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A layered perovskite oxide Y0.8Ca0.2BaCoFeO5+d (YCBCF) was synthesized as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by citric acid-nitrates self-propagating combustion method. The phase and microstructure of YCBCF were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The average thermal expansion coefficient (TEC) of YCBCF was 14.6×10−6 K−1, which was close to other materials of SOFC at the range of RT-1000 °C. An open-circuit potential of 0.75 V and a maximum output power density of 426 mW/cm2 were obtained at 650 °C in a Sm0.2Ce0.8O1.9 (SDC)-based anode-supported SOFC by using humidified (∼3% H2O) hydrogen as fuel and static air as oxidant. The results indicated that the YCBCF was a promising cathode candidate for IT-SOFCs.

Solid oxide electrolyzers have attracted a great deal of interest in recent years because they can convert electrical energy into chemical energy with high efficiency. Ni/YSZ cathodes are generally utilized for high temperature electrolysis of H 2 O and CO 2 in oxygen-ion conducting solid oxide electrolyzers; however, such electrodes can only operate under reducing conditions. In an atmosphere without a flow of reducing gas, cathodes based on La 0.2 Sr 0.8 TiO 3+ δ (LST) are a promising alternative. Solid Oxide Electrolyzers with LST cathodes without pre-reduction were used at 700 °C for the electrolysis of 3%H 2 O/97%N 2 and 100%CO 2 , and promising polarization impedance data were obtained in both atmospheres. The electrochemical results indicated that the electrochemical reduction of the La 0.2 Sr 0.8 TiO 3+ δ cathode was the main process at low electrical voltages, while the electrolysis was the main process at high voltages because ion transportation in the electrolyte limited the overall efficiency. The electrolysis of H 2 O was determined to be more efficient than the electrolysis of CO 2 under the same conditions. The Faraday efficiencies of H 2 O and CO 2 were 85.0% and 24.7%, respectively, at 700 °C and a 2 V applied potential.

Nano-sized CSO (Ce 0.80 Sm 0.20 O 2− δ ) and CSCO (Ce 0.79 Sm 0.20 Cu 0.01 O 2− δ ) were synthesized by the PVA assisted combustion method, and then characterized by the structure of PVA–cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA–cation complexes (PVA–(Ce 3+ ,Sm 3+ ) and PVA–(Ce 3+ ,Sm 3+ ,Cu 2+ )) were formed by coordinating metal cations to hydroxyl groups, as well as the COO −1 group derived from the oxidation of PVA with NO 3 −1 . Low temperatures (around 200 °C) caused intense combustion reactions, resulting in the direct crystallization of cubic fluorite nano-CSO (10–20 nm) and nano-CSCO (10–15 nm) crystals with homogeneous element distribution. This slight compositional modification of CSO by co-doping with 1 mol% CuO resulted in a significantly lowered densification temperature, as well as enhanced mechanical and electrical property. The strength improvement can be ascribed to the dense and fine-grained microstructure without normal grain coarsening, resulting in a transgranular-dominant fracture mode during strength testing.

Synthetic hydrocarbon fuels from CO2/H2O are proposed as alternatives to hydrogen as an energy carrier to enable a carbon neutral energy cycle, given their inherent advantages of high H/C ratio and convenience of storage and transportation. Here we demonstrate the successful electrochemical reduction of CO2 into CO and CH4 in a proton conducting solid oxide electrolyser based on BaCe0.5Zr0.3Y0.16Zn0.04O3 − δ (BCZYZ) electrolyte and a composite iron/iron oxide cathode. The production of CH4 and CO reaches 0.07 and 3.25 ml min−1 cm−2, respectively, with 1.5 A cm−2 at 614 °C. The overall CO2 conversion rate in the electrochemical reduction process is 65%.

This paper presents Pervoskite-type BaCo0.7Ta0.1Fe0.2O3−δ (BCTF) cathode for intermediate temperature proton conducting solid oxide fuel cells (SOFCs). BCTF with cubic phase shows excellent structural stability and adequate chemical stability against CO2/H2O in contrast to BaCo0.8Fe0.2O3−δ. Conductivity of BCTF reaches above 10 S cm−1 in air at intermediate temperatures. Composite cathode polarization resistance (BCTF/BaZr0.1Ce0.7Y0.2O3−δ) in a symmetric cell based on proton conducting BaZr0.1Ce0.7Y0.2O3−δ (BCZY) electrolyte was as low as 0.1 Ω cm2 at 700 °C. The maximum output of anode-supported thin-film SOFC with BCTF/BCZY composite cathode and BCZY electrolyte reaches 255 mW cm−2 when employing humidified H2 as fuel and static air as oxidizer.

A NiO–YSZ anode-supported hollow fiber solid oxide fuel cell (HF-SOFC) has been fabricated with redox stable (La0.75Sr0.25)0.95Cr0.5Mn0.5O3−δ–Sm0.2Ce0.8O1.9–YSZ (LSCM–SDC–YSZ) composite cathode. The characterization of NiO–YSZ hollow fibers prepared by the phase inversion method is focused on the microstructure, porosity, bending strength and electrical conductivity. A thin YSZ electrolyte membrane (about 10 μm) can be prepared by a vacuum-assisted dip-coating process and is characterized in terms of microstructure and gas-tightness. The performance of the as-prepared HF-SOFC is investigated at 750–850 °C with humidified H2 as fuel and ambient air as the oxidant. The peak power densities of 513, 408 and 278 mW cm−2 can be obtained at 850, 800 and 750 °C, respectively, and the corresponding interfacial polarization resistances are 0.14, 0.29 and 0.59 Ω cm2. The high performance at intermediate-to-high temperatures could be attributed to thin electrolyte and proper composite cathode with low interfacial polarization resistance. The low interfacial polarization resistance suggests potential applications of LSCM–SDC–YSZ composite oxides as the redox stable cathode. This investigation indicates that the redox stable LSCM–SDC–YSZ is a promising cathode material system for the next generation YSZ-based HF-SOFC. The results will be expected to open up a new phase of the research on the micro-tubular SOFCs.

