Effect of stoichiometric ratio of organic fuel to oxidizer on performance of La0.8Sr0.2CoO3 catalysts for CH4 combustion

Perovskite-type La_0.8Sr_0.2CoO₃ mixed oxides were prepared by d,l-alanine solution combustion synthesis and used successfully in CH₄ combustion as catalysts. These samples were characterized by means of XRD, FTIR, BET, and H₂-TPR methods. The effects of stoichiometric ratio (φ) of organic fuel to oxidizer on the structure and catalytic activities of the catalysts were studied. The results indicate that all La_0.8Sr_0.2CoO₃ mixed oxides with different φ have perovskite structures. Their structures and catalytic activities vary along with the change of φ. The catalytic activity of La_0.8Sr_0.2CoO₃ mixed oxide with φ = 1.52 is the best among all the samples, whose T ₅₀ and T ₁₀₀ (the temperatures of methane conversions reaching 50 and 100%, respectively) are respectively 470 °C and 550 °C, which can be explained in terms of the smaller of average crystal size, higher specific surface area, bigger lattice distortion, lower activation energy, and higher mobility of chemically adsorbed oxygen on the surface and vacancy of the catalysts.     

磷钨酸对甲酸在碳载Pd催化剂上电氧化的促进作用

利用X射线能量色散(EDS)谱、X射线衍射(XRD)谱和电化学等技术研究了电解液中磷钨酸(PWA)对直接甲酸燃料电池(DFAFC)中甲酸在碳载Pd(Pd/C)催化剂上电氧化的促进作用. 研究结果发现, 因吸附的PWA能促进甲酸在Pd/C催化剂上的脱氢而加速了甲酸的电氧化. 这种促进作用与PWA的浓度有关, 当PWA的浓度低于0.15 mg/mL时, 该促进作用随PWA的浓度的增加而增加; 当PWA的浓度高于0.15 mg/mL时, 过多吸附的PWA会覆盖过多Pd/C催化剂的活性点而使其电催化性能随PWA的浓度增大而降低. 因此, 当电解液中PWA的浓度为0.15 mg/mL时, Pd/C催化剂对甲酸氧化的电催化性能最好.     

Lactococcus lactis catalyses electricity generation at microbial fuel cell anodes via excretion of a soluble quinone

Lactococcus lactis is a gram-positive, normally homolactic fermenter that is known to produce several kinds of membrane associated quinones, which are able to mediate electron transfer to extracellular electron acceptors such as Fe³⁺, Cu²⁺ and hexacyanoferrate. Here we show that this bacterium is also capable of performing extracellular electron transfer to anodes by utilizing at least two soluble redox mediators, as suggested by the two-step catalytic current developed. One of these two mediators was herein suggested to be 2-amino-3-dicarboxy-1,4-naphthoquinone (ACNQ), via evaluation of standard redox potential, ability of the bacterium to exploit the quinone when exogenously provided, as well as by high performance liquid chromatography coupled with UV spectrum analysis. During electricity generation, L. lactis slightly deviated from its normal homolactic metabolism by excreting acetate and pyruvate in stoichiometric amounts with respect to the electrical current. In this metabolism, the anode takes on the role of electron sink for acetogenic fermentation. The finding that L. lactis self-catalyses anodic electron transfer by excretion of redox mediators is remarkable as the mechanisms of extracellular electron transfer by pure cultures of gram-positive bacteria had previously never been elucidated.     

Stability of Fe‐N‐C Catalysts in Acidic Medium Studied by Operando Spectroscopy

Fundamental understanding of non‐precious metal catalysts for the oxygen reduction reaction (ORR) is the nub for the successful replacement of noble Pt in fuel cells and, therefore, of central importance for a technological breakthrough. Herein, the degradation mechanisms of a model high‐performance Fe‐N‐C catalyst have been studied with online inductively coupled plasma mass spectrometry (ICP‐MS) and differential electrochemical mass spectroscopy (DEMS) coupled to a modified scanning flow cell (SFC) system. We demonstrate that Fe leaching from iron particles occurs at low potential (<0.7 V) without a direct adverse effect on the ORR activity, while carbon oxidation occurs at high potential (>0.9 V) with a destruction of active sites such as FeN_xC_y species. Operando techniques combined with identical location‐scanning transmission electron spectroscopy (IL‐STEM) identify that the latter mechanism leads to a major ORR activity decay, depending on the upper potential limit and electrolyte temperature. Stable operando potential windows and operational strategies are suggested for avoiding degradation of Fe‐N‐C catalysts in acidic medium.     

