Microtubular Solid Oxide Fuel Cells Research Articles

3D printing of porous zirconia support for solid oxide fuel cells with high cell performance

This work reports the preparation and characterization of a 3D-printed porous 3 mol% yttria-stabilized zirconia (3YSZ) inert-supported micro-tubular solid oxide fuel cell (MT-SOFC) with high cell performance. For the first time, the impacts of pore-former particle size and mass fraction on the microstructure of 3D-printed porous 3YSZ, along with the influences of debinding atmosphere and pre-sintering temperature on the flexural strength and the shrinkage rate, were comprehensively explored. Optimal results were achieved using a particle size of 3 μm and a mass fraction of 30 wt.%, facilitating the preparation of a printable 3YSZ photocurable slurry with a relatively low apparent viscosity of 4.2 Pa·s at a shear rate of 30 s-1. Notably, 3D-printed porous 3YSZ debound in nitrogen and sintered in air at 1400 °C exhibited the highest flexural strength of ∼80.2 MPa compared to debinding in air or vacuum. Based on flexural strength and shrinkage rate considerations, the 3D-printed porous 3YSZ debound in nitrogen and pre-sintered at 1150 °C was deemed suitable as an inert support for SOFC. Cells prepared using this optimized approach demonstrated exceptional performance, achieving a maximum power density of 876.8 mW·cm–2 at 850 °C, surpassing inert-supported MT-SOFCs fabricated using traditional methods. The outstanding cell performance underscores the successful application of 3D printing technology in preparing porous 3YSZ inert supports for SOFCs, offering an attractive approach for cell preparation and porous ceramics.

Optimization of the BSCFM5-Based Cathode Layer in the Microtubular Solid-Oxide Fuel Cells and the Study of Its Effect on the Power Characteristics

Optimization of the BSCFM5-Based Cathode Layer in the Microtubular Solid-Oxide Fuel Cells and the Study of Its Effect on the Power Characteristics

Microtubular solid oxide fuel cells with a two-layer LSCF/BSCFM5 cathode

In this study, we present the development of microtubular solid oxide fuel cells (MT-SOFC) with a two-layer cathode: a composite cathode functional layer (CFL) adjacent to the buffer layer (BL) and a cathode current-collecting layer (CCCL). CFL consists of a mixture of BL material Ce0.9Sm0.2O1.95 (SDC) and perovskite Ba0.5Sr0.5Co0.75Fe0.2Mo0.05O3-δ (BSCFM5), which has a high exchange rate with oxygen. The widely used cathode material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with high electrical conductivity was used as the CCCL. A significant increase in the peak power density of the MT-SOFC to 1.2 W/cm2 at 850 °C was achieved using the proposed two-layer cathode.

Double Conductive Ni-pads for a kW-class micro-tubular solid oxide fuel cell stack

Double Conductive Ni-pads (DCNPs) are prepared for the anode collector of micro-tubular solid oxide fuel cells (MTSOFCs) to fabricate a kW-class MTSOFC stack. The dimensions of the pad, in terms of width and length, are approximately 3.1 mm and 11.3 mm respectively. COMSOL Multiphysics software is utilized to simulate the multi-physical field of a single cell and SOFC stack to study anodic DCNPs current distribution and mass transfer operated at various voltages. A 160-cell stack consists of eight 20-cell sub-stacks exhibits a maximum power output exceeding 1 kW at an operating temperature of 700 °C. Furthermore, long-term operation tests under constant current or constant voltage conditions are conducted on both the 20-cell sub-stack and the 80-cell stack, demonstrating excellent performance and stability when utilizing DCNPs as anode collectors. The application potential for DCNPs as anode collectors in micro-tubular solid oxide fuel cells extends to various fields including auxiliary power units or high-power stacks, thereby introducing new possibilities for MTSOFC technology.

