Aligned Vertical Mass Transfer Channels in 2D Monolayered Fe-N-C Carbon Honeycomb for Efficient Oxygen Reduction

Abstract

Construction of favorable transfer pathways that ensure rapid mass transfer capability is critical for the design of Fe-N-C electrocatalysts. Typically, two-dimensional (2D) Fe-N-C catalysts exhibit fast mass transfer in the in-plane direction; however, their microporous nature limits mass transfer efficiency in the vertical direction. Herein, we report the fabrication of 2D monolayered Fe-N-C carbon honeycomb catalysts (2D Fe-CH) with aligned vertical mass transfer channels between each porous carbon polyhedron. The 2D monolayered architecture ensures efficient in-plane mass transfer, while the meticulously designed vertically aligned channels enhancing mass transfer in the perpendicular direction. These aligned channels enable maximum exposure of Fe single atoms and improve the accessibility of these active sites. Compared to the 2D monolayered Fe-N-C carbon particle array catalyst (2D Fe-CPA) without vertical channels, the 2D Fe-CH catalyst demonstrates significantly enhanced performance toward the oxygen reduction reaction. The half wave potential reaches up to 0.891 V vs. RHE in 0.1 M KOH. Molecular dynamics simulations combined with DRT analysis reveal that the enhanced performance is attributed to the presence of vertically aligned mass transfer channels.