Operando Isotopic Exchange in Solid Oxide Fuel Cells: Oxygen-Transport Dependency on Applied Potential

The oxygen isotopic exchange technique is a powerful tool to investigate the oxygen transport kinetics in an oxide solid. In a solid oxide fuel cell, isotopic surface exchange and diffusion coefficients are classically determined by using the Isotopic Exchange Depth Profiling method followed by ex situ SIMS characterizations. Despite its relevance, the utilization of in situ or operando techniques to measure the isotopic exchange under an electrical bias remains marginal. We developed here a set-up which enables operando monitoring of oxygen exchange in SOFC type cells under polarization. The system has been used for studying the oxygen mobility dependency upon polarization on a symmetrical Pt/YSZ/Pt cell (YSZ: yttria-stabilized zirconia). Homomolecular and heterolytic exchange reactions were undertaken to investigate the oxygen activation step and discriminate the limiting step among the sequence of elementary steps which constitute the oxygen transport process in the SOFC system. Oxygen ions incorporation into the dense ionic conductor was identified to be the rate determining step, and its first order rate constant dependency on applied potential was established.     

ReaxFF reactive force field for the Y-doped BaZrO3 proton conductor with applications to diffusion rates for multigranular systems

Proton-conducting perovskites such as Y-doped BaZrO 3 (BYZ) are promising candidates as electrolytes for a proton ceramic fuel cell (PCFC) that might permit much lower temperatures (from 400 to 600 degrees C). However, these materials lead to relatively poor total conductivity ( approximately 10 (-4) S/cm) because of extremely high grain boundary resistance. In order to provide the basis for improving these materials, we developed the ReaxFF reactive force field to enable molecular dynamics (MD) simulations of proton diffusion in the bulk phase and across grain boundaries of BYZ. This allows us to elucidate the atomistic structural details underlying the origin of this poor grain boundary conductivity and how it is related to the orientation of the grains. The parameters in ReaxFF were based entirely on the results of quantum mechanics (QM) calculations for systems related to BYZ. We apply here the ReaxFF to describe the proton diffusion in crystalline BYZ and across grain boundaries in BYZ. The results are in excellent agreement with experiment, validating the use of ReaxFF for studying the transport properties of these membranes. Having atomistic structures for the grain boundaries from simulations that explain the overall effect of the grain boundaries on diffusion opens the door to in silico optimization of these materials. That is, we can now use theory and simulation to examine the effect of alloying on both the interfacial structures and on the overall diffusion. As an example, these calculations suggest that the reduced diffusion of protons across the grain boundary results from the increased average distances between oxygen atoms in the interface, which necessarily leads to larger barriers for proton hopping. Assuming that this is the critical issue in grain boundary diffusion, the performance of BYZ for multigranular systems might be improved using additives that would tend to precipitate to the grain boundary and which would tend to pull the oxygens atoms together. Possibilities might be to use a small amount of larger trivalent ions, such as La or Lu or of tetravalent ions such as Hf or Th. Since ReaxFF can also be used to describe the chemical processes on the anode and cathode and the migration of ions across the electrode-membrane interface, ReaxFF opens the door to the possibility of atomistic first principles predictions on models of a complete fuel cell.     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO–YSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃–YSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-μm-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03 W/cm² at 650, 700, 800, and 850 °C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.

     

真空注浆法制备YSZ电解质膜管及其在固体氧化物燃料电池中的应用

以吡啶为分散剂,采用真空注浆法制备出膜厚为0.2mm、长度为140mm的致密YSZ电解质膜管。研究了烧结温度对样品致密度和离子导电率的影响.用1650℃烧结2h制备的致密YSZ电解质膜管组装成固体氧化物燃料电池,以氢气和煤气为燃料,研究了电池在500～900℃的电化学性能.实验结果表明,用真空注浆法可制备出高质量和高密度的YSZ电解质膜管,在1600℃烧结后,其相对密度已达到理论密度的98.1%,接近理论密度.单电池的开路电压最大值为1.213V,最大输出功率为0.48W.以氢气为燃料的燃料电池性能明显高于以煤气为燃料的电池性能.     

