固体氧化物燃料电池的热力学及电化学应用基础

固体氧化物燃料电池是一种典型的电化学装置，可以把燃料气和空气（或氧气）的化学能直接转化为电能。电池的整个反应过程可以根据还原剂和氧化剂反应自由焓来进行热力学计算。对于最简单的氢气和氧气的反应来说，可以根据可逆反应平衡方程式计算电池的可逆功，而且SOFC系统和外部环境的热交换也是可逆的。SOFC作为一种伴生热能的发电装置，对热力学的理解必不可少。所以本文将首先介绍一下SOFC的热力学基础，而作为一种电化学发电装置，需要系统了解SOFC的电化学基础，其中重点介绍SOFC的电化学分析曲线——i-V曲线。     

可逆固体氧化物电池电极材料研究进展

可逆固体氧化物电池(RSOC)是一种全固态电化学能量转换装置,可以实现化学能和电能的高效洁净可逆转换,有望应用于智能电网领域实现削峰填谷以及规模化可再生能源的转化存储。由于RSOC需要分别在固体氧化物燃料电池(SOFC)及固体氧化物电解池(SOEC)模式下进行可逆、循环切换工作(存在放电/供电及氧化/还原气氛变化),对电极材料性能和物理化学稳定性要求高,迫切需要提高电极催化活性和氧化还原稳定性。介绍了RSOC的工作原理,综述了目前RSOC电极材料的研究成果及研究现状,分析了可逆对称电极材料在RSOC中的应用前景并展望了其未来的发展方向。     

Three‐Dimensional Computational Fluid Dynamics Modeling of a Planar Solid Oxide Fuel Cell

A three‐dimensional computational fluid dynamics model was developed to study the performance of a planar solid oxide fuel cell (SOFC). The governing equations were solved with the finite volume method. The model was validated by comparing the simulation results with data from literature. Parametric simulations were performed to investigate the coupled heat/mass transfer and electrochemical reactions in a planar SOFC. Different from previous two‐dimensional studies the present three‐dimensional analyses revealed that the current density was higher at the center along the flow channel while lower under the interconnect ribs, due to slower diffusion of gas species under the ribs. The effects of inlet gas flow rate and electrode porosity on SOFC performance were examined as well. The analyses provide a better understanding of the working mechanisms of SOFCs. The model can serve as a useful tool for SOFC design optimization.     

固体氧化物燃料电池系统及其应用

对固体氧化物燃料电池系统和单体电池及其工作原理、材料组成等作了简要介绍,并介绍了固体氧化物燃料电池在电厂混合发电方面与燃气轮机组成的联合系统技术以及以天然气为燃料家庭热电联产方面的应用。并指出固体氧化物燃料电池由于其高效、环保清洁将是未来能源利用的主要方式。     

Modeling of a Tubular‐SOFC: The Effect of the Thermal Radiation of Fuel Components and CO Participating in the Electrochemical Process

A mathematical model based on first principles is developed to study the effect of heat and electrochemical phenomena on a tubul solid oxide fuel cell (SOFC). The model accounts fordiffusion, inherent impedance, transport (momentum, heat and mass transfer) processes, internal reforming/shifting reaction, electrochemical processes, and potential losses (activation, concentration, and ohmic losses). Thermal radiation of fuel gaseous components is considered in detail in this work in contrast to other reported work in the literature. The effect of thermal radiation on SOFC performance is shown by comparing with a model without this factor. Simulation results indicate that at higher inlet fuel flow pressures and also larger SOFC lengths the effect of thermal radiation on SOFC temperature becomes more significant. In this study, the H₂ and CO oxidation is also studied and the effect of CO oxidation on SOFC performance is reported. The results show that the model which accounts for the electrochemical reaction ofCO results in better SOFC performance than other reported models. This work also reveals that at low inlet fuel flow pressures the CO and H₂ electrochemical reactions are competitive and significantly dependent on the CO/H₂ ratio inside the triple phase boundary.     

