Abstract
Ball milling is a relative simple and promising technique for preparation of inorganic oxide–carbon type of composites. Novel TiO2-C and Ti0.8Mo2O2-C type of composites containing multi-layer graphene were prepared by ball milling of graphite in order to get electrocatalyst supports for polymer electrolyte membrane fuel cells. Starting rutile TiO2 was obtained from P25 by heat treatment. Carbon-free Ti0.8Mo2O2 mixed oxide, prepared using our previously developed multistep sol–gel method, does not meet the requirements for materials of electrocatalyst support, therefore parent composites with Ti0.8Mo2O2/C = 75/25, 90/10 and 95/5 mass ratio were prepared using Black Pearls 2000. XRD study of parent composites proved that the oxide part existed in rutile phase which is prerequisite of the incorporation of oxophilic metals providing CO tolerance for the electrocatalyst. Ball milling of TiO2 or parent composites with graphite resulted in catalyst supports with enhanced carbon content and with appropriate specific surface areas. XRD and Raman spectroscopic measurements indicated the changes of graphite during the ball milling procedure while the oxide part remained intact. TEM images proved that platinum existed in the form of highly dispersed nanoparticles on the surface of both the Mo-free and of Mo-containing electrocatalyst. Electrocatalytic performance of the catalysts loaded with 20 wt% Pt was studied by cyclic voltammetry, COads-stripping voltammetry done before and after the 500-cycle stability test, as well as by the long-term stability test involving 10,000 polarization cycles. Enhanced CO tolerance and slightly lower stability comparing to Pt/TiO2-C was demonstrated for Pt/Ti0.8Mo2O2-C catalysts.
Highlights
The chemical energy of hydrogen can be transformed efficiently to electricity by means of polymer electrolyte membrane fuel cells (PEMFCs) [1]
Our previous works have showed that high temperature heat treatment (600 °C, 8 h, Ar atmosphere) is essential for the formation of the mixed oxide phase in the T i(1−x)MoxO2-C type of composites [25]
As an effect of ball milling a definite broadening of the peak characteristic for the carbonaceous material appeared in the X-ray powder diffraction (XRD) pattern of sample R-G indicating the change of the starting graphite
Summary
The chemical energy of hydrogen can be transformed efficiently to electricity by means of polymer electrolyte membrane fuel cells (PEMFCs) [1]. Significant efforts have been made to develop novel electrocatalysts for PEMFCs, state of art systems still use CO and corrosion sensitive Pt/C catalysts. The electrolysis of water is playing an increasingly important role, hydrogen fuel is still obtained in large quantities by steam reforming from fossil sources [5]. A critical issue of the usage of hydrogen from the latter source is the presence of carbon monoxide contaminant that poisons the platinum-based catalyst of the PEMFC. The development of novel corrosion resistant catalysts with improved CO tolerance is considered to be an important research goal [6]
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