Synthesis of nanostructured electrocatalysts based on magnetron ion sputtering

Nanostructured platinum catalysts for electrochemical systems with proton-exchange membranes (PEMs) have been synthesized by magnetron ion sputtering on a carbon support. The design of the powder support stirrer has been optimized to ensure uniform surface coverage with platinum metal nanoparticles. The deposition parameters (discharge power, deposition time, and bias voltage) that make it possible to obtain electrocatalysts with a large specific surface area (up to 44 m²/g) have been determined. The resulting catalysts have been studied by transmission electron microscopy and X-ray diffraction. The samples with platinum particles 3 to 4 nm in size uniformly distributed over the carbon surface and forming a single phase exhibit the greatest efficiency. The electrodes based on the synthesized electrocatalysts have been tested in a liquid electrolyte and as a component of a fuel cell and PEM water electrolyzer. The voltage across the fuel cell with the synthesized Pt/C electrocatalyst (44 m²/g) at a current density of 1 A/cm² is as high as 0.55 V, which corresponds to a specific power of 550 mW/cm². Qualitative correlations between the parameters of the synthesized catalysts and the deposition conditions have been established.     

Development of sulfonated poly (ether ether ketone) electrolyte membrane for applications in hydrogen sensor

The future economy is projected as hydrogen economy and fuel cells are set to become the energy source either replacing or augmenting the present oil based technology. A sulfonated poly ether ether ketone (SPEEK) membrane as the electrolyte for hydrogen sensor that operates at room temperature was developed in our lab. The electrolyte used was SPEEK, which is a proton conducting solid polymer membrane. The membranes were characterized using various available techniques like TGA, XRD, SEM, etc. The durability was studied using the Fenton’s reagent. The proton conducting ability was analyzed using impedance spectroscopy. The catalysts considered were platinum for the cathode and three different catalysts (Pt, Pt/Pd and Pd) for the anode. The MEAs were evaluated for their performance in hydrogen sensor and the one with platinum catalyst at the anode gave the best response among the three indicating its suitability for the SPEEK membrane for hydrogen sensor.     

Assessment of Glucose Oxidase Based Enzymatic Fuel Cells Integrated With Newly Developed Chitosan Membranes by Electrochemical Impedance Spectroscopy

Considerably stable enzymatic fuel‐cells (single cell and 5‐cells stack) were prepared by using chitosan based membranes along with glucose oxidase attached bioanode. Continuous operation of fuel‐cells were monitored under short circuit conditions reaching half‐life over a week. Detailed analysis for the effects of pH, temperature, buffer types and concentration on different type of in‐house produced chitosan membranes were performed by electrochemical impedance spectroscopy (EIS). EIS was utilized to observe, total electrolyte resistance, charge transfer properties, mass transfer and double layer effects on integrated fuel cells (single cell and 5‐cells stack). Performance of the fuel cells was also analyzed by the polarization experiments. Current density of the fuel cell increased at higher operation temperatures not only due to better enzyme kinetics, but also due to increase in electrolyte (membrane+buffer solution) conductivity. Buffer concentration in the fuel (glucose) solution was found as an important parameter. Under optimum fuel cell operation conditions (i. e. 30–40 °C, pH 5 0.3 M buffer solution), maximum current densities of 3.0–3.2 mA cm^?2 were reached. Low‐power devices (i. e. a calculator, step motor) were powered with 5‐cell stack producing 3 mW at 1.3 V.     

Separation of Platinum(IV) and Iron(III) with Liquid Membranes under Electrodialysis Conditions

The recovery of platinum(IV) from hydrochloric acid solutions containing an excess amount ofiron(III) with liquid tri-n-octylamine-1'2-dichloroethane membranes under conditions of galvanostatic dialysiswas studied. The influence exerted by the current density, by the composition of aqueous solutionsand liquid membranes on the rate of platinum(IV) transport and efficiency of separation of the metals wasanalyzed and the optimal process conditions were determined.     

Synthesis and characterization of sulfonated polyimide membranes for direct methanol fuel cell

The sulfonated polyimide (SPI) membranes for direct methanol fuel cell (DMFC) were synthesized with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,2′-benzidinedisulfonic acid (BDSA), 4,4′-oxydianiline (ODA) through classical two-step methods: (1) preparation of sulfonated poly(amic acid) (SPAA) precursors with different sulfonation levels by controlling the molar ratio of BDSA to ODA, and (2) thermal imidization of the SPAA films. The chemical structure and the imidization from SPAA membranes were characterized by FT-IR with temperature, and the sulfonation levels were determined by elemental analysis. The thermal stability of the membranes was also characterized by TGA. From water uptake and small angle X-ray scattering (SAXS) experiments for different sulfonation levels, it was found that the number of water clusters in SPI membranes increased as the water uptake of membranes increased, but the size of water cluster was not changed with the sulfonation levels. The proton conductivity and the methanol permeability of SPI membrane showed a sudden leap like a percolation phenomenon around 35 mol% of sulfonation level. The SPI membranes exhibited relatively high proton conductivity and extremely low methanol permeability, and showed the feasibility of suitable polymer electrolyte membranes (PEM) for DMFC.     

