Flat Tubular Cell Research Articles

Highly robust and porous cathode current collecting layer for flat-tubular solid oxide fuel cell stack applications

Solid oxide fuel cells (SOFCs) have gained great attention as a stationary power generation application due to their high efficiency, fuel flexibility and environmental friendliness. The devices and power age could be revolutionized with the commercialization of these technologies. The SOFC-based stationary power generator is one step closer to commercialization however, it is delayed due to the inherent bottleneck of insufficient long-term durability. The cathode current collecting layer (CCCL) is crucial in stack applications to minimize the contact loss between cell and metallic interconnects. Herein, we report an easy-to-fabricate and highly robust CCCL to boost electrochemical performance and long-term durability of flat tubular (FT) short stack. The tailored structure of the CCCL was employed in the fabrication of the FT short-stack. The G/Ag porous structure exhibited increased porosity of 61.2 %, thereby enhancing the mass transport and improving the overall performance and long-term durability. The four-cell FT stack was manufactured without an interconnect and open air-gas channel. Subsequently, the FT short-stack is tested for performance and long-term durability for elapsed 5000 h at a chronopotentiometry test. The porous layer of graphite/Ag on the cathode layer maintained structural integrity without defects and mechanical failure. Consequently, the stack voltage remains stable throughout operation owing to improved structural stability and uniform temperature distribution across four FT cell stack.

New design and performance evaluation of 1 kW-class reversible solid oxide electrolysis-fuel cell stack using flat-tubular cells

A new type of solid oxide cell (SOC) stack using fuel-electrode-supported flat-tubular cells has been developed for reversible fuel cell/electrolysis cell (FC/EC) operation at 700 °C. The flat-tubular cell in which the end of the tube is plugged and the fuel channels inside the cell are connected through the punched holes reaches the easy scale-up and compact stack volume while sustaining its durability benefits. In this configuration, a metallic cassette-type building block is used to securely mount the cell and serves as the current collector. The power generation and hydrogen production performance are investigated using the I–V test. For a 30-layer stack with 100 cm2 of an active area of a single cell, 1 kW of power generation at +43.7 A and 502 L h−1 of H2 production at −40.0 A are achieved in FC and EC modes, respectively. Additionally, it shows high durability against 500 h of steady-state H2 production as well as against 50 FC/EC cyclic operations with a rapid switching rate (2 h cycle−1). Based on these results, we demonstrate its high potential as a promising flat-tubular r-SOC stack for highly efficient power generation and H2 production.

Simulation of hydrogen and coal gas fueled flat-tubular solid oxide fuel cell (FT-SOFC)

Solid oxide fuel cells (SOFCs) are considered an important technology in terms of high efficiency and clean energy generation. Flat-tubular solid oxide fuel cell (FT-SOFC) which is a combination of tubular and planar cell geometries stands out with its performance values and low costs. In this study, the performance of an FT-SOFC is analyzed numerically by using finite element method-based design as a result of changing parameters by using different fuels which are pure hydrogen and coal gas with various proportions of CO. In addition, cell performance values for different temperatures were analyzed and interpreted. Analyzes have been performed by using COMSOL Multiphysics software. The rates of CO composition used are 10%, 20%, and 40%, respectively. In addition, the air was used as the oxidizer in all cases. The cell voltage and average cell power of the FT-SOFC were examined under the 800 °C operating condition. The maximum power value and current density value were obtained as 710 W/m2 and 1420 A/m2 for the flat-tubular cell, respectively. As a result of the study, it was observed that the maximum cell power densities increased with increasing temperature. Analysis results showed that FT-SOFCs have suitable properties for different fuel usage and different operating temperatures. High-performance values and design features in different operating conditions are expected to make FT-SOFC the focus of many studies in the future.

Stable LSM/LSTM bi-layer interconnect for flat-tubular solid oxide fuel cells

A bi-layer interconnect with La0.8Sr0.2MnO3 and La0.4Sr0.6Ti0.6Mn0.4O3 (LSM/LSTM) is applied to anode-supported button cells and flat-tubular cells. Using a button cell, SEM images and gas permeation tests confirm that the bi-layer possesses a dense microstructure. The area specific resistance (ASR) of the LSM/LSTM remains nearly constant under oxidizing/reducing atmospheres with varying gas concentrations. For comparison, an LSM/LST with the same thickness is prepared; an increase in the ASR is observed as the concentration of H2 feed to the LST side decreases. The difference in the ASR of LSM/LST can be explained by exposure to a relatively high oxygen partial pressure and partial destruction of the interfacial LST layer region where oxygen diffuses from the LSM layer. Flat-tubular cells with the LSM/LSTM bi-layer interconnect achieve a maximum power density (MPD) of 463 mW cm−2 using humidified H2 fuel and air at 800 °C. With decreasing H2 concentration in the fuel, the polarization resistance increases rather than the ohmic resistance, implying that the LSM/LSTM interconnect provides stable conduction property. In comparison with the conventional LSM/LST interconnect cell, it shows improved stability and performance as the concentration of H2 in the fuel decreases.

