfate adsorption. The anomalous dependence of the charge transfer coefficient with temperature was then explained by the thermal change of the double layer structure and the variation of the coverage of adsorbed species on Pt. The more sensitive effect for Pt/C-Nafion than for smooth Pt-Nafion was ascribed to the stronger interaction between the components when the nanoparticles are involved.     

Silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ as cathodes for a proton conducting solid-oxide fuel cell

Electrochemical performance of silver-modified Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF-Ag) as oxygen reduction electrodes for a protonic intermediate-temperature solid-oxide fuel cell (SOFC-H⁺) with BaZr_0.1Ce_0.8Y_0.1O₃ (BZCY) electrolyte was investigated. The BSCF-Ag electrodes were prepared by impregnating the porous BSCF electrode with AgNO₃ solution followed by reducing with hydrazine and then firing at 850 °C for 1 h. The 3 wt.% silver-modified BSCF (BSCF-3Ag) electrode showed an area specific resistance of 0.25 Ω cm² at 650 °C in dry air, compared to around 0.55 Ω cm² for a pure BSCF electrode. The activation energy was also reduced from 119 kJ mol⁻¹ for BSCF to only 84 kJ mol⁻¹ for BSCF-3Ag. Anode-supported SOFC-H⁺ with a BZCY electrolyte and a BSCF-3Ag cathode was fabricated. Peak power density up to 595 mW cm⁻² was achieved at 750 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel, higher than around 485 mW cm⁻² for a similar cell with BSCF cathode. However, at reduced temperatures, water had a negative effect on the oxygen reduction over BSCF-Ag electrode, as a result, a worse cell performance was observed for the cell with BSCF-3Ag electrode than that with pure BSCF electrode at 600 °C.     

New ionic diffusion strategy to fabricate proton-conducting solid oxide fuel cells based on a stable La2Ce2O7 electrolyte

A composite of NiO–BaZr_0.1Ce_0.7Y_0.2O_3−δ (NiO-BZCY) was successfully prepared by a simple one-step-combustion process and applied as an anode for solid oxide fuel cells based on stable La₂Ce₂O₇ (LCO) electrolyte. A high open circuit voltage of 1.00 V and a maximum power density of 315 mW cm⁻² were obtained with NiO-BZCY anode and LCO electrolyte when measured at 700 °C using humidified hydrogen fuel. SEM-EDX and Raman results suggested that a thin BaCeO₃-based reaction layer about 5 μm in thickness was formed at the anode/electrolyte interface for Ba cations partially migrated from anode into the electrolyte film. Impedance spectra analysis showed that the activation energy for LCO conductivity differed with the anode materials, about 52.51 kJ mol⁻¹ with NiO-BZCY anode and 95.08 kJ mol⁻¹ with NiO-LCO anode. The great difference in these activation energies might suggest that the formed BaCeO₃ reaction layer could promote the proton transferring numbers of LCO electrolyte.     

Identification of oxygen reduction processes at (La,Sr)MnO3 electrode/La9.5Si6O26.25 apatite electrolyte interface of solid oxide fuel cells

Oxygen reduction reaction of (La,Sr)MnO₃ (LSM) cathode on La_9.5Si₆O_26.25 apatite (LSO) electrolyte is studied over the temperature range 750–900 °C and the oxygen partial pressure range 0.01–1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (σ₁) is basically independent of oxygen partial pressure. The activation energy of σ₁ is 188 ± 15 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 1150 °C, and decreases to 120 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 850 °C, which is close to 80–110 kJ mol⁻¹ observed for the same electrode process at LSM/YSZ interface. The reaction order with respect to PO₂$P_{{\text{O}}_2}$ and the activation energy of the electrode process associated with low frequency arc (σ₂) are generally close to that of σ₂ at the LSM/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSM/LSO interface as compared to that at LSM/YSZ interface. The impedance responses of O₂ reduction reaction at the LSM/LSO interface are significantly higher than that at the LSM/YSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSM electrode on LSO electrolyte. At the sintering temperature of 1000 °C, the impedance responses of O₂ reduction reaction is 1.74 Ω cm² at 900 °C, which is significantly smaller than that of LSM electrode sintered at 1150 °C.     

