Hollow mesoporous carbon nanocages with Fe isolated single atomic site derived from a MOF/polymer for highly efficient electrocatalytic oxygen reduction

Abstract

Exploring sustainable and highly active electrocatalysts for the oxygen reduction reaction (ORR) is vital for the development and application of energy conversion technologies. Here, we prepared Fe-isolated single atomic site (ISAs)-supported hollow mesoporous carbon nanocages (Fe-ISAs/H-CNs). Using zeolitic imidazolate framework (ZIF-8) as the templates, the iron precursor was used as the Fe source for doping, and also acted as the initiator to promote the polymerization of pyrrole for constructing the shell. In addition, the H cations released by pyrrole polymerization diffused into the interior of ZIF-8 through the pores and further broke the structure of ZIF-8, resulting in porous MOF–polymer nanocomposites (ZIF-8/Fe@PPy). After thermal treatment, the obtained Fe-ISAs/H-CN exhibited a higher half-wave potential (E_1/2 = 0.87 V), exceptional kinetic current density (J_k = 32.82 mA cm⁻² at 0.80 V), high stability, and superior tolerance to methanol crossover, exceeding those of commercial Pt/C catalyst and most previously reported non-precious-metal catalysts in alkaline media. The excellent catalytic behavior was attributable to hollow carbon nanocages and the feature of Fe single atoms with the Fe–N₄ configuration, which provided more active sites and was beneficial to create highly interconnected electron connection channels that facilitated oxygen exchange, reactant diffusion, and electron conduction, thus changing the reaction kinetics.