A cobalt-free cubic perovskite oxide Sm0.5Sr0.5Fe0.8Cu0.2O3−δ (SSFCu) was investigated as a novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficient (TEC) of SSFCu was close to that of Sm0.2Ce0.8O1.9(SDC) electrolyte and the electrical conductivity of SSFCu sample reached 72–82 S cm−1 in the commonly operated temperatures of IT-SOFCs (400–600 °C). Symmetrical electrochemical cell with the configuration of SSFCu/SDC/SSFCu was applied for the impedance study and area specific resistance (ASR) of SSFCu cathode material was as low as 0.085 Ω cm2 at 700 °C. Laboratory-sized tri-layer cells of NiO-SDC/SDC/SSFCu were operated from 450 to 700 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. A maximum power density of 808 mW cm2 was obtained at 700 °C for the single cell.

Zirconia single crystal nano-particles containing pores were prepared by a sol–gel-hydrothermal method. The unique character of the particles is that some irregular pores are embedded within the single crystals. The results of XRD, TEM and FT-IR show that the gaseous hydrolysates of the superstoichiometric urotropine are the origin of the pores. The gel structure and the hydrothermal treatment are the required conditions resulting in the pores in crystals. The formation mechanism was proposed: zirconia gel was formed after the reaction of ZrOCl 2 with urotropine. The superstoichiometric urotropine was dissolved and distributed uniformly in the gel. The small pores were generated because gaseous hydrolysates of urotropine were constrained in the gel during the hydrothermal treatment. During the process of the amorphous gel transferred into the crystals, some of the pores coarsened with the crystals growth. Big pores disappeared due to the break of the crystals. And only the small pores were remained in the interior of crystals, which could hardly be eliminated by the subsequent crystal growth if the calcination temperature is below 550 °C. Thus, the zirconia nano-particles containing pores were generated.

Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe 0.5 Zr 0.3 Y 0.2 O 3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700 °C, the charging current (in SOFC mode) is 251 mA cm −2 at 0.7 V, and the electrolysis current densities (in SOEC mode) reaches −830 mA cm −2 at 1.5 V with 50% H 2 O–air and H 2 as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance ( R H ) is 0.07 Ωcm 2 and low frequency resistances ( R L ) are 0.37 Ωcm 2 . While in SOEC mode, R H is 0.15 Ωcm 2 , twice of that in SOFC mode, and R L is only 0.07 Ωcm 2 , about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that R H in OCV mode is about 0.13 Ωcm 2 , close to R H in SOEC mode, while R L in OCV mode is 0.39 Ωcm 2 , close to R L in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.

A cobalt-free perovskite oxide Ba0.5Sr0.5Fe0.8Cu0.2O3−δ (BSFC) is employed as a cathode material for intermediate-temperature proton-conducting solid oxide fuel cells. Symmetrical electrochemical cell with the configuration of BSFC-BZCY/BZCY/BSFC-BZCY is applied for the impedance study. The single cell, consisting of BSFC-BZCY/BZCY/NiO-BZCY structure, is assembled and tested from 600 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and the static air as the oxidant. A maximum power density of 430 mW cm−2 is obtained at 700 °C for the single cell. Long-term stability of the BSFC-BZCY/BZCY/NiO-BZCY single cell at 600 °C for 40 h has also been studied. Preliminary results demonstrat that cobalt-free oxide BSFC is a very promising cathode for application in proton-conducting solid oxide fuel cells.

The perovskite La 0.6 Sr 0.4 Co 0.8 Cu 0.2 O 3− δ (LSCCu) oxide is synthesized by a modified Pechini method and examined as a novel cathode material for low-temperature solid oxide fuel cells (LT-SOFCs) based upon functional graded anode. The perovskite LSCCu exhibits excellent ionic and electronic conductivities in the intermediate-to-low-temperature range (400–800 °C). Thin Sm 0.2 Ce 0.8 O 1.9 (SDC) electrolyte and NiO–SDC anode functional layer are prepared over macroporous anode substrates composed of NiO–SDC by a one-step dry-pressing/co-firing process. A single cell with 20 μm thick SDC electrolyte on a porous anode support and LSCCu–SDC cathode shows peak power densities of only 583.2 mW cm −2 at 650 °C and 309.4 mW cm −2 for 550 °C. While a cell with 20 μm thick SDC electrolyte and an anode functional layer on the macroporous anode substrate shows peak power densities of 867.3 and 490.3 mW cm −2 at 650 and 550 °C, respectively. The dramatic improvement of cell performance is attributed to the much improved anode microstructure that is confirmed by both SEM observation and impedance spectroscopy. The results indicate that LSCCu is a very promising cathode material for LT-SOFCs and the one-step dry-pressing/co-firing process is a suitable technique to fabricate high performance SOFCs.

A dense BaCe 0.8 Sm 0.2 O 5+ δ (BCS) electrolyte was fabricated on a porous anode by in situ drop-coating to develop a simple and cost-effective route to fabricate proton-conducting solid oxide fuel cells (SOFCs). Layered perovskite-structure oxides SmBaCuCoO 5+ δ (SBCC) and SmBaCuFeO 5+ δ (SBCF) were prepared and the electrical conductivity, the thermal expansion coefficient and electrochemical performance were investigated as potential cathode materials for proton-conducting SOFCs. Thermal expansion coefficients of SBCC and SBCF were suitable for BCS electrolyte and the electrical conductivity of the SBCC is higher than that of the SBCF. The maximum power density of 449 mW cm 2 and 333 mW cm 2 at 700 °C were obtained for the SBCC/BCS/NiO–BCS and SBCF/BCS/NiO–BCS cells, respectively. The interfacial polarization resistances for SBCC and SBCF cathode are as low as 0.137 Ω cm −2 and 0.196 Ω cm −2 at 700 °C, respectively. The results indicate that the SBCC and SBCF are promising cathode materials for proton-conducting SOFCs.

