操作条件对PBI/H3PO4体系高温PEMFC的性能影响

全面研究了PBI/H3PO4体系高温质子交换膜燃料电池(PEMFC)的操作性能,研究了温度、压力、阴极气体成分(空气/氧气)对电池稳态操作性能的影响,同时,测试了电池的变压变温和变负载操作曲线,并且运用电化学交流阻抗谱的方法解释了操作条件对电池性能影响的原因,同时应用薄膜旋转圆盘电极技术初步研究了氧还原反应在两种不同的反应界面(Pt/C-PBI/H3PO4和Pt/C-Nafion/H2SO4)的差别。     

ZrO2基固体氧化物燃料电池中电荷输运研究

分析了以甲烷为燃料气体、空气为氧化气体的固体氧化物燃料电池中电子、氧离子在电池的阴极、阳极和电解质中的输运过程以及电子导电型电极有效反应区结构.具体研究了Pt|YSZ|Ag固体氧化物燃料电池(SOFC)的输出功率与电池运行温度的关系并与实验结果进行了对照,探讨了燃料电池中的主要电荷输运过程与电极有效反应区结构的关系以及它们对电池性能的影响因素.研究表明:在固体氧化物燃料电池中,电解质/电极/气体所形成的三相界面的结构、电极本身的导电性能和运行温度都直接影响电池的性能.     

Ni/YSZ阳极材料的制备及性能研究

Ni/YSZ金属陶瓷是固体氧化物燃料电池(SOFC)目前广泛使用的阳极材料。对采用机械混合法制备的Ni/YSZ金属陶瓷的显微结构和电性能进行了研究,试样分别在1300℃、1325℃、1350℃、1375℃和1400℃烧结2h,然后在800℃、H2气氛下还原4h。测试了在不同烧结温度下生成的NiO/YSZ复合材料和Ni/YSZ金属陶瓷的密度,并计算了其相对密度。通过X射线衍射(XRD)法分析了不同试样的相组成。通过扫描电子显微镜(SEM)法和光学显微镜,观察了其微观结构,发现氧化钇稳定的氧化锆(YSZ)形成了连续的网络结构,Ni颗粒均匀地分布在网络结构中,这有助于电导率的提高。用四端子法进行了电导率测试,确定了理想的烧结温度为1400℃。实验结果表明,1400℃烧结试样在800℃、H2气氛下还原4h,气孔率达到25%。在600～800℃之间,其电导率高达103.3S/cm。说明Ni/YSZ金属陶瓷适合作中温固体氧化物燃料电池(IT-SOFC)阳极材料。     

两种不同阴极材料的固体氧化物燃料电池

研制了两种不同阴极材料的固体氧化物燃料电池Pt|YSZ|Ag和LSM |YSZ|Ag ,并测试了电池的开路电压与运行温度的变化关系。由实验可知 ,随着温度的升高电池的开路电压增大 ,它们的变化趋势不仅受温度的影响 ,还与阴极材料的结构、导电性能和反应机制有关。Pt|YSZ|Ag中电池Pt阴极具有电子导电性 ,电化学反应有效区域局限在三相界面 ,但Pt催化活性高 ,Pt|YSZ|Ag具有较好的中温输出性能。LSM |YSZ|Ag电池中LSM阴极具有电子 离子混合导电性 ,其电化学反应有效区域由三相界面扩展到两相界面 ,但在温度较低时LSM催化活性较低 ,在较高温度下才有高催化活性 ,因而LSM |YSZ|Ag在高温下输出性能明显提高     

恒流电泳沉积YSZ电解质薄膜的燃料电池研究

采用恒流电泳沉积(EPD)的方法,在NiO-YSZ阳极基底上制备出较为致密的氧化钇稳定的氧化锆(YSZ)固体电解质薄膜,1300℃共烧结5h后得到具有一定厚度的YSZ薄膜。利用SEM对YSZ薄膜的形貌与膜厚进行了表征。在此基础上,以La0.6Sr0.4Co0.2Fe0.8O3(LSCF)为阴极制成单电池,并对单电池的性能及阻抗谱进行了测试,在650℃时得到单电池的最大开路电压为0.84V,单电池在750℃时的最大电流密度为0.64A/cm2,最大功率密度达145mW/cm2;800℃时的短路电流密度接近0.9A/cm2,最大功率密度达200mW/cm2。阻抗谱测试结果表明,电解质部分的电阻占电池内阻的1/4~1/3;电极在-电解质界面处存在的孔洞对电池的性能产生了不利的影响。     

