SOFCo Planar Solid Oxide Fuel Cell

SOFCo-EFS Holdings LLC has developed a multi-layer, planar solid oxide fuel cell (SOFC) stack that has the potential to provide superior performance and reliability at reduced costs. Our approach combines state-of-the-art SOFC materials with the manufacturing technology and infrastructure established for multi-layer ceramic (MLC) packages for the microelectronics industry. With the proper selection of SOFC materials, implementation of MLC fabrication methods offers unique designs for stacks. Over the past two years, substantial progress has been made in the design and manufacturing development of our second-generation stack. Effective stack and manifold seals have been developed. Cell performance has been improved and relatively low non-cell contributions to stack resistance have been achieved. Stack development has been facilitated through the implementation of two key test methods: (1) a 10-cm single-cell test to bridge the gap in performance data obtained from button cell tests (used for cell R&D) and stack tests; and (2) a novel instrumented short stack (<5 cells) that allows for effective isolation of individual contributions to stack resistance. As a result of progress made to date, a clear pathway for improving stack performance has been established, thereby building confidence that commercial stack performance targets will be reached.     

Fabrication of a Flat Tubular Segmented‐in‐series Solid Oxide Fuel Cell Using Decalcomania Paper

A flat tubular segmented‐in‐series (SIS) solid oxide fuel cell (SOFC) was fabricated using decalcomania paper. The performance of a two‐cell stack with 4.5‐mm‐wide electrodes was investigated in a temperature range of 650–800 °C. The decalcomania paper allowed fabrication of the SIS‐SOFC on all sides of the flat tubular support and achieve an effective electrode area larger than that obtained using typical SOFC fabrication techniques such as screen printing or slurry coating. SEM observations revealed that each component layer was flat, uniformly thick, and well adherent to adjacent layers. Measured values of open circuit voltages were very close to the theoretical values; confirming that the processing technique utilizing decalcomania paper is suitable for SIS‐SOFC fabrication. The power densities of the two‐cell‐stack were 437.4, 375.6, 324.6, and 257.1 mW cm⁻² at 800, 750, 700 and 650 °C, respectively.     

SOFC氧离子导体电解质材料的研究进展及性能优化策略

典型的固体氧化物燃料电池(SOFC)由致密电解质、多孔阴极和阳极三部分构成。其中,电解质介于阴极和阳极之间,是一种具有全固态结构的氧化物陶瓷材料。电解质是SOFC的核心部件之一,是电池工作温度和电池性能的决定性因素。目前,对于高温电解质材料的研究与应用已经相对成熟。但是,在电池高温运行条件下,会导致电极和电解质界面反应、密封困难及使用寿命变短等问题。因此,SOFC电解质的发展逐渐趋向于中温化。但随着工作温度的降低,电解质欧姆阻抗(Ro)势必增大,使得电池的电导率下降。基于此,电解质在中温下的性能提升以及优化近年来备受关注。文中综述了几种不同类型的氧离子导体电解质最新研究进展,并论述了SOFC中低温运行条件下电解质性能提升的主要优化策略。     

Fabrication and Operation of Tubular Segmented‐In‐Series (SIS) Solid Oxide Fuel Cells (SOFC)

A tubular segmented‐in‐series (SIS) solid oxide fuel cell (SOFC) sub module for intermediate temperature (700–800 °C) operation was fabricated and operated in this study. For this purpose, we fabricated porous ceramic supports of 3 YSZ through an extrusion process and analyzed the basic properties of the ceramic support, such as visible microstructure, porosity, and mechanical strength, respectively. After that, we fabricated a tubular SIS SOFC single cell by using dip coating and vacuum slurry coating method in the case of electrode and electrolyte, and obtained at 800 °C a performance of about 400 mW cm^–2. To make a sub module for tubular SIS SOFC, ten tubular SIS SOFC single cells with an effective electrode area of 1.1 cm² were coated onto the surface of the prepared ceramic support and were connected in series by using Ag + glass interconnect between each single cell. The ten‐cell sub module of tubular SIS SOFC showed in 3% humidified H₂ and air at 800 °C a maximum power of ca. 390 mW cm^–2.     

