Mass transfer is critical in catalytic processes, especially
when
the reactions are facilitated by nanostructured catalysts. Strong
efforts have been devoted to improving the efficacy and quantity of
active sites, but often, mass transfer has not been well studied.
Herein, we demonstrate the importance of mass transfer in the electrocatalytic
oxygen reduction reaction (ORR) by tailoring the pore sizes. Using
a confined-etching strategy, we fabricate boron- and nitrogen-doped
carbon (B,N@C) electrocatalysts featuring abundant active sites but
different porous structures. The ORR performance of these catalysts
is found to correlate with diffusion of the reactant. The optimized
B,N@C with trimodal-porous structures feature enhanced O2diffusion and better activity per heteroatomic site toward the ORR
process. This work demonstrates the significance of the nanoarchitecture
engineering of catalysts and sheds light on how to optimize structures
featuring abundant active sites and enhanced mass transfer.