Experimental Study on High-Efficiency Microtubular Solid Oxide Fuel Cell Stacks Using Various Fuels

: Microtubular solid oxide fuel cells (mtSOFCs) are a clean and low carbon emission power generation technology that has great prospects in the field of portable power generation. Improving the power generating efficiency and broadening the variety of fuels available can significantly improve the performance of portable power generation devices based on mtSOFCs. In this study, mtSOFC stacks assembled by mounting modular substacks in an array on a designed fuel/air distribution base were tested. By changing the connection of the substacks’ current collection nodes, the influence of circuit connection modes on the overall output performance of the stack was studied. At a temperature of 700℃ and a fuel feed of hydrogen, the mtSOFC stack composed of 6 substacks in series can achieve a maximum power of 296 W. Fuel cascade utilization was realized by transferring the spent fuel gas from the upstream substacks to the downstream substacks. A maximum power generation efficiency of 45.7% was achieved in the two-cascade stack. The feasibility of using liquified fuel gas (ammonia, propane and diesel) as fuel for the mtSOFC stack has also been experimentally verified. A total continuous discharge time of more than 100 h was achieved at an average power ≥ 180 W under different fuel conditions.Key words: Microtubular SOFC; Substack array; Fuel cascade utilization; Liquified fuel gas; Ammonia

Solid Oxide Fuel Cells for Aviation

Airbus has revealed ZEROe, three concepts for the world’s first zero-emission commercial aircraft which could be brought to market by 2035. The ZEROe concept aircrafts, which support Airbus’ commitment to lead the decarbonisation of the aviation industry, all rely on hydrogen as a primary power source, which would be deployed via a hybrid-hydrogen configuration featuring modified gas-turbine engines complemented by fuel cells for electrical power. Although the Proton Exchange Membrane (PEM) technology is one of the most matured fuel cell types, Airbus Central Research and Technology (CRT) is also investigating novel SOFC concepts for potential hybrid-hydrogen configurations.The Solid Oxide Fuel Cell (SOFC) offers major benefits, namely electrical efficiency and fuel versatility, for hybrid-electric aircraft propulsion. Although the SOFC’s area specific power density has drastically increased within the last decade, more needs to be done to make the technology accessible for aviation applications. The combined development of novel SOFC concepts and corresponding manufacturing processes are regarded as key objectives for the SOFC activities at Airbus Central Research and Technology. Airbus is designing, manufacturing and testing SOFC concepts with the aim to achieve highest gravimetric power densities.Novel manufacturing technologies for metallic and ceramic materials have the potential to enable lighter functional layers for SOFCs with increased intrinsic mechanical stability and surface area. Different cell concepts with an optimized current collection are currently under development at Airbus. The micro-tubular and monolithic SOFC are seen as the most promising concepts, whereas around 2 kW/kg on a cell level has recently been achieved in a performance test at Airbus.

Design and Fabrication of an Easily Assembled Anode Supported Microtubular SOFC Stack

Microtubular solid oxide fuel cells have shown many advantages that make them suitable for mobile and portable applications. In this study, a microtubular SOFC stack consisting of 8 cells was designed and fabricated using a metallic current collector and interconnect, enabling a pluggable modular design pattern. To avoid the difficulty of high-temperature sealing, the cold sealing method was adopted, where the temperature at the sealing position was under 130°C when the stack was operated at 700°C. The open circuit voltage (OCV) reached over 4 V while the power output reached over 20 W with a 2 (in series)×4 (in parallel) array. The stack module can be further connected in series or in parallel to satisfy larger power requirements.

An efficient multi-point impedance method for real-time monitoring the working state of solid oxide fuel cells

During the practical operation of commercial solid oxide fuel cells (SOFCs), it is significant and urgent to implement a non-destructive and timely diagnosis of performance degradation. However, the method, which can completely fulfill the above requirements, is still not available. This study presents a novel approach, the multi-point impedance (MPI) method, which enables in-situ and real-time monitoring of the operating state of commercial SOFCs. The method involves two critical steps: the determination of characteristic frequencies using the distribution of relaxation time (DRT) and the selection of reference frequencies for calculating impedances. The reliability of the MPI method is evaluated both theoretically and experimentally. The results of theoretical investigation reveal that the MPI method can accurately estimate the resistances of resistance-capacitance (RC) components. Subsequently, the MPI method is employed to monitor the working state of commercial microtubular SOFCs (MT-SOFCs) during the stability test. The experimental results show that by using the MPI method, the impact of different electrochemical processes on the durability of MT-SOFCs can be clearly clarified. Combining the theoretical and experimental studies, it demonstrates that the MPI method can serve as an efficient and simple diagnostic approach for real-time monitoring SOFCs.

Solid Oxide Fuel Cells for Aviation

The Solid Oxide Fuel Cell (SOFC) offers major benefits, namely electrical efficiency and fuel versatility, for hybrid-electric aircraft propulsion. The combined development of novel SOFC concepts and corresponding manufacturing processes are regarded as key objectives for the SOFC activities at Airbus Central Research and Technology. Airbus is designing, manufacturing and testing SOFC concepts with the aim to achieve highest gravimetric power densities. Novel manufacturing technologies for metallic and ceramic materials have the potential to enable lighter functional layers for SOFCs with increased intrinsic mechanical stability and surface area. Different cell concepts with an optimized current collection are currently under development at Airbus. The micro-tubular and monolithic SOFC are seen as the most promising concepts, whereas around 2 kW/kg on a cell level has recently been achieved in a performance test at Airbus.

