甲烷在SOFC阳极中反应的条件和规律

以8%mol Y2O3稳定的ZrO2(8YSZ)为电解质、Ni-8YSZ为阳极,研究了不同电流密度、甲烷浓度和反应温度下,甲烷在固体氧化物燃料电池(SOFC)中由部分氧化到完全氧化转变的规律。在1 000℃下、甲烷浓度为4.2%时,由部分氧化转变为完全氧化的临界电流密度为0.384~0.512 A/cm2,该值与甲烷浓度及温度成正比。     

Degradation mechanism of Ni-based anode in low concentrations of dry methane

Degradation mechanism of Ni_0.5Cu_0.5-Gd_0.2Ce_0.8O_1.9 (CGO) bimetallic anode in low concentrations of dry methane is studied with a (La_0.75Sr_0.25)_0.95MnO_3−δ-CGO cathode supported SOFC. Leakage tests suggested that as-prepared cells are well-sealed by glass ring at elevated temperatures. OCV of as-prepared cell in each concentration of CH₄ is over 1.2 V, indicating that the ScSZ electrolyte film prepared by a dual drying pressing method is dense enough. It is found that rapid degradation phenomenon easily occurred at relatively high current density in 7.4 and 14.8% of dry methane in the performance test. XRD and EIS analyses indicated that the degradation of the Ni_0.5Cu_0.5-CGO anode at high current density could be mainly attributed to the re-oxidation of Ni. GC results showed that the re-oxidation of Ni always occurred at a relatively high p(H₂O), which always appeared at a relatively high current density. The degraded cell is successfully recovered by burning the anode with O₂ and re-reducing with H₂.     

太阳能喷射式制冷系统性能分析

叙述了太阳能增压喷射式制冷的原理和系统工作过程. 探讨了太阳能喷射式制冷系统研究的进展状况.通过计算研究了多种制冷剂对喷射器工作性能和系统制冷系数的影响.应用数学模拟的方法,分析了太阳能增压喷射式制冷系统在实际日照条件下的工作性能.结果表明,这种系统能够利用太阳能提供实际需要的制冷量.     

A mathematical model of a tubular solid oxide fuel cell with specified combustion zone

A numerical model has been developed to simulate the effect of combustion zone geometry on the steady state and transient performance of a tubular solid oxide fuel cell (SOFC). The model consists of an electrochemical submodel and a thermal submodel. In the electrochemical model, a network circuit of a tubular SOFC was adopted to model the dynamics of Nernst potential, ohmic polarization, activation polarization, and concentration polarization. The thermal submodel simulated heat transfers by conduction, convention, and radiation between the cell and the air feed tube. The developed model was applied to simulate the performance of a tubular solid oxide fuel cell at various operating parameters, including distributions of circuits, temperature, and gas concentrations inside the fuel cell. The simulations predicted that increasing the length of the combustion zone would lead to an increase of the overall cell tube temperature and a shorter response time for transient performance. Enlarging the combustion zone, however, makes only a negligible contribution to electricity output properties, such as output voltage and power. These numerical results show that the developed model can reasonably simulate the performance properties of a tubular SOFC and is applicable to cell stack design.     

Rapid degradation mechanism of Ni-CGO anode in low concentrations of H2 at a high current density

Cathode-supported solid oxide fuel cell (SOFC) consisting of a Ni-Gd_0.2Ce_0.8O_1.9 (Ni-CGO) anode with a Sc₂O₃-doped ZrO₂ (ScSZ) electrolyte on a (La_0.75Sr_0.25)_0.95MnO_3−δ (LSM)+CGO cathode substrate was fabricated via a dual drying pressing followed by co-firing method. Open circuit voltage (OCV) of as-prepared cell in pure H₂ reached 1.238 at 800 °C, indicating that the ScSZ electrolyte film prepared by the present method was dense enough and the cell was in a well-sealed state. Performance degradation phenomenon of Ni-CGO anode in low concentration of H₂ was investigated by gradual loading of the system current. Re-oxidation of Ni, which was not caused by O₂ in the case of mechanical damage, was supposed to occur at a high current density. According to the EIS and SEM analysis results, it is inferred that the Ni could be oxidized by the oxygen ion at a high current density in low concentration of H₂ as well as by the produced H₂O with a high p(H₂O)/p(H₂) ratio. In this case, the performance of the degraded cell was unable to be directly regenerated by hydrogen reduction unless the anode was firstly burnt in O₂ before reduced in H₂. It is possible that H₂O molecules covered on the NiO due to oxidation of Ni by H₂O, which hindered NiO to be reduced by H₂, could be moved out by O₂ burning.     

以干甲烷为燃料的SOFC阳极反应及材料的研究进展

描述了在固体氧化物燃料电池 (SOFC) 阳极上可能发生的化学反应及电化学反应,以及以干甲烷为燃料气时阳极上的反应机制.介绍了目前主要的 SOFC 阳极材料,即Ni基材料、Cu基材料及CeO2基氧化物的特点及研究进展.     

A droplet size dependent multiphase mixture model for two phase flow in PEMFCs

A droplet size dependent multiphase mixture model is developed in this paper, and the droplet size in the gas channel can be considered as a parameter in this multiphase mixture model, which includes the effect of gas diffusion layer (GDL) properties and the gas drag function and cannot be considered in the commonly used multiphase mixture model in the references. The three-dimensional two phase and non-isothermal simulation of the PEMFCs with a straight flow field is performed. The effect of droplet size on the liquid remove, the effect of liquid water on the heat transfer and the effect of gas flow pattern on the heat and mass transfer are mainly investigated. The simulation results show that the large droplet is hard to be dragged by the gas, so it produces large water saturation. The results of the heat transfer show that the liquid water hinders the heat transfer in the GDL and catalyst layer, so it produces the large relative high temperature area, and there are large temperature difference and water saturation in the PEMFCs operated with coflow pattern compared with counter flow pattern.     

质子交换膜燃料电池内部传热传质三维模拟

针对常规流场质子交换膜燃料电池提出了三维非等温数学模型。模型考虑了电化学反应动力学以及反应气体在流道和多孔介质内的流动和传递过程,详细研究了水在质子膜内的电渗和扩散作用。计算结果表明,反应气体传质的限制和质子膜内的水含量直接决定了电极局部电流密度的分布和电池输出性能;在电流密度大于0.3~0.4A/cm2时开始出现水从阳极到阴极侧的净迁移;高电流密度时膜厚度方向存在很大的温度梯度,这对膜内传递过程有较大影响。     

DQC—I智能流速仪电源的改进

DQC-I智能流速仪是便携式仪器中的一种,它具有便携式仪器的特点。要求电源必须是体积小巧,并具有相当容量的直流电源,由于受巡回检测环境条件的限制,只能选用电池供电,因此,尽量降低仪器的功耗,延长电池使用寿命成了仪器研制中的首要问题。为了解决这一问题最终选择MAX757电源转换芯片,实验数据表明使用MAX757进行电源转换效果很好,达到了预期目的。