Modelling and Performance Evaluation of Solid Oxide Fuel Cell for Building Integrated Co‐ and Polygeneration

Models of fuel cell based combined heat and power systems, used in building energy performance simulation codes, are often based on simple black or grey box models. To model a specific device, input data from experiments are often required for calibration. This paper presents an approach for the theoretical derivation of such data. A generic solid oxide fuel cell (SOFC) system model is described that is specifically developed for the evaluation of building integrated co‐ or polygeneration. First, a detailed computational cell model is developed for a planar SOFC and validated with available numerical and experimental data for intermediate and high temperature SOFCs with internal reforming (IT‐DIR and HT‐DIR). Results of sensitivity analyses on fuel utilisation and air excess ratio are given. Second, the cell model is extended to the stack model, considering stack pressure losses and the radiative heat transfer effect from the stack to the air flow. Third, two system designs based on the IT‐DIR and HT‐DIR SOFCs are modelled. Electric and CHP efficiencies are given for the two systems, as well as performance characteristics, to be used in simulations of building integrated co‐ and polygeneration systems.     

氧化锆基固体电解质研究

电解质是固体氧化物燃料电池（SOFC）的核心部件,其性能的优良直接决定燃料电池的应用前景。氧化锆基陶瓷具有较高的离子电导率、良好的结构和化学稳定性,是理想的固体电解质材料。本文综合介绍了各种掺杂元素对氧化锆基固体电解质性能的影响,电解质薄膜制备方法和研究现状。并对氧化锆基固体电解质的研究方向进行了展望。     

Temperature Measurement and Distribution Inside Planar SOFC Stacks

In this work, a kind of thin K‐type thermocouple and self‐developed CAS‐I sealant were used to assembly solid oxide fuel cell (SOFC) stacks and temperatures of unit cells inside a planar SOFC stack were measured. The open circuit voltage testing of the stack and characterization of the interface between sealant and components suggested excellent sealing effect by applying the developed method. The effect of discharging direct‐current on temperature and temperature distribution inside the designed SOFC stack was investigated. The results showed that the discharging current had a great impact and the gas flow rate had a slight impact on the temperatures of unit cells. Temperature distribution of unit cells inside the stack was much non‐uniform and there is a significant temperature difference between various components of the stack and heating environment. The relationship between temperatures and cell performance showed that the worse the cell performance, the higher the cell surface temperature. When the stack was discharged at a constant current and the temperature of cell surface was over 950 °C, the higher the temperature, the more drop the corresponding voltage.     

Effect of Creep of Ferritic Interconnect on Long‐Term Performance of Solid Oxide Fuel Cell Stacks

High‐temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and coefficient of thermal expansion (CTE) compatibility with other components for most of the solid oxide fuel cells (SOFCs). However, creep deformation becomes relevant for a material when the operating temperature exceeds or even is less than half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the SOFCs under development are around 1,073 K. With around 1,800 K of the melting temperature for most stainless steel (SS), possible creep deformation of ferritic IC under the typical cell operating temperature should not be neglected. In this paper, the effects of IC creep behaviour on stack geometry change and the stress redistribution of different cell components are predicted and summarised. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the changes in fuel‐ and air‐channel geometry due to creep of the ferritic SS IC, therefore indicating possible changes in SOFC performance under long‐term operations. The ferritic IC creep model was incorporated into software SOFC‐MP and Mentat‐FC, and finite element analyses (FEAs) were performed to quantify the deformed configuration of the SOFC stack under the long‐term steady‐state operating temperature. It was found that the creep behaviour of the ferritic SS IC contributes to narrowing of both the fuel‐ and the air‐flow channels. In addition, stress re‐distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.     

Optimization of physical parameters of solid oxide fuel cell electrode using electrochemical model

To enhance the performance of anode-supported solid oxide fuel cell (SOFC), an electrochemical model has been developed in this study. The Butler-Volmer equation, Ohm’s law and dusty-gas model are incorporated to predict the activation, ohmic and concentration overpotentials, respectively. The optimal cell microstructure and operating parameters for the best current-voltage (J-V) characteristics have been sought from the information of the exchange current density and gas diffusion coefficients. As the cell temperature rises, the activation and ohmic overpotentials decrease, whereas the concentration overpotential increases due to the considerable reduction of gas density at the elevated temperature despite the increased diffusion coefficient. Also, increasing the hydrogen molar fraction and operating pressure can further augment the maximum cell output. Since there exists an optimum electrode pore size and porosity for maximum cell power density, the graded electrode has newly been designed to effectively reduce both the activation and concentration overpotentials. The results exhibit 70% improved cell performance than the case with a non-graded electrode. This electrochemical model will be useful to simply understand overpotential features and devise the strategy for optimal cell design in SOFC systems.     

