Impact of framework structure of ordered mesoporous carbons on the performance of supported Pt catalysts for oxygen reduction reaction

Ordered mesoporous carbons (OMCs) are investigated as support materials for Pt catalysts for oxygen reduction reaction (ORR). Three types of OMCs (CMK-3, CMK-3G, and CMK-5) are prepared by a nanocasting method using ordered mesoporous silica, SBA-15, as a template. These OMCs with the same hexagonal mesostructure have different carbon frameworks and graphiticity, which can affect their surface area and microporosity. Pt nanoparticles with an average size of 1 nm are uniformly supported on the three OMCs and Ketjenblack® and their electrochemical performance and durability are evaluated. Pt/CMK-3G exhibits the highest electrochemically active surface area, kinetic current density, mass activity, and half-wave potential, whereas Pt/CMK-3 shows the lowest values. Pt/CMK-3G also shows the highest ORR activity after an accelerated durability test, with a minimal shift in half-wave potential. The higher ORR activity of Pt/CMK-3G is attributed to the formation of highly crystalline Pt particles as well as its highly graphitic, crystalline carbon structure, which causes the weak adsorption of surface oxide and a strong interaction between the Pt particles and the support. Moreover, we can establish that the mass activity of the catalysts is nearly inversely proportional to the micropore volume of the carbon supports.