Layered perovskite LaBaCuFeO5+x (LBCF) and LaBaCuCoO5+x (LBCC) oxides are synthesized by a modified Pechini method and examined as potential cathode materials for intermediate-temperature protonic ceramic membrane fuel cells (IT-PCMFCs). Thin proton-conducting BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte and NiO–BaZr0.1Ce0.7Y0.2O3−δ (NiO–BZCY) anode functional layer are prepared over porous anode substrates composed of NiO–BaZr0.1Ce0.7Y0.2O3−δ by a one-step dry-pressing/co-firing process. Laboratory-sized quad-layer cells of NiO-BYCZ/NiO-BYCZ/BYCZ/LBCF (LBCC) are operated from 550 to 700 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. The single cell with LBCF cathode shows peak power densities of only 327 mW cm−2 at 700 °C and 105 mW cm−2 for 550 °C, while the single cell with LBCC cathode shows peak power densities of 432 and 171 mW cm−2 at 700 and 550 °C, respectively. The dramatic improvement of cell performance is attributed to higher cobaltites catalytic activity than that of ferrites for IT-PCMFCs, which is in good agreement with the results of impedance measurement.

A new concept of solid oxide fuel cells (SOFCs), the simple SOFCs, that is simply composed of an electronic conductor and an ionic conductor is investigated, which evidently simplifies the assembly and further maintenance of the cell system. High-performance interconnect material chromium deficient lanthanum calcium chromites La0.7Ca0.3Cr0.97O3−δ (LCC97) perovskite oxides are prepared by a modified Pechini method and examined as both anode and cathode materials for SOFCs based on the state-of-the-art YSZ electrolyte. Chemical compatibility, sintering character, electrical conductivity and thermal expansion are investigated to characterize the compatibilities of LCC97 with YSZ. The XRD analysis indicates LCC97 chemically compatible with YSZ. The LCC97 sintered at 1250 °C have the conductivity of 62.0 S cm−1 at 850 °C in air, which is about 2.6 times as high as that of La0.7Ca0.3CrO3−δ with no chromium deficiency. At 850 °C, the ASRs is only 0.15 Ω cm2 for LCC97–YSZ composite cathode. LCC97-based simple SOFCs (LCC97–YSZ/YSZ/LCC97–YSZ) offer promising performance using H2 as fuel and thick YSZ electrolytes. An open-circuit potential of 1.06 V, a maximum power density of 92.1 mW cm−2, and a polarization resistance of the electrodes of 2.17 Ω cm2 are achieved at 850 °C.

BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (BZCY7) exhibits adequate proton conductivity as well as sufficient chemical and thermal stability over a wide range of SOFC operating conditions, while layered SmBa 0.5 Sr 0.5 Co 2 O 5+ δ (SBSC) perovskite demonstrates advanced electrochemical properties based on doped ceria electrolyte. This research fully takes advantage of these advanced properties and develops novel protonic ceramic membrane fuel cells (PCMFCs) of Ni-BZCY7|BZCY7|SBSC. The results show that the open-circuit potential of 1.015 V and maximum power density of 533 mW cm −2 are achieved at 700 °C. With temperature increase, the total cell resistance decreases, among which electrolyte resistance becomes increasingly dominant over polarization resistance. The results also indicate that SBSC perovskite cathode is a good candidate for intermediate temperature PCMFC development, while the developed Ni-BZCY7|BZCY7|SBSC cell is a promising functional material system for next generation SOFCs.

The layered perovskite structure oxide NdBaCo2O5+δ (NBCO) with rapid oxygen ion diffusion and surface exchange kinetics was synthesized by auto ignition process and initially examined as a cathode for proton-conducting fuel cells (H-SOFCs). The single cell, consisting of NdBaCo2O5+δ (NBCO)/BaZr0.1Ce0.7Y0.2O3−δ (BZCY)/NiO–BaZr0.1Ce0.7Y0.2O3−δ (BZCY) structure, was assembled and tested from 650 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and air as the oxidant. A maximum power density of 438 mW cm−2 at 700 °C was obtained for the single cell and electrochemical performance of the cell was studied.

A novel layered perovskite oxide PrBaCuCoO5+i (PBCCO) is employed as a potential cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Thermal expansion and electrochemical performance on samarium-doped ceria (SDC) electrolyte are evaluated. The thermal expansion coef- ficient (TEC) of PrBaCuCoO5+i (PBCCO) is close to that of SDC electrolyte and electrical conductivity of PrBaCuCoO5+i (PBCCO) reaches the general required value of cathode material. Symmetrical electro- chemical cell with the configuration of PrBaCuCoO5+i (PBCCO)/SDC/PrBaCuCoO5+i (PBCCO) applied for the impedance studies, the area specific resistance of PrBaCuCoO5+i (PBCCO) cathode is as low as 0.047 � cm2 at 700

In order to develop a simple and cost-effective route to fabricate proton-conductor intermediate-temperature SOFCs, a dense BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte was fabricated on a porous anode by in situ drop-coating. The PrBaCuFeO5+δ (PBCF) composite oxide with layered perovskite structure was synthesized by auto ignition process and examined as a novel cathode for proton-conductor IT-SOFCs. The single cell, consisting of PBCF/BZCY/NiO-BZCY structure, was assembled and tested from 600 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and the static air as the oxidant. An open-circuit potential of 1.01 V and a maximum power density of 445 mW cm−2 at 700 °C were obtained for the single cell. A relatively low interfacial polarization resistance of 0.15 Ω cm2 at 700 °C indicated that the PBCF is a promising cathode for proton-conductor IT-SOFCs.

