Micro-solid oxide fuel cells: status, challenges, and chances

Abstract  

Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode (i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics.     

LSM-infiltrated LSCF cathodes for solid oxide fuel cells

Mixed ionic-electronic conductors in the family of La_xSr_1–xCo_yFe_1–yO_3–δ have been widely studied as cathode materials for solid oxide fuel cells (SOFCs). However, the long-term stability was a concern. Here we report our findings on the effect of a thin film coating of La_0.85Sr_0.15MnO_3–δ (LSM) on the performance of a porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) cathode. When the thicknesses of the LSM coatings are appropriate, an LSM-coated LSCF electrode showed better stability and lower polarization (or higher activity) than the blank LSCF cathode without LSM infiltration. An anode-supported cell with an LSM-infiltrated LSCF cathode demonstrated at 825 °C a peak power density of ～1.07 W/cm², about 24% higher than that of the same cell without LSM infiltration (～0.86 W/cm²). Further, the LSM coating enhanced the stability of the electrode; there was little degradation in performance for the cell with an LSM-infiltrated LSCF cathode during 100 h operation.     

X-ray absorption spectroscopic studies on solid oxide fuel cells and proton-conducting ceramic fuel cells

X-ray absorption spectroscopy (XAS) is one of the best techniques to obtain the information on the electronic and local structures of materials. In the last few decades, XAS becomes a common analytical technique for the investigation of solid oxide fuel cells and proton-conducting ceramic fuel cells. In particular, operando and/or advanced XAS measurements can be recently available with the increased accessibility of synchrotron radiation. In this article, recent trends of solid oxide fuel cell and proton-conducting ceramic fuel cell researches using XAS are overviewed.     

Calcium-containing cathodic material for solid oxide fuel cells

Using the citrate sol-gel method, a new complex oxide Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 is synthesized. It is shown that this compound is crystallized in the rhombically distorted version of perovskite structure (a = 0.53397(8), b = 0.7470(1), c = 0.52810(6) nm). The phase is characterized by a low coefficient of thermal expansion (CTE) (13.8 ppm K^?1) and high electric conductivity (135 S/cm at 900°C). The chemical reaction between Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 and the YSZ and GDC electrolyte materials is studied. The material is highly reactive and reacts with YSZ and GDC at 900°C and 1070°C, respectively. It is concluded that Ca_0.75Y_0.25Co_0.15Mn_0.85O_2.92 is a promising cathodic material for solid oxide fuel cells, provided a reliable protection SDC sublayer is formed between the cathode and the YSZ membrane.     

Cathode performance and oxygen-ion transport mechanism of copper oxide for solid-oxide fuel cells

Various copper oxide cathode materials were studied over a YSZ tube at 800 °C and an oxygen partial pressure of 0.21 atm. It was found that the cathode performance of CuO may be improved by doping Ag metal into it. However, an optimal doping content exists and is around 50 mol% Ag. It was also found that copper oxide itself possess enough oxygen vacancies needed for the role of a mixed conductor. The activation energy for the lattice-oxygen reduction and migration has been calculated to be 55.4 kJ/mol. By the use of electrochemical measurements over Ag-YSZ/CuO electrodes, models for the two-layer electrode have been proposed and justified for oxygen-ion transport mechanisms at low and high overpotentials, respectively; thus, the roles of CuO on the cathode behavior of the electron and oxygen-ion conductivities were well identified. Electronic Publication     

Silver incorporation into cathodes for solid oxide fuel cells operating at intermediate temperature

Silver (Ag) at 0.1–2.0 wt% was incorporated into cathodes for solid oxide fuel cells as a catalyst for oxygen reduction. A novel processing route for Ag incorporation ensuring a very homogeneous Ag ion distribution is presented. From the results of X-ray powder diffraction it can be concluded that the La_0.65Sr_0.3MnO_3– perovskite phase is already formed at 900 °C. The solubility of Ag in the crystal lattice in this type of perovskite was below 1 wt%. The electrochemical tests of these materials show that there is only a slight catalytic effect of Ag. Scanning electron microscopy reveals a low mechanical contact of the cathode grains to the electrolyte due to the low cathode sintering temperature that was chosen.     

Low-temperature direct ammonia fuel cells: Recent developments and remaining challenges

Low-temperature direct ammonia fuel cells (DAFCs) are fueled directly by ammonia, a carbon-neutral fuel stored in the liquid state under low pressure. Liquid ammonia has advantages over compressed hydrogen gas, including higher energy density and facilitated distribution and refill. The beginning-of-life performance reported until recently for low-temperature DAFCs has been substantially lower than that of polymer electrolyte fuel cells fueled by hydrogen. We discuss here promising recent advances in electrocatalyst development, cell performance, and cell performance stability for low-temperature DAFCs, including beginning-of-life peak power density of 420 mW/cm², and operation over several days at constant current. In addition, we describe technology gaps that must be closed for low-temperature DAFCs to achieve the performance required for practical applications.     