Design and Fabrication of an Easily Assembled Anode Supported Microtubular SOFC Stack

Anode-supported micro-tubular solid oxide fuel cell has shown many advantages which make it suitable for portable devices. In this study, we developed a micro-tubular SOFC stack and module using a metallic current collector and interconnector which enabling pluggable modular design pattern. In order to ensure the sealing performance, we adopted the low-temperature sealing method and the temperature at the sealing position is under 130℃ while the stack is operated at 750℃.The stack was made of 8 micro-tubular cells, which were connected in series and parallel, in a 2×4 array. The open circuit voltage (OCV) was above 4.22V, thus the single cell’s OCV value could reach about 1.06V. The stack module can be further connected in series or in parallel to satisfy larger power requirements.

Surface decoration of ceria nanoparticles as propane/air partial oxidation catalyst integrated in a micro-tubular solid oxide fuel cell

ABSTRACT In this study, a ceria (CeO2) support, synthesized using a hydrothermal method, was decorated with nano-sized Ni-particles using an impregnation method. A micro-tubular solid oxide fuel cell (MTSOFC) was integrated with a corundum tube, in which the Ni-CeO2 (10 wt% Ni) served as the catalyst for partial oxidation (POX). Using propane and air, there was no noticeable deactivation in the MTSOFC over a 48-h period. The maximum power density (MPD) was 0.57 W cm −2 at 700°C using propane and air (12.3 vol% propane), which is 0.01 W cm−2 higher than the cell using 20 vol% of hydrogen (0.56 W cm −2). When using propane and air as fuel and operating at 700°C, MPD values for intermediate and inlet current collector modes were 0.57 and 0.48 W cm−2, respectively. Carbon deposition at the fuel inlet was determined to be the primary cause of low current collection efficiency.

Understanding the polymer binder effect on the microstructure and performance of micro-tubular solid oxide fuel cells with continuously graded pores fabricated by the phase inversion method

Micro-tubular solid oxide fuel cells (MT-SOFCs) have recently attracted great attentions because of their great thermal shock resistance, fast start-up capability, and increased volumetric power density compared with the planar SOFCs and conventional tubular SOFCs. In this work, three representative MT-SOFCs with different anode microstructures are fabricated by varying the polymer binders used in the phase inversion slurry. A superior anode substrate with graded pore distribution is obtained, moreover, the dense skin layer close to the inner surface is effectively eliminated when the polyethersulfone (PESf)/polyethylenimine (PEI) blend material instead of PESf material or PEI material is utilized as the polymer binder. Meanwhile, no secondary impurity phase is detected in the anode supports prepared by these three polymer binders, indicating the good adaptability of these polymer binders. Additionally, three single cells are assembled based on these anode supports, and a maximum power density of 630 mW∙cm−2 is obtained for the cell fabricated by the PESf/PEI blend polymer binder at 750 °C, which is strongly higher than 201 and 330 mW∙cm−2 for PEI polymer binder and PESf polymer binder at the same temperature, respectively. Moreover, the electrode polarization resistance is largely decreased from 2.53 to 0.662 Ωcm2 by changing the polymer binder from PEI polymer binder to PESf/PEI blend polymer binder. The fitting results obtained based on the polarization model reveal that the greatly improved electrochemical performance can be explained by the accelerated gas transportation in the anode. Our findings demonstrate that the PESf/PEI blend material is a promising polymer binder candidate for MT-SOFC fabrication through the phase inversion method.

Effects of Radial and Circumferential Flows on Power Density Improvements of Tubular Solid Oxide Fuel Cells

Improving the power density of SOFC stacks will accelerate their integration into mobile applications. We developed a 3D Multiphysics model validated by experimental results from early studies to examine the effect of radial and circumferential flows on the power density improvements in a micro-tubular SOFC. The inserts were placed inside the fuel channel to generate flow in different directions. The effects of geometric parameters of these inserts on flow and mass transfer in the fuel channel and porous anode were analyzed. We demonstrate that the radial flow enables the fuel to penetrate directly into the porous anode, increasing the local fuel concentration and enhancing the fuel diffusion to the anode triple-phase boundaries. We found that the circumferential flow has a negligible effect on the diffusion process in the anode and on the increase in power density. The impact of local convective and diffusive mass transfer mechanisms on power density improvement is analyzed using the local Péclet number along the axial direction. Enlarging the radial velocity component perpendicular to the porous anode could effectively increase the power density of the micro-tubular SOFC by 37%. This study helps improve our understanding of mass transfer in fuel channels and helps build a foundation for SOFC channel designs and optimizations.

