固体氧化物燃料电池发电系统的模拟与优化

固体氧化物燃料电池是21世纪最有希望作为分布式电源和大型电站的清洁高效的发电技术之一。针对1MW固体氧化物燃料电池发电系统,建立了描述SOFC电池堆电化学过程和特性的模型,并在此基础上建立了基于Aspen Plus软件平台的SOFC发电系统模型,对其系统参数进行了灵敏度分析和优化。     

管式固体氧化物燃料电池机理模型与性能分析

针对Siemens-Westinghouse公司阴极支撑型(AES)管式固体氧化物燃料电池,耦合电极内部离子传导、电子传导、气体扩散、热量传递及电化学反应过程,建立了全面考虑活化极化、欧姆极化与浓差极化损失的管式SOFC横截面方向二维微观机理模型。模型计算结果与文献中实验数据吻合较好,模拟结果表明：电池横截面方向的组分浓度和电流密度的分布与SOFC的运行工况密切相关。连接器的存在和尺寸对电池工作性能均有较强影响。对于所研究的阴极支撑型SOFC,电池性能会受到氧气在多孔阴极中扩散过程的限制,改善多孔电极的微观结构可有效提高电池运行性能。     

锂离子软包电池的极化分析

结合锂离子电池充电基本特性,以软包电芯为研究对象,从极化的角度研究了锂离子电池的内阻变化及其对低温性能的影响。在低温性能方面,极化越大的电芯相对来说电压平台降低,直流电阻越大。分析充放电IR Drop特性,结合极化超电势衰减方程,建立电芯平衡电压与固相、液相扩散的模型,通过此模型,可以快速识别电芯发生衰减的影响因素,解决锂离子电池寿命评估周期长成本高的问题。     

高温质子交换膜燃料电池机理模型研究进展

建立高温质子交换膜燃料电池的机理模型可以加深对其内部传递现象和反应机理的认识,同时可以预测不同参数下燃料电池的性能,对优化电池的操作条件和结构参数等具有重要的指导意义。对现有的高温质子交换膜燃料电池机理模型进行了评述,分析了基于磷酸掺杂聚苯并咪唑膜(H3PO4/PBI)不同维数的稳态和动态模型及基于其他复合膜模型的优点和不足,并指出了高温质子交换膜燃料电池模型的研究方向。     

钒离子浓度对全钒液流电池极化分布的影响

基于物质传递方程、电荷传递方程和电化学动力学方程提出了浓差极化系数的概念,建立了全钒液流电池二维模型,利用有限元法研究了钒电池极化过程,并对电极区域极化的分布进行了定量评估。研究表明:增加钒离子浓度,电极表面和溶液本体浓度趋同,活化极化和浓差极化减小,这种现象在高电流密度下尤为明显;浓度的增加也使得浓差极化系数减小,物质传递的影响减小,浓差极化相对于整个极化影响越来越弱;从进口到出口,浓差极化系数逐渐增加;电极与集流体接触面的浓差极化系数比电极中间区域高得多。     

PEMFC冷却剂循环条件下冷启动数值模拟

质子交换膜燃料电池(PEMFC)具有高能量比、环境友好、工作温度低等优点，可用作未来新能源汽车的能量来源，具有很好的发展前景。然而零下温度启动时，电池内水结冰堵塞通道，严重影响电池启动性能及寿命。提出了PEMFC冷启动三维多物理场数值模型，考虑了冷却剂流动与传热的影响，对冷启动过程组分浓度、电势、温度、含冰量等参数进行了可视化分析。数值模拟结果与试验吻合良好，表明模型可用于预测电池冷启动性能并用于机理研究。     

多层水系流延和共烧法制备具有阳极功能层固体氧化物燃料电池

采用多层水系流延和共烧方法制备具有阳极功能层的单电池。阳极基底、阳极功能层、电解质层和阴极层分别为Ni-YSZ、Ni-ScSZ、YSZ和LSM-ScSZ。在H2/空气气氛中,分别在700、750、800℃测试具有阳极功能层的单电池,其最大功率密度分别为：0.30、0.55W/cm2和0.8W/cm2;其对应的电池欧姆电阻（R0）分别为0.39、0.30cm2和0.19cm2。电池的极化电阻则分别为1.28、0.91cm2和0.62cm2。采用相同工艺制备无阳极功能层的单电池,其在700、750、800℃的最大功率密度分别为0.21、0.31W/cm2和0.56W/cm2,对应的R0为0.41、0.39cm2和0.28cm2。电池的极化电阻为1.40、1.27cm2和0.91cm2。这说明采用的多层水系流延和共烧法制备的固体氧化物燃料电池的阳极功能层能有效减小电池的活化极化,从而提高单电池的电化学性能。     

