Carbide Derived Carbon as a Possible Catalyst Support for PEMFC

Abstract

During last ten years various carbides have been used as raw material for synthesis of micromesoporous carbons with exact pore size distribution. It has been recognized that, depending on the heat-treatment temperatures, different carbon materials exhibit different properties, such as surface area, porosity, electrical conductivity and cathodic oxygen electroreduction activity [1-4].In addition, an intensive research has focused on the development of electrocatalyst for the oxygen electroreduction reaction (ORR) because in a PEM fuel cell, the major limit on performance is the slow cathodic oxygen electroreduction process[5-7].The main aim of this work was to investigate the behavior of the micromesoporous carbon supports, prepared from WTiC2, TiC, Mo2C using chlorination process at various temperatures from 750°C to 1100°C (with specific surface area 360 m2g-1, 880 m2g-1 and 2020 m2g-1, respectively), as a electrocatalysts for the ORR [1,2,8,9] and to analyze ORR kinetics in 0.1 M KOH solution. For comparison commercially available VulcanXC72®was also used.Raman spectroscopy, XRD, SEM-EDX, HRTEM methods were applied for structural and electronic characterization of the materials [8,9]. Gas adsorption at liquid nitrogen temperature was used for the porosity analysis of the materials under discussion.The electrochemical measurements were carried out in a three-electrode electrochemical cell. Several important reaction parameters, such as the number of electrons involved in the ORR, Tafel slopes, and the kinetic rate constant for the ORR, were obtained from the RDE measurements.Potentials were measured against Hg|HgO|0.1M KOH reference electrode. Rotating disc electrode (RDE) data were measured at rotation rates from 0 to 3000 rpm (potential scan rate v=10 mV∙s-1) and in the region of potentials from +0.21 to -0.75 V vs. Hg|HgO|0.1M KOH. Cyclic voltammograms were measured at potential scan rates (v mV/s) 5, 10, 20, 30, 50, 70, 100, 150 and 200, in the case of both Ar and O2saturated solution.Electrochemical data for unmodified micromesoporous carbon electrodes show that the catalytic ORR activity and mechanism noticeably depends on the porous structure of a carbon electrode, i.e. mainly on the micro/meso porosity and specific surface area of electrode under study.C(Mo2C) showed two times higher activity compared to data reported in the literature [7] and somewhat more positive half-wave potential values compared with previously studied amorphous carbon materials. The Tafel plot for the C(Mo2C), is divided into two linear parts. It is also concluded that the partially graphitized carbon C(Mo2C) with a large number of edge plane sites has higher electrocatalytic activity towards oxygen reduction in alkaline media, compared with amorphous carbons studied previously [1-4]. Acknowledgements:This work was supported by the Estonian Centre of Excellence in Science Project TK117T "High-technology Materials for Sustainable Development", the Estonian Energy Technology Program project SLOKT 10209T, the Materials Technology project SLOKT12180T.