The effect of carbon nanofiber properties as support for PtRu nanoparticles on the electrooxidation of alcohols

Carbon nanofibers (CNFs) characterized by different mean diameter, BET surface area, pore volume and crystallinity were prepared and studied as supports for PtRu nanoparticles to investigate the influence of the support characteristics on the performance for the electrooxidation of alcohols. A modified microemulsion procedure was used to deposit the metal nanoparticles minimizing the effect of the support on the catalyst particle size. PtRu nanoparticles of ca. 2 nm size were obtained despite the relatively low surface area of CNFs (95-185 m(2) g(-1)) with a good distribution on the surface as confirmed by TEM micrographs and the high values of the electrochemically active surface areas (110-140 m(2) g(-1)) determined by electrochemical CO stripping. The most appropriate PtRu dispersion was achieved for those carbon nanofibers showing the best compromise in terms of BET surface area and graphicity. A cross-analysis of the supports physico-chemical properties, ECSA and mass activity for the methanol and ethanol oxidation reactions suggests that both PtRu dispersion and electronic properties as determined by the effect of CNF crystallinity play a significant role in determining the electrocatalytic activity. Different electrocatalytic activity behavior with CNF properties were found for methanol and ethanol. Methanol oxidation is favored using highly crystalline CNFs as PtRu support, despite their low surface area, whereas ethanol oxidation is hindered by diffusional problems when using highly graphitic CNFs due to their low pore volume, so the activity is maximized supporting PtRu on CNFs with a more accessible porosity. (c) 2012 Elsevier B.V. All rights reserved.