Three Dimensional Numerical Analysis of 1kW Class Anode Supported Flat Tubular Solid Oxide Fuel Cell Stack

Three dimensional numerical analysis of 1 kW flat tubular solid oxide fuel cell (FT-SOFC) stack that embedded in RPG is conducted. In this present analysis, steady state heat and mass transfer, species concentration and electrochemical reactions along with their losses are analyzed for FT-SOFC stack using two types of fuels; humidified hydrogen and reformed natural gas. However, the final objective of this numerical study is to design a complete 1 kW fuel cell stack system, which will be comprised of FT-SOFC stack, heat exchangers, after burner and integrated reformer. It is interesting to note that fuel cell operate best when they are fed with pure hydrogen which is quite clear from the result mentioned below. The reason is that inert gases are built up at higher current density causing concentration polarization in case of reformed gas. But the problem with pure hydrogen is its storage. An important feature of solid oxide fuel cell is its fuel flexibility. To take advantage, reformed natural gas is employed as alternative fuel as it contains more than 70 % hydrogen & more than 10% CO which act as a fuel. In the numerical computation process, governing equations for continuity, momentum, mass and energy conservation are solved simultaneously. The distribution of the reaction fields in Anode-supported FT-SOFC are found similar to those in the planar SOFC. However, the concentration and activation polarizations in FT-SOFC can be reduced by additional reactant diffusion through the porous ribs of the fuel channel. The present 1kW class stack consists of 80 anodes supported flat tubular (FT) SOFC’s, arranged parallel in a group of 40 cells each. The FT cells are positioned in vertical direction and placed in a preheated air enclosure whereas as fuel gas is supplied through the bottom manifold. To effectively conduct a three-dimensional (3-D) computational analysis of the flat-tubular stack, a commercial ANSYS Fluent 13.0 code is used. The User defined function (UDF an in house code) is also utilized for the simulation of electrochemical reactions, losses in cell voltage due to activation, ohmic and concentration. The changes on the voltage and power of the SOFC stack, current density distribution, temperature distribution, and species concentrations in relation to varying amounts of reaction gas flow are analyzed. To calculate activation loss during electrochemical reactions in cells, the different experimental formulas of exchange current density presented by Achenbach et al., Costamagna et al., Campanari et al. and Aguiar et al. were used. The formula of Achenbach indicates that only partial pressure of H2, an anode reactant, influences the determination of activation loss. By contrast, the formula of Costamagna et al. shows that both reactant H2 and product H2O affect the determination of activation loss. Although the reaction orders of the reactants and products observed by the two authors are different. Both Achenbach and Costamagna show a reaction order close to stoichiometry of electrochemical reaction in the anode. In this selected part of project, numerical study of FT-SOFC stack is done with both pure hydrogen and reformed natural gas. The I-V-P curves of the experimental and calculation results conducted on the basis of the different formulas were compared to identify a most suitable model for the SOFC stack in this current work. The electrical powers of stack system obtained from experiment using pure hydrogen and reformed natural gas are 1203 W, 1123 W respectively. Whereas, electrical powers of stack system obtained from numerical simulation are 1220 W, 1168 W respectively. The error between the calculated and experimental I-V-P curves of SOFC stack is around 4 %. The analysis is envisioned to facilitate advancements in design for Flat Tubular SOFC stacks as well as system operation for practical applications. Figure 1

Evaluation of cost reduction potential for 1 kW class SOFC stack production: Implications for SOFC technology scenario

Recently, a commercial version of a residential solid oxide fuel cell (SOFC) system with a flat tubular cell has been developed. However, the system cost still remains very high, which is a barrier to its widespread use. In this study, the potential for cost reductions in SOFC stack production was investigated in order to contribute to the viability of the widespread use of such residential SOFC systems in future. A cost analysis of 700 W SOFC stack production based on a process integration modeling was conducted. The present bottom–up approach enabled us to perform a sensitivity analysis with a variety of parameters in terms of cell design, the production process and cell performance. This allowed us to investigate the effects of these factors on the production cost, thereby revealing the quantitative impact of each technological improvement on the cost reduction potential. The present analysis also revealed innovation pathways which could result in technology scenarios where residential SOFC systems could reach a break-even point in comparison with the baseload electricity cost. The analysis of the cost reduction potential presented here provides a useful viewpoint for developing a research strategy for state-of-the-art SOFC technology.

