Abstract
The carbon corrosion behavior of several carbon support materials for proton exchange membrane fuel cell (PEMFC), including commercial carbon black (Vulcan XC-72, Ketjen black ECP300, Ketjen black ECP600), graphitized carbon black and multi-wall carbon nanotubes (MWCNTs), was investigated by using the electrochemical quartz crystal microbalance (EQCM) method. The mass change during cyclic voltammetry (CV) in deaerated 0.5 M H2SO4 solution at 298 K can be observed by the frequency change of EQCM. During the positive scan, the carbon surface oxides were formed and accumulated on the carbon surface leading to an increase of the mass as the potential increasing. In the higher potential region, a drop in mass associated to carbon loss was observed which was attributed to the gasification of surface carbon oxides to carbon dioxide. Examine the mass change rate and mass drop onset potential, the behavior of electrochemical carbon corrosion was discussed. The influence of specific surface area and graphitization of carbon supports were also investigated in this study. The results indicate that high BET surface area carbon blacks rendered less resistant to electrochemical carbon corrosion. Graphitized XC-72 and MWCNTs with higher graphitization degrees appear more intrinsically resistant to electrochemical carbon corrosion. The commercial carbon support Vulcan XC-72 was graphitized by conventional high temperature heat treatment at various temperatures to increase the graphitization and improve the electrochemical corrosion stability of commercial carbon support Vulcan XC-72. The result shows XC-72 can be obviously increase the graphitization after 2200℃ conventional high temperature heat treatment. Meanwhile, the BET surface area and the surface functional groups of carbon support XC-72 was strongly decreased after heat treatment. After oxygen plasms treatment, the graphitized XC-72 carbon black has increased the BET surface area and the O/C ratio of surface similar to the as-received XC-72. Therefore, oxygen plasma treatment is an effective method to provide graphitized carbon blacks with surface functional groups that can act as anchoring sites to favor dispersion and deposition of platinum particles on their surface and could be helpful to prevent platinum particles agglomeration. Comparing to conventional high temperature heat treatment, carbon support XC-72 can be graphitized rapidly by SPS method only within few minutes. Moreover, the SPS treated carbon support XC-72 do not suffer from high levels of hydrophobic character which can create problems with active phase dispersion and ink formulations. The results revealed that the SPS is an effective method to enhance the electrochemical stability and surface properties of carbon blacks for the application of PEMFC.