Slow Morphological Change of Perfluorinated Ionomer as Deduced From 1H NMR Spectra of Confined Water

The behaviour of water molecules confined in the perfluorinated ionomer membrane, which is widely used for polymer electrolyte fuel cells, was investigated by 1H NMR spectroscopy. The 1H NMR spectra of water molecules confined in the membrane presented characteristic features depending on temperature and hydrated conditions. On the basis of the observations of the variations in the 1H NMR signals, it was deduced that the polymer underwent very slow conversions among distinct morphologies depending on temperatures and humidified conditions below 348 K. A plausible scheme of the local conversion of the states of the water molecules associated with the morphological changes of the polymer was proposed

Estimation of water contents of polymer electrolytes by 1H NMR spectroscopy

Water molecules confined in perfluorinated ionomer membranes which are widely used for polymer electrolyte fuel cells, presented apparently a single 1H NMR peak in hydrated states because of the rapid exchange among the water molecules at the distinct segments of the polymer. The peak shifted to the lower field with decreasing the water content due to the decrease of the fraction of the bulk water molecules which present a peak at higher field. The chemical shifts were found to be well correlated with the peak area. The water peak for MEA (Membrane Electrode Assembly) showed also similar behaviors to the membranes. From the relationship between the chemical shift and the peak area of the confined water peak we demonstrated the potential that the chemical shift could be utilized to estimate the water content in the hydrated membranes and MEA

The Effect of Platinum Deposition on the Water Photo-Reduction at p-Cu2O Semiconductor Electrodes with Visible Light Irradiation

The surface of a p-Cu2O semiconductor photoelectrode was modifi ed by electrodeposition of Pt nanoparticles and analyzed by XRD, SEM, XPS, and EIS (electrochemical impedance spectrometry) methods besides photocurrent measurements. The XRD, SEM, and XPS analyses showed the fabrication of Cu2O fi lm and the deposition of Pt particles. On the electrodeposition of Pt nanoparticles, cathodic photocurrent was enhanced. The EIS analysis suggested that Pt nanoparticles enhance the charge transfer process to the solution

Enhanced Photoelectrocatalytic Activity of FTO/WO3/BiVO4 Electrode by Modified With Gold Nanoparticles for Water Oxidation Under Visible Light Irradiation

Gold nanoparticles were successfully deposited on FTO/WO3/BiVO4 electrode surface by means of electrolysis of AuCl4 - ions. The composite films were characterized by SEM, XPS and XRD techniques. An increase in photocurrent and a negative shift of onset potential for water oxidation were observed upon modification of the electrode surface with the Au particles. The electrochemical impedance spectroscopy was used to confirm the acceleration of charge transfer process by Au deposition at the electrode surface. The photocurrent action spectrum did not correlate with the plasmonic absorbance of Au nanoparticles at 560 nm, suggesting that the Au nanoparticles increased charge separation without undergoing a plasmon resonance effect under visible light irradiation

Generation and Detection of Reactive Oxygen Species in Photocatalysis

The detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS), i.e., superoxide anion radical (•O2-), hydrogen peroxide (H2O2), singlet oxygen (1O2), and hydroxyl radical (•OH) in photocatalysis, were surveyed comprehensively. Consequently, the major photocatalyst used in heterogeneous photocatalytic systems was found to be TiO2. However, besides TiO2 some representative photocatalysts were also involved in the discussion. Among the various issues we focused on the detection methods and generation reactions of ROS in the aqueous suspensions of photocatalysts. On the careful account of the experimental results presented so far we proposed the following apprehension; adsorbed •OH could be regarded as trapped holes, which are involved in a rapid adsorption-desorption equilibrium at the TiO2-solution interface. Because the equilibrium shifts to the adsorption side, trapped holes must be actually the dominant oxidation species whereas •OH in solution would exert the reactivity mainly for non-adsorbed reactants. The most probable routes of generating intrinsic ROS at the surfaces of two polymorphs of TiO2, anatase and rutile, were discussed along with some plausible rational reaction processes. In addition to the four major ROSs, three ROSs, that is organic peroxides, ozone, and nitric oxide, which are less common in photocatalysis are also briefly reviewed

Behavior of Water molecules in pefcs as studied by 1H NMR spectroscopy

Water molecules confined in perfluorinated ionomer membranes which are extensively used for polymer electrolyte fuel cells, presented characteristic 1H NMR spectra reflecting the difference in the morphology. For the hydrated membrane the water molecules at the distinct segments of the polymer undergo rapid exchange to give an apparent single signal. The signal shifts to the higher field with increasing the water content due to the increase of the fraction of the bulk water molecules. On shortage of bulk water the morphological conversion takes place. The membrane of such morphology exhibits a spectrum with separated regions at room temperature regardless of the water content, since the morphology prohibit the rapid exchange among the water molecules localized at the distinct segments. The characteristic spectral changes of water molecules associated with the chemical exchange among the water molecules in the different water domains and the change of the polymer morphology were demonstrated

Reconsideration of Intrinsic Band Alignments within Anatase and Rutile TiO2

It has been long believed that potential of the conduction-band bottom (ECB) of anatase is 0.2 eV higher (more negative) than that of rutile. However, according to the recent theoretical calculation and X-ray photoelectron experiments, the ECB of anatase was suggested to be lower than that of rutile to the contrary. This discrepancy could be explained on the assumption that the previously reported ECB of TiO2 obtained by the electrochemical measurements for anatase reflected the domination of conduction band for the direct-bandgap of 3.8 eV but not for the indirect-bandgap of 3.2 eV. This amendment would support the band alignments recently suggested by theoretical calculations