液体催化燃料电池的放大试验研究

液体催化燃料电池技术是一种基于电化学原理将生物质能直接转化为电能的绿色、高效生物质燃料电池发电技术。为了研究大功率的液体催化燃料电池技术发电性能,对液体催化燃料电池进行了功率放大试验研究。开发出放电面积为100cm2的单电池,通过将组建的小型燃料电池组和中型燃料电池组串联,搭建出一个发电功率为52 W的燃料电池电堆,并对该燃料电池电堆的泵损耗和造价成本进行初步分析。结果表明,该燃料电池电堆的泵损耗为9. 87 W,占电堆发电功率的19%,整个燃料电池系统的总造价成本为1. 55万元。     

DMFC多孔Pt-Ru阳极甲醇氧化宏观动力学模型化

本文旨在建立和求解DMFC多孔阳极甲醇氧化宏观动力学理论数模。根据Pt-Ru催化剂上双位机理,得到包含CO和OH覆盖率的甲醇水解本征动力学表达式;通过对该多孔阳极微元体积中的物料和电（荷）量衡算,导出了描述电极中浓度和超电势分布的两个耦联的模型方程。经量纲1化后,获得以量纲1变量和准数表示的普遍化宏观动力学数模。该模型包括催化层厚度l、比表面积a、有效扩散系数D_e和有效液相电导率κ_e等工程参数,特别是包括了与动力学参数相关且作为厚度变量函数的CO和OH覆盖率。进而,文中还给出了DMFC多孔阳极效率因子和极化曲线的计算公式。该数模为一非线性二阶微分方程组边值问题,经解耦,可得到两个同解的微分方程。用Newman的BAND（J）程序对方程进行数值求解,并在每一节点计算中嵌入一个计算CO和OH覆盖率的子程序。将模型预测值与甲醇氧化多孔阳极的极化实验数据进行对比发现：当宏观电流密度较低时二者能很好相符;当宏观电流密度较高、CO₂形成气泡的影响变大时,实验值有规律地偏低于预测值。详细的宏观动力学分析表明：提高催化剂Pt位甲醇电分解活性以减少功率损失、优化多孔电极微观和宏观结构以削弱两相流影响,应是改善该阳极性能的重要课题。本工作也可为直接乙醇燃料电池（DEFC）、直接硼氢化物燃料电池（DBFC）阳极的理论分析提供参考。     

质子交换膜燃料电池仿真模型研究进展

质子交换膜燃料电池具有高效清洁等优势,是一种潜力巨大的绿色能源技术。数学模型作为一种合理可靠的工具,通过模拟电池内部的电化学传热传质过程,研究运行参数和结构参数对电池性能和寿命的影响,可以指导电池的优化设计。本文综述了近年来燃料电池催化层、气体扩散层和流道的研究模型,整理了各部件建模的影响因素和优化方法,以期对燃料电池建模以及电池各部件的优化设计起到参考作用。文中指出,考虑到现在仿真存在的局限性,未来主要研究方向为燃料电池系统研究与机理模型的结合、催化层微观结构的建模、非贵金属催化剂建模、气体扩散层衰减模型研究、大面积流道模型、三维模型温度分布研究以及全尺寸质子交换膜燃料电池模型的开发。     

Modeling a Reversible Solid Oxide Fuel Cell as a Storage Device Within AC Power Networks

A reversible solid oxide fuel cell (RSOFC) system, consisting of a RSOFC stack, heat store, and electrical inverters to convert DC to AC power, is shown by computer modeling to have the potential to efficiently store electrical energy. This paper describes the modeling of a single RSOFC, based on a proposed cell geometry, empirical data on the resistivities of the components, and calculation of activation and diffusion polarization resistances from electrochemical theory. Data from ac impedance spectroscopy measurements on symmetrical cells are used to model RSOFC impedance. A RSOFC stack is modeled by electrically linking the individual cells inside a pressurized vessel. A phase change heat store is added to improve energy storage efficiency. The model is implemented in MATLAB®/Simulink®. Two competing inverter control schemes are compared, trading off DC bus ripple against AC power quality. It is found that selection of appropriate DC bus capacitance is important in certain scenarios, with potential system cost implications. It is shown that the system can store electrical energy at an efficiency of 64% over a single discharge–charge cycle, i.e., hydrogen to electricity and heat to hydrogen.     

A validated multi‐scale model of a SOFC stack at elevated pressure

This paper presents a multi‐scale model of a solid oxide fuel cell (SOFC) stack consisting of five anode‐supported cells. A two‐dimensional isothermal elementary kinetic model is used to calculate the performance of single cells. Several of these models are thermally coupled to form the stack model. Simulations can be carried out at steady‐state as well as dynamic operation. The model is validated over a wide range of operating conditions including variation of temperature, gas composition (both on anode and cathode side), and pressure. Validation is carried out using polarization curves and impedance spectra. The model is then used to explain the pressure‐induced performance increase measured at constant fuel utilization of 40%. Results show that activation and concentration overpotentials are reduced with increasing pressure.     