柠檬酸盐法制备的La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 夹层对阴极性能的影响

考察了在Sm0.5Sr0.5CoO3(SSC)-La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5)/LSGMC5界面中加入柠檬酸盐法合成的LSGMC5夹层对界面的影响。考察了含不同温度焙烧的LSGMC5夹层的SSC-LSGMC5/LSGMC5/LSGMC5组合的微观结构及电化学性能。当夹层焙烧温度高于1 623 K时,夹层与电极的结合优于无夹层的电极/电解质界面,具有大的两相界面面积及三相界面长度。制备的组合的氧还原性能依赖于夹层以及电极的焙烧温度,含有1 673 K烧结夹层、1 123 K焙烧电极的样品具有最高的活性。与含固相法制备的LSGMC5夹层的样品相比,采用含柠檬酸盐法制备的夹层的组合具有更小的欧姆电阻及更高的氧还原活性。     

N,Sn掺杂的TiO_2对Pt/C电催化活性的影响

研究了N及Sn元素掺杂的TiO2(NTT)对Pt/C电催化活性的影响,并在全增湿及低增湿工况下,考察了NTT/Pt/C催化剂所构成的质子交换膜燃料电池(PEMFC)的性能。制备了N及Sn掺杂的TiO2,X射线光电子光谱法(XPS)、透射电子显微镜法(TEM)及X射线衍射光谱法(XRD)表征说明N及Sn元素已经掺入到TiO2中,其颗粒平均粒径为14.3nm,晶形为单一锐钛矿型。以不同比例混入Pt/C催化剂后,对NTT/Pt/C共混催化剂进行了循环伏安扫描和旋转圆盘电极测试,研究了其对Pt/C催化剂电化学活性面积及氧还原半波电位的影响;并在不同增湿条件下,在单电池中对NTT/Pt/C及Pt/C催化剂进行了测试。结果发现NTT不仅可以促进Pt/C催化剂活性,并且具有一定的保水能力,在低增湿工况下可以显著提升PEMFC的性能。     

磷酸浓度与温度对Pt/C催化氧还原反应的影响

采用旋转圆盘电极分析技术分析高温质子交换膜燃料电池中磷酸浓度和温度对Pt/C催化氧还原反应的影响。Pt/C催化氧还原反应的动力学电流密度和扩散极限电流密度随着磷酸浓度的增加逐渐减小,当磷酸浓度增至100%时,电流密度降为0,氧还原催化过程完全被抑制;而磷酸温度的升高则会使电流密度有所增加,但增量很小,不能满足实际应用的需要。磷酸浓度的增加对Pt/C催化氧还原反应具有严重的抑制作用,而温度变化的影响有限。     

甲醇阳极制备工艺

对甲醇阳极的制备工艺进行了研究。通过对甲醇阳极不同的气体扩散层的研究,得出由碳黑和聚四氟乙烯(PTFE)形成的气体扩散层制成的电极电池性能最好,气体扩散层中PTFE的最佳含量为20%。通过甲醇阳极横断面的扫描电镜(SEM)与X射线散射图谱(EDS)分析,探讨了气体扩散层影响电池性能的原因。同时对碳纸支持层的影响也进行了研究。阴极空气近于大气压条件下,阳极Pt含量3.5mg/cm2,阴极Pt含量1.6mg/cm2,1mol/L甲醇浓度,电池温度60℃条件下,电池的开路电压为0.66V,0.4V时电池的电流密度为60mA/cm2,0.2V时电流密度为120mA/cm2。     

