Sublayer-enhanced atomic sites of single atom catalysts through in situ atomization of metal oxide nanoparticles

Abstract

Carbon supported single atom catalysts (SACs) show outstanding potential as effective electrocatalysts in energy storage and conversion devices. However, the low surface-active site density associated with most SACs constrains their practical applications. By controlling the layers of FeSA through the in situ atomization of graphene supported metal oxide nanoparticles (NPs), we demonstrate that the Fe–N₄–C active sites increase from 1 to 3 layers as the catalyst loading increases. The turnover frequency (TOF) for the oxygen reduction reaction (ORR) is doubled because the sublayer Fe–N_x–C could tune the electron density by increasing the energy gap between the d-band centre and the fermi level, weakening the adsorption of intermediates and further reducing the reaction overpotential in comparison to a single-layer Fe–N₄. The sublayer-enhanced catalysts achieve an optimum activity for the ORR with a half-wave potential of 0.901 V under alkaline conditions and 0.74 V under acidic conditions, significantly higher performance in comparison to that of single layer active sites. Potential applications of these newly-developed catalysts were demonstrated in Zn–air batteries and fuel cells. This work provides a new way to achieve high TOF by controlling the layer of single atom active sites and offers new strategies to overcome the low-density atomic sites for SACs.