On the use of gamma irradiation crosslinked PVA membranes in hydrogen fuel cells

There is growing interest in the use of fuel cells (FC) with hydrogen as the main fuel for stationary, mobile, and transportation applications. In the FC concept membranes play increasingly important roles. Polymer electrolyte membrane fuel cells (PEMFCs) are considered as the most promising fuel cell technology for a wide range of applications due to the stable operation, the high energy generation yield and the simplicity of the system.In this work, we develop different types of membranes based on poly(vinyl alcohol) (PVA). PVA is a water-soluble polymer that is used in practical applications because of its easy preparation, excellent chemical resistance, thermal and mechanical properties. Crosslinking of the PVA was performed by gamma irradiation since radiation chemistry is found to be a very effective method for constructing three-dimensional polymeric networks. The samples prepared in this way were then immersed in the alkaline solution over a certain period of time to turn them into conductive membranes. Ionic conductivity of the PVA hydrogels, was then measured as a function of concentration of KOH solutions and temperature. Cyclic voltammetry of these PVA hydrogel electrolytes was performed to determine the width of the electrochemical stability window.We examined these membranes impregnated with saturated 6 M KOH electrolyte as polymer membrane for fuel cells application. Our experiments showed that PEMFCs with PVA and Nafion^® membranes had similar polarization curves, under same conditions. Furthermore, PVA membranes proved to be stable during the real cell tests. This study offers a possibility for more earnest approach to the use of PVA membranes for fuel cell applications.     

Rapid diagnostics of characteristics and stability of fuel cells with proton-conducting electrolyte

Processes underlying the degrading of membrane-electrode assemblies of hydrogen-air fuel cells with Nafion 212 and MF-4SK membranes under the conditions of their accelerated stress testing and long-term life tests are analyzed. The cathode platinum catalyst corrosion was shown to be the main cause of the degrading of the fuel cell’s kinetically controlled current-voltage characteristics; the corrosion is accompanied by the platinum nanoparticles’ growth and the platinum ion partial transfer into the membrane. The overvoltage components of the membrane-electrode assembly and their changing during accelerated stress testing are determined. The voltage decrease at currents >0.5 A/cm² is shown to be mainly caused by the transport and ohmic resistance growth. The transport resistance components are calculated; the dependence of the cathode active layer resistance on the platinum catalyst surface area is revealed.     

亚油酸铂靶向脂质体与癌细胞膜相互作用的电子自旋共振研究

本文用马来酰亚胺自旋标记(MSL)技术研究了亚油酸铂靶向脂质体与肿瘤细胞膜的相互作用, 以及它们对ESR谱的影响。亚油酸铂靶向脂质体的存在, 使MSL的乳腺癌细胞膜和S180实体瘤细胞膜的W和S的比值发生了变化, 结果表明亚油酸铂可以作用于癌细胞膜影响膜蛋白巯基结合部位, 并使癌细胞膜表面蛋白质构象改变。     

PEMFC阴极催化层结构分析

采用CCS法（catalyst coated substrate）构建铂纳米颗粒（Pt-NPs）和铂纳米线（Pt-NWs）双层催化层结构,分析其对单电池电化学性能的影响。对于富铂/贫铂双层铂纳米颗粒结构,靠近质子交换膜侧的富铂层中致密的铂颗粒结构能促进ORR速率,而靠近气体扩散层一侧的具有更高的孔隙率和平均孔尺寸的贫铂层,有利于反应气体的传输和扩散,当贫富铂层铂载量比为1:2时,单电池测试表现出最优性能,在0.6 V时的电流密度达到了1.05 A·cm^-2,峰值功率密度为0.69 W·cm^-2,较常规单层催化层结构提升了21%。在以Pt-NPs作为基底层时生长Pt-NWs时,得到了梯度分布的双层结构。铂颗粒的存在促进了铂前驱体的还原,并为新形成的铂原子提供了沉积位置。在Pt-NPs基底上生长的Pt-NWs具有更均匀的分布以及更致密的绒毛结构,并且自然形成了一种梯度分布。优化后的Pt-NWs催化层在0.6 V时的电流密度提高了21%。含有双层催化层结构的膜电极具有更高的催化剂利用率,对阴极催化层结构的优化和制备提供了新思路。     

