Oxygen reduction activity dependence on the mesoporous structure of imprinted carbon supports

Two mesoporous carbons (with 15 (CIC-15) and 26 nm (CIC-26) diameter pores) were synthesized using a silica colloid imprinting method, loaded with 10 wt.% Pt, and then evaluated (against Vulcan (TM) carbon (VC)) as oxygen reduction (ORR) catalysts for use in proton exchange membrane fuel cells. Both Pt/CICs reproducibly out-performed Pt/VC, with Pt/CIC-15 demonstrating higher ORR activity than Pt/CIC-26, despite its smaller pore size and lower surface area. Transmission electron tomography showed that the Pt nanoparticles (4-5 nm diameter) are fully deposited throughout the pores of the CICs and that the pore distribution in CIC-26 is partially ordered, while CIC-15 shows no ordering of its pores. Importantly, using the powerful imaging capabilities of transmission electron tomography, a first-time correlation is demonstrated between the ORR activity and the wall thickness of the carbon support materials. Pt/CIC-15 has significantly thicker walls, giving a lower measured electronic resistance, a lower ORR Tafel slope, and thus better performance overall compared to Pt/CIC-26. (C) 2010 Elsevier B.V. All rights reserved.