A novel anode supported BaCe0.7Ta0.1Y0.2O3−δ electrolyte membrane for proton-conducting solid oxide fuel cell

A novel composition of BaCe_0.7Ta_0.1Y_0.2O_3−δ (BCTY10) electrolyte membrane was successfully fabricated on porous NiO-BCTY10 anode substrate. The anode was prepared through a route combining a solid state reaction and a wet chemical method. After sintering at 1450 °C for 5 h, the BCTY10 membrane showed adequate chemical stability against CO₂ and H₂O. With a mixture of La_0.7Sr_0.3FeO_3−δ (LSF) and BaCe_0.7Zr_0.1Y_0.2O_3−δ (BZCY7) as cathode, a single fuel cell with 25 μm thick BCTY10 electrolyte generated maximum power densities of 195, 137, 84, 44 mW/cm² at 700, 650, 600 and 550 °C, respectively. The interface resistance of the cell under open circuit condition was also investigated.     

A strategy of tailoring stable electrolyte material for high performance proton-conducting solid oxide fuel cells (SOFCs)

A facile strategy was proposed to synthesize Nb-containing BaCeO₃-based material, which is a potential electrolyte for proton-conducting solid oxide fuel cells (SOFCs), via a wet chemical route while the conventional synthesis of Nb-containing oxides relied on the solid state reaction method due to the unavailability of suitable Nb-precursors such as Nb-nitrates resulting in a less desirable fuel cell performance when used as an electrolyte. The BaCe_0.7Nb_0.1Y_0.2O_3 − δ (BCNY) electrolyte material in this study persisted a good chemical stability against CO₂ and exhibited good performance in the fuel cell application. The fuel cell with BCNY electrolyte film showed a high performance of 533 mW cm^− 2 at 700 °C. This cell performance based on BCNY electrolyte was superior to that of many stable modified BaCeO₃-based proton-conducting SOFCs where the electrolytes were tailored by other strategies. This result indicated that the strategy presented in this study could be an effective way to prepare a stable electrolyte for high performance proton-conducting SOFCs, which could advance the development of proton-conducting SOFCs.     

Chemically stable anode-supported solid oxide fuel cells based on Y-doped barium zirconate thin films having improved performance

Anode-supported solid oxide fuel cells (SOFCs) based on thin BaZr_0.8Y_0.2O_3 ? δ (BZY) electrolyte films were fabricated by pulsed laser deposition (PLD) on sintered NiO–BZY composite anodes. After in situ reduction of NiO to Ni, the anode substrates became porous, while retaining good adhesion with the electrolyte. A slurry-coated composite cathode made of La_0.6Sr_0.4Co_0.2Fe_0.8O_3 ? δ (LSCF) and BaCe_0.9Yb_0.1O_3 ? δ (BCYb), specifically developed for proton conducting electrolytes, was used to assemble fuel cell prototypes. Depositing by PLD 100 nm thick LSCF porous films onto the BZY thin films was essential to improve the cathode/electrolyte adhesion. A power density output of 110 mW/cm² at 600 °C, the largest reported value for an anode-supported fuel cell based on BZY at this temperature, was achieved. Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the different contributions to the total polarization losses.     

Enhancement of electrochemical performance and thermal compatibility of GdBaCo2/3Fe2/3Cu2/3O5+δ cathode on Ce1.9Gd0.1O1.95 electrolyte for IT-SOFCs

Transition-metal doped double-perovskite structure oxides GdBaCo_2/3Fe_2/3Ni_2/3O_5+δ (FN-GBCO), GdBaCo_2/3Fe_2/3Cu_2/3O_5+δ (FC-GBCO), GdBaCoCuO_5+δ (C-GBCO) and pristine GdBaCo₂O_5+δ (GBCO) were synthesized via a citrate combustion method. The thermal-expansion coefficient (TEC) and electrochemical performance of the oxides were investigated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The TEC exhibited by the FC-GBCO cathode up to 900 °C is 14.6 × 10^?6 °C^?1, which is lower than the value of GBCO (19.9 × 10^?6 °C^?1). Area specific resistances (ASR) of 0.165 Ω cm² at 700 °C and 0.048 Ω cm² at 750 °C were achieved for the FC-GBCO cathode on a Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte. An electrolyte supported (300 μm thick) single-cell configuration of FC-GBCO/CGO/Ni-CGO attained a maximum power density of 435 mW cm^?2 at 700 °C. The unique composition of GBCO co-doped with Fe and Cu ions in the Co sites exhibited reduced TEC and enhancement of electrochemical performance and good chemical compatibility with CGO, and this composition is proving to be a potential cathode for IT-SOFCs.     