乙醇在Ni-ZnO-ZrO_2-YSZ阳极SOFC上的发电性能

为考察乙醇用于固体氧化物燃料电池的可行性,用柠檬酸溶胶-凝胶制备阳极催化材料Ni-ZnO-ZrO2,利用机械混合法制备Ni-ZnO-ZrO2-YSZ(Y2O3稳定的ZrO2)阳极。用涂覆法,在YSZ电解质上,制备了Ni-ZnO-ZrO2-YSZ/YSZ/LSM(La0.85Sr0.15MnO3)与Ni-YSZ/YSZ/LSM的单体电池。在不同蒸发器操作温度、电池操作温度和乙醇蒸气流量下,以乙醇为燃料进行发电实验,对两种阳极的电池发电性能进行比较。实验结束后,用SEM检测了两种电池阳极的表面。结果表明,Ni-ZnO-ZrO2-YSZ阳极SOFC的电池输出性能明显高于Ni-YSZ阳极,且Ni-ZnO-ZrO2-YSZ阳极具有较好的抗积炭能力。     

Remarkable Enhancement of O2 Activation on Yttrium‐Stabilized Zirconia Surface in a Dual Catalyst Bed

Yttrium‐stabilized zirconia (YSZ) has been extensively studied as an electrolyte material for solid oxide fuel cells (SOFC) but its performance in heterogeneous catalysis is also the object of a growing number of publications. In both applications, oxygen activation on the YSZ surface remains the step that hinders utilization at moderate temperature. It was demonstrated by oxygen isotope exchange that a dual catalyst bed system consisting of two successive LaMnO₃ and YSZ beds without intimate contact drastically enhances oxygen activation on the YSZ surface at 698 K. It can be concluded that LaMnO₃ activates the triplet ground‐state of molecular oxygen into a low‐lying singlet state, thereby facilitating the activation of the O₂ molecule on the YSZ oxygen vacancy sites. This phenomenon is shown to improve the catalytic activity of the LaMnO₃‐Pd/YSZ system for the partial oxidation of methane.     

Theoretical Aspects on Doped-Zirconia for Solid Oxide Fuel Cells: from Structure to Conductivity

Solid oxide fuel cells (SOFCs) are regarded to be a key clean energy system to convert chemical energy (e.g. H₂ and O₂) into electrical energy with high efficiency, low carbon footprint, and fuel flexibility. The electrolyte, typically doped zirconia, is the "state of the heart" of the fuel cell technologies, determining the performance and the operating temperature of the overall cells. Yttria stabilized zirconia (YSZ) have been widely used in SOFC due to its excellent oxide ion conductivity at high temperature. The composition and temperature dependence of the conductivity has been hotly studied in experiment and, more recently, by theoretical simulations. The characterization of the atomic structure for the mixed oxide system with different compositions is the key for elucidating the conductivity behavior, which, however, is of great challenge to both experiment and theory. This review presents recent theoretical progress on the structure and conductivity of YSZ electrolyte. We compare different theoretical methods and their results, outlining the merits and deficiencies of the methods. We highlight the recent results achieved by using stochastic surface walking global optimization with global neural network potential (SSW-NN) method, which appear to agree with available experimental data. The advent of machine-learning atomic simulation provides an affordable, efficient and accurate way to understand the complex material phenomena as encountered in solid electrolyte. The future research directions for design better electrolytes are also discussed.     

Influence of cathode functional layer composition on electrochemical performance of solid oxide fuel cells

Journal of Solid State Electrochemistry - In this work, anode-supported solid oxide fuel cells (SOFC) were tested with a yttria-stabilized zirconia (YSZ) (8 mol%...     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO?CYSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃?CYSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-??m-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03?W/cm² at 650, 700, 800, and 850?°C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.     

Estimation of oxygen ionic conductivity in nickel-zirconia composite by oxygen permeation method

The oxygen transport in the nickel-zirconia composite was investigated using the oxygen permeation method. A disk-shaped sample made of nickel (40 vol%) and yttria-stabilized zirconia (YSZ) was used to construct a permeation cell. By exposing one side of the sample to a CO₂ gas stream and the other side to a CO stream at elevated temperatures, oxide ions were extracted from CO₂ and transported to the other side to oxidize CO. The oxygen permeation flux through the composite was determined by analyzing the effluent from the permeation cell, and the oxygen ionic conductivity of the composite was derived from the permeation data and the oxygen partial pressures. It was shown that the oxygen ionic conductivity of the composite YSZ fraction was about one third of that for the single-phase zirconia ceramic, and the activation energy associated with the transport of oxide ions in the composite is somewhat greater than that of the single-phase zirconia.     

