Self-assembled mesostructured CoFeO nanoparticle superstructures for highly efficient oxygen evolution.

Self-assembly of colloidal nanoparticles (NPs) into well-defined superstructures has been recognized as one of the most promising ways to fabricate rationally-designed functional materials for a variety of applications. Introducing hierarchical mesoporosity into NP superstructures will facilitate mass transport while simultaneously enhancing the accessibility of constituent NPs, which is of critical importance for widening their applications in catalysis and energy-related fields. Herein, we develop a colloidal co-assembly strategy to construct mesostructured, carbon-coated CoFeO NP superstructures (M-C@CFOSs), which show great promise as highly efficient electrocatalysts for the oxygen evolution reaction (OER). Specifically, organically-stabilized SiO NPs are employed as both building blocks and sacrificial template, which co-assemble with CoFeO NPs to afford binary NP superstructures through a solvent drying process. M-C@CFOSs are obtainable after in situ ligand carbonization followed by the selective removal of SiO NPs. The hierarchical mesoporous structure of M-C@CFOSs, combined with the conformal graphitic carbon coating derived from the native organic ligands, significantly improves their electrocatalytic performance as OER electrocatalysts when compared with nonporous CoFeO NP superstructures. This work establishes a new and facile approach for designing NP superstructures with hierarchical mesoporosity, which may find wide applications in energy storage and conversion.