Influences of fuel crossover on cathode performance in a micro borohydride fuel cell

Influences of borohydride crossover on cathode performance were studied in a micro direct borohydride fuel cell (DBFC). The results showed that fuel crossover resulted in decreases in open circuit potentials of cathodes. On the other hand, effects of fuel crossover on cathode overpotentials strongly depended on the cathode material. The Pt/C cathode demonstrated a small potential drop of 0.11 V, while the Ag/C cathode had a much larger potential drop of 0.26 V under the same condition. Fuel crossover was found to be depressed during current operations. It is possible that fuel depletion happened around the anode during operation, resulting in a decrease of fuel concentration gradient across the membrane and thus less crossover. Experiments also showed that a balance in wet-proof property is essential for the cathode in the direct borohydride fuel cell and the stability of cell performance was mainly dependent on wet-proof durability of the cathode.     

碘的选择性吸附方法及其应用——Ⅰ.铜基铂对碘的吸附和解吸性能

铜基铂在 pH≤6.2的多种酸性介质中,对 I~- 都有很高的吸附效率(>99％),吸附速度快、选择性高。每立方厘米吸附剂的吸附容量约为0.7mg碘。淋洗收率取决于吸附碘量及淋洗碱液浓度,在 1.5cm~3的柱上,对>80μg的碘,用 10—15个柱体积的 0.3NNaOH淋洗,可接近定量回收。产品液放化纯度≥99.9％;化学纯度也高。铜基铂耐辐照性能良好,可重复使用。适用于多居里级放射性碘的制备等多种用途。纯铜粉对I~-的吸附和解吸规律与铜基铂相同,唯吸附容量、抗干扰等性能较差。     

电化学氧化锆氧传感器的多孔铂电极(连载三)——(三)多孔铂电极的影响因素探讨

用SEM、EDAX、数字图象技术和直流电极极化测量等手段分析了加热温度、时效时间、成分扩散及氧浓度对电极性能的影响。研究结果表明,电极形貌显著地受其加热温度的影响,这导致当电极加热温度升高后,电极的极化程度也增大,而电极形貌受时效时间的影响很小;扩散到Pt电极中的Al元素会显著地加剧电极极化。而且在低氧浓度下,电极的极化程度也大为加剧。     

Microstructural, compositional and magnetic characterization of electrodeposited and annealed Co-Pt-based thin films

Near-equiatomic Co-Pt thin films with thicknesses of 520 nm were deposited from a single electrolyte onto glass-based Au-coated substrates using the electrodeposition method. The as-deposited Co-Pt-based films were annealed at temperatures from 500 ºC to 700 ºC for 1 h. The phase formation, microstructure and the magnetic properties were analyzed. It was found that with an increase of the annealing temperature the coercivity increases up to 1.18 T due to the transformation to the L1₀ phase. In contrast to the coercivity the saturation magnetization and the remanence were found to decrease upon annealing, due to the decrease of the Co concentration in the Co-Pt film because of the oxidation and the interdiffusion reactions between the Co-Pt thin film and the substrate.     

Impedimetric approach for monitoring the formation of biofilms on metallic surfaces and the subsequent application to the detection of bacteriophages

This paper describes an impedimetric method for monitoring the formation of bacterial biofilms on the surface of platinum and gold electrodes and its application for the indirect detection of bacteriophages. Impedance spectroscopy measurements showed that the biofilm capacitance, C_biofilm, the parameter of the electrical circuit which modelled the biofilm growth, was sensitive both to the biofilm growth and to its degradation as a consequence of the bacteriophage infection. Impedance results were compared with optical and confocal microscopy studies showing a good correlation. These results guarantee further work in this area to develop portable devices for the detection of bacteriophages.     

Analysis of Gd Level and Pt Dispersion on Ceria Support for Isobutane Steam Reforming

Ceria-supported platinum catalysts were used to produce hydrogen by isobutane steam reforming. The influence of gadolinia, as a trivalent cationic oxide (M₂O₃) dopant at 0–20%, is investigated here. The gadolinia content in the catalysts did not correlate well with reforming activity. The platinum dispersion ranged from 29 to 38% as measured by the propylene hydrogenation method and it did correlate well with reforming activity.     

