Large-scale production of low-cost, highly-stable, two-dimensional (2D) crystals now become an important challenge for many applications including energy conversion and storage. Here, we demonstrate an efficient and eco-friendly method for the scalable synthesis of 2D crystals and their applications for energy conversion and storage. The first approach involves edge-selective functionalization of graphite into graphene nanoplatelets (GnPs) by a simple mechanochemical ball-milling process (Figure 1a). The first top-down approach is an important step toward high-yield exfoliation of three-dimensional graphite into high-quality 2D graphitic crystals with minimal basal plane distortion (Figure 1b). The second bottom-up approach is scalable synthesis of 2D crystals with periodic holes and heteroatoms via polycondensation between Ax and By monomers (x or y > 2) (Figure 1c). The resultant holey 2D crystals displayed outstanding electrochemical performance (Figure 1d) . Our findings suggest that the 2D crystals can be simply prepared and conveniently used as base materials for a wide range of applications from wet chemistry to device applications.

Large-scale production of low-cost, highly-stable, two-dimensional (2D) crystals now become an important challenge for many applications including energy conversion and storage. Here, we demonstrate an efficient and eco-friendly method for the scalable synthesis of 2D crystals and their applications for energy conversion and storage. The first approach involves edge-selective functionalization of graphite into graphene nanoplatelets (GnPs) by a simple mechanochemical ball-milling process (Figure 1a). The first top-down approach is an important step toward high-yield exfoliation of three-dimensional graphite into high-quality 2D graphitic crystals with minimal basal plane distortion (Figure 1b). The second bottom-up approach is scalable synthesis of 2D crystals with periodic holes and heteroatoms via polycondensation between Ax and By monomers (x or y > 2) (Figure 1c). The resultant holey 2D crystals displayed outstanding electrochemical performance (Figure 1d) . Our findings suggest that the 2D crystals can be simply prepared and conveniently used as base materials for a wide range of applications from wet chemistry to device applications.