Multiscale model for solid oxide fuel cell with electrode containing mixed conducting material

Solid oxide fuel cells (SOFCs) with electrodes that contain mixed conducting materials usually show very different relationships among microstructure parameters, effective electrode characteristics, and detailed working processes from conventional ones. A new multiscale model for SOFCs using mixed conducting materials, such as LSCF or BSCF, was developed. It consisted of a generalized percolation micromodel to obtain the electrode properties from microstructure parameters and a multiphysics single cell model to relate these properties to performance details. Various constraint relationships between the activation overpotential expressions and electric boundaries for SOFC models were collected by analyzing the local electrochemical equilibrium. Finally, taking a typical LSCF‐SDC/SDC/Ni‐SDC intermediate temperature SOFC as an example, the application of the multiscale model was illustrated. The accuracy of the models was verified by fitting 25 experimental I‐V curves reported in literature with a few adjustable parameters; additionally, and several conclusions were drawn from the analysis of simulation results. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3786–3803, 2015     

Thermodynamic Analysis of an Integrated SOFC,Solar ORC and Absorption Chiller for Tri‐generation Applications

Thermodynamic performance assessment of an integrated tri‐generation energy system for power, heating and cooling production is conducted through energy and exergy analyses. Sustainability assessment is performed and some parametric studies are undertaken to analyze the impact of system parameters and environmental conditions on the system performance. The tri–generation system consists of (a) an internal reforming tubular type solid oxide fuel cell (IR‐SOFC), which works at ambient pressure and fueled with syngas, (b) a combustor and a air heat exchanger, (c) a heat recovery and steam generation unit (HRSG), (d) a two‐ stage Organic Rankine cycle (ORC) driven by exhaust gases of SOFC, (e) parabolic trough solar collectors (PTSC), and (f) a lithium‐bromide absorption chiller (AC) cycle driven by exhaust gases from SOFC unit. The largest irreversibility occurs at the SOFC unit due to high temperature requirement for reactions. Fuel utilization factor, recirculation ratio, dead state conditions, and solar unit parameters have influential effects on the system efficiencies. Energy and exergy efficiencies of tri‐generation unit become 85.1% and 32.62%, respectively, for optimum SOFC stack and environmental conditions. The overall system energy and exergy efficiencies are 56.25% and 15.44% higher than that of conventional SOFC systems, respectively.     

A thermodynamically consistent framework for non-isothermal modelling of local heat generation and electromotive force in SOFC single electrodes

Mathematical models for single electrode reversible heat and non-isothermal electromotive force (EMF) of a solid oxide fuel cell (SOFC) are developed. These models estimate the volumetric reversible heat generation and EMF of electrochemical reactions, within each electrode at local conditions of temperature and pressure, based on entropy change of half reactions. The resulting equations are thermodynamically consistent. They inherently obey the conservation of energy law as the electrochemical energy released added to the heat of reactions at each electrode equate the enthalpy change of the reacted species. The equations are implemented to model electrodes in a tubular micro- solid oxide fuel cell (TμSOFC). The thermodynamic consistency of the model is numerically confirmed as the enthalpy of the reactants equates the electric energy released by the cell plus the sum of electrode heats plus electrolyte Ohmic heat. The effect of thermal gradients on the cell's overall EMF is found to be negligible. The reversible and irreversible heat generation of each electrode are distinguished. Overall, the anode is found to be endothermic, and the cathode exothermic.     

铋离子掺杂固体氧化物燃料电池阴极材料的研究进展

固体氧化物燃料电池(SOFC)是一种可以将燃料中的化学能直接转化为电能的发电装置,具有燃料选择灵活、效率高、环境友好等优点。基于SOFC运行成本和长期稳定性的要求,降低工作温度已成为当前研究的热点。传统阴极较低的催化活性制约了SOFC的技术发展,因此开发具有良好催化性能的阴极材料至关重要。大量的研究表明,铋离子的掺杂能够有效提高材料的电导率和氧催化活性。从铋离子掺杂的角度出发,综述了铋离子掺杂对阴极材料的制备、结构、电导率和电化学性能的影响,并对掺铋SOFC阴极材料未来的发展趋势进行了展望。     

A Novel Cell‐Array Design for Single Chamber SOFC Microstack

A novel design of single chamber solid oxide fuel cell (SC‐SOFC) microstack with cell‐array arrangement is fabricated and operated successfully in a methane–oxygen–nitrogen mixture. The small stack, consisting of five anode‐supported single cells connected in series, exhibits an open circuit voltage (OCV) of 4.74 V at the furnace temperature of 600 °C and a maximum power output of 420 mW (total active electrode area is 1.4 cm²) at the furnace temperature of 700 °C. A gas mixture of CH₄/O₂ = 1 leads to best performance and stability.     