以活性炭为燃料的固体氧化物燃料电池(英文)

采用注浆成型法制备了管状电解质支撑的固体氧化物燃料电池(SOFC),电解质材料为YSZ,阳极和阴极材料都采用银.将活性炭不加任何气体直接用作电池的燃料.电池的有效面积为2.5cm2,在800℃时给出最大功率为16mW,其开路电压随温度的变化与理论结果一致.此电池在30mA的恒电流下连续稳定运行了37h,通过电化学反应消耗了加入电池中碳燃料的42%(w),证明了电池的工作是可以自维持的.与使用石墨燃料的SOFC相比,此电池的运行稳定性得到了明显的提高,因为活性炭比石墨具有大得多的微孔率和表面积.电池运行37h后很快衰减,燃料烧结和燃料量减少造成碳表面积减小可能是衰减的主要原因.电化学阻抗谱测试结果表明电池的极化电阻在电池的总损耗中占主导.通过对电池反应机理进行分析,认为发生在阳极/电解质界面的CO电化学氧化反应和发生在碳燃料表面的Boudouard反应构成的循环维持了电池的运行,因此通过添加促进上述两个反应的催化剂,可提高电池的性能.     

固体氧化物燃料电池——材料与前瞻(英文)

本文依据固体氧化物燃料电池(SOFC)于运作条件下的基本性能,诸如化学稳定性、电迁移、催化和热机械性能等评述SOFC组成部分(电极材料和电解质)的基本性质.示明由氧偏离化学计量比引起的电极材料结构缺陷与其电子性质及催化活性之间的相互关系,提出单室燃料电池概念.     

Development of solid–oxide fuel cell for reduced operating temperatures

A technique for formation of electrolyte thin films with the thickness of 6–10 μm of zirconia stabilized by yttria (YSZ) is developed on the basis of the method of chemical deposition from the vapor phase of organometallic compounds (MOCVD). Planar electrochemical cells based on film electrolyte with a supporting anode with the working surface area of 12 cm² were manufactured. A solid-oxide fuel cell (SOFC) based on two fuel cells was developed and its life cycle tests at reduced operating temperatures (<800°C) were carried out for 400 h. The maximum power density reached in the SOFC tests was 316 mW/cm².     

Interface proximity effects on ionic conductivity in nanoscale oxide-ion conducting yttria stabilized zirconia: an atomistic simulation study

We present an atomistic simulation study on the size dependence of dopant distribution and the influence of nanoscale film thickness on carrier transport properties of the model oxide-ion conductor yttria stabilized zirconia (YSZ). Simulated amorphization and recrystallization approach was utilized to generate YSZ films with varying thicknesses (3-9 nm) on insulating MgO substrates. The atomic trajectories generated in the molecular dynamics simulations are used to study the structural evolution of the YSZ thin films and correlate the resulting microstructure with ionic transport properties at the nanoscale. The interfacial conductivity increases by 2 orders of magnitude as the YSZ film size decreases from 9 to 3 nm owing to a decrease in activation energy barrier from 0.54 to 0.35 eV in the 1200-2000 K temperature range. Analysis of dopant distribution indicates surface enrichment, the extent of which depends on the film thickness. The mechanisms of oxygen conductivity for the various film thicknesses at the nanoscale are discussed in detail and comparisons with experimental and other modeling studies are presented where possible. The study offers insights into mesoscopic ion conduction mechanisms in low-dimensional solid oxide electrolytes.     