Electrochemical reactivity of magnesium hydride toward lithium: New synthesis route of nano-particles suitable for hydrogen storage

Electrochemical conversion reaction of MgH₂ with Li ion enables the production of in-situ nanometric Mg and MgH₂ particles so-called (nano-Mg) _INSITU and [(nano-MgH₂)_INSITU] showing interesting hydrogen sorption properties with hydrogen absorption at 100 °C under 10 bars of hydrogen pressure (PH₂) and desorption at 200 °C under primary vacuum, respectively. Differential Scanning Calorimetry (DSC) measurements of MgH₂ electrochemically prepared confirmed a decrease in the desorption temperature from 416 °C to 295 °C and in the heat of formation from −74 kJ mole mol⁻¹ (H₂)⁻¹ to −56 kJ mol⁻¹ (H₂)⁻¹ for commercial (particle size diameter: 10 μm–100 μm) and as prepared MgH₂ hydride (particle size: 10 nm–40 nm), respectively.     

Application of phosphoric acid and phytic acid-doped bacterial cellulose as novel proton-conducting membranes to PEMFC

Novel proton-conducting polymer electrolyte membranes have been prepared from bacterial cellulose by incorporation of phosphoric acid (H₃PO₄/BC) and phytic acid (PA/BC). H₃PO₄ and PA were doped by immersing the BC membranes directly in the aqueous solution of H₃PO₄ and PA, respectively. Characterizations by FTIR, TG, TS and AC conductivity measurements were carried out on the membrane electrolytes consisting of different H₃PO₄ or PA doping level. The ionic conductivity showed a sensitive variation with the concentration of the acid in the doping solution through the changes in the contents of acid and water in the membranes. Maximum conductivities up to 0.08 S cm⁻¹ at 20 °C and 0.11 S cm⁻¹ at 80 °C were obtained for BC membranes doped from H₃PO₄ concentration of 6.0 mol L⁻¹ and, 0.05 S cm⁻¹ at 20 °C and 0.09 S cm ⁻¹ at 60 °C were obtained for BC membranes doped from PA concentration of 1.6 mol L⁻¹. These types of proton-conducting membranes share not only the good mechanical properties but also the thermal stability. The temperature dependences of the conductivity follows the Arrhenius relationship at a temperature range from 20 to 80 °C and, the apparent activation energies (E_a) for proton conduction were found to be 4.02 kJ mol⁻¹ for H₃PO₄/BC membrane and 11.29 kJ mol⁻¹ for PA/BC membrane, respectively. In particular, the membrane electrode assembly fabricated with H₃PO₄/BC and PA/BC membranes reached the initial power densities of 17.9 mW cm⁻² and 23.0 mW cm⁻², which are much higher than those reported in literature in a real H₂/O₂ fuel cell at 25 °C.     

Pr2NiO4–Ag composite cathode for low temperature solid oxide fuel cells with ceria-carbonate composite electrolyte

Pr₂NiO₄–Ag composite was synthesized and evaluated as cathode component for low temperature solid oxide fuel cells based on ceria-carbonate composite electrolyte. X-ray diffraction analysis reveals that the formation of a single phase K₂NiF₄–type structure occurs at 1000 °C and Pr₂NiO₄–Ag composite shows chemically compatible with the composite electrolyte. Symmetrical cells impedance measurements prove that Ag displays acceptable electrocatalytic activity toward oxygen reduction reaction at the temperature range of 500–600 °C. Single cells with Ag active component electrodes present better electrochemical performances than those of Ag-free cells. An improved maximum power density of 695 mW cm⁻² was achieved at 600 °C using Pr₂NiO₄–Ag composite cathode, with humidified hydrogen as fuel and air as the oxidant. Preliminary results suggest that Pr₂NiO₄–Ag composite could be adopted as an alternative cathode for low temperature solid oxide fuel cells.     