Effect of pretreatments on the anode structure of solid oxide fuel cells

An important objective in the development of solid oxide fuel cell (SOFC) is to produce thin stabilized zirconia electrolytes that are supported upon the nickel–zirconia composite anode. Although this will reduce some of the problems associated with SOFCs by permitting lower temperature operation, this design may encounter problems during start- up. The first step in a start-up involves the reduction of nickel oxide in the anode to metallic nickel and increase of three-phase boundary will be beneficial for further reaction. In this study, two pretreatment methods are investigated for their effects on the performances of SOFC. Performances of the SOFCs are influenced by the pretreatment conditions, which included exposure of the cells to dilute H₂/O₂ either under open-circuit or closed-circuit conditions before their performance studies. By carrying out the methods, the pretreatment using the closed circuit is found to attain much higher performances effectively and efficiently. Accompanying with SEM and element analysis, increase of three-phase boundary is considered to give rise to changes in the anode microstructure, leading to activation of the anode. Mechanisms of NiO in anode reducing to Ni and porous structure via different pretreatments and their effects on the anode microstructure are proposed.     

A 3D fibrous cathode with high interconnectivity for solid oxide fuel cells

A three-dimensional (3D) fibrous cathode of solid oxide fuel cell was fabricated by using eggshell membranes (ESMs) as the template. This cathode possesses high porosity and interconnectivity, and low polarization resistance. A single fuel cell with the 3D fibrous Sm_0.5Sr_0.5CoO₃/Ce_0.8Sm_0.2O_1.9 cathode shows significantly improved performances at low operating temperatures (500–600 °C) as compared with the cell prepared with the ESM-templated cluster cathode in our previous study.     

Preparation of electrolyte membranes for micro tubular solid oxide fuel cells

Yttria-stabilized zirconia (YSZ) micro tubular electrolyte membranes for solid oxide fuel cells (SOFCs) were prepared via the combined wet phase inversion and sintering technique. The as-derived YSZ mi- cro tubes consist of a thin dense skin layer and a thick porous layer that can serve as the electrode of fuel cells. The dense and the porous electrolyte layers have the thickness of 3-5 μm and 70-90 μm, respectively, while the inner surface porosity of the porous layer is higher than 28.1%. The two layers are perfectly integrated together to preclude the crack or flake of electrolyte film from the electrode. The presented method possesses distinct advantages such as technological simplicity, low cost and high reliability, and thus provides a new route for the preparation of micro tubular SOFCs.     

通过溅射与退火制备的用于固体氧化物燃料电池的氧化钆掺杂氧化铈电解质隔层

采用溅射或溅射与退火相结合的方法制备了一系列氧化钆掺杂的氧化铈（GDC）隔层,并考察了其对固体氧化燃料电池性能的影响. 结果表明,200 ℃下溅射获得了立方结构氧化钆掺杂的氧化铈均匀薄膜,在900-1100 ℃范围内的退火处理使得GDC薄膜致密,从而有效阻止了氧化钇掺杂的氧化锆电解质与阴极材料之间的反应,大幅度提高了电池的电化学性能.     

Lanthanum-strontium cuprate: A promising cathodic material for solid oxide fuel cells

Samples of lanthanum-strontium cuprate LaSrCuO_3.61 are synthesized by a solid-phase method at 1473 K, in air. Electron diffraction patterns reveal low-intensity satellites whose position is described in the reciprocal space by the (3 + 2)-dimensional space group I4/mmm(αα0, α-α0)00mg. Using a five-layer cell LaSrCuO_4-δ|YSZ|LaSrCuO_4-δ|YSZ|LaCuO_4-δ prepared by isostatic hot pressing, the ionic component of conductivity of LaSrCuO_4-δ is determined (σ_{1179 K} = 3.8 × 10^?3 S cm^?1), which is commensurate with other mixed conductors based on complex oxides of cobalt and iron.     

不同含钴阴极在YSZ薄膜电解质固体氧化物燃料电池中的性能

固体氧化物燃料电池阴极材料的阻抗对固体氧化物燃料电池的性能有较大影响.我们通过XRD、对称电池以及单电池性能测试等方法比较系统地研究了4种最为常用的含钴阴极材料直接用于钇稳定化氧化锆（YSZ）电解质薄膜与通过引入SDC夹层后用于YSZ电解质薄膜后的性能.我们发现,不同的含钴阴极材料与YSZ材料之间都不同程度地发生相反应,在应用于YSZ电解质薄膜上时,相反应大大降低了含钴阴极材料的性能,在使用了SDC夹层后,单电池的功率输出显著提高.     

