COMMUNICATION
(1 of 7)2D material is an excellent starting point for developing catalysts, size-selective membranes, and electronics and energy storage devices because of its atomic thickness and "nano-effect." [1] However, pores that serve as tunnels for target species are often preferred and need to be introduced in some cases. Graphene itself is an example as it is not permeable to gas species, metal ions, and liquid molecules. In order to realize their successful application in molecular sieves and energy storage, recently new graphene nanomesh and holey graphene are created to achieve excellent transport across the plane and ultimate access to the inner surfaces. [2] The common hole-making methods are postprocessing of graphene, such as ultraviolet-induced oxidative etching and lithography. [2c,d] The general chemical/mechanical exfoliation method for graphene is not applicable to synthesize porous graphene because high-crystalline peelable porous graphite cannot be produced.2D layered double hydroxide (LDH) is another important member of the 2D material family and has shown exciting perspectives in many fields, especially in electrocatalysis (e.g., the hydrogen and oxygen evolution reactions (HER and OER) in water splitting). [3] However, as opposed to graphene, the 2D hydroxide with in-plane pores has rarely been reported so far. If the common chemical-exfoliation strategy of 2D metal hydroxide were to be applied to synthesize holey 2D hydroxide, getting high-quality porous single-crystalline precursor would be the crucial prerequisite because most porous materials are amorphous or polycrystalline. [4] Fortunately, recently we have developed mesoporous single-crystalline Co(OH) 2 nanoplates via a copolymer-templating technique, which makes the synthesis of holey hydroxide 2D material possible. [5] OER is the oxidative half reaction of water splitting that involves the transfer of four protons and four electrons. [3d,6] Therefore, it is kinetically sluggish and always requires conspicuous overpotential. [3d,6,7] The precious-metal catalysts, e.g., IrO 2 and RuO 2 , despite performing well on the catalysis toward OER, are extremely scarce on the earth and also expensive, so earth-abundant transition-metal electrocatalysts including oxides/hydroxides and their derivatives have been developed recently. [8] Especially, some reports pointed that transition-metal LDH can be exfoliated into 2D nanosheets with large anisotropy to get extraordinarily improved catalytic performances, because Creating nanosized pores in 2D materials can increase the edge sites, improve the mass transfer, and contribute to different physical properties, which shows potential applications in many fields including filtration membranes, electronics and energy storage devices, and catalysts. An iconic member of this type of material is porous graphene. Herein, a unique 2D layered double hydroxide (LDH) nanomesh is designed and synthesized as a new class of 2D holey materials. It represents the first case of exfoliation method for p...