可逆固体氧化物燃料电池氧电极材料的研究进展

可逆固体氧化物燃料电池（RSOC）是一种集固体氧化物燃料电池（SOFC）和固体氧化物电解池（SOEC）于一体的全固态电化学能源转换装置,可以将燃料中的化学能和电能相互高效转化。本文基于RSOC的工作过程和氧电极的电催化机理,分析和讨论氧电极结构的分层问题及对其材料的要求。本文按照单钙钛矿型（锰基、钴基、铁基）、双钙钛矿型和非钙钛矿型氧电极的研究现状进行分类综述,分别从氧电极材料的制备、极化电阻、电催化活性及其与不同的电解质和燃料极材料相匹配几个方面,讨论RSOC在SOFC和SOEC模式下的放电和电解的行为,分析RSOC氧电极的特性。针对氧电极与电解质分层的问题,提出制备中间过渡层、开发新型具有超氧化学计量比和高氧离子传导速率的氧电极材料以及制备一体化对称电池的解决方案,并指出双钙钛矿将是RSOC氧电极的重要候选材料之一。本文将为RSOC氧电极的设计、制备和优化提供重要的参考和依据。     

SOFC内部重整反应与电化学反应耦合机理

以经过预重整反应的混合气为原料的固体氧化物燃料电池（SOFC）内部,甲烷蒸气重整反应与电化学反应同时发生在阳极多孔介质中,二者受到不同的操作与设计参数的影响,对电池总体性能起着决定性作用。编制了三维数值模拟程序,对由多孔阳极层、气体流动管道、固体支撑平板构成的单个复合管道进行了研究。结果显示：重整反应主要发生在多孔材料靠近流动管道的薄层内,只有靠近管道入口处才能在较深处进行;电化学反应发生在多孔层与电解质的交界面处;重整反应生成的H2、CO扩散到多孔材料底部参加电化学反应;电化学反应生成的热量供重整反应使用。说明研究范围内,SOFC阳极复合通道具有较好的传热、传质性能,化学/电化学反应存在较好的耦合关系。     

Control Loop Design and Control Performance Study on Direct Internal Reforming Solid Oxide Fuel Cell

A solid oxide fuel cell (SOFC) stack is a complicated nonlinear power system. Its system model includes a set of partial differential equations that describe species, mass, momentum and energy conservation, as well as the electrochemical reaction models. The validation and verification of the control system by experiment is very expensive and difficult. Based on the distributed and lumped model of a one‐dimensional SOFC, the dynamic performance with different control loops for SOFC is investigated. The simulation result proves that the control system is appropriate and feasible, and can effectively satisfy the requirement of variable load power demand. This simulation model not only can prevent some latent dangers of the fuel cell system but also predict the distributed parameters' characteristics inside the SOFC system.     

Microkinetic Modeling of Nickel Oxidation in Solid Oxide Cells: Prediction of Safe Operating Conditions

Oxidation of the nickel electrode is a severe aging mechanism of solid oxide fuel cells (SOFC) and solid oxide electrolyzer cells (SOEC). This work presents a modeling study of safe operating conditions with respect to nickel oxide formation. Microkinetic reaction mechanisms for thermochemical and electrochemical nickel oxidation are integrated into a 2D multiphase model of an anode‐supported solid oxide cell. Local oxidation propensity can be separated into four regimes. Simulations show that the thermochemical pathway generally dominates the electrochemical pathway. As a consequence, as long as fuel utilization is low, cell operation considerably below electrochemical oxidation limit of 0.704 V is possible without the risk of reoxidation.     