A flat-tubular solid oxide fuel cell with a dense interconnect film coated on the porous anode support

An interconnect in an anode-supported flat-tubular solid oxide fuel cell (SOFC) electrically connects unit cells and separates fuel and oxidant gases in a stack. An anode-supported flat-tubular SOFC with a highly conductive and dense interconnect film is developed. The dense interconnect film having an n-type conducting layer on the reducing side and a p-type conducting layer on the oxidizing side is fabricated on a porous anode support by a simple and cost-effective screen-printing process, followed by co-sintering with the anode and the electrolyte. The interconnect exhibits low resistance and high stability in a dual atmosphere. The anode-supported flat-tubular cell with the ceramic interconnect shows a power density as high as 360mWcm−2 at 850°C.

Development of Anode-Supported Flat-Tube Solid Oxide Fuel Cell (SOFC) Stack with High Power Density

An anode-supported flat tubular SOFC stack for intermediate temperature (700~800oC) operation was fabricated and operated in this study. For this purpose, we fabricated anode-supported flat tubular cells by optimization of the current collecting method and the induction brazing process. After that, we designed a compact fuel and air manifold by adopting a simulation technique to uniformly supply fuel and air gas into the stack and a unique seal and insulation method to make a more compact stack. To assemble the stack, the prepared anode-supported flat tubular cells with an effective electrode area of 90 cm2 were connected in series to 30 bundles, in which one unit bundle consists of two flat tubular cells connected in parallel. The performance of the stack in 3 % humidified H2 and air at 750oC showed a maximum electrical power of 921 W.

Fabrication and operation of a 1 kW class anode-supported flat tubular SOFC stack

A 1 kW class anode-supported flat tubular SOFC stack for intermediate temperature (700–800 °C) operation was fabricated and operated in this study. For this purpose, we fabricated anode-supported flat tubular cells by optimization of the current collecting method and the induction brazing process. After that, we designed a compact fuel and air manifold by adopting a simulation technique to uniformly supply fuel and air gas into the stack and a unique seal and insulation method to make a more compact stack. To assemble the stack, the prepared anode-supported flat tubular cells with an effective electrode area of 90 cm 2 were connected in series to 30 bundles, in which one unit bundle consists of two flat tubular cells connected in parallel. The performance of the stack in 3% humidified H 2 and air at 750 °C showed a maximum electrical power of 921 W (fuel utilization ratio = 25.2%).

연료극 지지체식 평관형 고체산화물 연료전지 단위 번들의 제조 및 성능

한국에너지기술연구원에서는 중온 (<TEX>$700{\sim}800^{\circ}C$</TEX>) 작동용 연료극 지지체 평관형 SOFC 스택을 구성하는 단위 번들을 개발했다. 연료극 지지체 평관형 셀은 Ni/YSZ 서밋 연료극 지지체 튜브, 8몰% <TEX>$Y_2O_3$</TEX> stabilized <TEX>$ZrO_2$</TEX> (YSZ) 전해질, <TEX>$LaSrMnO_3$</TEX> (LSM)과 LSM-YSZ composite 및 <TEX>$LaSrCoFeO_3(LSCF)$</TEX>로 구성된 다중층 공기극으로 구성됐다. 제조된 연료극지지체 평관형 셀은 유도 브레이징 법에 의해 페리틱 (ferritic) 금속 캡에 접합됐고, 공기극의 전류집전을 위해 공기극 외부에 Ag 선 및 <TEX>$La_{0.6}Sr_{0.4}CoO_3(LSCo)$</TEX> paste를 이용했으며, 연료극의 전류집전은 Ni felt, wire, 그리고 paste를 이용했다. 단위 번들을 만들기 위한 연료극 지지체 평관형 셀의 반응 면적은 셀 당 <TEX>$90\;cm^2$</TEX> 이었으며, 2개의 셀이 병렬로 연결되어 1개의 단위 번들이 됐고, 총 12개의 단위 번들이 직렬로 연결되어 스택을 구성한다. 공기 및 3%의 가습된 수소를 산화제 및 연료로 사용한 단위 번들의 운전 결과 최대 성능은 <TEX>$800^{\circ}C$</TEX>에서 <TEX>$0.39\;W/cm^2$</TEX>의 출력이 나타났다. 본 연구를 통해 연료극 지지체 평관형 SOFC 셀의 기본 기술과 KIER 만의 독특한 연료극 지지체 평관형 SOFC 스택을 구성하는 단위 번들의 개념을 확립할 수 있었다. KIER has been developing the anode-supported flat tubular solid oxide fuel cell unit bundle for the intermediate temperature(<TEX>$700{\sim}800^{\circ}C$</TEX>) operation. Anode-supported flat tubular cells have Ni/YSZ cermet anode support, 8 moi.% <TEX>$Y_2O_3$</TEX> stabilized <TEX>$ZrO_2(YSZ)$</TEX> thin electrolyte, and cathode multi-layer composed of Sr-doped <TEX>$LaSrMnO_3(LSM)$</TEX>, LSM-YSZ composite, and <TEX>$LaSrCoFeO_3(LSCF)$</TEX>. The prepared anode-supported flat tubular cell was joined with ferritic stainless steel cap by induction brazing process. Current collection for the cathode was achieved by winding Ag wire and <TEX>$La_{0.6}Sr_{0.4}CoO_3(LSCo)$</TEX> paste, while current collection for the anode was achieved by using Ni wire and felt. For making stack, the prepared anode-supported flat tubular cells with effective electrode area of <TEX>$90\;cm^2$</TEX> connected in series with 12 unit bundles, in which unit bundle consists of two cells connected in parallel. The performance of unit bundle in 3% humidified <TEX>$H_2$</TEX> and air at <TEX>$800^{\circ}C$</TEX> shows maximum power density of <TEX>$0.39\;W/cm^2$</TEX> (@ 0.7V). Through these experiments, we obtained basic technology of the anode-supported flat tubular cell and established the proprietary concept of the anode-supported flat tubular cell unit bundle.

