Engineering the type and size of porosity in carbon catalyst supports used in membrane electrode assemblies of fuel cells has attracted great interest recently. The effort is motivated by the goal of improved electrocatalyst dispersion, long-term chemical stability, and facilitated fuel flow. To date, various carbon catalyst supports including carbon black, graphene, and carbon nanotubes have been studied, yet efforts are still being made to investigate novel catalyst supports for enhanced fuel cell performance. In this work, I conducted a systematic study using hierarchical porous carbons (HPCs) as fuel cell catalyst supports to understand the effect of porosity on fuel cell performance. HPCs combine into a single material platform three different kinds of porosity: macropores (> 50 nm), mesopores (2 – 50 nm), and micropores (< 2 nm). By modifying the ice-templating method developed previously in the Giannelis group, the size of mesopores with high fidelity could be controlled. HPCs featuring high surface area (> 1000 m2/g) and pore volume (~ 2.3 cm3/g), moderate electrical conductivity (~ 1 S/cm), with different mesopore size ranging from 4 nm to 20 nm were demonstrated. To further increase the electrical conductivity without altering the hierarchical porous structure, carbon additives such as graphene nanoplatelets (GN) and carbon nanotubes into HPCs were introduced. In addition, the effect of post thermal treatment was investigated. The resulting composite material (HPCs-GN) shows a surface area 2 times higher than that of Vulcan XC-72 with comparable electrical conductivity. Finally, microscopy images demonstrate smaller average nanoparticle size of platinum (Pt) supported on HPCs even at high catalyst loading (40 wt%) compared with commercial Pt on Vulcan XC-72.