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。     

质子传导陶瓷电解质燃料电池特性分析

An electrolyte model for the solid oxide fuel cell (SOFC) with proton conducting perovskite electrolyte is developed in this study, in which four types of charge carriers including proton, oxygen vacancy (oxide ion), free electron and electron hole are taken into consideration. The electrochemical process within the SOFC with hydrogen as the fuel is theoretically analyzed. With the present model, the effects of some parameters, such as the thickness of electrolyte, operating temperature and gas composition, on the ionic transport (or gas permeation) through the electrolyte and the electrical performance, i.e., the electromotive force (EMF) and internal resistance of the cell, are investigated in detail. The theoretical results are tested partly by comparing with the experimental data obtained from SrCe0.05M0.05O3-α(M=Yb, Y) cells.     

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.     

金属陶瓷阳极材料的高效固体氧化物燃料电池研究

固体氧化物燃料电池(SOFC)利用金属陶瓷作阳极材料,具有能量转换效率高、燃料适用性强和无腐蚀等优点,是当今一种先进的能量转换装置。本文分析了固体氧化物燃料电池在电解质和电极材料方面的性能和特点,研究了金属陶瓷阳极材料及SOFC单电池的伏安特性和性能,探讨了固体氧化物燃料电池的应用和发展前景。     

The Use of Methane‐Containing Syngas in a Solid Oxide Fuel Cell: A Comparison of Kinetic Models and a Performance Evaluation

The nickel‐based anodes of solid oxide fuel cells (SOFCs) can catalytically reform hydrocarbons, which make natural gas, gasification syngas, etc., become potential fuels in addition to hydrogen. SR and water–gas shift (WGS) often occur inside SOFCs when operated on these fuels. Their reaction rates affect the partial pressures of hydrogen and carbon monoxide, the local temperatures and the related Nernst voltages. Consequently, the reaction rates affect the electrochemical reactions in the fuel cell. Three different kinetic models were used to characterize methane SR in a tubular SOFC; the results of each model were evaluated and compared. The polarizations of the fuel cell results of these models were validated against experimental data. The performance of a fuel cell operated with different fuels and based on a selected kinetic model was further studied in terms of the anode oxygen partial pressure, the thermo‐electrochemical distribution, and the system level performance.     

A detailed model for transport processes in a methane fed planar SOFC

In the present work the basic transport processes occurring in a planar solid oxide fuel cell (SOFC) were simulated. The Navier-Stokes and energy equations, including convective and diffusive terms, were numerically solved by the commercial CFD-ACE⁺ program along with the mass and charge transport equations. To achieve this, a three-dimensional geometry for the planar fuel cell has been built. It was also assumed that the feedstream was a mixture of methane and steam in a ratio avoiding carbon formation. In accordance with the literature, the steam reforming reaction, the water-gas shift reaction as well as electrochemical reactions were introduced to the model. The spatial variation of the mixture's velocity, the temperature profiles and the species concentrations (mass fractions) were obtained. Furthermore, the effect of temperature on the produced current density was investigated and compared to the outcomes from isothermal imposed conditions.     

The transient operation of a solid oxide fuel cell monolith under forced periodic reversal of the flow

The forced periodic reversal of the flow is proposed for the case of a Solid Oxide Fuel Cell (SOFC) monolith. A one-dimensional non-steady state heterogeneous model is applied to an investigation of H₂ electrochemical oxidation in a co-current flow solid oxide monolithic fuel cell. Results are reported on the transient evolution along the reactor, of the species conversion, temperature distribution, thermodynamic energy conversion efficiency and volumetric power density. This novel transient operation of an SOFC leads to improved and highly efficient performances, thus allowing for a combination of the concepts of a regenerative heat preheater and of an electrocatalytic converter, in a single SOFC monolithic assembly.     

