Acatalytic procedure incorporated with a concentration-jump chemical relaxation methodwas proposed, based on detectionby UV-VIS spectrophotometry. The chemical relaxation process of Fe(Ⅲ)-bipyridyl complex reduced to Fe(Ⅱ)-bipyridyl byphotoreduction in the presence of cobalt(Ⅱ) as a catalyst had been studied. The systemwas first pre-equilibrated, and afterwardsa perturbation (concentration-jump) of Fe(Ⅲ), which is about 30% of the pre-equilibrium concentration was introduced. Thesystem was allowed to relax to a new state of equilibrium, and the relaxation process was recorded. The calibration graphof relaxation time (1/τ) and cobalt concentration is linear for 0-2.5mgml-1. The 3σdetection limit is 12ng ml-1, and therelative standard deviation for 1mgml−1 level ofCo2+is 3.6% (n=4). The procedure had been validated by the determinationof cobalt in a certified reference material and a soil sample, with coefficients of variances of 1.3 and 2.9%, respectively. Arecovery test is also performed for the soil sample by spiking, and the recovery of 98% was obtained.

The CO poisoning effect on carbon-supported platinum catalysts (at a loading of 0.5mg Pt/cm2 per electrode) in polymerelectrolyte membrane fuel cells (PEMFC) has been investigated in a temperature range from 125 to 200℃ with the phosphoricacid-doped polybenzimidazole membranes as electrolyte. The effect is very temperature-dependent and can be sufficiently suppressedat elevated temperature. By defining the CO tolerance as a voltage loss less than 10mV, it is evaluated that 3% CO inhydrogen can be tolerated at current densities up to 0.8 A/cm2 at 200℃, while at 125℃ 0.1% CO in hydrogen can be tolerated atcurrent densities lower than 0.3 A/cm2. For comparison, the tolerance is only 0.0025% CO (25ppm) at 80℃ at current densitiesup to 0.2 A/cm2. The relative anode activity for hydrogen oxidation was calculated as a function of the CO concentration andtemperature. The effect of CO2 in hydrogen was also studied. At 175℃, 25% CO2 in the fuel stream showed only the dilutioneffect.

Phosphoric acid doped polybenzimidazole (PBI) and PBI composite membranes have been prepared in the present work.The PBI composites contain inorganic proton conductors including zirconium phosphate (ZrP), (Zr(HPO4)2•nH2O), phosphotungsticacid (PWA), (H3PW12O40•nH2O) and silicotungstic acid (SiWA), (H4SiW12O40•nH2O). The conductivity ofphosphoric acid doped PBI and PBI composite membranes was found to be dependent on the acid doping level, relativehumidity (RH) and temperature. A conductivity of 6.8×10-2 S cm-1 was observed for PBI membranes with a H3PO4 dopinglevel of 5.6 (mole number of H3PO4 per repeat unit of PBI) at 200℃ and 5% RH. A higher conductivity of 9.6×10-2 S cm-1was obtained by composite of 15 wt.% of ZrP in a PBI membrane under the same conditions. Homogeneous membraneswith good mechanical strength were prepared by introducing PWA (20-30 wt.%) and SiWA (20-30 wt.%) into PBI, and theirconductivity were found to be higher than or comparable with that of the PBI membrane at temperatures up to 110℃.

On-board generation of hydrogen by methanol reforming is an efficient and practical option to fuel PEMFC especially for vehicle propulsionpurpose. The methanol reforming can take place at temperatures around 200℃ with a nearly 100% conversion at a hydrogen yield of about400L (h kg catalyst)−1. The CO content in the reformate gas at this temperature is less than 0.2vol.%. The recently developed high temperature PEMFC based on acid-doped PBI membranes can operate in the same temperature range and tolerate a few percent of CO in the feeding gas.The high CO tolerance makes it possible to use the reformate gas directly from the reformer without further CO removal. Integration of hightemperature PEMFC with a reformer is expected to improve the system efficiency and simplify the system construction and operation. Thepresent work has demonstrated this possibility.

Polybenzimidazole (PBI) membranes have been prepared with different molecular weights. When doped with phosphoric acid the membranes exhibit proton conductivity and have beenproposed for use as electrolyte in fuel cells. The swelling, mechanical strength, gaspermeability and proton conductivity were studied for the pristine and acid doped PBI membranes. When doped with 5 moles phosphoric acid per mole repeat unit of the polymer, alevel necessary to obtain high enough proton conductivity, a volume swelling by ca. 120%was observed, resulting in separation of the polymer backbones. The separation in turnreduces the mechanical strength of the membrane especially at high temperatures from 120 to 180℃. High molecular weight of the polymers improves the mechanical strength. Anotherconsequence is the increased H2 and O2 permeability through the membrane. In thetemperature range from 120 to 180℃, the hydrogen permeability was found to be 1.6 to 4.3×10-12mol.cm.cm-2.s-1.bar-1 and 1.2 to 4.0×10-10mol.cm.cm-2. s-1.bar-1 for pristine and aciddoped PBI membranes, respectively, while for oxygen it was 5.0 to 10 10-14mol.cm.cm-2.s-1.bar-1 and 3.0 to 9.4×10-11mol.cm.cm-2.s-1.bar-1, respectively. Conductivity measurementsshowed little influence of the polymer molecular weight.