Novel BaCo0.7Fe0.3−yNbyO3−δ (y = 0–0.12) as a cathode for intermediate temperature solid oxide fuel cell

The BaCo_0.7Fe_0.3?yNb_yO_3?δ oxides (BCFNy, y = 0.00–0.12) were synthesized by the conventional solid state reaction process and investigated as a novel cathode for intermediate temperature solid oxide fuel cells(IT-SOFCs). Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y ? 0.04. The unit cell volumes increased with y, reached a maximum at y = 0.10, and then decreased. The niobium doping concentration also had a significant effect on the electrochemical performance of BCFNy materials. Among the various BCFNy oxides tested, BCFN0.10 possessed the smallest interfacial polarization resistance (R_p). The R_p was as low as 0.9406, 0.1300, 0.0211, and 0.0082 Ω cm² at 500, 600, 700, and 800 °C, respectively. With a 220 μm-thick Sm_0.2Ce_0.1O_1.9 (SDC) as electrolyte and BCFN0.10 as the cathode, a fuel cell provides maximum power densities of 202, 350, 569, 820, and 1006 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively. The encouraging results suggested that BCFN0.10 was a very promising cathode material for IT-SOFCs.     

Electrode properties of Sr doped La2CuO4 as new cathode material for intermediate-temperature SOFCs

High performance La_2−xSr_xCuO_4−δ (x = 0.1, 0.3, 0.5) cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFCs) were prepared and characterized. The investigation of electrical properties indicated that La_1.7Sr_0.3CuO₄ cathode has low area specific resistance (ASR) of 0.16 Ω cm² at 700 °C and 1.2 Ω cm² at 500 °C in air. The rate-limiting step for oxygen reduction reaction on La_1.7Sr_0.3CuO₄ electrode changed with oxygen partial pressure and measurement temperature. La_1.7Sr_0.3CuO₄ cathode exhibits the lowest overpotential of about 100 mV at a current density of 150 mA cm⁻² at 700 °C in air.     

Cobalt-free cathode material SrFe0.9Nb0.1O3−δ for intermediate-temperature solid oxide fuel cells

A cobalt-free cubic perovskite oxide, SrFe_0.9Nb_0.1O_3?δ (SFN) was investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results showed that SFN cathode was chemically compatible with the electrolyte Sm_0.2Ce_0.8O_1.9 (SDC) for temperatures up to 1050 °C. The electrical conductivity of SFN sample reached 34–70 S cm^?1 in the commonly operated temperatures of IT-SOFCs (600–800 °C). The area specific resistance was 0.138 Ω cm² for SFN cathode on SDC electrolyte at 750 °C. A maximum power density of 407 mW cm^?2 was obtained at 800 °C for single-cell with 300 μm thick SDC electrolyte and SFN cathode.     

High performance protonic ceramic membrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte based PCMFCs with stable Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode were investigated. Using thin membrane BZCY7 electrolyte (about 15 μm in thickness) synthesized by a modified Pechini method on NiO-BZCY7 anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.015 V, a maximum power density of 486 mW cm⁻², and a low polarization resistance of the electrodes of 0.08 Ω cm² was achieved at 700 °C. The results have indicated that BZCY7 proton-conducting electrolyte with BSZF cathode is a promising material system for the next generation solid oxide fuel cells.     

A mixed-conducting BaPr0.8In0.2O3 − δ cathode for proton-conducting solid oxide fuel cells

A mixed ionic and electronic conductor, BaPr_0.8In_0.2O_3 − δ (BPI), was synthesized and examined as a cathode material for proton-conducting solid oxide fuel cells (H-SOFCs). X-ray diffraction analysis revealed that BPI had a perovskite structure and showed satisfactory tolerance to CO₂ and H₂O and good chemical compatibility with BaZr_0.1Ce_0.7Y_0.1 Yb_0.1O_3 − δ (BZCYYb) electrolyte. Test cells with a single-phase BPI cathode exhibited excellent electrochemical performances, demonstrating a peak power density of ~ 688 mW cm^− 2 at 750 °C. Furthermore, the cells with a BPI cathode showed very stable power output at a cell voltage of 0.7 V at 600 °C over 100 h, suggesting that BPI is a promising alternative cathode for H-SOFCs.     

Electrochemical performances of LaBaCuFeO5+x and LaBaCuCoO5+x as potential cathode materials for intermediate-temperature solid oxide fuel cells

Layered perovskite-structure oxides LaBaCuFeO_5+x (LBCFO) and LaBaCuCoO_5+x (LBCCO) were prepared and the electrical conductivity and electrochemical performance were investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity of LBCCO is much higher than that of LBCFO. Area specific resistances of LBCFO and LBCCO cathode materials on Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte are as low as 0.21 Ω cm² and 0.11 Ω cm² at 700 °C, respectively. The maximum power density of the LBCFO/SDC/Ni-SDC and LBCCO/SDC/Ni-SDC cells with 300 μm thick electrolytes attains 557 mW cm^?2 and 603 mW cm^?2 at 800 ^oC, respectively. Preliminary results demonstrated that the layered perovskite-structure oxides LBCFO and LBCCO are very promising cathode materials for application in IT-SOFCs.     