YSZ传导膜H_2S固体氧化物燃料电池

研究了Y2O3稳定的ZrO2(YSZ)氧离子传导膜H2S固体氧化物燃料电池性能。掺杂NiS、电解质、Ag粉和淀粉制备了双金属复合MoS2阳极催化剂,掺杂电解质、Ag粉和淀粉制备了复合NiO阴极催化剂,用扫描电镜对YSZ和膜电极组装(MEA)进行了表征,比较了不同电极催化剂的性能和极化过程,考察了不同温度对电池性能的影响。结果表明,双金属复合MoS2/NiS阳极催化剂在H2S环境下比Pt和单金属MoS2催化剂稳定,复合NiO阴极催化剂比Pt性能好,在电极催化剂中加入Ag可显著提高电极的导电性;与Pt电极相比,复合MoS2阳极和复合NiO阴极催化剂的过电位较小,阳极的极化比阴极侧小;温度升高,电池的电流密度与功率密度增加,电化学性能变好。在750℃、800℃、850℃和900℃及101.13 kPa时,结构为H2S、(复合MoS2阳极催化剂)/YSZ氧离子传导膜/(复合NiO阴极催化剂)、空气的燃料电池最大功率密度分别为30 mW/cm2、70 mW/cm2、155 mW/cm2及295 mW/cm2、最大电流密度分别为120 mA/cm2、240 mA/cm2、560 mA/cm2和890 mA/cm2。     

A novel multistep dip-coating method for the fabrication of anode-supported microtubular solid oxide fuel cells

A novel multistep dip-coating method was developed and successfully applied to the fabrication of anode-supported microtubular solid oxide fuel cells (SOFCs) using carbon rods as combustible cores. The fabricated microtubular SOFCs consisted of Ni-yttria-stabilized zirconia (YSZ), YSZ, strontium-doped lanthanum manganite (LSM)–YSZ, and LSM as the anode, electrolyte, cathode, and cathode current collector materials, respectively. To investigate the role of anode porosity on cell performance, two types of anode supports were prepared: one without a pore former and the other with a 10 wt.% graphite pore former. The microstructural features of the microtubular SOFCs were examined using scanning electron microscope images whereas the electrochemical performance was characterized by electrochemical impedance spectroscopy measurements as well as I–V characteristic curves. The results showed that the method used is a simple and low-cost alternative to conventional methods for the fabrication of microtubular SOFCs. We found that the anode porosity played an important role in improving the overall performance of the microtubular SOFC by reducing the concentration polarization.     

一种高活性 Ni掺杂 La0.6Sr0.4FeO3-δ作为碳基燃料固体氧化物燃料电池对称电极

固体氧化物燃料电池(SOFCs)是一种在中高温下可以直接将储存在燃料中的化学能转换成电能的全固态电化学反应装置.因其具有能量转换效率高、环境友好、全固态结构以及可以使用碳氢化合物燃料等优点,近年来受到了广泛的关注.在诸多电极材料当中, Ni基金属陶瓷是 SOFCs中最常使用的阳极材料,这是由于金属 Ni具有优良的电子电导和催化性能.然而当使用碳基化合物燃料时,传统的 Ni金属陶瓷阳极材料面临严重的积碳、Ni颗粒长大以及硫中毒等问题.这些问题不仅会影响 SOFCs的寿命,而且还会严重地降低 SOFC的商业化进程.因此,开发具有高催化活性、抗积碳的阳极材料对碳氢化合物为燃料的固体氧化物燃料电池的发展至关重要.与金属基阳极相比,氧化物阳极的热膨胀系数与电解质材料更匹配,性能的可调控性更强.铁酸锶镧(LSF)是一种分子式为 ABO3的钙钛矿结构的氧化物,在高温下具有较高的电子电导率.据报道 LSF作为阴极材料时,表现出了良好的性能.但是 LSF作为阳极材料时,却存在着催化性能不足的问题.我们研究了 Ni掺杂的 La0.6Sr0.4FeO3-δ(LSFN),以提高其作为 SOFCs阳极材料的催化性能.同时采用将 LSFN在 SOFC工作气氛下原位还原的方法,在 LSFN颗粒表面原位生长出分布均匀的纳米颗粒.透射电镜分析结果表明该偏析的颗粒为 Ni-Fe合金.有报道显示, Ni-Fe合金对碳氢化合物氧化具有良好的催化活性,所以在 LSFN颗粒表面生成这种合金颗粒有利于提高阳极材料的催化活性.对于 Ni-Fe合金以均匀的纳米颗粒析出的原因,还有待进一步研究.为了研究 LSFN作为 SOFC电极材料的性能,我们采用浸渍法将 LSFN前驱体溶液浸渍到氧化钇稳定氧化锆(YSZ)一体化电池的对称多孔骨架中,经过焙烧,得到了具有对称结构的 SOFC单电池.所使用的 YSZ一体化骨架为中间层薄而致密,两边厚而多孔的三层结构,这种结构可以显著地降低电解质的厚度,从而达到降低单电池的阻抗的目的.这一新型对称电池结构具有如下优点：阳极表面上可能发生的硫毒化和积碳问题有可能通过将阳极和阴极反用而消除;氧化剂(空气)将冲走吸附在电极上的硫和碳粒子,从而使电极得以再生.此外,氧化还原稳定的阴极预期将提高阴极的寿命.对单电池的电化学测试结果表明, LSFN电极材料的最佳浸渍量为30 wt%,这是因为较低的 LSFN浸渍量(<30 wt%),不能形成连续的电子传导网络,电极的电子传导能力不足;而 LSFN电极材料的浸渍量高于30 wt%时则会降低电极反应的三相界面,从而影响电池的性能.在750oC下, LSFN为电极的单电池在以湿润 C3H8为燃料时其开路电压(OCV)达到了约1.18 V,高于以 H2为燃料电池的电压.以 CH4为燃料时, LSFN为电极的单电池的开路电压远高于 LSF为电极的单电池.在750oC下,以 C3H8为燃料时, LSFN和 LSF为电极的电池的峰值输出功率密度分别达到400和230 mW/cm2.这些结果表明,通过 Ni掺杂和原位焙烧,在 LSFN电极颗粒表面制备了均匀分布的 Ni-Fe合金纳米颗粒,极大地提高了铁酸锶镧材料对碳基燃料的催化活性.长期放电测试结果表明, LSF为电极的单电池在测试过程中,尾气可以收集到类似焦油状的黑色物质;而 LSNF为电极的单电池在测试过程中并没有观察到明显的焦油状物质生成.通过气相色谱-质谱联用分析,发现所产生的焦油状物质主要成分是含苯环、碳碳双建或碳碳三键的烃类.这说明 LSF电极只能使 C3H8部分氧化, LSFN对 C3H8等碳氢化合物燃料的氧化具有高的催化活性和良好的耐久性. Ni掺杂的 La0.6Sr0.4FeO3-δ阳极材料是一种有希望的碳基燃料 SOFCs对称电极.     

