PhD candidate Zhi Qiao is developing porous graphitic carbon with a balance between graphitization and porosity for the support of Pt-based fuel cell catalysts.
With environmental concerns arising in every corner of the world, proton-exchange membrane fuel cells (PEMFCs) has emerged as one of the promising technologies that offer an alternate method for the production of energy in the form of electricity. Ideally, PEMFCs would take hydrogen and oxygen as the reactants with water and electricity produced as the products. Precious metal-based catalysts (often platinum(Pt) based) are employed as the catalysts to drive the reaction forward for this carbon-free technology. In fact, the performance of the precious metal-based catalyst is the most crucial component to commercialize PEMFCs.
The current state of the art of PEMFCs catalysts are Pt and Pt-alloys need support to provide the most promising catalytic activity and durability. Different conductive material has been studied as the support for Pt-based active sites, including nanostructured carbons, conductive diamonds, conductive oxides, and carbides. Among them, the nanostructured carbon material is believed the most beneficial material with high surface area, high electrical conductivity and strong interactions with Pt. However, carbon corrosion could occur when operating the PEMFCs with high oxygen concentration, low pH, and high electrode potential conditions. High degree of graphitization of carbon could improve corrosion resistance; however, it always leads to low surface area and porosity for dispersing Pt nanoparticles and efficient mass transports. Graphitized carbon represented by carbon nanotubes (CNTs) and amorphous carbon represented by mesoporous carbon are the two types of carbon material that attracted significant attention in recent years. Nevertheless, neither of them could reach the balance between graphitization and porosity, which is believed to be the most desired control to supported Pt nanoparticles.
Gang Wu research on catalysts for PEMFCs focuses on the development of designed porous graphitic carbon with a balance between graphitization and porosity for the support of Pt-based catalysts. The approach takes advantages of 3D polymer hydrogel in combination with Mn, in which 3D hydrogel provides high porosity at multiple scales, and Mn catalyzes the graphitization of carbon structure. Therefore, the favorable porous morphology help to improve the dispersion and utilization of Pt nanoparticles. The binary polyaniline (PANI) and polypyrrole (PPy) are found superior to the individual polyaniline, generating more stable and favorable carbon. Mn plays a critical role in improving the resistance of carbon corrosion by increasing the degree of graphitization. The synthesis scheme of the material can be found in Figure 1. Compared with commercial XC-72 carbon black support Pt (Pt/C), remarkably enhanced stability and minimized carbon loss were identified for the PGC supported one through accelerated stress tests (ASTs) at a high potential range in both aqueous electrolyte and membrane electrode assemblies (MEAs). Less aggregation of Pt nanoparticles was also observed, which may be due to unique carbon structure and nitrogen doping on carbons strengthening interactions between PGC and Pt nanoparticles. The newly developed porous graphitic carbon support derived from PANI/PPy-Mn Hydrogel by Qiao exhibited significantly enhanced stability for oxygen reduction reaction (ORR) in acidic media for PEMFCs. This new carbon material may provide a solution to address challenging issues of carbon supports for PEMFCs.