Performance of a direct methanol fuel cell (DMFC) at low temperature: Cathode optimization

The effects of Pt loading, Nafion content in the cathode and membrane–electrode assembly (MEA) preparation techniques (CCS_cathode/CCS_anode and CCM_cathode/CCS_anode) on the performance of MEAs for direct methanol fuel cells (DMFC) were studied. The MEA performance was analyzed with polarization curves, electrochemical impedance spectroscopy and scanning electron microscopy data. It was shown, that the cathode prepared by the catalyst coated membrane (CCM) method forms a mainly microporous and mesoporous structure, whereas the catalyst coated substrate (CCS) method generates macroporosity together with micropores and mesopores. The power density of the CCM_cathode/CCS_anode typed MEAs strongly depends on the CCM-cathode composition: Pt loading and Nafion content in the cathode. Nafion (10.7 wt.%) was found to be an optimum for DMFC performance, and at this composition, the power density gradually increased with the Pt loading up to 6.0 mg cm⁻². At higher Nafion contents, a significant mass transfer limitation at high Pt loadings occurs. Comparing the CCM and CCS methods of the cathode fabrication, the latter revealed a higher power density, which reached 104 mW cm⁻² at 0.4 V and 70 °C owing to the lack of significant mass transfer limitations. This behavior indicates that in addition to Pt loading and Nafion content, the cathode pore structure is critical to DMFC MEA performance.     

Enhancement of fuel cell properties in polyethersulfone and sulfonated poly (ether ether ketone) membranes using metal oxide nanoparticles for proton exchange membrane fuel cell

The proton exchange membrane (PEM) was synthesized using polyethersulfone (PES), sulfonated poly (ether ether ketone) (SPEEK) and nanoparticles. The metal oxide nanoparticles such as Fe₃O₄, TiO₂ and MoO₃ were added individually to the polymer blend (PES and SPEEK). The polymer composite membranes exhibit excellent features regarding water uptake, ion exchange capacity and proton conductivity than the pristine PES membrane. Since the presence of sulfonic acid groups provides by added SPEEK and the unique properties of inorganic nanoparticles (Fe₃O₄, TiO₂ and MoO₃) helps to interconnect the ionic domain by the absorption of more water molecules thereby enhance the conductivity value. The proton conductivity of PES, SPEEK, PES/SPEEK/Fe₃O₄, PES/SPEEK/TiO₂ and PES/SPEEK/MoO₃ membranes were 0.22 × 10^?4 S/cm, 5.18 × 10^?4 S/cm, 3.57 × 10^?4 S/cm, 4.57 × 10^?4 S/cm and 2.67 × 10^?4 S/cm respectively. Even though the blending of PES with SPEEK has reduced the conductivity value to a lesser extent, hydrophobic PES has vital role in reducing the solvent uptake, swelling ratio and improves hydrolytic stability. Glass transition temperature (T_g) of the membranes were determined from DSC thermogram and it satisfies the operating condition of fuel cell system which guarantees the thermal stability of the membrane for fuel cell application.     

An effective 3D target recognition model imitating robust methods of the human visual system

This paper presents a model of 3D object recognition motivated from the robust properties of human vision system (HVS). The HVS shows the best efficiency and robustness for an object identification task. The robust properties of the HVS are visual attention, contrast mechanism, feature binding, multi-resolution, size tuning, and part-based representation. In addition, bottom-up and top-down information are combined cooperatively. Based on these facts, a plausible computational model integrating these facts under the Monte Carlo optimization technique was proposed. In this scheme, object recognition is regarded as a parameter optimization problem. The bottom-up process is used to initialize parameters in a discriminative way; the top-down process is used to optimize them in a generative way. Experimental results show that the proposed recognition model is feasible for 3D object identification and pose estimation in visible and infrared band images.     