NiO-YSZ-石墨水系浆料的研制及其在注浆成型制备固体氧化物燃料电池中的应用

Ni-YSZ(钇稳定氧化锆)金属陶瓷普遍被用作固体氧化物燃料电池(SOFC)的阳极材料,其氧化物浆料的性质对湿法制备的SOFC的性能具有重要影响. 通过zeta 电位分析,研究了NiO-YSZ双分散相水系浆料的稳定性. 对六种分散剂作用于NiO、YSZ 表面的zeta 电位进行研究,发现采用的阴离子分散剂和两性分散剂使NiO 和YSZ在水中带有相反电荷而引起迅速絮凝; 采用阳离子分散剂聚二烯二甲基氯化铵(PDAC)时,NiO 和YSZ因带有正电荷相互排斥而稳定分散于水中,在此基础上,加入作为SOFC阳极造孔剂的石墨,采用聚乙烯吡咯烷酮(PVP)作为石墨的分散剂,制备出了NiO-YSZ-石墨的稳定水系浆料. 采用此浆料通过注浆成型制得阳极支撑管,进而组装成SOFC单电池. 该单电池在800℃时最大功率密度达到509 mW·cm^-2; 扫描电镜(SEM)分析表明电极与电解质间接触良好,阳极孔洞分布均匀.     

Comparison of characteristics of solid oxide fuel cells with YSZ and CGO film solid electrolytes formed using magnetron sputtering technique

The work describes the methods of manufacturing single cells of solid oxide fuel cell (SOFC) with thin–film YSZ and CGO electrolytes and also with the bilayer YSZ/CGO electrolyte. Formation of YSZ and CGO films on the supporting NiO–YSZ anode of SOFC was carried out using the combined electron–ionic–plasma deposition technique. The microstructure and phase composition of the formed coatings are studied and also comparative analysis of electrochemical characteristics of single fuel cells with different electrolytes is performed. It is shown that the maximum power density of 1.35 W/cm² at the temperature of 800°C is obtained for the cell with bilayer YSZ/CGO electrolyte. However, the highest performance at lower working temperatures (650–700°C) is characteristic for the fuel cell with single–layer CGO electrolyte; its power density is 600–650 mW/cm².     

固体氧化物燃料电池最新发展动态——第五届固体氧化物燃料电池国际会议内容介绍

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