Analysis of proton exchange membrane fuel cell polarization losses at elevated temperature 120 °C and reduced relative humidity

Polarization losses of proton exchange membrane (PEM) fuel cells at 120 °C and reduced relative humidity (RH) were analyzed. Reduced RH affects membrane and electrode ionic resistance, catalytic activity and oxygen transport. For a cell made of Nafion^® 112 membrane and electrodes that have 35 wt.% Nafion^® and 0.3 mg/cm² platinum supported on carbon, membrane resistance at 20%RH was 0.407 Ω cm² and electrode resistance 0.203 Ω cm², significantly higher than 0.092 and 0.041 Ω cm² at 100%RH, respectively. In the kinetically controlled region, 20%RH resulted in 96 mV more cathode activation loss than 100%RH. Compared to 100%, 20%RH also produced significant oxygen transport loss across the ionomer film in the electrode, 105 mV at 600 mA/cm². The significant increase in polarization losses at elevated temperature and reduced RH indicates the extreme importance of designing electrodes for high temperature PEM fuel cells since membrane development has always taken most emphasis.     

Compact Integrated Optical Immunosensor using Replicated Chirped Grating Coupler Sensor Chips

A novel compact multichannel integrated optical sensor module isdescribed. Its performance is demonstrated by measurement of the mass adsorption of an analyte molecule to the transducer surface by refractometry in an immunosensor experiment. The signal transduction is achieved by means of chirped grating couplers, which allow simple yet highly functional sensor modules to be built. The experiments were performed with high-sensitivity replicated polycarbonate TiO(2) waveguide sensor chips for detecting the binding of rabbit immunoglobulin to immobilized protein A. Aresolution of ?3 pg/mm(2) surface mass coverage was obtained in a dual-channel module with size 10 cm x 10 cm x10 cm.     

Sorption of citrus flavour compounds on XAD‐7HP resin during the debittering of grapefruit juice

Grapefruit juice made from concentrate was debittered using a laboratory‐scale downflow column packed with XAD‐7HP adsorbent resin. Sorption of the bitter principle naringin was analysed by high‐performance liquid chromatography. In addition, the influence of the debittering process on the flavour of the juice was investigated using headspace gas chromatography for the volatile flavour compounds α‐pinene, β‐myrcene, d‐limonene, α‐terpineol and β‐caryophyllene. Kinetic constants were determined for all substances using the Lagergren adsorption model. The debittered juices showed a selective shift in their reduced flavour profile. Reduction of naringin to 51.28% of its initial value led to a decrease in α‐terpineol to 43.05%, whereas the other flavour compounds ranged from 76.27% (β‐myrcene) to 92.76% (β‐caryophyllene). The column flow rate influenced the adsorption of α‐terpineol and naringin. The highest affinity for adsorption was consistently observed for the off‐flavour α‐terpineol, which indicates a promising option for its selective removal from processed juices during debittering.     

等径弯曲通道制备的超细晶铜的疲劳性能

研究了等径弯曲通道(ECAP)变形后的超细晶T3铜在恒应力幅控制条件下的疲劳寿命和循环形变行为.通过扫描电镜观察了疲劳试样表面的滑移带,并利用电子背散射技术观察了疲劳前、后晶粒尺寸的变化.结果表明,超细晶T3铜具有较高的疲劳极限(σ-1=153 Mpa),是粗晶铜疲劳极限的2倍.在低周疲劳域内表现出疲劳软化,而在高周疲劳域内表现比较稳定的疲劳行为,甚至出现疲劳硬化.类似驻留滑移带(PSB)的剪切带与最后一次挤压的剪切面一致,剪切带的形成和晶界滑移是疲劳裂纹形核和疲劳断裂的主要原因.     

Reliability and wearout characterisation of LEDs

LEDs play a key role as an active element in electronic circuitry – for example in optocouplers. Their life time strongly depends on the operation conditions. Degradation usually starts by the generation of both reverse and forward bias direction pinpoint leakage paths. When the resistance of such a path becomes lower than the regular operational resistance in forward direction, it will start to act as a bypass. Then, reduced and inhomogeneous emission is the first degradation indicator. The paper describes degradation mechanisms and their characterisation.     

Reading distance degradation mechanisms of near-field RFID devices

In case of operation distance degradation, frequently RFID chips are extracted from their tags and electrically/physically analysed. However, manifold mechanisms based on interaction effects between package and device, exist. This paper examines and highlights these mechanisms, giving also valuable hints for the failure analyst.     

Steam reforming of hexadecane over a Rh/CeO2 catalyst in microchannels: Experimental and numerical investigation

Hexadecane is chosen as diesel surrogate to experimentally and numerically investigate diesel reforming in microchannels coated with Rh/CeO₂. A detailed kinetic model is presented and discussed using experimental data on steam reforming of not only hexadecane but also of methane and propane providing a more detailed understanding also of conversion of hexadecane fragments. The turnover frequencies of these linear alkanes were found to be inversely proportional to the number of carbon atoms per hydrocarbon molecule. Based on these results, a kinetic model was developed that links a global reaction equation for the dissociative adsorption of long-chain hydrocarbons with an elementary surface reaction mechanism of steam reforming of methane over Rh/Al₂O₃ catalysts. The model adequately describes the observed correlation between turnover frequency and the number of carbon atoms the hydrocarbon contains. Furthermore, a significant impact of the ceria support on the reformate composition was observed.     

Palladium(0) Nanoparticles on Glass‐Polymer Composite Materials as Recyclable Catalysts: A Comparison Study on their Use in Batch and Continuous Flow Processes

Palladium particles were generated by reduction of palladate anions bound to an ion exchange resin inside microreactors. The size and distribution of the palladium particles differed substantially depending on the degree of cross‐linking and the density of ion exchange sites on the polymer/glass composites, the latter parameter having a larger influence than the former. The polymer phase of the composite materials was used for the loading with clusters composed of palladium particles which are 1 to 10 nm in diameter. The reactivity and stability of six different palladium‐doped polymer/glass composite samples for transfer hydrogenations was investigated both under conventional and microwave heating in the batch mode as well as under continuous flow conditions using the cyclohexene‐promoted transfer hydrogenation of ethyl cinnamate as a model reaction. Regarding the heating method it was found that catalysts that are composed of larger metal particles perform better under microwave irradiating conditions whereas samples with smaller particle sizes perform better under conventional heating. Comparing batch experiments with flow‐through experiments the latter technique gives better conversion. Reusability was better in microwave heated experiments than in traditional heating.