透光导电金属及氧化铂半导体薄膜的制备与表征

通过PPh~3对“非保护型”铂金属纳米簇进行表面修饰,并将其萃取至甲苯中,制备的PPh~3修饰的Pt金属钠米簇于空气中可自发地在玻璃表面生长出均匀透光的金属钠米簇薄膜。该金属钠米簇薄膜经空气中加热处理后可转化为透光导电的氧化铂半导体薄膜。考察了金属钠米簇薄膜生长过程中UV-vis吸收光谱的变化。采用SEM和TEM等方法,表征了纳米簇的粒径及膜的多孔结构,由此解释了其透光原因。研究了薄膜的导电性与处理条件的关系,并采用XPS表征了处理过程中的物质变化。初步探索了PPh~3-Pt纳米簇自发成膜过程的机理,确定了氧气在此过程中的重要作用。     

Synthesis and characterization of high molecular weight hexafluoroisopropylidene‐containing polybenzimidazole for high‐temperature polymer electrolyte membrane fuel cells

A high molecular weight, thermally and chemical stable hexafluoroisopropylidene containing polybenzimidazole (6F‐PBI) was synthesized from 3,3′‐diaminobenzidine (TAB) and 2,2‐bis(4‐carboxyphenyl) hexafluoropropane (6F‐diacid) using polyphosphoric acid (PPA) as both the polycondensation agent and the polymerization solvent. Investigation of polymerization conditions to achieve high molecular weight polymers was explored via stepwise temperature control, monomer concentration in PPA, and final polymerization temperature. The polymer characterization included inherent viscosity (I.V.) measurement and GPC as a determination of polymer molecular weight, thermal and chemical stability assessment via thermo gravimetric analysis and Fenton test, respectively. The resulting high molecular weight polymer showed excellent thermal and chemical stability. Phosphoric acid doped 6F‐PBI membranes were prepared using the PPA process. The physiochemical properties of phosphoric acid doped membranes were characterized by measuring the phosphoric acid doping level, mechanical properties, and proton conductivity. These membranes showed higher phosphoric acid doping levels and higher proton conductivities than the membranes prepared by the conventional membrane fabrication processes. These membranes had sufficient mechanical properties to be easily fabricated into membrane electrode assemblies (MEA) and the prepared MEAs were tested in single cell fuel cells under various conditions, with a focus on the high temperature performance and fuel impurity tolerance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4064–4073, 2009     

Electrodialysis Separation of Copper(II) and Platinum(IV) with Liquid Membranes Based on Di(2-Ethylhexyl)Phosphoric Acid

Separation of copper(II) and platinum(IV) in extraction from binary acid chloride solutions with liquid membranes containing technical-grade di(2-ethylhexyl)phosphoric acid with addition of tri-n-octyl amine in 1,2-dichloroethane under the conditions of the galvanostatic electrodialysis was studied. The influence exerted by the current density and composition of aqueous solutions and liquid membranes on the rate and selectivity of copper(II) extraction was analyzed. The optimal conditions of metal separation were determined.     

Sulfonated poly(ether sulfone)/sulfonated polybenzimidazole blend membrane for fuel cell applications

Polymer blending is used to modify or improve the dimensional and thermal stability of any two different polymers or copolymers. In this study, both sulfonated polybenzimidazole homopolymer (MS-p-PBI 100) and sulfonated poly(aryl ether benzimidazole) copolymers (MS-p-PBI 50, 60, 70, 80, 90) were successfully synthesized from commercially available monomers. The chemical structure and thermal stability of these polymers was characterized by ¹H NMR, FT-IR and TGA techniques. Blend membranes (BMs) were prepared from the salt forms of sulfonated poly(ether sulfone) (PES 70) and MS-p-PBI 100 using dimethylacetamide (DMAc). These blend membranes exhibited good stability in boiling water. The blending of 1 wt.% of MS-p-PBI 100 and 99 wt.% of PES 70 to produce the blend membrane BM 1 reduced membrane swelling, thus leading to good dimensional stability and comparable proton conductivity. Hence, BM 1 was chosen for the fabrication of a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) applications. This paper reports on PEMFC and DMFC performance under specific conditions.     