The effects of ionomer content on PEM water electrolyser membrane electrode assembly performance

In this study, the effects of Nafion^® ionomer content in membrane electrode assemblies (MEAs) of polymer electrolyte membrane (PEM) water electrolyser were discussed. The MEAs were prepared with a catalyst coated membrane (CCM) method. The catalysts inks with Nafion ionomer could form uniform coatings deposited on the membrane surfaces. SEM and area EDX mapping demonstrated that anode catalyst coating was uniformly distributed, with a microporous structure. The contents of Nafion ionomer were optimized to 25% for the anode and 20% for cathode. A current density of 1 A cm⁻² was achieved at terminal voltage 1.586 V at 80 °C in a PEMWE single cell, with Nafion 117, Pt/C as cathode, and Ru_0.7Ir_0.3O₂ as anode.     

Kinetic study of Nafion degradation by Fenton reaction

To predict the durability of polymer electrolyte membranes in fuel cells, the degradation reactions of Nafion 117 films were studied as oxidation reactions with hydroxyl radicals as oxidation accelerators. The radical species were generated by the Fenton reaction between hydrogen peroxide (H₂O₂) and iron ions (Fe²⁺). The Nafion degradation kinetics were estimated by fluorine ion (F⁻) generation. The H₂O₂ and Nafion degradation reactions fit a pseudo-first-order rate constant. The values of the activation energy and frequency factor are 85 kJ mol⁻¹ and 3.97 × 10⁸ s⁻¹ for H₂O₂ decomposition in the presence of a Nafion film and 97 kJ mol⁻¹ and 9.88 × 10⁸ s⁻¹ for F⁻ generation. The Nafion surface morphology became rough after reaction for 12 h; small cracks, approximately 100 μm in length, were observed at temperatures below 60 °C. These cracks connected to make larger gaps of approximately 1 mm at temperatures above 70 °C. We also found a linear relationship between H₂O₂ consumption and F⁻ generation. The rate constant is temperature dependent and expressed as ln(d[F⁻]/d[decomposed H₂O₂]) = −19.5 × 10³ K⁻¹ + 42.8. F⁻ generated and H₂O₂ consumed along with the Nafion degradation conditions can be predicted using this relation.     

Dehydrogenation characteristics of ammonia borane via boron-based catalysts (Co–B,Ni–B,Cu–B) under different hydrolysis conditions

In the present study, dehydrogenation characteristics of ammonia borane (NH₃BH₃) catalyzed via boron-based catalysts under different hydrolysis conditions were investigated. A series of boron-based catalysts (Co_1−x–B_x, Ni_1−x–B_x, and Cu_1−x–B_x, x: 0.25, 0.50, 0.75) were prepared by sol–gel method. Gels were calcinated at different temperatures (250 °C, 350 °C, and 450 °C) in order to obtain the boron-based catalysts. XRD characterizations revealed that Co–B, Ni–B, and Cu–B crystalline structures were formed during calcination at 450 °C. Hydrogen generation measurements were performed in order to determine the optimum composition of the boron-based catalyst. The maximum hydrogen generation rates were 7607 ml min⁻¹ gcat⁻¹, 3869 ml min⁻¹ gcat⁻¹ and 1178 ml min⁻¹ gcat⁻¹ for Co_0.75B_0.25, Ni_0.75B_0.25 and Cu_0.75B_0.25, respectively. Furthermore, the hydrolysis of NH₃BH₃ was performed at 20 °C, 40 °C, 60 °C and 80 °C under magnetic stirring (750 rpm), ultrasonic irradiation and non-stirring in order to determine how these parameters effect hydrolysis. Activation energies (E_a) were calculated by evaluation of the kinetic data. Under ultrasonic irradiation, the E_a in the presence of Co_0.75B_0.25, Ni_0.75B_0.25 and Cu_0.75B_0.25 were 40.85 kJ mol⁻¹, 43.19 kJ mol⁻¹ and 48.74 kJ mol⁻¹, respectively, which compares favorably with results reported in the literature. Thus, the catalytic activities of the boron-based catalysts were found to be Cu < Ni < Co and the best reaction condition for the catalytic hydrolysis of NH₃BH₃ was determined to be non-stirring < magnetic stirring < ultrasonic irradiation.     

