Generalized assembly of sandwich-like 0D/2D/0D heterostructures with highly exposed surfaces toward superior electrochemical performances

Heterostructures composed of two-dimensional (2D) nanosheets and zero-dimensional (0D) nanoparticles (NPs) have attracted increasing attention because of the synergy arising from the coupling interactions between the two mixed-dimensional components. Despite recent advances, it remains a challenge to fabricate 2D/0D heterostructures with clean and accessible surfaces, which is highly desirable for the diversity of catalytic, sensing, and energy storage applications. Herein, we report a generalized methodology that enables the facile assembly of sandwich-like 0D/2D/0D heterostructures with facilitated mass-transport channels and exposed surface active sites. A ligand-exchange strategy with HBF₄ is employed to strip off the surface-coating ligands of colloidal NPs, rendering them positively charged and dispersible in polar solvents. This allows subsequent electrostatic assembly of NPs with oppositely charged 2D nanosheets to afford sandwich-like 0D/2D/0D heterostructures. The barely covered surfaces and the advantageous architectures of such sandwich-like 0D/2D/0D heterostructures induce the desired synergistic effect, making them particularly suitable for electrochemical energy storage and conversion. We demonstrate this by employing MXene/NiFe₂O₄ and MXene/Fe₃O₄ heterostructures for high-performance electrocatalytic oxygen evolution and supercapacitors, respectively.