Synthesis and characterization of cathode catalysts for use in direct methanol fuel cells

Abstract

In this work a modified pol yo I method was developed to synthesize in-house catalysts. The method was modified for maximum delivery of product and proved to be quick and efficient as well as cost effective. The series of IH catalysts were characterized using techniques such as UV -vis and FT -IR spectroscopy, TEM, XRD, ICP and CV. The polyol method developed effectively reduced and deposited Pt nanoparticles onto different carbon supports. Functionalization of some of the supports was also successfully carried out through acid oxidative treatment which introduced carboxylic acid and hydroxyl groups onto the surface of the supporting material, which was supported by FT-IR which demonstrated that there was a relative increase in absorbance of functionalities viz., carboxylic acid (l270 em") and hydroxyl groups on the surface of the acid treated MWCNT's-F compared to the untreated MWCNT's. Addition of a sedimentation promoter proved to increase the amount of metal deposition on the support thereby improving the loading dramatically. It was also found that addition of a specific amount of water in the polyol method allowed one to control the particle growth during the deposition phase on the various carbon supports investigated namely; XC-72 carbon, MWCNT's and MWCNT's-F. The in-house catalysts synthesized namely; PtJC-IH, PtJMWCNT's-IH and PtJMWCNT's-F-IH all displayed narrow particle size distributions with average mean particle sizes of 2-5 nm, 2-6 nm and 3-6 nm respectively which was in good agreement with particle size measurements obtained from XRD using the Scherrer formula. All measured CV's obtained for the series of IH catalysts prepared by this protocol were comparable with the commercial catalyst. The IH catalysts displayed the characteristic XRD peaks associated with Pt on carbon supports in acidic media. The ORR measurements for PtJMWCNT's-F-iH (functionalised) proved to be slightly superior (0.058 Azcm") compared to that of the commercial catalyst (0.047 Alcm2) at a potential of O.3V.