Strategies for probing Pt-based electrocatalyst and ionically conductive membrane materials: voltammetry of Pt, PtRu and PtV nanoparticles and infrared studies of membrane hydration

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Title: Strategies for probing Pt-based electrocatalyst and ionically conductive membrane materials: voltammetry of Pt, PtRu and PtV nanoparticles and infrared studies of membrane hydration
Author: Basnayake, Rukma Sanjeewanie Tissera
Abstract: Materials aspects of low temperature ( < 100 °C ) fuel cell systems were investigated . The first studies presented examine properties of nanometer scale catalyst materials toward the electrochemical oxidation of carbon monoxide (CO ) and methanol (CH3OH ) in acid electrolyte solutions . Catalyst samples studied include carbon supported Pt (C /Pt ) , Pt black , PtRu and PtV . Special focus was on bimetallic materials prepared using sonochemistry . The second area discussed explores hydration in Nafion thin film and freestanding membrane materials . Effects of hydration on Nafion backbone and side -chain groups and interactions of solvent with the polymer were investigated with the use of transmission infrared spectroscopy . For the C /Pt containing 40 wt . % Pt catalyst , the average yields of CO2 from electrochemical oxidation of 0 .3 M CH3OH in 0 .1 M acid electrolyte solutions determined following 180 s electrolysis periods exceeded 50 % for potentials ¡Ý 0 .6 VRHE . Experiments on PtRu nanoparticles prepared through a sonochemical method show the PtRu materials have properties of uniform bulk alloys . In studies of CH3OH and CO oxidation , sonochemically prepared (SC ) PtRu samples containing 10 at . % Ru (XRu = 0 .1 ) and 50 at . % Ru (XRu = 0 .5 ) displayed activities relative to the catalyst active surface area consistent with responses for bulk PtRu having similar composition . Studies of SC PtV showed the material has high resistance toward poisoning by adsorbed CO . However , PtV was not as active as Pt black toward CH3OH oxidation . For the membrane material Nafion , vibrational modes of polymer bands and water inside membrane pores and channels were identified by infrared spectroscopy and observed to be sensitive to film hydration . In the H+ exchanged form , -SO3 - groups were shifted to -SO3H and water was easily removed upon exposure to a few torr of vacuum at 95 °C . In contrast , residual water was retained by membrane exchanged with Na+ after exposure to these conditions for up to 72 hours . The permeation of CH3OH and acetone ( (CH3 )2CO ) into Na+ exchanged freestanding (Nafion 112 ) membrane was also examined . The C -H and O -H stretching modes of CH3OH were perturbed in a manner that suggests the polymer disrupts hydrogen bonding interactions within the solvent , similar to the effect it exerts on pure water . For acetone , the C -H stretching modes were not shifted appreciably compared to those of the bulk liquid . However , the carbonyl band was affected , indicating the likely importance of dipolar interactions between solvent molecules and polar groups on the polymer . Control experiments performed with poly (hexafluoropropylene -co -tetrafluoroethylene ) (FEP ) membrane did not show evidence for water or CH3OH permeation , which demonstrates the critical role played by the ion filled channels and pores in facilitating solvent transport within Nafion membrane .
URI: http : / /hdl .handle .net /2346 /12869
Date: 2006-12

Citation

Basnayake, Rukma Sanjeewanie Tissera Strategies for probing Pt-based electrocatalyst and ionically conductive membrane materials: voltammetry of Pt, PtRu and PtV nanoparticles and infrared studies of membrane hydration. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /12869 .

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