A new design of metal supported micro-tubular solid oxide fuel cell with sandwich structure

Micro-tubular solid oxide fuel cell (MT-SOFC) is considered as a promising choice for portable applications. In this work, we developed a novel metal supported MT-SOFC with porous 430 stainless steel support| 430 stainless steel-SSZ| SSZ| porous SSZ sandwich structure by dip coating and one-step co-sintering technology. The metal supported MT-SOFC showed good connection between each function layer and exhibited a significant maximum power density of 271 mW cm−2 at 800 °C. Although the power density showed about 19.6% off after 14 thermal cycles between 600 °C and 800 °C, and about 5% per 100 h degradation rate during the 200 h long-term stability test at 700 °C and 0.7 V, the structure of the single cell could be maintained well and no crack and Sr diffusion was observed. As the result, the ohmic resistance of the cell kept unchanged during the thermal cycling and long-term test. The relatively fast degradation was attributed to the Ni and LSM particles coarsening and agglomeration, which will be improved in the further work. This work presented a low-cost and simple way to fabricate the metal supported MT-SOFCs with good electrochemical performance.

A study of mass transfer characteristics of secondary flows in a tubular solid oxide fuel cell for power density improvement

The low power density has impeded wider adoption of solid oxide fuel cell stacks in powering vehicles and airplanes. The stack power density could be improved by the secondary flow in the radial direction induced by inserts in fuel channels. In this study, we constructed a numerical model to examine the effect of secondary flows on the electrochemical performance of a counter-flow type micro-tubular SOFC with an insert consisting of several humps. We show the secondary flow could enhance the fuel convective mass transfer in the diffusion layer of the porous anode, enabling more fuel to enter the porous anode and more produced steam to leave the reaction layer. This significantly improves the methane reforming and electrochemical reaction rates. We also examined the influence of the geometric parameters of the inserts on the electrochemical performance of the SOFC. We demonstrate that by increasing the insert radius and number of humps, the output power density increases at the expense of higher pumping power requirements. However, the enhanced electrochemical reactions outweigh the demand for pumping power. Our work demonstrates the effectiveness of secondary flows on the SOFC electrochemical performance improvement and helps build a foundation for SOFC channel designs and optimizations. Highlights The effects of secondary flows on the electrochemical reactions are discussed. The secondary flow in radial direction could improve the SOFC power density. The influence of the insert geometric parameters is analyzed.

Propane-fuelled microtubular solid oxide fuel cell stack electrically connected by an anodic rectangular window

A current collecting window (0.4 cm2), without an electrolyte and cathode, is located in the middle of an anode and connected electrically to the cathode of another microtubular solid oxide fuel cell (MTSOFC) when building a short stack. No apparent open-circuit voltage (OCV) drops were observed during 31 thermal cycles for an 8-cell stack using H2 and syngas. Furthermore, 24.1, 53.6 and 103.5 W power levels are achieved employing this current collecting mode at 700 °C for an 8, 10 and 20-cell stack, respectively. The propane-fuelled 8-cell stack has a maximum power density (MPD) of 0.30 W cm−2 when integrated with a catalytic partial oxidation (CPOX) reformer, at a flow rate of 0.32 g min−1 of propane. A Pt-Ru nanoparticle is fabricated by impregnation treatment of the alumina honeycomb ceramic support. The Pt-based catalyst, with an average size of ∼10.0 nm, is well distributed on the surface of the honeycomb ceramic channel. Moreover, Pt-Ru/Al2O3, as a CPOX catalyst, exhibits high propane conversions (94.2%) at 700 °C.

