Microtubular Solid Oxide Fuel Cells Research Articles

Micro-Scale Thermal Partial Oxidation Reforming of Liquid Fuels and Solid Oxide Fuel Cell Performance and Stability Analysis

Thermal partial oxidation of hydrocarbons to hydrogen and carbon monoxide (i.e., synthesis gas) is limited for conventional scale reactors due to soot formation under higher fuel/air equivalence ratios. Recent research into micro-scale (<4 mm diameter) thermal partial oxidation reactors with a controlled temperature of 800-900 °C has shown promise for conversion to synthesis gas without soot formation. Direct integration of Solid Oxide Fuel Cells (SOFCs) with these micro-scale thermal partial oxidation reactors has been proposed for portable power generation systems. In this work, the micro-scale thermal partial oxidation of methanol/air is investigated at fuel/air equivalence ratios from 1-5 and at a temperature of 800 °C. High conversion rates to synthesis gas are measured with a gas chromatograph for equivalence ratios between 1.5 and 3, with the concentration of hydrogen exceeding 10% and approaching chemical equilibrium predictions. A micro-tubular SOFC is integrated with the micro-scale thermal partial oxidation reformer to electrochemically oxidize the synthesis gas while generating power. SOFC polarization losses are investigated at different equivalence ratios and temperatures of the reformer with results indicating the mass transport losses decrease significantly as the equivalence ratio increases. Peak power densities occur when the synthesis gas concentration is maximized. Short term testing of the SOFC is stable no carbon deposition on the Ni-YSZ anode.

From biomass to power: High-performance reactor design for coking-resistant operation

Biomass gasification coupled with solid oxide fuel cell (SOFC) technology utilizes the gas generated from biomass gasification directly as fuel for SOFC, thereby realizing power generation from solid waste. This technology combines the carbon–neutral feature of biomass with the high efficiency and low emissions of SOFC, making it a promising route for clean energy generation. However, biomass gasification syngas possesses a complex composition, including a high concentration of inert gases, which imposes higher requirements on SOFC. This study developed a multi-channel, hierarchical structural design based on the commercial NiO-yttria-stabilized zirconia (YSZ) material system, realizing high-performance power generation using biomass gasification syngas. The results showed that the combination of a unique structural design and an enhanced interface electrochemical reaction effectively mitigates the influence from inert composition dilution. When operating in gasification syngas with nearly 60 % inert components, the power density can reach 2.07 W·cm−2 (750 °C). In addition, due to the spatial separation of the inert support region and the electrochemically active region, the effect of controlling the position of carbon deposits was achieved, demonstrating 100 h stable operation with dry biomass gasification syngas. Hence, the combination of micro-tubular SOFC with distinctive structural regulation and biomass gasification exhibits promising prospects for further development.

Investigation of a sacrificial template material suitable for fabrication of anode support microtubes in microtubular solid oxide fuel cells

This study investigates the use of various sacrificial template materials in the form of a solid rod, including wood, carbon fiber, polyamide, resin and polylactic acid (PLA), for fabricating anode supports in microtubular solid oxide fuel cells (SOFCs) via tape casting and isostatic pressing. Anode support strips, produced via tape casting, are wound around these sacrificial rods. The rods are then burnout through co-sintering to yield microtubular anode supports. The results highlight PLA as a particularly promising material due to its balance of cost and performance. A novel rod design involving hollow PLA pipe is then explored to enhance the fabrication process. The anode support tape length or the wall thickness of anode support microtube is also considered. Microtubular cells are fabricated on the anode supports by dip coating other cell layers, and electrochemical and microstructural investigations are carried out. The final cell provides 0.365 W/cm2 maximum power density at 800 °C under 0.3 NL/min hydrogen flow and stationary air. Moreover, a patterned microtubular anode support is successfully fabricated using a 3D printed PLA tube featuring an array of dimples. The overall findings indicate that the proposed methodology not only simplifies the manufacturing process but also supports the feasibility of producing high-performance microtubular SOFCs with enhanced electrolyte-electrode interfaces through patterned anode designs.

Effect of Continuous Electrolysis on the Power Generation Performance of a Microtubular Oxide Fuel Cell Using Intermediate Ring‐Shaped Collector

An anode‐support microtubular solid oxide fuel cell (MTSOFC) using an intermediate ring‐shaped electrode collector is simulated using COMSOL Multiphysics software to investigate current density distribution and mass transfer in both power generation and electrolysis modes. The cell is converted to power generation mode during continuous electrolysis, and the electrochemical performance of MTSOFC is tested to study the effect of electrolysis on the power generation performance. The power density output of the MTSOFC decreases from 250 to 150 mW cm−2 after only 40 h of continuous electrolysis. The microstructural changes in different regions during operation are observed through posttest analysis conducted on the fuel inlet, electrochemical reaction concentration region, and fuel outlet of the microtubular cell. The local agglomeration of nickel occurs in the concentrated region of the electrochemical reaction, while the coarsening of nickel oxidation mainly takes place at the fuel inlet and outlet.

Enhancing multi-channel electrode structures in ceramic fuel cells: Influence of channel geometry on mass transport and electrochemical performance

Solid oxide fuel cell (SOFC) is a promising electrochemical power generation technology that contributes to the decarbonization of the energy field. The electrode-supported design enables the use of thinner electrolytes, but inevitably brings additional gas diffusion resistance, which in turn leads to higher anodic concentration polarization. Therefore, additional structural design of the electrodes is necessary to ensure efficient operation and mass transport resistance minimization. In this study, anode-supported micro-tubular SOFCs with different multi-channel geometries have been attempted, during which samples with 4 channels exhibit unique elliptical structure due to meticulous manipulation. In addition, the 4-channel samples have been compared to the single-channel and 7-channel counterparts, exploring the influential mechanism of the anode micro-structure on gas transfer and electrochemical performances. The study found that the 4-channel cell has the best geometric controllability, with its minimum gas diffusion path reduced to below 50 μm, such thin electrochemical active region (EAR) accounts for >50 % of the entire external surface. Efficient utilization of the geometric surface area considerably facilitates the fuel transport to reach anode/electrolyte interface. By enhancing the mass transport efficiency, the maximum power density of the 4-channel cell reached 1.40 W cm−2 (750 °C), which is 22.8 % and 102.9 % higher than that of the 7-channel and single-channel cells under the same conditions. The highly efficient anode design additionally exhibited exceptional structural integrity and mechanical robustness, thereby ensuring the steady operation of the cell.

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.