Direct Synthesis of Fluorinated Carbon Materials via a Solid-State Mechanochemical Reaction Between Graphite and PTFE

Fluorinated carbon materials (FCMs) have received significant attention, because of their exceptional stability, which is associated with the strong C-F bonding, the strongest among carbon single bonds. However, the fluorination of carbon materials requires extremely toxic and moisture-sensitive reagents, which makes it inapplicable for practical uses. Here, a straightforward and relatively safe method are reported for the scalable synthesis of FCMs, by mechanochemical depolymerization of polytetrafluoroethylene (PTFE) and fragmentation of graphite. The resultant FCMs are evaluated as anode materials for lithium-ion batteries (LIBs). An optimized FCM delivered capacities as high as 951.6 and 329.3 mAh g ⁻¹ at 0.05 and 10 A g ⁻¹, respectively. It also demonstrated capacity retention as high as 76.6% even after 1000 cycles at 2.0 A g ⁻¹.     

Cationization of Waxy and Normal Corn and Barley Starches by an Aqueous Alcohol Process

When an aqueous alcoholic-alkaline solvent was used, cationization of normal and waxy corn and barley starches was achieved with high degrees of substitution (DS) and reaction efficiency (RE) in the absence of gelatinization inhibitor salts. Ethanol was a more effective solvent than methanol or 2-propanol, and alcohol concentrations could vary between 35–65%. Maintaining a starch to water ratio of 1:1 (w/w) was critical, but DS values were proportional to the concentration of cationic reagent, 3-chloro-2-hydroxypropyltrimethylammonium chloride. At 50°C, cationization was essentially complete within 6h but nearly the same DS could be achieved in 1h at 70°C.     

Effect of Aqueous Ethanol Cationization on Functional Properties of Normal and Waxy Starches

Cationic starch ethers of normal and waxy corn, normal and waxy barley and normal pea starch were prepared by an aqueous alcoholic process for evaluation of their functional properties as compared to the native starch controls. The native starches exhibited a wide range in average granule size (10–21 μm diameter), amylose content (0–34%) and swelling power (13–31). Cationization to degrees of substitution (DS) of 0.030–0.035 with 3-chloro-2-hydroxypropyltrimethylammonium chloride resulted in marked increases in swelling power of all starches, with little corresponding increases in starch solubility. Cationization also decreased the onset of endothermic transitions and pasting temperatures quite substantially, and promoted the development of sharp peak viscosities in the amylographs of all normal and waxy starches, including that of pea starch. Final cold viscosities of the cationic starches exhibited positive setbacks, and the cooked starch gels, after storage for 7 days at 4°C and −15°C, showed no syneresis. All cationic starches except for waxy corn were more susceptible to α-amylase hydrolysis than native control starches. The general improvement in functional properties, especially in the waxy corn, waxy barley and pea starches, due to the aqueous alcoholic-alkaline cationization process would greatly enhance their industrial applications.     

Effect of Cross Linking on Functional Properties of Cationic Corn Starch

Native corn starch was cross linked with phosphorus oxychloride (POCl₃) before and after cationization to DS 0.04 in an aqueous ethanolic-alkaline solvent with no adverse effects on the cationization reaction rate. Cross linking at six levels of POCl₃ (7.5–120μ1/50g starch) demonstrated that the gelatinization temperatures of cationic starch increased but enthalpies of gelatinization (ΔH) decreased in proportion to the amount of added POCl₃. Amylograph viscosities increased with level of POCl₃ up to a maximum of 45μl POCl₃ and then decreased markedly at higher concentrations of POCl₃. At 30–45μl POCl₃, the amylograph viscosities of cationic corn starch increased very rapidly and remained uniformly high throughout the rest of the heating and cooling cycle. At this level of cross linking and cationization, the modified starch could be used industrially as an adhesive or in paper manufacture at more dilute concentrations and with less energy input for mixing the slurry than would be required for cationic starches which exhibit high peak viscosities but negative setbacks on cooling.     

Preparation of Amphoteric Starches During Aqueous Alcoholic Cationization

Use of an aqueous alcoholic-alkaline solvent allowed cationization and phosphorylation to be combined in simultaneous or sequential processes in the production of amphoteric starch. Degrees of substitution required by the paper industry were obtained in normal corn, pea and barley starches, and in waxy corn and barley starches without the need for drying and heating the cationic starches to complete the phosphorylation reaction. The amphoteric starches had increased welling power, lower gelatinization temperatures, improved paste consistency and stability, and increased α-amylase digestibility than native controls, while gel syneresis after cold storage was eliminated.