Low Nickel, Ceria Zirconia-Based Micro-Tubular Solid Oxide Fuel Cell: A Study of Composition and Oxidation Using Hydrogen and Methane Fuel

The study examines the effect of using low nickel (Ni) with high ceria (CeO2) anode content towards the oxidation of H2 and CH4 fuel by evaluating the activation energy of the ohmic process and charge transfer process. Using a micro-tubular solid oxide fuel cell (MT-SOFC), the anodes are made up of 50% YSZ with varying NiO:CeO2 percentages from 0% NiO, 50% CeO2 to 50% NiO, 0% CeO2. The performance is measured based on maximum power density (MPD), electrochemical impedance spectroscopy (EIS) and activation energy, Ea of the ohmic (Rohm) and charge transfer (Rct) processes. We found that by lowering the Ni content to lower than 50% NiO, anode conductivity will drop by 7-fold. An anode containing 37.5% NiO, 12.5% CeO2 yield MPD of 41.1 and 2.9 mW cm−2 when tested on H2 and CH4 fuels thus have the lowest Ni content without an abrupt negative effect on the MPD and EIS. The significant effect of conductivity drops on MPD and EIS are observed to occur at 25% NiO, 25% CeO2 and lower NiO content. However, anode content of 25% NiO, 25% CeO2 has the lowest Ea for Rct (29.74 kJ mol−1) for operation in CH4, making it the best anode composition to oxidize CH4. As a conclusion, an anode containing 25% NiO:25% CeO2:50% YSZ and 37.5% NiO:12.5% CeO2:50% YSZ shows promising results in becoming the low Ni anode for coking-tolerant SOFC.

Experimental investigation on the effect of anode functional layer on the performance of anode supported micro-tubular SOFCs

In this study, anode supported micro-tubular solid oxide fuel cells (SOFCs) are fabricated by extrusion method and the effects of powder size, thickness and sintering temperature of the anode functional layer (AFL) on the electrochemical performance is experimentally investigated. For this purpose, four different commercial NiO powders are tested as initial powder for the fabrication of the anode functional layer. The thickness of AFL is also considered by varying the number of coatings. After deciding the optimum initial NiO powder size used in AFL and AFL thickness, the effect of pre-sintering temperature is examined. The performance tests are performed at an operating temperature of 800 °C under hydrogen and air. The microstructures of the samples are also investigated by a scanning electron microscope. The best peak power density is obtained as ∼0.5 W/cm2 from the cell having a single layer anode functional layer pre-sintered at 1250 °C prepared by NiO powders with 4 m2/g surface area.

Local heat transfer enhancement by recirculation flows for temperature gradient reduction in a tubular SOFC

ABSTRACT The large temperature gradient in solid oxide fuel cells (SOFCs) severely degrades their operation reliability. In this study, we have developed a numerical model to examine the effect of local heat transfer enhancement on the temperature gradient reduction in a counter-flow type micro-tubular SOFC. The local heat transfer is enhanced by placing turbulators in the SOFC air channel. We show that turbulators in air channels could induce recirculation flow, which increases the local convective heat transfer coefficient and facilitates the heat dissipation from electrodes to air stream. A spatial temperature gradient diagram is proposed to analyze the influences of turbulator radii, locations and pitches on the cell axial temperature gradient reduction. The turbulator effectively decreases the largest temperature gradient and reduces the region where the temperature gradient is higher than 30℃/cm. We also compare the temperature profile and air-side pressure drop between tubular SOFCs with turbulators and thin air channels. The SOFC with turbulators is demonstrated to achieve comparable heat transfer performance but at a lower air-side pressure drop than that with a thin air channel. Our work demonstrates the effectiveness of local heat transfer enhancement on SOFC temperature gradient reduction and proposes a new diagram to quantitatively evaluate the impact of the thermal management methods through local heat transfer enhancement.

A New Design Using Metal Wire Brushes as the Current Collector and Catalyst Carrier for Internal Reforming of Micro-Tubular SOFCs

In this study, a novel current collecting method of inserting metal wire brushes into anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) was designed and demonstrated. The proposed design enabled a tight and stable contact between the wires and the interior surface of the anode, which led to good performance of the SOFC. Different metal wire materials were utilized, and copper–zinc wire brushes (CZWBs) showed better performance than stainless steel wire brushes (SSWBs). The MT-SOFCs using CZWBs achieved a maximum power density of 290 mW cm−2 and a minimum ohmic resistance of 0.66 Ω∙cm2 at 700 °C in a hydrogen stream. The brush size was shown to have little effect on the ohmic resistance. A long-term discharge test (108 h) was also carried out. The feasibility of using metal wire brushes as internal reforming catalyst carriers was experimentally verified. The SSWBs loaded with Pt catalyst could realize effective reforming of methane, demonstrating the potential of the proposed design to use hydrocarbon fuels for power generation.