Unique ZrO 2 crystals within pores were prepared by a sol–gel-hydrothermal method and characterized by XRD, TG/DTA, TEM, SEM, and N 2 adsorption–desorption isotherms. Results show that the dried sol–gel was converted into monoclinic zirconia crystals after calcined above 550 °C. The crystal sizes of the zirconia single crystal were in the range of 20–70 nm. A number of irregular pores were embedded within the zirconia crystals. This unique structure was obtained due to the combination of sol–gel and hydrothermal treatments.

Protonic ceramic membrane fuel cells (PCMFCs) based on oxide proton conductors exhibit more advantages than traditional solid oxide fuel cells (SOFCs) based on oxygen-ion conducting electrolytes, such as low activation energy and high energy efficiency. In order to develop a simple and cost-effective route to fabricate PCMFCs with SrCo 0.9 Sb 0.1 O 3− δ (SCS) cubic perovskite cathode, a dense BaCe 0.5 Zr 0.3 Y 0.16 Zn 0.04 O 3− δ (BCZYZn) electrolyte was fabricated in situ metal oxide on a porous anode support by gel-casting and suspension spray, which is cost-effective, easy to realize, and suitable for mass-production. The key part of this process is to directly spray well-mixed suspension of BaCO 3 , CeO 2 , ZrO 2 , Y 2 O 3 and ZnO instead of pre-synthesized BCZYZn ceramic powder on the anode substrate. With SCS cubic perovskite cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H 2 as fuel and the static air as oxidant. An open-circuit potential of 0.987 V, a maximum power density of 364 mW cm −2 , and a low polarization resistance of the electrodes of 0.07 Ω cm 2 was achieved at 700 °C.

In order to reduce fabrication cost and process time, porous cordierite membranes with micro-filtration function were prepared by a simple co-sintering process from the low-cost industrial grade powder. Aqueous medium ball-milling was used as the effective classification method to obtain the fine powders with narrow particle size distribution. Then, the sintering characteristics of the selected two types of cordierite powders were studied by dilatometric measurements. And the effects of co-sintering temperature on the main properties of the prepared membranes were investigated such as micro-structure morphology and pore size distribution. The results prove that the co-sintering of two-layer cordierite membranes (45.0 and 15.0 μm thick) was feasible because of their low difference in sintering shrinkage behavior. The co-sintered tubular cordierite micro-filtration membranes showed some characteristics such as crack-free morphology, average pore diameters of 1.55 and 2.17 μm, 60.0 μm in total thickness and narrow pore size distribution.

The SrCo0.9Sb0.1O3–δ (SCS) composite oxide with cubic perovskite structure was synthesized by a modified Pechini method, and examined as a novel cathode for intermediate-to-low temperature solid oxide fuel cells (ILT-SOFCs). At 700°C and under open-circuit condition, a symmetrical SCS cathode on Sm0.2Ce0.8O1.9 (SDC) electrolyte showed a low polarization resistance (Rp) of 0.09 Ωcm2 in air. A porous layer of SCS was deposited on an anode-supported fuel cell, consisting of a ∼30 μm thick dense electrolyte of SDC prepared by a cost-effective dip coating process, and an NiO-SDC cermet as an anode (Ni-SDC/SDC/SCS). The single cells obtained were tested with humidified (∼3% H2O) hydrogen as fuel and static air as oxidant. A high open-circuit voltage of 0.86 V, a maximum power density of 354 mW/cm2, and a low polarization resistance of the electrodes of 0.13 Ωcm2 was achieved at 650°C.

The perovskite-type Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ –BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (BSCF–BZCY) composite oxides were synthesized by a modified Pechini method and examined as a novel composite cathode for intermediate-to-low temperature protonic ceramic membrane fuel cells (ILT-PCMFCs). Thin proton-conducting BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (BZCY) electrolyte and NiO–BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ (NiO–BZCY) anode functional layer were prepared over porous anode substrates composed of NiO–BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ by a one-step dry-pressing/co-firing process. A laboratory-sized quad-layer cell of NiO–BZCY/NiO–BZCY(∼50 μm)/BZCY(∼20 μm)/BSCF–BZCY(∼50 μm) was operated from 550 to 700 °C with humidified hydrogen (∼3% H 2 O) as fuel and the static air as oxidant. A high open-circuit potential of 1.009 V, a maximum power density of 418 mW cm −2 , and a low polarization resistance of the electrodes of 0.10 Ω cm 2 was achieved at 700 °C. These investigations have indicated that proton-conducting BZCY electrolyte with BSCF perovskite cathode is a promising material system for the next generation solid oxide fuel cells (SOFCs).

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered SmBaCo2O5+x (SBCO) cathode, a dense BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte was fabricated on a porous anode by in situ screen printing. The porous NiO–BaZr0.1Ce0.7Y0.2O3−δ (NiO–BZCY) anode was directly prepared from metal oxide (NiO, BaCO3, ZrO2, CeO2 and Y2O3) by a simple gel-casting process. An ink of metal oxide (BaCO3, ZrO2, CeO2 and Y2O3) powders was then employed to deposit BaZr0.1Ce0.7Y0.2O3−δ (BZCY) thin layer by an in situ reaction-sintering screen printing process on NiO–BZCY anode. The bi-layer with 25 μm dense BZCY electrolyte was obtained by co-sintering at 1400 °C for 5 h. With layered SBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H2 as fuel and the static air as oxidant. A high open-circuit potential of 1.01 V, a maximum power density of 382 mW cm−2, and a low polarization resistance of the electrodes of 0.15 Ω cm2 was achieved at 700 °C.