Fabrication and characterization of anode-supported single chamber solid oxide fuel cell based on La0.6Sr0.4Co0.2Fe0.8O3−δ–Ce0.9Gd0.1O1.95 composite cathode

Anode-supported solid oxide fuel cells consisting of nickel–gadolinium doped ceria (NiO–CGO, 60:40 wt%) anode, gadolinium doped ceria (CGO) electrolyte and lanthanum strontium cobaltite ferrite–gadolinium doped ceria (LSCF–CGO) cathode are developed and operated under single-chamber conditions, utilizing methane/air mixture. The cell performance is optimized regarding the electrolyte microstructure, cathode composition and testing conditions. The performance of the cell improves with the decrease of the thickness of the electrolyte and the increase of the ratio of methane to oxygen. The test cell with LSCF–CGO cathode (70:30 wt%) that was sintered at 1100 °C for 2 h and 150 μm dense electrolyte exhibits the maximum power output of ∼260 mW cm⁻² at 600 °C in CH₄/O₂ = 2 atmosphere.     

Cobalt-free composite cathode for SOFCs: Brownmillerite-type calcium ferrite and gadolinium-doped ceria

A cobalt-free composite Ca₂Fe₂O₅ (CFO) – Ce_0.9Gd_0.1O_1.95 (GDC) is investigated as a new cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Gd_0.1Ce_0.9O_1.95 (GDC) electrolyte. The cathodes had brownmillerite structure with x wt.% Gd_0.1Ce_0.9O_1.95 (GDC) – (100−x) wt.% Ca₂Fe₂O₅ (CFO), where x = 0, 10, 20, 30 and 40. The effect of GDC incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the CFO–GDC composites is investigated. The composite cathode of 30 wt.% GDC – 70 wt.% CFO (CG30) coated on Gd_0.1Ce_0.9O_1.95 electrolyte showed the lowest area specific resistance (ASR), 0.294 Ω cm² at 700 °C and 0.122 Ω cm² at 750 °C. The TEC of the CG30 cathode was 13.1 × 10⁻⁶ °C⁻¹ up to 900 °C, which is a lower value than for CFO alone (13.8 × 10⁻⁶ °C⁻¹). Long-term thermal stability and thermal cycle testing of CG30 cathodes were performed. Stable ARS values were observed during both tests without delamination at the cathode–electrolyte interface. An electrolyte-supported single cell with a 300-μm-thick GDC electrolyte and an anode-supported single cell with ∼10-μm-thick yttria-stabilized zirconia (YSZ) with a GDC buffer layer attained maximum power densities of 395 mW cm⁻² at 750 °C and 842 mW cm⁻² at 800 °C, respectively. The unique composite composition of CG30 demonstrates enhanced electrochemical performance and good thermal stability for IT-SOFCs.     

A comparative study of Sm0.5Sr0.5MO3−δ (M = Co and Mn) as oxygen reduction electrodes for solid oxide fuel cells

Sm_0.5Sr_0.5MO_3−δ (M = Co and Mn) materials are synthesized, and their properties and performance as cathodes for solid oxide fuel cells (SOFCs) on Sm_0.2Ce_0.8O_1.9 (SDC) and Y_0.16Zr_0.92O_2.08 (YSZ) electrolytes are comparatively studied. The phase structure, thermal expansion behavior, oxygen mobility, oxygen vacancy concentration and electrical conductivity of the oxides are systematically investigated. Sm_0.5Sr_0.5CoO_3−δ (SSC) has a much larger oxygen vacancy concentration, electrical conductivity and TEC than Sm_0.5Sr_0.5MnO_3−δ (SSM). A powder reaction demonstrates that SSM is more chemically compatible with the YSZ electrolyte than SSC, while both are compatible with the SDC electrolyte. EIS results indicate that the performances of SSC and SSM electrodes depend on the electrolyte that they are deposited on. SSC is suitable for the SDC electrolyte, while SSM is preferred for the YSZ electrolyte. A peak power density as high as 690 mW cm⁻² at 600 °C is observed for a thin-film SDC electrolyte with SSC cathode, while a similar cell with YSZ electrolyte performs poorly. However, SSM performs well on YSZ electrolyte at an operation temperature of higher than 700 °C, and a fuel cell with SSM cathode and a thin-film YSZ electrolyte delivers a peak power density of ∼590 mW cm⁻² at 800 °C. The poor performances of SSM cathode on both YSZ and SDC electrolytes are obtained at a temperature of lower than 650 °C.     