Distortions in Electrochemical Impedance Spectroscopy Measurements Using 3‐Electrode Methods in SOFC. II. Effect of Electrode Activity and Relaxation Times

The 3‐electrode configuration is commonly applied to quantify the overpotential of anodes or cathodes in solid‐oxide fuel cells (SOFC). In this type of set‐up, a reference electrode (RE) is used to isolate the potential loss of one electrode from that of the entire cell; however, erroneous results can be obtained whenever the RE does not precisely separate the potential drop between the two active electrodes. In this study, we present the results of a theoretical and experimental analysis focused on verifying the effectiveness of the 3‐electrode configuration in electrochemical impedance spectroscopy measurements for the kinetic characterisation of SOFC electrode reactions. The focus of this paper is on the distortion of impedance measurements caused by differences in the area‐specific polarisation resistance and impedance time constants of the working and counter electrodes. The results obtained numerically and experimentally, both for planar and tubular SOFC cell geometries, prove the reliability of the theoretical model used. From the systematic simulation presented here and in our previous work, it was possible to formulate general guidelines for the design of 3‐electrode experimental SOFC. The theoretical model used here can also be used to verify the consistency of EIS measurements obtained with thin planar cells.     

Dynamic modelling and control of planar anode-supported solid oxide fuel cell

Most solid oxide fuel cell (SOFC) modelling efforts emphasize steady-state cell operation. However, understanding the dynamic behaviour is essential to predict the performance and limitations of SOFC power systems. This article presents the development of a SOFC dynamic model and a feedback control scheme that can maintain output voltage despite load changes. Dynamic responses are determined as the solutions of coupled partial differential equations derived from conservation laws of charges, mass, momentum and energy. To obtain the performance curve, the dynamic model is subjected to varying load current for different fuel specifications. From such a model, the voltage responses to step changes in the fuel concentration and load current are determined. Low-order dynamic models that are sufficient for feedback control design are derived from the step responses. The development of the partial differential equation model is outlined and the limitations of the control system are discussed.     

Use of effective conductivities and unit cell-based supraelements in the numerical simulation of solid oxide fuel cell stacks

The numerical simulation of current and temperature distribution in monolithic solid oxide fuel cell (SOFC) stacks requires fast computers because of the large number of mesh points required in casting a complex solid geometry into a finite difference form and the necessity to solve coupled, nonlinear differential equations. By analogy with the modelling of radiative heat transfer in packed bed reactors, a significant degree of simplification is achieved by defining effective electric and thermal conductivities for the repeating unit cell elements, identified as the basic building blocks of the SOFC stack. The effective conductivities are approximated by closed form formulae derived from the principles of electrostatics and heat conduction. The effect of radiation across the gas channels is incorporated into the expressions for the effective thermal conductivity. Using this approach, the unit cell geometry, local mass transfer processes and reaction kinetics are expressed in terms of a supraelement model in a finite difference grid for the numerical calculation of temperature and potential distributions in a stack by an iterative process. The simplifications thus provided render simulations of three-dimensional SOFC stacks tractable for desktop processors. By using the foregoing approach to numerical simulation, a parametric study of a cross-flow type SOFC is presented, and some of the results are compared with the available experimental data     

Dynamic modeling of a finite volume of solid oxide fuel cell: The effect of transport dynamics

A dynamic model for a finite volume of cell based on physical principles is built in the form of a nonlinear state-space model to investigate dynamic behaviors of tubular solid oxide fuel cell (SOFC) and develop a control relevant model for further control studies. Dynamic effects induced by diffusions, intrinsic impedance, fluid dynamics, heat exchange and direct internal reforming/shifting (DIR) reactions are all considered. Cell temperature, ingredient mole fractions, etc. are the state variables and their dynamics are investigated. Dynamic responses of each variable when the external load changes are simulated. Simulation results show that fuel flow, inlet pressure and temperature have significant effects on the dynamic performance of SOFC. Further it is shown that, compared to other inlet flow properties, cathode side air inlet temperature has the most significant effect on SOFC solid phase temperature and performance. Compared with inlet pressures and temperatures, the effect of flow velocity is not significant. Simulation also indicates that the transient response of SOFC is controlled mainly by the dynamics of cell temperature owing to its large heat capacity.