The SrCo0.9Sb0.1O3-delta (SCS) composite oxide with cubic perovskite structure was synthesized by a modified Pechini method and examined as a novel cathode for protonic ceramic membrane fuel cells (PCMFCs). At 700 degrees C and under open-circuit condition, symmetrical SCS cathode on BaZr0.1Ce0.7Y0.2O3-delta (BZCY7) electrolyte showed low polarization resistances (R-p) of 0.22 Omega cm(2) in air. A laboratory-sized tri-layer cell of NiO-BZCY7/BZCY7/SCS was operated from 500 to 700 degrees C with humidified hydrogen (similar to 3% H2O) as fuel and the static air as oxidant. A high open-circuit potential of 1.004V, a maximum power density of 259mWcm(-2), and a low polarization resistance of the electrodes of 0.14 Omega cm(2) was achieved at 700 degrees C.

A thin Ba3Ca1.18Nb1.82O9−δ (BCN18) membrane electrolyte was prepared by a novel and facile method on a NiO–BCN18 anode substrate. The interesting aspect of the method was the adoption of a in situ reaction of BaCO3, CaCO3, and Nb2O5 on the anode substrate to prepare a dense BCN18 membrane. The BCN18 membrane obtained, which was about 15 μm in thickness and showed high chemical stability against H2O and CO2, attained a high density after sintering at 1400°C. The elemental composition of the BCN18 membrane prepared was identified by energy-dispersive X-ray spectroscopy analysis. With La0.7Sr0.3FeO3−σ (LSF) as the cathode, the fuel cell performance with the structure of Ni–BCN18/BCN18/LSF was studied.

A green BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (BZCY) electrolyte layer was deposited on porous anode substrate (BZCY:NiO = 35:65, in weight ratio) by a suspension spray. In this process, the suspension was prepared by directly ball-milling the mixed BaCO 3 , CeO 2 , ZrO 2 and Y 2 O 3 powders in ethanol for 24 h. Then the bi-layers were co-sintered at 1400 °C for 5 h in air to obtain dense and uniform electrolyte membrane in the thickness of 10 μm. With Nd 0.7 Sr 0.3 MnO 3− δ cathode, a fuel cell was assembled. It was tested from 600 °C to 700 °C using humid hydrogen as fuel and air as oxidant. The cell at 700 °C exhibited 1.02 V for open circuit voltage (OCV), 450 mW/cm 2 for peak output and 0.18 Ω cm 2 for electrode polarizations under open circuit conditions, respectively. The results indicate that it is feasible to fabricate thin electrolyte membrane for solid oxide fuel cells (SOFCs) by this simple, cost-effective and efficient technique.

In order to develop a cost-effective route to fabricate solid oxide fuel cells (SOFCs), a dense Ce 0.8 Sm 0.2 O 1.9 (SDC) electrolyte was fabricated on a porous cathode based on a mixed conducting La 0.8 Sr 0.2 FeO 3− δ (LSF) via a suspension spray/co-firing process. For the purpose of shrinkage matching between the cathode support and the electrolyte membrane, nano-SDC1 powder for the easily sinterable electrolyte was synthesized with ammonia as the precipitant from the nitrates, whereas SDC2 powder prepared by modified glycine–nitrate method (GNP) was added into cathode to favor the shrinkage of La 0.8 Sr 0.2 FeO 3− δ (LSF) . Sm-doped ceria solid solution was directly formed during precipitation at 50 °C, and this is ascribed to the role of OH − . The powders calcined at 800 °C for 2 h were still uniform and exhibited an average particle size of 20 nm. The bi-layer with 10 μm dense SDC electrolyte was obtained by co-sintering at 1250 °C for 5 h. A thin and well-adherent anode was formed by depositing ultra-fine NiO–SDC powders, followed by sintering at 1000 °C. The obtained single cells were tested with humidified (3% H 2 O) hydrogen as fuel and the static air as oxidant. The maximum power density reached 67.2 mW/cm 2 at 600 °C.

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. BaZr0.1Ce0.7Y0.2O3−δ (BZCY7) electrolyte based PCMFCs with stable Ba0.5Sr0.5Zn0.2Fe0.8O3−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. Keywords: Solid oxide fuel cells, BaZr0.1Ce0.7Y0.2O3−δ, Ba0.5Sr0.5Zn0.2Fe0.8O3−δ, Protonic ceramic membrane fuel cells, Cathode

A stable, easily sintered perovskite oxide BaCe0.5Zr0.3Y0.16Zn0.04O3-delta (BCZYZn) as an electrolyte for protonic ceramic mernbrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3-delta (BSZF) perovskite cathode was investigated. The BCZYZn perovskite electrolyte synthesized by a modified Pechini method exhibited higher sinterability and reached 97.4% relative density at 1200 degrees C for 5 h in air, which is about 200 degrees C lower than that without Zn dopant. By fabricating thin membrane BCZYZn electrolyte (about 30 mu m in thickness) on NiO-BCZYZn anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.00V, a maximum power density of 236 mWcm(-2), and a low polarization resistance of the electrodes of 0.17 Omega cm(2) were achieved at 700 degrees C. This investigation indicated that proton conducting electrolyte BCZYZn with BSZF perovskite cathode is a promising material system for the next generation solid oxide fuel cells. (C) 2008 Elsevier B.V. All rights reserved.

