Smallest [5,6]Fullerene as Building Blocks for 2D Networks with Superior Stability and Enhanced Photocatalytic Performance.

The assembly of molecules to form covalent networks can create varied lattice structures with physical and chemical properties distinct from those of conventional atomic lattices. Using the smallest stable [5,6]fullerene units as building blocks, various 2D C₂₄ networks can be formed with superior stability and strength compared to the recently synthesized monolayer polymeric C₆₀. Monolayer C₂₄ harnesses the properties of both carbon crystals and fullerene molecules, such as stable chemical bonds, suitable band gaps, and large surface area, facilitating photocatalytic water splitting. The electronic band gaps of C₂₄ are comparable to those of TiO₂, providing appropriate band edges with sufficient external potential for overall water splitting over the acidic and neutral pH range. Upon photoexcitation, strong solar absorption enabled by strongly bound bright excitons can generate carriers effectively, while the type-II band alignment between C₂₄ and other 2D monolayers can separate electrons and holes in individual layers simultaneously. Additionally, the number of surface-active sites of C₂₄ monolayers are three times more than that of their C₆₀ counterparts in a much wider pH range, providing spontaneous reaction pathways for the hydrogen evolution reaction. Our work provides insights into materials design using tunable building blocks of fullerene units with tailored functions for energy generation, conversion, and storage.