球磨方法对氧还原催化剂性能的影响

采用滚动球磨、行星式球磨和摇摆振动球磨等方法,制备了碳载二氧化锰氧还原催化剂,并组装了锌空电池。用扫描电镜(SEM)对催化剂和催化膜形貌进行了表征,以恒流法检测了空气电极的极化行为和锌空电池在室温下的放电性能。采用摇摆振动球磨方法制备的碳载二氧化锰催化剂具有优良的氧还原催化性能,当电位为1.1 V(vs.Zn)时,空气电极电流密度达到226 mA/cm2;终止电压为1.0 V时,锌空电池比能量可达427 Wh/kg。     

Charge storage at the Pt/YSZ interface

The electrochemical behavior of Pt/YSZ electrodes in oxygen containing atmosphere at 450 °C has been investigated by double-step chronoamperometry and programmed linear sweep cyclic voltammetry. The response of the O₂(g),Pt/YSZ system in these experiments could be separated into a time dependent and a steady state contribution, the former being dominated by pseudocapacitive processes. It is proposed that Pt–O type species were stored via different processes at three different locations in the O₂(g),Pt/YSZ system: (1) Build-up of a platinum oxide monolayer at the Pt/YSZ binary interface. (2) Formation of Pt-O species at the triple phase boundary and their spreading-out along the Pt/gas interface. (3) Growth of the platinum oxide layer from the binary Pt/YSZ interface toward the bulk of the platinum electrode.     

Thermodynamic Stability and Interfacial Impedance of Solid-Electrolyte Cells with Noble-Metal Electrodes

In solid-electrolyte cells, the electrode-electrolyte interfacial stability and impedance are found to be dependent on temperature, atmosphere, current density, microstructure and the process history of the cell. The modifications induced by temperature and oxygen pressure on the impedance spectra of Pt/Yttria-stabilized zirconia (YSZ) and Pd/YSZ interfaces have been studied. The interfacial impedance was controlled by adsorption/desorption of oxygen with a Langmuir-type dependency. When the surface coverage was small, the interfacial impedance decreased with increase in temperature and . In certain temperature and regimes and depending on the process history, the metal electrode formed stable oxygen-containing species. In this region, the interfacial impedance increased markedly and its dependence also changed. Anodic and cathodic currents altered the local thermodynamic conditions at the charge-transfer sites and accordingly influenced the interfacial impedance. The concentration of oxygen-containing species and the interfacial microstructure are shown to influence the shape of the impedance response. Pt was found to form a neck at the YSZ electrolyte and Pd did not. The electrode polarization in the case of Pt/YSZ interface corresponded to one impedance-response arc signifying charge-transfer resistance at the three-phase boundary (TPB), gas/Pt/YSZ interface. For the Pd/YSZ interface, the electrode polarization corresponded to two impedance-response arcs at low . The high-frequency response is related to charge transfer at the TPB and the low frequency to the gas-phase mass transfer.     

Electrical characterization of the platinum/YSZ interfaces in SOFCs via micro-contact impedance spectroscopy

The concept of micro-contact in electrodes was incorporated into AC two-probe impedance spectroscopy in order to clarify the electrode-related responses in solid oxide fuel cells (SOFCs). The pointed contact of one electrode was combined with the planar electrode as a counterpart in characterizing an YSZ (yttria-stabilized zirconia)/Pt interface of SOFCs. The micro-contact in electrodes induced the decrease in capacitance and the increase in impedance and amplified the bulk responses in YSZ due to the constricted electroding area. The bulk-related portions can be separated from the interfacial polarization of Pt, even though the electrolyte/electrode interface was found to be very sensitive to the measurement condition, i.e., the oscillating voltage. The resolved bulk and interfacial resistances were analyzed using a concept of “spreading resistance.’’ Furthermore, the electrode-related issues were ramified for the application of impedance spectroscopy to the solid oxide fuel cells.     

CH_4-O_2型管状固体氧化物燃料电池电性能的研究

研制了管状固体氧化物燃料电池(SOFC)试验系统,电池的结构形式分别是:(一)Pt|YSZ|Pt(+)和(-)Pt|YSZ|La(Sr)MnO_3(+)以CH_4为燃料,O_2为氧化剂气体,对所研制的管状SOFC试验电池的电性能进行了研究.考察了500～700℃温度范围内的电流电压特性和电流功率特性.研究结果表明,甲烷无需经水蒸汽转化,直接送入SOFC试验电池系统,就有明显的电流产生,电池的输出电流和输出功率随温度的升高而显著提高.分析了甲烷在SOFC内直接进行电化学反应的机理,固体电解质可作为离子源或离子接受体,形成反应活性位,控制金属电极催化剂的功函,促进甲烷在阳极的氧化反应.     

