Electrochemical and material characterization of hybrid SP2/SP3 carbon powders for use in electrochemical power sources

Abstract

Proton-exchange membrane fuel cells (PEMFC's) are promising candidates for the green conversion of hydrogen into electrical energy. A considerable problem preventing the large scale applications of PEMFC's is the inadequate durability of the material components, such as the degradation of the supported electrocatalyst layer. Carbon black (CB) is commonly used as the carbon support, however its stability is limiting for long term PEMFC use. CB in the cathode is oxidized in the start and stop cycling of the PEMFC, detaching Pt nanoparticles and promoting agglomerations,which leads to performance loss. This degradation is due to the aggressive conditions to which the carbon is exposed, such as high water content, low pH, high potential (1.4V vs RHE) and high oxygen concentration. Greg Swain's group at Michigan State University is proposing a new approach to solve the cathode oxidation problem in PEMFC's. This strategy involves the preparation, characterization and electrochemical performance of conducting diamond power. High surface area materials are being prepared by forming a layer of boron-doped ultrananocrystalline diamond (B-UNCD)over the surface of various substrate powders. Conducting diamond is highly corrosion resistant at the open circuit voltage of a PEMFC (ca. 1.0 V) and at potentials that are even more positive. Therefore, it is expected that the corrosion resistance and durability of prepared diamond powders will be much superior that of conventional sp 2 carbon support materials, such as CB. Within this context, the proposed project intends to characterize hybrid sp 2 /sp 3 materials through various techniques. The techniques that will be used are X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy, BET gas adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). These analyses will enable the distinction of sp 2 versus and sp 3 bonded carbon domains and also will possibilitate a correlation to be made between the micro and nanoscale structure of the carbon and the observed electrochemical properties. Additionally, hybrid diamond/nanographene for application in supercapacitors powders are being made, in which B-UNCD coating is formed over sp 2 /sp 3 carbon powders. If time is available,initial electrochemical testing of these materials will also be performed. (AU)