Ni–YSZ-supported tubular solid oxide fuel cells with GDC interlayer between YSZ electrolyte and LSCF cathode

Highly sinterable gadolinia doped ceria (GDC) powders are prepared by carbonate coprecipitation and applied to the GDC interlayer in Ni–YSZ (yttria stabilized zirconia)-supported tubular solid oxide fuel cell in order to prevent the reaction between YSZ electrolyte and LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ) cathode materials. The formation of highly resistive phase at the YSZ/LSCF interface was effectively blocked by the low-temperature densification of GDC interlayer using carbonate-derived active GDC powders and the suppression of Sr diffusion toward YSZ electrolyte via GDC interlayer by tuning the heat-treatment temperature for cathode fabrication. The power density of the cell with the configuration of Ni–YSZ/YSZ/GDC/LSCF–GDC/LSCF was as high as 906 mW cm⁻², which was 2.0 times higher than that (455 mW cm⁻²) of the cell with the configuration of Ni–YSZ/YSZ/LSM(La_0.8Sr_0.2MnO_3−δ)–YSZ/LSM at 750 °C.     

Scheme of thermal compression of hydrogen (TCH) using MmNi4.25Al0.75 recovered with ethyl alcohol and handled under non protective atmospheres

A MmNi_4.25Al_0.75 intermetallic was obtained by low energy mechanical alloying and low temperature heating at 600 °C for 24 h under Ar. The intermetallic was recovered from milling chamber using ethyl alcohol, dried, stored and handled under air at room conditions. Structure was characterized by XRD. A maximum stability temperature of 160 °C was obtained from non-isothermal DSC measurement under air. The kinetics of oxidation at 200 °C was analyzed. A maximum reaction degree (α = 0.1) was obtained after 2500 s of treatment. The hydrogen sorption properties of samples were studied by volumetric measurements. Hydrogen maximum mass percent capacity (mass %) was reached in less than 300 s. The thermodynamic sorption properties were measured. Values of ΔH_f = −29 ± 2 kJ mol⁻¹ and ΔS_f = 197 ± 10 J mol⁻¹ K⁻¹ were obtained for absorption process and ΔH_d = 28 ± 2 kJ mol⁻¹ and ΔS_d = 189 + 10 J mol⁻¹ K⁻¹ were obtained for desorption process. From these results, a one-stage of thermal compression of hydrogen is proposed with a standard compression ratio (R_c) of 5.71 in the 25–80 °C range.     

GdBaCo2O5+x layered perovskite as an intermediate temperature solid oxide fuel cell cathode

GdBaCo₂O_5+x (GBCO) was evaluated as a cathode for intermediate-temperature solid oxide fuel cells. A porous layer of GBCO was deposited on an anode-supported fuel cell consisting of a 15 μm thick electrolyte of yttria-stabilized zirconia (YSZ) prepared by dense screen-printing and a Ni–YSZ cermet as an anode (Ni–YSZ/YSZ/GBCO). Values of power density of 150 mW cm⁻² at 700 °C and ca. 250 mW cm⁻² at 800 °C are reported for this standard configuration using 5% of H₂ in nitrogen as fuel. An intermediate porous layer of YSZ was introduced between the electrolyte and the cathode improving the performance of the cell. Values for power density of 300 mW cm⁻² at 700 °C and ca. 500 mW cm⁻² at 800 °C in this configuration were achieved.     