Morphology and Transport Properties of Hybrid Materials Based on Perfluorinated Membranes,Polyaniline, and Platinum

The transport properties and morphological characteristics of perfluorinated membranes after deposition of the layer of platinum dispersion on the surface are studied. The significant effect of preliminary modification of perfluorinated membraned with polyaniline on the diffusion permittivity of the composite and the morphology of the layer of platinum dispersion is determined. Testing the composites as proton conductors with a catalytic layer on the surface in an air–hydrogen fuel cell has shown the effect of the asymmetry of the electrochemical characteristics of the membrane–electrode assembly at various orientations of the layer of platinum dispersion towards hydrogen and air flows. A higher catalytic activity of the composite membranes in the oxygen reduction reaction is determined in the case platinum dispersion is deposited onto the membrane preliminarily modified with polyaniline.

     

High Dispersion and Electrocatalytic Properties of Platinum on Functional Multi‐Walled Carbon Nanotubes

Platinum (Pt) nanoparticles were electrochemically dispersed on 4‐aminobenzene monolayer‐grafted multi‐walled carbon nanotubes (MWNTs) by a potential‐step method. The structure and nature of the resulting Pt‐MWNT composites were characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The electrocatalytic properties of Pt‐MWNT composites for methanol oxidation have been investigated by cyclic voltammetry (CV) and high electrocatalytic activity can be observed. This may be attributed to the small particle size, high dispersion of platinum particles and the particular properties of MWNT supports. The results imply that the Pt‐MWNT composites have good potential applications in direct methanol fuel cell (DMFC). Additionally, the long‐term cycling stability of platinum catalysts was also investigated.     

Anisotropic diffusion of water in perfluorosulfonic acid membrane and hydrocarbon membranes

Polymer electrolyte membranes that are applied for polymer electrolyte fuel cell (PEFC) retain water in their three-dimensional network structure. Diffusion behavior of water in the membranes was analyzed by pulsed field gradient (PFG)-NMR method to estimate diffusion coefficient of proton species as water or hydronium ion. The membrane samples were put in a sample tube vertically or horizontally toward to the field gradient axis under determined temperature and humidity conditions. As the results, anisotropic diffusion behavior of water in the membranes was indicated. Anisotropic properties depended on the sample type, preparation conditions of the wet membranes, and measurement conditions. A perfluorosulfonic acid membrane tended to have smaller anisotropy while hydrocarbon membranes showed greater anisotropy.     

Properties of proton-conducting Nafion-type membranes with Nanometer-thick polyaniline surface layers

The study is directed to the improving of proton-conducting Nafion-type membranes for using in fuel cells with direct oxidation of liquid fuels. Nanometer-thick layer of polyaniline (in its conducting emerald-dine form) was deposited onto the membrane surface by in situ polymerization. The structure of the polyaniline layer is studied, as well as the properties of thus modified membranes (electronic and proton conduction, permeability for methanol, thermal stability). A method of platinum catalyst deposition onto the Nafion-modifying polyaniline layer is developed.     

Development of nano-catalyzed membrane for PEM fuel cell applications

Nano-catalyzed membrane with different platinum (Pt) catalyst loadings (0.25 to 1 mg cm^?2) was investigated for proton exchange membrane fuel cell applications, and the Pt loading on the Nafion membrane was prepared by non-equilibrium impregnation reduction method. The prepared catalyzed membranes were subjected to various characterisations, namely, X-ray diffraction, high-resolution scanning electron microscopy (HRSEM) with energy-dispersive X-ray, cyclic voltammetry, polarisation and electrochemical impedance spectroscopy. The polycrystalline fcc cubic structure and the particle size of Pt catalyst were estimated by X-ray diffraction analysis. The membrane with 0.4 mg cm^?2 of Pt loading exhibits a favourable surface morphology which is confirmed by HRSEM image. Electrochemical investigations were clearly evident that the uniform distributions of Pt particles with fine pores on Nafion membrane facilitated the three-phase boundary which leads to a better cell performance. Electrochemical impedance spectroscopy demonstrated that the cell constructed using 0.4 mg cm^?2 of platinum-loaded membrane has lower resistance than the other Pt loading.     

A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short-circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni₃S₂ is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon-supported palladium (Pd/C) anode to establish a membrane-free, room-temperature formate fuel cell that operates under benign neutral pH conditions. Proof-of-concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm⁻², significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane-free fuel cells.     

新型燃料电池质子交换膜──含叔丁基的磺化聚芳醚砜

以3,3'-二磺酸钠基-4,4'-二氯二苯砜(SDCDPS)、叔丁基对苯二酚(TBHQ)、二氟二苯酮(DFBP)为原料,利用亲核缩聚反应,通过调整磺化单体(SDCDPS)和非磺化单体(DFBP)的比例与叔丁基对苯二酚(TBHQ)共聚,合成了不同磺化度的聚芳醚砜.聚合物成膜后的研究结果表明,该膜具有良好的机械性能和电化学性能,可能在质子交换膜燃料电池中得到应用.