A dense $${\text{BaCe}}_{{\text{0}}{\text{.8}}} {\text{Sm}}_{{\text{0}}{\text{.2}}} {\text{O}}_{{\text{3 - }}\delta } $$ (BCSO) membrane was fabricated by a modified suspension spraying on porous NiO–BCSO anode support. In the process, the suspension was directly prepared by ball-milling the BaCO3, CeO2, and Sm2O3 powders in ethanol. A dense and uniform electrolyte layer in the thickness of 10 μm was successfully prepared on porous anode support by suspension spray process after co-sintering at 1,400 °C for 5 h. With $${\text{Nd}}_{{\text{0}}{\text{.7}}} {\text{Sr}}_{{\text{0}}{\text{.3}}} {\text{MnO}}_{{\text{3 - }}\sigma } $$ (NSMO) cathode, a single cell was assembled and tested with hydrogen and ammonia as fuels, respectively. The hydrogen-fueled cell exhibits 1.01 V for open circuit voltage (OCV) and 560 mW/cm2 for peak power density at 700 °C. In comparison, the cell in ammonia displays a similar performance (1.02 V for OCV and 530 mW/cm2 for output), which indicates the liquid ammonia is a promising substitute for hydrogen. Moreover, the fuel cell displays good interface contacts. To sum up, ammonia-fueled solid oxide fuel cells prepared by this simple suspension spray is an alternative way to promote the commercialization.

A NiO/Yttrium-stabilized zirconia (YSZ) transition layer and/or a SDC function layer were introduced into the anode/electrolyte and/or electrolyte/cathode interface to decrease the activation polarization resulted from the mass transfer at electrode/electrolyte interface. With a NiO/YSZ transition layer, the activation polarization simulated from I–V curves drops from 4.42 to 2.42 Ω cm2 at 600 °C, about 45% less than that of cell I; with additional SDC function layer, no activation polarization is obviously observed. The cell performance was also remarkably improved with the introduction of both the transition layer and the SDC function layer. Peak power densities of 187 and 443 mW cm−2 at 600 and 650 °C, respectively, were achieved for a single cell with both a transition layer and a function layer, with an increment of 87% and 95% compared to that of the cell without any structural improvement, and about 30% and 25% compared to that of the cell with only anode transition layer. The study by ac impedance spectroscopy technique also indicated that the interfacial polarization resistance, the main source of cell resistance, could be effectively reduced by interface improvement.

In order to prepare a dense proton-conductive Ba(Zr0.1Ce0.7)Y0.2O3−δ (BZCY7) electrolyte membrane, a proper anode composition with 65% Ni2O3 in weight ratio was determined after investigating the effects of anode compositions on anode shrinkages for co-sintering. The thermal expansion margins between sintered anodes and electrolytes, which were less than 1% below 750 °C, also showed good thermal expansion compatibility. A suspension spray combined with particle gradation method had been introduced to prepare dense electrolyte membrane on porous anode support. After a heat treatment at 1400 °C for 5 h, a cell with La0.5Sr0.5CoO3−δ (LSCO) cathode was assembled and tested with hydrogen and ammonia as fuels. The outputs reached as high as 330 mW cm−2 in hydrogen and 300 mW cm−2 in ammonia at 700 °C, respectively. Comparing with the interface of another cell prepared by dry-pressing method, this one also showed a good interface contact between electrodes and electrolyte. To sum up, this combined technique can be considered as commercial fabrication technology candidate.

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered GdBaCo 2 O 5+ x (GBCO) cathode, a dense BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (BZCY7) electrolyte was fabricated on a porous anode by gel-casting and suspension spray. The porous NiO–BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (NiO–BZCY7) anode was directly prepared from metal oxide (NiO, BaCO 3 , ZrO 2 , CeO 2 and Y 2 O 3 ) by a simple gel-casting process. A suspension of BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ powders synthesized by gel-casting was then employed to deposit BaZr 0.1 Ce 0.7 Y 0.2 O 3− δ (BZCY7) thin layer by pressurized spray process on NiO–BZCY7 anode. The bi-layer with 10 μm dense BZCY7 electrolyte was obtained by co-sintering at 1400 °C for 5 h. With layered GBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H 2 as fuel and the static air as oxidant. An open-circuit potential of 0.98 V, a maximum power density of 266 mW cm −2 , and a low polarization resistance of the electrodes of 0.16 Ω cm 2 was achieved at 700 °C.

(Pr–Nd)1−ySryMnO3−δ (P-NSM, y = 0.2, 0.25, 0.3, 0.35) powders made from commercial Pr–Nd mixed oxide, as well as (Pr1−xNdx)0.7Sr0.3MnO3−δ (PN3SM, x = 0, 0.5, 0.7, 1) were synthesized by a glycine-nitrate process and characterized as cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC). XRD patterns showed the powders had formed pure perovskite phase after being calcined at 800 °C for 2 h. (Pr–Nd)0.7Sr0.3MnO3−δ (P-N3SM) achieved a high conductivity of 194 S cm−1 at 500 °C and showed a good chemical stability against YSZ at 1150 °C. And the thermal expansion coefficient of P-N3SM/YSZ cathode was 11.1 × 10−6 K−1, which well matched YSZ electrolyte film. The tubular SOFC with P-N3SM/YSZ cathode exhibited the maximum power densities of 415, 367, 327 and 282 mW cm−2 at 850, 800, 750 and 700 °C, respectively, which indicated P-N3SM was potentially applied in SOFC for low cost.

A microwave-induced monomer gelation and gel combustion synthesis process was successfully developed to synthesize well-dispersed Pr 0.35 Nd 0.35 Sr 0.3 MnO 3− δ (PNSM)/YSZ composite cathode powders for tubular solid oxide fuel cells (SOFCs). The thermo-gravimetric (TG) analysis of as-prepared ash indicated the decomposition process of most of metal nitrates during gel combustion. The X-ray diffraction (XRD) pattern of the powders calcined at 1000 °C showed only pure PNSM and YSZ phase. Transmission electron microscopy (TEM) revealed that the morphology of powders was characterized with the YSZ particles enwrapped by fine PNSM particles so that PNSM/YSZ composite powders were much better-dispersed compared with the powders made simply by mechanical mixing process. The cell made from PNSM/YSZ composite powder showed lower cathode ohmic resistance and polarization resistance, and produced higher power density subsequently.

