Synthesis and characterization of surfactant-stabilized PVC nanocatalysts for fuel cell applications

Platinum nanocatalysts supported on Vulcan XC-72 carbon have been synthesized through the reduction of chloroplatinic acid with formic acid, using surfactant tetraoctylammonium bromide (TOAB) as the stabilizer in the solvent tetrahydrofuran (THF). These nanocatalysts are synthesized by changing the molar ratio of TOAB to chloroplatinic acid, i.e., N/Pt ratio of 0.76, 0.38, and 0.19. A control catalyst that does not contain TOAB is also synthesized by this method for comparison purposes. Comparison of the morphological properties of these catalysts by transmission electron microscopy (TEM) reveals that the N/Pt ratio of 0.76 catalyst has well-separated smaller particles (2.2 nm) than the other lower molar ratio and control catalysts. X-ray diffraction (XRD) analysis indicates the presence of platinum in the fcc phase and the average size of the particles calculated from the XRD peak widths agreed well with the TEM results. X-ray photoelectron spectroscopic (XPS) measurement of the 0.76 ratio catalyst reveals that a higher amount of Pt exists in its metallic state (73.64% of Pt(O) and 26.36% Pt(II)) and the data are on par with that of the E-TEK catalyst. Stabilization effect of the TOAB on the surface of platinum particles has been discussed with respect to the different N/Pt molar ratios. The XPS technique has been exploited to prove the presence of coverage of TOAB and its subsequent removal from the surface of the Pt particles, which is considered to be the crucial step prior to the electrochemical measurements. Electrochemical measurements have demonstrated that the surface area of the 0.76 ratio catalyst is higher than that of the lower molar ratios (0.38 and 0.19).