Lung-Inspired catalyst layers: Understanding pore accessibility in hierarchically porous carbon electrocatalysts

Hierarchically porous carbons are at the cutting edge of materials for electrochemical devices. The porous structure enables flow inside the material, while graphitic regions provide conductivity and dopants create catalytic sites. Hierarchically porous carbons have high specific surface area, exposing many active sites and improving mass transport to these sites. Nevertheless, such carbons are limited by low volumetric current densities – making typical electrodes thick, and blocking access to some of the inner surface area.

We hypothesize that there exists a better type of porosity, than a random mixture of small and large pores – namely, a lung-structured catalyst layer. This requires that pores are interconnected and aligned, directing the reactant smoothly from larger pores into smaller pores and utilizing the entire surface area.

We studied a range of templated carbons, aiming to elucidate the role of intra- and inter-particle porosity in lung-inspired catalyst layers. We use ZnO rods and trees, spanning 10– 1000 nm in length, to investigate the effect of flow channels and of particle dimensions on the flow in catalyst layers. We are investigating the effect of active site accessibility on electrocatalytic performance by using the oxygen reduction reaction (ORR) as a model reaction, and to correlating it to other physical characterizations of the material.