Ultrathin platinum-group metal coated hierarchical flowerlike gold microstructure: Electrochemical design and characterization

The deliberate tailoring of hierarchical flowerlike gold microstructure (HFGMs) at the ultrathin level is an ongoing challenge and could introduce opportunities for new fabrication and application in many fields. In this paper, a templateless, surfactantless, electrochemical strategy for fabrication of ultrathin platinum-group metal coated HFGMs is proposed. HFGMs were prepared by simple electrodeposition on an indium tin oxide (ITO) substrate. The resulting HFGMs enables the deposition of an ultrathin overlayer through copper underpotential deposition (UPD), followed by spontaneous replacement of the copper with the platinum-group metal to yielded a uniform and ultrathin Pt-group metal layer on the HFGMs surface. Thus prepared bimetallic “core-shell” sample has been characterized by cyclic voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray maps and X-ray diffraction (XRD). This is a very general and powerful technique for the fabrication of hierarchical, ultrathin coating, bimetallic “core-shell” microstructure, which, in turn, opens up the possibility of building more complex multicomponent hierarchical microstructure with potential application, such as electrocatalysis, biosensors and nanodevices, etc.     

The influence of solution pH on rates of an electrocatalytic reaction: Formic acid electrooxidation on platinum and palladium

We found for the first time that solution pH makes a significant difference in the rate of a prototypical electrocatalytic reaction, formic acid electrooxidation, under conditions where H⁺ and OH⁻ do not adsorb strongly on the surface, and we demonstrate that the results can be explained using the Marcus model. We changed the pH of formic acid solutions and found enhanced oxidation on Pd and Pt black catalysts with increased pH. The interpolated current density for the oxidation of 1 M HCOOH in 0.1 M perchlorate electrolyte after 2 min at 0.22 V vs. SHE on Pt increased 30-fold from 0.005 to 0.17 mA cm⁻² as the pH was increased from 1 to 5, while for Pd there was a 4-fold increase from 0.12 to 0.53 mA cm⁻². The data was also interpolated at a current density of 0.1 mA cm⁻², and the potential required to reach this current shifted negative 62 mV per pH on palladium and 56 mV per pH on platinum. A 24 h experiment compared two solution pH, in which the higher pH demonstrated remarkably stronger performance. In addition, the potential for oxidation of surface CO shifts negative on both catalysts, as much as ∼57 mV per pH on Pd.     

Room temperature synthesis of colloidal platinum nanoparticles

Efficient preparation of stable dispersions of platinum nanoparticles from platinous chloride (K₂PtCl₄) was achieved by simultaneous addition of capping polymer material. The size of platinum nanoparticles was controlled by changing the ratio of concentration of capping polymer material to the concentration of platinum cation used. The morphology of colloidal particles were studied by means of UV-visible spectrophotometry and transmission electron microscopy (TEM). Particle size increased with low reagent concentration. The change in absorption spectra with the particle size was observed, i.e. blue shift attributed to decrease in particle size Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Effect of methanol, ethylene glycol and their oxidation by-products on the activity of Pt-based oxygen-reduction catalysts

Direct-oxidation fuel cells (DOFC) are promising electrochemical devices for various applications. In addition to methanol (MeOH), alternative fuels are being tested in a search for lower toxicity, safer handling, and higher energy density. Ethylene glycol (EG) was employed as one of such fuels. However, DOFCs face several problems, such as fuel crossover through the membrane during its operation. This not only lowers the cell potential but also poisons the catalyst for the oxygen-reduction reaction (ORR). Experiments were performed on the poisoning of Pt and Pt-alloy ORR catalysts (both commercial and homemade, by electroless deposition), by fuels and their oxidation by-products. At 25 °C, methanol poisoning was found to be reversible and the catalytic activity measured afterwards in a fuel-free solution and the electrochemical surface area (ECSA) were enhanced. The effect of poisoning by methanol and ethylene glycol and their oxidation intermediates is reported here for the first time. The severity of poisoning was found to be MeOH ? formaldehyde < formic acid. In solutions of EG and its oxidation by-products, the poisoning order was EG ≤ glycolic acid < oxalic acid, the poisoning of all three being more severe than that of methanol. The catalysts most resistant both to MeOH and EG poisoning were commercial acid-treated PtCo and homemade PtCoSn. The reasons for the enhanced tolerance were investigated and PtCoSn was found to be the less active both in the methanol and ethylene glycol oxidation processes.