Bottom electrode structures of Pt/Ru and Ru deposited on polycrystalline silicon by MOCVD for DRAM capacitor

Abstract

The electrode structures of Pt/Ru and Ru on polycrystalline silicon (poly-Si) were prepared by metalorganic chemical vapor deposition (MOCVD) for high dielectric constant (Ba, Sr)TiO₃(BST) capacitor integration. The electrode structures of Pt/Ru/poly-Si annealed above 700°C for 1h in oxygen atmosphere showed a smooth surface ·microstructure without any second phases on the platinum. The specific contact resistance of Pt/Ru and poly-Si in Pt/Ru/poly-Si structures annealed at 800°C was about 1.5 × 10^?5 Ω-cm². The step coverage of Ru film deposited at 150°C was 76% and those of Pt film deposited at 300°C on Ru (deposited at 150°C) was about 61.3%.     

质子交换膜燃料电池Pt/C催化剂的回收再利用

回收质子交换膜燃料电池(PEMFC)失效的Pt/C催化剂,通过高温灼烧得到贵金属Pt渣。Pt渣经适量王水溶解、煮沸、浓缩和再稀释制成H2PtCl6溶液。以H2PtCl6为Pt的前驱体,采用无机胶体法重新制备出PEMFC用Pt/C催化剂。透射电子显微镜测试结果表明,采用优化的工艺条件所制备的Pt/C催化剂平均粒径为2.6nm,且分散性好、粒度均匀。X射线衍射分析表明,催化剂中Pt(111)晶面的相对含量较高,其面间距较小,且催化剂的结晶度略有降低,这些结构特点对催化氧还原反应是有利的。循环伏安法测试表明所制备的Pt/C催化剂对氢和氧电极过程具有良好的电催化性能。     

Difference in microstructure between PZT thin films on Pt/Ti and those on Pt

Abstract

PZT thin films were synthesized by sol-gel on a Pt/Ti double layer bottom electrode or on a Pt single layer bottom electrode to investigate the bottom electrode dependence of PZT film structure. On Pt/Ti, <111> oriented perovskite grains with 50–100 nm lateral size were densely packed. On Pt, large perovskite grains (2?3 μm) were surrounded by fine pyrochlore grains (about 5 nm), and no certain orientation was observed. TEM and EDX analyses suggested that a fraction of Ti in the Pt/Ti layer diffused along Pt grain boundaries up to the Pt surface and was oxidized during the PZT annealing process. A model for the crystallization of sol-gel derived PZT was proposed, in which TiOx particles at the Pt surface act as nucleation sites for PZT crystallization. This model well explained the experimental results.     

Degradation mechanisms of SrBi2Ta2O9 ferroelectric thin film capacitors during forming gas annealing

Abstract

The effects of annealing in forming gas (5% hydrogen, 95% nitrogen; FGA) are studied on spin coated SrBi₂Ta₂O₉ (SBT) thin films. SBT films on platinum bottom electrode are characterized with and without platinum top electrode by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), High Temperature X-Ray Diffraction (HT-XRD) and Secondary Ion Mass Spectrometry (SIMS).

High Temperature X-Ray Diffraction (HT-XRD) of blanket Ti/Pt/SBT films in forming gas revealed that the bismuth layered perovskite structure of the SBT is stable up to approx. 500°C. SIMS analysis of Pt/SBT/Pt samples annealed in deuterated forming gas (5% D₂, 95% N₂) showed that the hydrogen accumulates in the SBT layer and at the platinum interfaces next to the SBT. After FGA of blanket SBT films, tall platinum-bismuth whiskers are seen on the SBT surface.

Performing the FGA of the whole Pt/SBT/Pt/Ti stack, two different results are found. For the samples with a high temperature annealing (HTA) step in oxygen after top electrode patterning, top electrode peeling is observed after FGA. For the samples without a HTA step after top electrode patterning, no peeling is observed after FGA.