Operating Characteristics of Advanced 500W Class Anode-supported Flat Tubular SOFC stack in KIER

KIER has been developing the anode supported flat tubular SOFC stack for the intermediate temperature (700~800oC) operation. For this purpose, we have first fabricated anode supported flat tubular cells by the optimization between the current collecting method and the induction brazing process. After that we designed the compact fuel & air manifold by adopting the simulation technique to uniformly supply fuel & air gas and the unique seal & insulation method to make the more compact stack. For making stack, the prepared anode-supported flat tubular cells with effective electrode area of 90 cm2 connected in series with 12 modules, in which one module consists of two cells connected in parallel. The performance of stack in 3 % humidified H2 and air at 800 oC shows maximum power of 507 W. Through these experiments, we obtained basic & advanced technology of the anode-supported flat tubular cell and established the proprietary concept of the anode-supported flat tubular SOFC stack in KIER

연료극 지지체식 평관형 고체산화물 연료전지 특성 연구

Anode-supported flat tubular solid oxide fuel cell (SOFC) was investigated to increase the cell power density. The anode-supported flat tube was fabricated by extrusion process. The porosity and pore size of Ni/YSZ ( yttria-stabilized zirconia) cermet anode were , respectively. The Ni particles in the anode were distributed uniformly and connected well to each other particles in the cermet anode. YSZ electrolyte layer and multilayered cathode composed of composite, LSM, and were coated onto the anode substrate by slurry dip coating, subsequently. The anode-supported flat tubular cell showed a performance of . The electrochemical characteristics of the flat tubular cell were examined by ac impedance method and the humidified fuel enhanced the cell performance. Areal specific resistance of the LSM-coated SUS430 by slurry dipping process as metallic interconnect was and then decreased to after 450hr. On the other hand, the LSM-coated Fecralloy by slurry dipping process showed a high area specific resistance.

Fabrication and Characteristics of Anode-Supported Flat Tubular SOFC

An anode-supported flat tubular solid oxide fuel cell was fabricated to increase the cell power density and thermal stability by combining the merits of tubular and planar type cell structure. An anode-supported flat tube was fabricated by extrusion process. The porosity and pore size of the flat anode tube were 50.6% and 0.23 μm, respectively. The Ni particles were distributed uniformly and connected well in the cermet. A YSZ electrolyte layer with gas tightness was produced by slurry dipping process. The anode-supported flat tube cell showed cell performance of 225 mW/cm 2 (0.6V, 375 mA/cm 2 ) and operated for 300 h without degradation in cell performance. As ceramic interconnect for flat-tube cell stack, La 0.75 Ca 0.27 CrO 3 was synthesized by the Pechini method and coated onto the anode substrate in the form of a narrow band by plasma spray; a dense ceramic interconnection layer was obtained. Fe-16Cr alloy coated with LSM ((La 0.85 Sr 0.15 ) 0.9 MnO 3 ) as metallic interconnector indicated good sinterability in Ar+10% H 2 atmosphere, which had areal specific resistance of 148 mΩ cm 2 at 750°C in air which decreased to 43 mΩ cm 2 after 450 h. We obtained basic technology for an anode-supported flat tubular cell through this work. By using the flat tube cells, we designed and fabricated the anode-supported flat tube stack with high power density.