Preparation and characterization of nanocrystalline Ce0.8Sm0.2O1.9 for low temperature solid oxide fuel cells based on composite electrolyte

Nanocrystalline Ce_0.8Sm_0.2O_1.9 (SDC) has been synthesized by a combined EDTA–citrate complexing sol–gel process for low temperature solid oxide fuel cells (SOFCs) based on composite electrolyte. A range of techniques including X-ray diffraction (XRD), and electron microscopy (SEM and TEM) have been employed to characterize the SDC and the composite electrolyte. The influence of pH values and citric acid-to-metal ions ratios (C/M) on lattice constant, crystallite size and conductivity has been investigated. Composite electrolyte consisting of SDC derived from different synthesis conditions and binary carbonates (Li₂CO₃–Na₂CO₃) has been prepared and conduction mechanism is discussed. Water was observed on both anode and cathode side during the fuel cell operation, indicating the composite electrolyte is co-ionic conductor possessing H⁺ and O²⁻ conduction. The variation of composite electrolyte conductivity and fuel cell power output with different synthesis conditions was in accordance with that of the SDC originated from different precursors, demonstrating O²⁻ conduction is predominant in the conduction process. A maximum power density of 817 mW cm⁻² at 600 °C and 605 mW cm⁻² at 500 °C was achieved for fuel cell based on composite electrolyte.     

SrCo0.7Fe0.2Ta0.1O3−δ perovskite as a cathode material for intermediate-temperature solid oxide fuel cells

Perovskite oxide SrCo_0.7Fe_0.2Ta_0.1O_3−δ (SCFT) was synthesized by a solid–state reaction and investigated as a potential cathode material for intermediate-temperature solid oxide fuel cell (IT-SOFC). The single phase SCFT having a cubic perovskite structure was obtained by sintering the sample at 1200 °C for 10 h in air. Introduction of Ta improved the phase stability of SCFT. The SCFT exhibited a good chemical compatibility with the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte at 950 °C for 10 h. The average thermal expansion coefficient was 23.8 × 10⁻⁶ K⁻¹ between 30 and 1000 °C in air. The electrical conductivities of the SCFT sample were 71–119 S cm⁻¹ in the 600−800 °C temperature range in air, and the maximum conductivity reached 247 S cm⁻¹ at 325 °C. The polarization resistance of the SCFT cathode on the LSGM electrolyte was 0.159 Ω cm² at 700 °C. The maximum power density of a single-cell with the SCFT cathode on a 300 μm-thick LSGM electrolyte reached 652.9 mW cm⁻² at 800 °C. The SCFT cathode had shown a good electrochemical stability over a period of 20 h short-term testing. These findings indicated that the SCFT could be a suitable alternative cathode material for IT-SOFCs.     

Characterization of SmBaCoFeO5+δ−Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

The performance of SmBaCoFeO_5+δ (SBCF)–xCe_0.9Gd_0.1O_1.95 (GDC) (x = 0, 10, 30, 50, 60, wt%) composite cathodes has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) and electrochemical property measurements are employed to study the materials. The XRD results prove that there is no serious reaction between SBCF and GDC oxides even at 1000 °C. The thermal expansion behavior shows that the TEC value of SBCF cathode decreases greatly with GDC addition. The addition of GDC to SBCF cathode further reduces the polarization resistance. The lowest polarization resistance of 0.036 Ω cm² is achieved at 800 °C for SBCF–50GDC composite cathode. An electrolyte-supported fuel cell is prepared using SBCF–50GDC as cathode and NiO–GDC (65:35 by weight) as anode. The cell generates good performance with the maximum power density of 691 mW cm⁻², 503 mW cm⁻² and 337 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively. Preliminary results indicate that SBCF–50GDC is especially promising as a cathode for IT-SOFCs.     

Optimization of hot pressing parameters in membrane electrode assembly fabrication by response surface method

The aim of this research was to study the effect of the membrane electrode assembly fabrication factors on the performance of a passive micro direct methanol fuel cell by studying the hot pressing parameters. The MEA was prepared with a Nafion 117 membrane and porous electrodes having an active area of 1 cm² with Pt and Pt/Ru catalysts of 8 mg cm⁻² loading at the cathode side and anode side, respectively. The Design of Experiment work was performed with the Response Surface Method using the Central Composite Design. The One-factor-at-a-time method was used to select the significant level of factors for the DOE method, which are temperature in the range of 100–135 °C and pressure in the range of 6.0–16.0 kgf cm⁻². The results show that the proposed mathematical model in the Response Surface Method can be used adequately for prediction and optimization within the factor levels investigated. The combined optimum hot pressing parameters that gave the highest performance of 7.23 mW cm⁻² predicted in this study are temperature 130 °C and pressure 6 kgf cm⁻².