Tubular solid oxide fuel cells (SOFCs) with different Pr0.35Nd0.35Sr0.3MnO3/YSZ cathode layers made by slurry spraying, slurry dip-coating and paste brushing were assembled and compared in their performance. In order to improve cathode–electrolyte coherency and interface behavior, dip-coating process was also employed to make the dense electrolyte surface with porous morphology. Electrochemistry impedance spectroscopy (EIS) and current–voltage tests were carried out to characterize the interfaces and the cell performance. Compared with the cell made by normal paste brushing, the cells made by slurry spraying and dip-coating exhibited a decrease of about 50% in electrode polarization resistance and an increase of 67% in the peak power output at 750 °C.

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.

A nickel-based anode-supported solid oxide fuel cell (SOFC) was assembled with a 10 μm thick Ce0.8Sm0.2O2−δ (SDC) electrolyte and a Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathode. The cell performance was investigated with hydrogen and ammonia gas evaporated from liquefied ammonia as fuel. Fueled by hydrogen the maximum power densities were 1872, 1357, and 748 mW cm−2 at 650, 600, and 550 °C, respectively. While with ammonia as fuel, the cell showed the maximum power densities of 1190, 434, and 167 mW cm−2, correspondingly. The power densities lower than that predicted, particularly at the lower operating temperatures for ammonia fuel cell, compared to hydrogen fuel cell, could be attributed to actual lower temperature than thermocouple display due to endothermic reaction of ammonia decomposition as well as the rather larger inlet ammonia flow rate. The results demonstrated that the ammonia was a right convenient liquid fuel for SOFCs as long as it was keeping the decomposition completion of ammonia in the cell or before entering the cell.

In order to develop a cost effective route to fabricate solid oxide fuel cells (SOFC) with a proton conductive electrolyte, BaCe 0.9 Nd 0.1 O 3− δ (BCNO) powder was prepared by the modified Pechini method and a suspension of BCNO powder was then deposited as a thin layer by a spray process onto a NiO–BCNO anode. A bi-layer with very dense BCNO electrolyte was obtained by co-sintering at 1400 °C for 5 h. With La 0.5 Sr 0.5 CoO 3− δ (LSCO) as the cathode, single cells were assembled and tested with NH 3 and H 2 as fuels and static air as the oxidant. For a commercial liquid ammonia fuel at 700 °C, the OCV and the peak power density of a cell with a 20 μm thick BCNO electrolyte were 0.950 V and 315 mW/cm 2 , respectively. With H 2 fuel as a comparison, the values are correspondingly 0.951 V and 335 mW/cm 2 .

A polyvinyl alcohol assisted combustion synthesis method was used to prepare Ce 0.8 Sm 0.2 O 2− δ (SDC) powders for an intermediate temperature solid oxide fuel cell (IT-SOFC). The XRD results showed that this combustion synthesis route could yield phase-pure SDC powders at a relatively low calcination temperature. A thin SDC electrolyte film with thickness control was produced by a dry pressing method at a lower sintering temperature of 1250 °C. With Sm 0.5 Sr 0.5 Co 3 -SDC as the composite cathode, a single cell based on this thin SDC electrolyte was tested from 550 to 650 °C. The maximum power density of 936 mW cm −2 was achieved at 650 °C using humidified hydrogen as the fuel and stationary air as the oxidant.

In order to develop high performance intermediate temperature (

Ce 0.8 Sm 0.2 O 1.9 (SDC) powders have been synthesized by a combustion method with polyvinyl alcohol (PVA) as the fuel and nitrate as oxidizer. A calcination temperature of 350 °C was found to be sufficient for the formation of pure SDC powders. The cell parameters were calculated using the peak positions determined from the XRD patterns, and it was found that stoichiometric SDC powder could be obtained only when stoichiometric PVA fuel contents were used. The as-prepared SDC pellets exhibited 98% of the theoretical density sintered at 1300 °C. This shows that the SDC powders obtained by this combustion method have excellent sintering properties, which can densified at a relatively low sintering temperature. The powders made by this method, due to its high conductivity of 0.033 S cm −1 at 700 °C, are suitable for intermediate temperature solid oxide fuel cells (IT-SOFCs).

Cordierite-based porous ceramic micro-filtration membranes were prepared on tubular macro-porous cordierite supports using waste fly ash and basic magnesium carbonate as the starting materials by spray-coating, followed by dip-coating for modification. Optimization of the raw materials ratio was found to be necessary to avoid crack formation during sintering, which is demonstrated by the sintering shrinkage behavior of the samples with different basic magnesium carbonate content. Crystallization phase development of the prepared membranes was studied by XRD and TG/DTA. The results confirm that α-cordierite was formed above 1100 °C and that its crystallinity improved steadily with further increasing firing temperature. Furthermore, microstructure, pore properties and gas permeation flux of the membranes were investigated. The preferred sintering temperature for the tubular membranes was in the temperature range of 1150–1200 °C based on the results of XRD, SEM, pore-structure and nitrogen permeation. Cordierite-based porous membranes with average pore size in the range of 3.6–6.4 μm and nitrogen permeance of (7.52–9.82) × 104 m3 m−2 h−1 MPa−1 under the average pressure of 0.15 MPa have been obtained, which can be controlled by adjusting the sintering regime.