新型钴-聚吡咯-碳载Pt燃料电池催化剂的制备与表征

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳（Co-PPy-C）载Pt 催化剂（Pt/Co-PPy-C）,其中Pt 的总质量占20%. 利用透射电镜（TEM）、光电子射线能谱分析（XPS）和X射线衍射（XRD）研究了催化剂的结构,用循环伏安（CV）、线性扫描伏安（LSV）等方法考察了其电化学活性及氧还原反应（ORR）动力学特性及耐久性. Pt/Co-PPy-C电催化剂的金属颗粒直径约1.8 nm,略小于商用催化剂Pt/C（JM）颗粒尺寸（约2.5 nm）;催化剂在载体上分散均匀,粒径分布范围较窄. Pt/Co-PPy-C的电化学活性比表面积（ECSA）（75.1 m²·g^-1）高于商用催化剂的ECSA（51.3 m²·g^-1）. XPS测试表明,自制催化剂表面的Pt 主要以零价形式存在. 而XRD结果显示,自制催化剂中Pt（111）峰最强,Pt 主要为面心立方晶格. Pt/Co-PPy-C具有与Pt/C（JM）相同的半波电位;在0.9 V下,Pt/Co-PPy-C的比活性（1.21 mA·cm^-2）高于商用催化剂的比活性（1.04 mA·cm^-2）,表现出更好的ORR催化活性.动力学性能测试表明催化剂的ORR反应以四电子路线进行. CV测试1000 圈后,Pt/Co-PPy-C和Pt/C（JM）的ECSA 分别衰减了13.0%和24.0%,可见自制催化剂的耐久性高于商用Pt/C（JM）,在质子交换膜燃料电池（PEMFC）领域有一定的应用前景.     

以多聚甲醛为还原剂制备新型阳极Pt/CMK-3催化剂

 以多聚甲醛为还原剂,采用液相还原法制备了Pt/CMK-3直接甲醇燃料电池(DMFC)阳极催化剂,并采用透射电镜和X射线衍射技术对其进行了表征. 结果表明,有序介孔碳CMK-3具有规整的二维有序孔道结构,为DMFC中电子和燃料的传输提供了方便的路径,同时它较大的比表面积使得Pt纳米粒子很好地分散在其表面; Pt/CMK-3催化剂中Pt粒子的平均粒径为2.8 nm, 小于E-TEK公司的商品化Pt/XC-72和以甲醇为还原剂制备的Pt/C-M催化剂,并且粒径分布范围窄,结晶度低. 察了Pt/CMK-3催化剂对甲醇的电催化氧化性能,发现Pt/CMK-3催化剂对甲醇氧化的电催化性能优于Pt/XC-72和Pt/C-M催化剂.     

质子交换膜燃料电池MnO2-Pt/C复合催化剂阴极的富氧作用

质子交换膜燃料电池空气电极阴极催化剂的富氧作用是提高其性能的关键.应用化学氧化法制备MnO2-Pt/C复合催化剂,研究MnO2的富氧作用,应用CV、CP、TEM等方法表征该催化剂,并组装成单电池测试其性能.     

热处理对多元醇法制备的PtRu/C电催化剂的影响

采用热重、在线质谱、X射线衍射和透射电镜等技术研究了热处理对多元醇法制备的PtRu/C电催化剂催化活性的影响.结果表明,热处理前电催化剂表面吸附较多残余物种,在惰性气氛中200℃下热处理2h可以去除部分吸附物种.虽然热处理后电催化剂的平均粒径比热处理前稍有增大,但电催化剂颗粒的分散度仍较高.热处理后电催化剂催化甲醇电氧化反应的活性明显提高.     

Chemical and mechanical stability of EPDM in a PEM fuel cell environment

Proton exchange membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. Long-term durability of the fuel cell stacks depends heavily on the functionality of the elastomeric gasket material. Chemical and mechanical stability of the elastomeric material is of great concern to the overall performance of the fuel cell stacks. The degradation of a commercially available gasket material, ethylene-propylene-diene monomer (EPDM), was investigated in a simulated PEM fuel cell environment in this work. One solution and two temperatures, based on actual fuel cell operation, were used in this study. Optical microscopy was used to show the topographical changes on the sample surface. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the gasket material before and after exposure to the simulated PEM fuel cell environment over time. Atomic absorption spectrometry was used to identify the leachants in the soaking solution from the elastomeric material. Microindentation test and dynamic mechanical analysis (DMA) were conducted to assess the change of mechanical properties of the samples exposed to the environment. The atomic absorption spectrometer analysis shows that silicon and calcium were leached from the material into the soaking solution. The ATR-FTIR results indicate that the chemical changes were not apparent. The microindentation test and DMA results reveal that mechanical properties were not changed significantly.     

Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid-catalyzed crosslinking for proton exchange membrane fuel cells

Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01–0.19 S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H₂/O₂ fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm² (Pd/C) exhibited a peak power density of 220.3 mW/cm², which was close to that of Nafion 212 (214.0 mW/cm²) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.