Electrochemical performance of La-doped Sr2MgMoO6−δ in natural gas

Modification of the double perovskite Sr₂MgMoO_6−δ by La substitution has shown that Sr_2−xLa_xMgMoO_6−δ with 0.6 ⩽ x ⩽ 0.8 has better performance as the anode of a solid oxide fuel cell. With a Sr_1.2La_0.8MgMoO_6−δ anode, LSGM electrolyte, SrCo_0.8Fe_0.2O_3−δ cathode, and a La_0.5Ce_0.4O_1.7−δ buffer layer between the anode and the electrolyte, a maximum power density of 550 mW/cm² has been obtained for a SOFC operating on wet methane (3%H₂O) at 800 °C. The performance of the SOFC using C₂H₆ fuel, like that of CH₄, changes little on switching from dry C₂H₆ to 3% H₂O/C₂H₆, but improvement with wet C₃H₈ shows that some steam will need to be added to a moderately desulfurized natural-gas fuel.     

Development of micro-tubular SOFCs with an improved performance via nano-Ag impregnation for intermediate temperature operation

Micro-tubular solid-oxide fuel cell consisting of a 10-μm thick (ZrO₂)_0.89(Sc₂O₃)_0.1(CeO₂)_0.01 (ScSZ) electrolyte on a support NiO/(ScSZ) anode (1.8 mm diameter, 200 μm wall thickness) with a Ce_0.8Gd_0.2O_1.9 (GDC) buffer-layer and a La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)/GDC functional cathode has been developed for intermediate temperature operation. The functional cathode was in situ formed by impregnating the well-dispersed nano-Ag particles into the porous LSCF/GDC layer using a citrate method. The cells yielded maximum power densities of 1.06 W cm⁻² (1.43 A cm⁻², 0.74 V), 0.98 W cm⁻² (1.78 A cm⁻², 0.55 V) and 0.49 W cm⁻² (1.44 A cm⁻², 0.34 V), at 650, 600 and 550 °C, respectively.     

Cost-effective solid oxide fuel cell prepared by single step co-press-firing process with lithiated NiO cathode

A cost-effective cell fabrication process was developed for intermediate temperature solid oxide fuel cells (IT-SOFCs). Co-doped ceria Ce_0.8Gd_0.05Y_0.15O_1.9 (GYDC) was synthesized by carbonate co-precipitation method. Lithiated NiO was prepared by glycine-nitrate combustion method and adopted as cathode material for IT-SOFCs. Single cell was fabricated by one-step dry-pressing and co-firing anode, anode functional layer (AFL), electrolyte and cathode together at 1200 °C for 4 h. The cell presented decent performance and an overall electrode polarization resistance of 0.54 Ω cm² has been achieved at 600 °C. These results demonstrate the possibility of using lithiated NiO as cathode material for ceria-based IT-SOFCs and the development of affordable fuel cell devices is encouraged.     

Effects of CuO addition to anode on the electrochemical performances of cathode-supported solid oxide fuel cells

A cathode-supported electrolyte film was fabricated by tape casting and co-sintering techniques. (La_0.8Sr_0.2)_0.95MnO₃ (LSM95), LSM95/Zr_0.89Sc_0.1Ce_0.01O_2?x (SSZ), and SSZ were used as materials of cathode substrate, cathode active layer, and electrolyte, respectively. CuO–NiO–SSZ composite anode was deposited on SSZ surface by screen-printing and sintered at 1250 °C for 2 h. The effects of CuO addition to NiO–SSZ anode on the performance of cathode-supported SOFCs were investigated. CuO can effectively improve the sintering activity of NiO–SSZ. The assembled cells were electrochemically characterized with humidified H₂ as fuel and O₂ as oxidant. With 4 wt.% CuO addition, the ohmic resistance decreased from 3 to 0.46 Ω cm², and at the same time the polarization resistance decreased from 3.4 to 0.74 Ω cm². In comparison with the cell without CuO, the maximum power density at 850 °C increased from 0.054 to 0.446 W cm^?2 with 4 wt.% CuO addition.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

Preparation of an extremely dense BaCe0.8Sm0.2O3−δ thin membrane based on an in situ reaction

The thin membrane of BaCe_0.8Sm_0.2O_3−δ (BCS) with high quality was successfully fabricated on porous NiO–BCS anode substrate through a novel in situ reaction method. The key part of this method is to directly spray well-mixed suspension of BaCO₃, CeO₂ and Sm₂O₃ instead of pre-synthesized BCS ceramic powder on the anode substrate. After sintering at 1400 °C for 5 h, the extremely dense electrolyte membrane in the thickness of 10 μm is obtained. A single cell was assembled with La_0.7Sr_0.3FeO_3−σ as cathode and tested with humidified hydrogen as fuel at 650 °C. The open circuit voltage (OCV) and maximum power density respectively reach 1.04 V and 535 mW/cm². Interface resistance of cell under open circuit condition was also investigated.     

