Boosting the catalytic activity toward oxygen reduction via a heterostructure of porous iron oxide-decorated 2D NiO/NG nanosheets

Abstract

As a noble metal substitute, two-dimensional (2D) hierarchical nano-frame structures have attracted great interest as candidate catalysts due to their remarkable advantages – high intrinsic activity, high electron mobility, and straightforward surface functionalization. Therefore, they may replace Pt-based catalysts in oxygen reduction reaction (ORR) applications. Herein, a simple method is developed to design hierarchical nano-frame structures assembled via 2D NiO and N-doped graphene (NG) nanosheets. This procedure can yield nanostructures that satisfy the criteria correlated with improved electrocatalytic performance, such as large surface area, numerous undercoordinated atoms, and high defect densities. Further, porous NG nanosheet architectures, featuring NiO nanosheets densely coordinated with accessible holey Fe2O3 moieties, can enhance mesoporosity and balance hydrophilicity. Such improvements can facilitate charge transport and expose formerly inaccessible reaction sites, maximizing active site density utilization. Density functional theory (DFT) calculations reveal favored O2 adsorption and dissociation on Fe2O3 hybrid structures when supported by 2D NiO and NG nanomaterials, given 2D materials donated charge to Fe2O3 active sites. Our systematic studies reveal that synergistic contributions are responsible for enriching the catalytic activity of Fe2O3@NiO/NG in alkaline media – encompassing internal voids and pores, unique hierarchical support structures, and concentrated N-dopant and bimetallic atomic interactions. Ultimately, this work expands the toolbox for designing and synthesizing highly efficient 2D/2D shelled functional nanomaterials with transition metals, endeavoring to benefit energy conversion and related ORR applications.