固体氧化物燃料电池的研究进展

固体氧化物燃料电池(SOFC)是先进陶瓷材料的一种重要应用,可以通过电化学反应将燃料的化学能直接转换为电能。SOFC具有效率高、性能稳定、便携、低污染等优点,可以实现能源的有效清洁利用。本文结合国内外SOFC的研究情况,分析讨论了SOFC的技术优势、地方产业优势及产业难题,并结合国家政策方面对我国SOFC产业的未来发展做了展望。     

基于天然气自热重整的SOFC系统性能分析

建立一个天然气自热重整的固体氧化物燃料电池(SOFC)系统模型,利用Aspen Plus化工流程模拟软件链接基于Fortran语言编写的电堆模型,在质量守恒和能量守恒的基础上,分析不同参数对系统性能的影响。模拟结果表明:随着水碳比的增加,甲烷和一氧化碳的转化率增大,导致氢气和二氧化碳含量增加;氧碳比和系统效率在水碳比为1.5时达到最大。随着燃料利用率的增加,电流密度增大,导致空气过量系数增大,空气利用率降低;系统的总效率和净效率均随之增大。尾气温度随着水碳比和燃料利用率的增加均呈现下降趋势。系统的最大总效率和净效率分别为44.5%和39.2%。研究结果为进一步优化自热重整系统指明了方向。     

Anode-Supported Tubular Micro-Solid Oxide Fuel Cell

A tubular anode-supported "micro-solid oxide fuel cell" (μSOFC) has been developed for producing high volumetric power density (VPD) SOFC systems featuring rapid turn on/off capability. An electrophoretic deposition (EPD)-based, facile manufacturing process is being refined to produce the anode support, anode functional and electrolyte layers of a single cell. μSOFCs (diameter <5 mm) have two main potential advantages, a substantial increase in the electrolyte surface area per unit volume of a stack and also rapid start-up. As fuel cell power is directly proportional to the active electrolyte surface area, a μSOFC stack can substantially increase the VPD of an SOFC device. A decrease in tube diameter allows for a reduction in wall thickness without any degradation of a cell's mechanical properties. Owing to its thin wall, a μSOFC has an extremely high thermal shock resistance and low thermal mass. These two characteristics are fundamental in reducing start-up and turn-off time for the SOFC stack. Traditionally, SOFC has not been considered for portable applications due to its high thermal mass and low thermal shock resistance (start-up time in hours), but with μSOFCs' potential for rapid start-up, new possibilities for portable and transportable applications open up.     

Nano-structuring of solid oxide fuel cells cathodes

Different approaches are proposed for increasing the overall performance of solid oxide fuel cells (SOFC) by promoting the nano-structuring of perovskitic cathode layers. The formation of pore systems in the nanometer scale will make available a larger surface area (three-phase-boundary) for the electrocatalytic processes occurring on the air electrode. Two different concepts can be pursued for this purpose: (i) synthesis of thermally-stable mesoporous particles and ulterior deposition of them as macroporous films using coating techniques such as screen printing; and (ii) production of nano-structured films of regularly-arranged nano-sized particles of electrocatalytic materials over the dense electrolyte. The first progresses in the synthesis of nano-structured LSFC cathode layers following the first approach are depicted as well as their electrochemical characterization when using them as SOFC cathodes assembled on complete anode-supported (Ni-YSZ/YSZ) fuel cells.     

Ceramic Fuel Cells

A ceramic fuel cell in an all solid-state energy conversion device that produces electricity by electrochemically combining fuel and oxidant gases across an ionic conducting oxide. Current ceramic fuel cells use an oxygen-ion conductor or a proton conductor as the electrolyte and operate at high temperatures (>600°C). Ceramic fuel cells, commonly referred to as solid-oxide fuel cells (SOFCs), are presently under development for a variety of power generation applications. This paper reviews the science and technology of ceramic fuel cells and discusses the critical issues posed by the development of this type of fuel cell. The emphasis is given to the discussion of component materials (especially, ZrO₂ electrolyte, nickel/ZrO₂ cermet anode, LaMnO₃ cathode, and LaCrO₃ interconnect), gas reactions at the electrodes, stack designs, and processing techniques used in the fabrication of required ceramic structures.     

Study of a Single‐Chamber Solid Oxide Fuel Cell Microstack with V‐Shaped Congener‐Electrode‐Facing Configuration

Single‐chamber solid oxide fuel cell (SC‐SOFC) microstacks with V‐Shaped congener‐electrode‐facing configuration were fabricated and operated successfully in a box‐like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode‐facing‐anode two‐cell stack was higher than that of a cathode‐facing‐cathode two‐cell stack during the test procedure. For a three‐cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three‐cell stack in a gas mixture of 100 sccm N₂, 120 sccm CH₄, and 80 sccm O₂ were 3.0 V and 413 mW, respectively.