Electrochemical characterisation of MBaCo3ZnO7+δ (M = Y,Er, Tb) as SOFC cathode material with low thermal expansion coefficient

The electrochemical oxygen activation at high temperature was studied on a new class of oxygen-store material based on the system YBaCo₄O_7+δ. Three different porous layers made of YBaCo₃ZnO_7+δ, ErBaCo₃ZnO_7+δ and TbBaCo₃ZnO_7+δ were electrochemically tested as oxygen activation coatings and showed a very promising activity. The envisaged applications for these materials are principally as SOFC cathodes and as catalytic layer on oxygen membranes. The electrochemical performance followed the order Tb ? Y > Er at any tested temperature. Area specific resistance for the best performing material (TbBaCo₃ZnO_7+δ) ranges from 30 mΩ cm² at 850 °C to 0.46 Ω cm² at 650 °C. High temperature XRD showed that the thermal expansion coefficient (25–900 °C) in air of TbBaCo₃ZnO₇ is 9.45 × 10^?6 K^?1, which evidences the good thermochemical compatibility of this cobalt-rich electrocatalyst with YSZ/GDC electrolytes.     

Novel SrSc0.2Co0.8O3−δ as a cathode material for low temperature solid-oxide fuel cell

The SrSc_0.2Co_0.8O_3−δ (SSC) perovskite was investigated as a cathode material for low temperature solid-oxide fuel cell. The material showed an almost linear thermal expansion from room temperature to 1000 °C in air with the average thermal expansion coefficient of only 16.9 × 10⁻⁶ K⁻¹. The Sc-doping made the absence of Co⁴⁺ in SSC, which resulted in not only dramatically reduced thermal expansion coefficient but also extremely high oxygen vacancies concentrations in the lattice at low temperature. The area specific polarization resistance was 0.206 Ω cm² for SSC at 550 °C, which is about 52% lower than the value of a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ-based cathode. A peak power density as high as 564 mW cm⁻² was obtained at 500 °C based on a 20 μm thick Sm_0.2Ce_0.8O_1.9 electrolyte by adopting SSC cathode.     

A microfluidic glucose biofuel cell to generate micropower from enzymes at ambient temperature

A Y-shaped microfluidic channel is applied for the first time to the construction of a glucose/O₂ biofuel cell, based on both laminar flow and biological enzyme strategies. During operation, the fuel and oxidant streams flow parallel at gold electrode surfaces without convective mixing. At the anode, the glucose oxidation is performed by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from an interfering parasite reaction of O₂ at the anode and offers the advantage of using different streams of oxidant and fuel for optimal performance of the enzymes. Electrochemical characterizations of the device show the influence of the flow rate on the output potential and current density. The maximum power density delivered by the assembled biofuel cell reached 110 μW cm^?2 at 0.3 V with 10 mM glucose at 23 °C. The microfluidic approach reported here demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O₂ biofuel cell device.     

Composite cathode for IT-SOFC: Sr-doped lanthanum cuprate and Gd-doped ceria

Composite cathodes were synthesized via a citrate combustion method followed by an organic precipitation method. The cathodes were of K₂NiF₄-type crystal structure with x wt.% Ce_0.9Gd_0.1O_1.95 (CGO)–(100 ? x) wt.% La_1.96Sr_0.04CuO_4 + δ (LSC), where x = 0, 10, 20 and 30. The individual structural phases of the composite cathodes were characterized using a third-generation synchrotron source beamline powder X-ray diffractometer (XRD). The porous grain morphology of the CGO–LSC cathode composite for a symmetrical half-cell was determined from cross-sectional scanning electron microscopy images and elemental line profiles. The composite cathode was made of 20 wt.% CGO–80 wt.% LSC (CL20–80) and was coated onto a Ce_0.9Gd_0.1O_1.95 electrolyte. It showed the lowest area specific resistance (ASR) of 0.07 Ω cm² at 750 °C. An electrolyte-supported (300 μm thick) single-cell configuration of CL20–80/CGO/Ni-CGO attained a maximum power density of 626 mW cm^? 2 at 700 °C. The unique composite composition of CL20–80 demonstrates enhanced electrochemical performance and good chemical compatibility with the CGO electrolyte, as compared with the pure LSC (CL0–100) cathode for IT-SOFCs.