Computationally‐Efficient Simulation of Transport Phenomena in Fuel Cell Stacks via Electrical and Thermal Decoupling of the Cells

To overcome the prohibitive computational cost associated with detailed mechanistic models for fuel cell stacks, we derive an efficient computational strategy based on thermal and electrical decoupling of cells. The conditions that allow for decoupling are discussed and verified with a non‐isothermal model considering two‐dimensional conservation of mass, momentum, species, energy, charge, and electrochemistry for a 10‐cell proton exchange membrane fuel cell (PEMFC) stack. The derived strategy allows for simulation of large stacks comprising hundreds of cells at a low computational cost and complexity; e.g., for a PEMFC stack comprising 500 cells, the decoupled algorithm takes less than 30 min to solve and requires only 1 GB of random access memory.     

Modelling and Analysis of Electro‐chemical,Thermal, and Reactant Flow Dynamics for a PEM Fuel Cell System

In this paper an approach for the dynamic modelling of polymer electrolyte membrane fuel cells is presented. A mathematical formulation based on empirical equations is discussed and several features, exhibiting dynamic phenomena, are investigated. A generalized steady state fuel cell model is extended for the development of a method for dynamic electrochemical analysis. Energy balance and reactant flow dynamics are also explained through physical and empirical relationships. A well‐researched system (Ballard MK5‐E stack based PGS‐105B system) is considered in order to understand the operation of a practical fuel cell unit. Matlab‐SIMULINK^TM has been used in simulating the models. The proposed method appears to be relatively simple and consequently requires less computation time. Simulation results are compared with available experimental findings and a good match has been observed.     

Analysis of the Ripple Current in a 5 kW Polymer Electrolyte Membrane Fuel Cell Stack

Polymer electrolyte fuel cell systems are increasingly being used in applications requiring an inverter to convert the direct current (DC) output of the stack to an alternating current (AC). These inverters, and other time‐varying inputs to the stack such as the anode feed pressure, cause deviations from the average stack current, or ripple currents, which are undesirable for reasons of performance and durability. A dynamic fuel cell model has been developed and validated against experimental data for a 5 kW fuel cell stack, examining in detail the ripple current behaviour. It was shown that the ripple currents exceed the 2% maximum recommended value, and may lead to long‐term degradation of the fuel cell stack.     

PEM Fuel Cell Stack Cold Start Thermal Model

For passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick‐starting fuel cell systems are impeded by two problems: (i) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (ii) temperature‐dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub‐freezing startup conditions. Existing models lack the following features: (i) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (ii) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a model considering individual cell layers can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect. This paper presents and discusses results from simulations performed with a new, layered model.     

Portable Size DMFC‐Stack

A small, low temperature, direct methanol fuel cell stack for portable applications has been developed. Several flow field designs were investigated with respect to stable operation and high performance. Due to carbon dioxide and water production on the anode and cathode, respectively, methanol and oxygen access to the electrodes is hindered. During single cell operation the effect of both carbon dioxide evolution and water production on the current output was observed. The difference between parallel and serial feeding of both fuel and oxidant to the DMFC stack was also investigated. It was found that it is very important to remove reaction products from the active cell surface in order to ensure stable stack operation at low temperatures. The maximal power realised with the 12‐cell direct methanol fuel cell stack was 30 W.     

Modeling Flow Distribution for Internally Manifolded Direct Methanol Fuel Cell Stacks

A model is presented for the liquid feed direct methanol fuel cell, which describes the hydraulic behavior of an internally manifolded cell stack. The model is based on the homogeneous two‐phase flow theory and mass conservation equation. The model predicts the pressure drop behavior of an individual fuel cell, and is used to calculate flow distribution through fuel cell stack internal manifolds. The flow distribution of the two‐phase fluids in the anode and the cathode chambers is predicted as a function of cell operating parameters. An iterative numerical scheme is used to solve the differential equations for longitudinal momentum and continuity.     

Development of a Direct Alcohol Alkaline Fuel Cell Stack

Direct alcohol alkaline fuel cells (DAAFC) are one of the potential fuel cell types in the category of low temperature fuel cells, which could become an energy source for portable electronic equipment in future. In the present study, a simple DAAFC stack has been developed and studied to evaluate the maximum performance for a given fuel (methanol or ethanol) and electrolyte (KOH) at various concentrations and temperatures. The open circuit voltage of the stack of four cells was nearly 4.0 V. A particular combination, 2 M fuel (methanol or ethanol) and 3 M KOH, results in maximum power density of the stack. The maximum power density obtained from the DAAFC stack (25 °C) was 50 mW cm^–2 at 20 mA cm^–2 for methanol and 17 mA cm^–2 for ethanol. The stack power density corroborated with that obtained from a single cell, indicating there was no further loss in the stack.     

Stack Modelling of a Molten Carbonate Fuel Cell (MCFC)

A model of a molten carbonate fuel cell (MCFC) stack including internal steam reforming is presented. It comprises a symmetric section of the stack, consisting of one half indirect internal reforming unit (IIR) and four fuel cells. The model describes the gas phase compositions, the gas and solid temperatures and the current density distribution within the highly integrated system. The model assumptions, the differential equations and boundary conditions as well as the coupling equations used in the model are shown. The strategy to solve the system of partial differential equations is outlined. The simulation results show that the fuel cells within the stack operate at different temperatures. This is expected to have an impact on the voltages as well as the degradation rates within the individual fuel cells.