硬模板法制备固体氧化物燃料电池Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x包覆管状SDC立体阳极

为在固体氧化物燃料电池中有效利用干甲烷为燃料,需制作多孔立体阳极。采用硬模板法和浸渍法制备Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x包覆管状SDC阳极材料(Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC),为作对比,用溶胶凝胶法制备粉末状Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x,机械混合SDC粉末制备Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC。将这两种阳极材料分别制作电解质支撑的单电池Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC|YSZ|LSMYSZ与Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC|YSZ|LSM-YSZ,并进行发电性能测试以及长期稳定性实验。结果表明,800℃下,干甲烷环境中,Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC为阳极的单电池最大功率密度为324.99 m W/cm2,运行10 h后,电压下降5.60%;而以Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC为阳极的单电池最大功率密度达到384.54 m W/cm2,运行100 h后,电压未严重衰减。实验后阳极的SEM照片表明,Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x-SDC阳极内孔隙狭小,易被积炭堵塞;而Ni_(0.5)Cu_(0.5)Ba_(0.05)O_x/SDC阳极呈立体多孔结构,有利于燃料气体与反应后气体的扩散。催化剂颗粒均匀地包覆在SDC纤维管表面,有利于增加三相界面,提高电池的稳定性。     

车用燃料电池现状与电催化

本文综述了近年来车用燃料电池电催化的发展状况,分析了车用燃料电池电催化的发展趋势,重点介绍了大连化学物理研究所在燃料电池电催化方面的研究进展．指出车用燃料电池电催化的发展方向是提高现有铂基催化剂的活性,在保证车用燃料电池在变载等动态工况下的可靠性与寿命的前提下,应降低膜电极的贵金属铂用量,发展低铂／非铂电催化剂．针对车用燃料电池的使用条件,应发展抗燃料气与空气中杂质的电催化方法与抗腐蚀催化剂载体．从长远考虑,重点发展碱性聚合物膜燃料电池,拓展利于活化顺磁性氧的催化方法,有望摆脱车用燃料电池对铂催化剂的依赖．     

Alkaline polymer electrolyte fuel cells: Principle, challenges, and recent progress

Polymer electrolyte membrane fuel cells (PEMFC) have been recognized as a significant power source in future energy systems based on hydrogen. The current PEMFC technology features the employment of acidic polymer electrolytes which, albeit superior to electrolyte solutions, have intrinsically limited the catalysts to noble metals, fundamentally preventing PEMFC from widespread deployment. An effective solution to this problem is to develop fuel cells based on alkaline polymer electrolytes (APEFC), which no...     

基于高度非对称结构电解质中空纤维的微管式固体氧化物燃料电池制备

提出了一种简单而方便的微管式固体氧化物燃料电池(MT-SOFCs)的制备新方法.首先应用改进相转化-烧结技术制备由致密电解质表皮薄层和多孔支撑层构成的高度非对称结构电解质中空纤维膜(微管),在电解质中空纤维膜的多孔支撑层内通过化学镀法沉积Ni催化剂作为电池阳极,而致密电解质表皮层直接作为电解质膜,在电解质微管外表面用浆料涂层法制备电池的多孔阴极,烧结后即得到完整的MT-SOFC.应用该方法制备了Ni-YSZ|YSZ|LSCF微管式电池,该电池以H2/空气作原料气,在800℃时最大输出功率达到159.6mWcm-2.     

Preparation of microtubular solid oxide fuel cells based on highly asymmetric structured electrolyte hollow fibers

A simple and cost-effective method has been developed for the fabrication of microtubular solid oxide fuel cells (MT-SOFCs). Highly asymmetric electrolyte hollow fibers composed of a thin dense skin layer and a thick porous substrate are first prepared by a modified phase inversion/sintering technique. The porous substrate is then formed into the anode by deposition of a Ni catalyst via an electroless plating method inside the pores while the thin dense skin layer serves directly as the electrolyte film of ...     

LaNi0.6Fe0.4O3 as a cathode contact material for solid oxide fuel cells

In solid oxide fuel cells (SOFCs) the interconnects electrically link air and fuel electrodes on either side to produce a practical electrical power output. The long-term stability of intermediate temperature (650–800 °C) SOFC operation strongly depends on the composition of the ferritic steel interconnection material and the steel/ceramic interface. During high-temperature operation the Cr-containing ferritic steel forms an oxide scale at its surface, thereby causing high ohmic electrical contact resistance when connected to the surface of an electronically conducting ceramic cathode material. In the long run, the vaporization of Cr species from these oxide scales also affects the cathode activity, eventually leading to cell deterioration. One way of overcoming the problem is to incorporate another electronically conducting ceramic compliant layer, commonly known as the contact layer, between the cathode and metallic interconnect. In this contribution, LaNi_0.6Fe_0.4O₃ was tested as a cathode contact material. Its performance at 800 °C in the form of a ~50 μm thick film applied on two ferritic steel compositions was examined. After 600 h of testing, contact resistances of 60 and 160 mΩ cm² were obtained. The different values are explained by the variation in steel composition.     

薄膜型中温固体氧化物燃料电池 (SOFC)研制及性能考察

用一种廉价的湿化学方法 ,在Ni_YSZ阳极基膜上制备出致密的YttriaStabilizedZirconia(YSZ)薄膜 .薄膜的厚度约为 10 μm ,致密均匀 ,无裂纹等缺陷 .以Ni_YSZ阳极基膜 ,YSZ薄膜和锶掺杂锰酸镧阴极 (LSM )组装的SOFC单电池 ,在 80 0℃下功率密度达 0 1W /cm2 .研究分析表明 ,YSZ薄膜的IR降 (包括电极 /YSZ薄膜的接触电阻 )较小 ,不是影响电池性能的主要因素 ,大的阳极过电位是影响电池性能的主要因素 .