Improved performance of a direct methanol fuel cell by the highly-developed mesopores of the carbon nanofibers catalyst support

Abstract

A prepared carbon nanofibers with mesopores (P-CNFs) by electrospinning utilizing polystyrene (PS) and polyacrylonitrile (PAN) as the pore-forming agent and carbon matrix, respectively, to obtain a thinner catalyst layer which has an enhanced reaction activity for use in a direct methanol fuel cell (DMFC). A PS to PAN mass ratio of 1.00 yielded the highest mesopore volume with an average pore radius of 4.7 nm. PtRu and TiO₂ nanoparticles were coated on the P-CNFs, producing PtRu/P-TCCNFs, and used in a DMFC. The electrochemically active surface area (ECSA) of the PtRu/P-TCCNFs significantly surpassed that of the nonporous carbon nanofibers (PtRu/TCCNFs) and was nearly twice that of the commercially available catalyst, PtRu/C. The improvement of the ECSA value is mainly due to the increased surface area in the mesopore region that facilitates the catalyst nanoparticle dispersion thus preventing agglomeration. Consequently, the methanol oxidation reaction (MOR) mass activity of PtRu(32)/P-TCCNFs reached 438 mA/mg_-PtRu, exceeding that of PtRu(32)/TCCNFs and PtRu/C by 1.27 and 4.56 times, respectively. Furthermore, PtRu(32)/P-TCCNFs demonstrated a superior DMFC performance attributed to the thinner catalyst layer with the increased reaction site density and the reduced ohmic resistance, thus yielding a higher maximum power density.