Ammonia is considered to be one of the most promising candidates as the fuel for solid oxide fuel cells (SOFCs). In this work, nitrogen oxide formation was thermodynamically determined as a function of ammonia conversion rate and temperature. The result showed that more NO was formed at higher temperature. Therefore, ammonia was experimentally investigated as the fuel for an intermediate-temperature SOFC (IT-SOFC) consisted of a Ni–Ce0.8Sm0.2O1.9 (SDC) anode, an SDC (50 μm) electrolyte, and an Sm0.5Sr0.5CoO3−δ (SSC)–SDC cathode. The components of anode off-gas were analyzed both theoretically and experimentally, especially for the possibility of nitrogen oxide formation. Performances of the cells fueled with ammonia and hydrogen were quite similar at the same temperatures. Maximum power densities were 168.1 and 191.8 mW cm−2 at 600 °C with ammonia and hydrogen as the fuels, respectively. The electrode polarization resistances and electrolyte resistances of cells fueled by ammonia and hydrogen were characterized by AC impedance spectroscopy. The long-term endurance of cells in ammonia was also tested. Keywords: Solid oxide fuel cell, Ammonia, Doped ceria, AC impedance, Nitrogen oxide

Samarium-doped ceria (SDC) thin films were prepared from Sm(DPM)3 (DPM = 2,2,6,6-tetramethyl-3,5-heptanedionato) and Ce(DPM)4 using the aerosol-assisted metal–organic chemical vapor deposition method. α-Al2O3 and NiO-YSZ (YSZ = Y2O3-stabilized ZrO2) disks were chosen as substrates in order to investigate the difference in the growth process on the two substrates. Single cubic structure could be obtained on either α-Al2O3 or NiO-YSZ substrates at deposition temperatures above 450 °C; the similar structure between YSZ and SDC results in matching growth compared with the deposition on α-Al2O3 substrate. A typical columnar structure could be obtained at 650 °C on α-Al2O3 substrate and a more uniform surface was produced on NiO-YSZ substrate at 500 °C. The composition of SDC film deposited at 450 °C is close to that of precursor solution (Sm : Ce = 1 : 4), higher or lower deposition temperature will both lead to sharp deviation from this elemental ratio. The different thermal properties of Sm(DPM)3 and Ce(DPM)4 may be the key reason for the variation in composition with the increase of deposition temperature.

NiO–Ce0.8Sm0.2O1.9 (SDC) composites were synthesized using gel-casting technique. The electrochemical performance of the gel-cast (GC) Ni–SDC cermet as anode was investigated contrast with that fabricated from traditional mechanical mixing (MM) technique using fuel cells with about 35 μm-thick SDC electrolyte and Sm0.5Sr0.5CoO3–SDC cathode. Maximum power density of the cell with GC anode achieved 491 mW cm−2 at 600 °C, over 100 mW cm−2 larger than that with MM anode, inferring high catalytic activity of the GC anode. Impedance measurements on the fuel cell at open circuit showed that the anodic interfacial polarization resistance of the GC anode was 0.1 Ω cm2 lower than that of the MM anode. Long-term stability of the cell with GC anode in hydrogen was also performed, which showed that it can stabilize at least 7 days.

A dense yttria-stabilized zirconia (YSZ, 8 mol% Y 2 O 3 ) film was successfully fabricated by an electrostatic powder-coating process associated with suspension modifying on a porous anode (NiO/YSZ) substrate. The YSZ green powder layer formed by the unmodified process consisted of the loosely packed particles and could not be densified by sintering. After modifying this green layer by a suspension, a dense wet layer was formed that could be sintered at 1450 °C. SEM observations showed the film to be dense and approximately 8 μm thick. A single cell with this YSZ electrolyte on Ni/YSZ anode and Ag as cathode was assembled and tested in the temperature range from 550 to 750 °C. The open circuit voltage (OCV) and peak power density of the single cell at 750 °C was 1.1 V, which is very close to the theoretical value, and 142 mW/cm 2 , respectively. The results illustrate that YSZ membranes fabricated by this process are quite dense and gas tight.

NiO–SDC(Ce0.8Sm0.2O1.9) composites were synthesized using gel-casting technique with nitrate precursors. The composite oxides were formed after the gels were fired at 350 °C in flowing air. No reaction between NiO and CeO2 occurs as analyzed using X-ray diffraction (XRD). The average particle size was about 50 nm and specific surface area was 10 m2 g−1, when the powder was fired at 900 °C for 2 h. NiO–SDC cermets were prepared by firing the composites at 1350 °C. The electrical conductivities and porosities of the cermets were measured, for example, 360 S cm−1 at 600 °C for a cermet with 30% porosity, 35 vol.% Ni, and 35 vol.% SDC. And the electrochemical performance of Ni–SDC cermet as an anode was investigated using a fuel cell with 25-μm thick SDC electrolyte and Sm0.5Sr0.5CoO3-SDC cathode. Maximum power density was 618 mW cm−2 and 491 mW cm−2 at 650 and 600 °C, respectively, inferring high catalytic activity of the Ni–SDC anode. Impedance measurements on the fuel cell at open circuit showed that the interfacial polarization resistance of the Ni–SDC anode was negligible compared to the resistance of cathode and electrolyte.

The formation and growth mechanism of the wet membrane formed in dip-coating process was systematically studied on the consideration of the capillary colloid filtration and the film coating processes as well as an applied pressure. An expression to describe the growth rate of the wet membrane was derived. It can be denoted that the thickness of the wet membrane increases monotonously with the dipping time but a transition would occur due to the saturation of the capillaries in the substrate and the decrease of the capillary suction force. It is also shown that different mechanism has different effect on the thickness of the wet membrane: the wet membrane formed by film coating may dominate while the dipping time is short and the suspension viscosity is high; but for the suspensions with low viscosity, the capillary colloid filtration contributes more to the wet membrane growth, especially for longer dipping time. As long as the wet membrane exhibits a similar structure during the dip-coating process, the wet membrane thickness can be expressed as a function of the parameters, Δ P p , η , t , etc. And the expression derived in this work has been verified by the experimental data and proved to be valuable for the control of the membrane formation.