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Elemental two-dimensional (2D) materials possess distinct properties and superior performances across a multitude of fundamental and practical research fields. Although a tremendous number of earlier studies focus on graphene and...

The emerging nonlayered 2D materials (NL2DMs) are sparking immense interest due to their fascinating physicochemical properties and enhanced performance in many applications. NL2DMs are particularly favored in catalytic applications owing to the extremely large surface area and low‐coordinated surface atoms. However, the synthesis of NL2DMs is complex because their crystals are held together by strong isotropic covalent bonds. Here, nonlayered molybdenum phosphide (MoP) with well‐defined 2D morphology is synthesized from layered molybdenum dichalcogenides via surface‐confined atomic substitution. During the synthesis, the molybdenum dichalcogenide nanosheet functions as the host matrix where each layer of Mo maintains their hexagonal arrangement and forms isotropic covalent bonds with P that substitutes S, resulting in the conversion from layered van der Waals material to a covalently bonded NL2DM. The MoP nanosheets converted from few‐layer MoS2 are single crystalline, while those converted from monolayers are amorphous. The converted MoP demonstrates metallic charge transport and desirable performance in the electrocatalytic hydrogen evolution reaction (HER). More importantly, in contrast to MoS2, which shows edge‐dominated HER performance, the edge and basal plane of MoP deliver similar HER performance, which is correlated with theoretical calculations. This work provides a new synthetic strategy for high‐quality nonlayered materials with well‐defined 2D morphology for future exploration.

realized, PVSCs can rival the commercialized silicon solar cells and copper indium gallium selenide (CIGS) solar cells. [2] It is well known that efficient PVSCs require effective suppression of the nonradiative recombination that often originates from nonideal interface energy alignment as well as defects states. [8][9][10][11][12] Charge-transporting materials modification, surface defects passivation, and dimensional engineering are the most adopted strategies to suppress the nonideal interfacial recombination and reduce the energy losses in PVSCs. [13][14][15][16][17][18][19] Among them, the defects at the grain boundaries of 3D perovskite can act as recombination and trapstate centers for minority carriers, which are always considered detrimental to performance. [20] Therefore, the 3D/2D heterojunction architecture stands out as it can simultaneously passivate defects at grain boundaries, modify the interfacial energy alignment, and suppress the ion diffusion, thereby enhancing the device performance and long-term stability. [21][22][23][24][25][26] Currently, most 3D/2D heterostructures are contrived via the modification of perovskite precursor solutions or post-treatment of 3D perovskites. [5,[27][28][29][30][31][32][33][34] For example, Snaith et al. blended butylammonium-based 2D perovskite precursor solution with the cesium formamidinium lead halide perovskite solution to form a mixture of 2D and 3D-phase perovskite, which effectively inhibited nonradiative Perovskite solar cells (PVSCs) have drawn great attention due to their high processability and superior photovoltaic properties. However, their further development is often hindered by severe nonradiative recombination at interfaces that decreases power conversion efficiency (PCE). To this end, a facile strategy to construct a 3D/2D vertical heterostructure to reduce the energy loss in PVSCs is developed. The heterostructure is contrived through the van der Waals integration of 2D perovskite ((BA) 4 AgBiBr 8 ) nanosheets onto the surface of 3D-FAPbI 3 -based perovskites. The large bandgap of (BA) 4 AgBiBr 8 enables the formation of type-I heterojunction with 3D-FAPbI 3 -based perovskites, which serves as a barrier to suppress the trap-assisted recombination at the interface. As a result, a satisfying PCE of 24.48% is achieved with an improved open-circuit voltage (V OC ) from 1.13 to 1.17 V. Moreover, the 2D perovskite nanosheets can effectively mitigate the iodide ion diffusion from perovskite to the metal electrode, hence enhancing the device stability. 3D/2D architectured devices retain ≈90% of their initial PCE under continuous illumination or heating after 1000 h, which are superior to 3D-based devices. This work provides an effective and controllable strategy to construct 3D/2D vertical heterostructure to simultaneously boost the efficiency and stability of PVSCs.

Composition modulation and edge enrichment are established protocols to steer the electronic structures and catalytic activities of two-dimensional (2D) materials. It is believed that a heteroatom enhances the catalytic performance by activating the chemically inert basal plane of 2D crystals. However, the edge and basal plane have inherently different electronic states, and how the dopants affect the edge activity remains ambiguous. Here we provide mechanistic insights into this issue by monitoring the hydrogen evolution reaction (HER) performance of phosphorus-doped MoS2 (P-MoS2) nanosheets via on-chip electrocatalytic microdevices. Upon phosphorus doping, MoS2 nanosheet gets catalytically activated and, more importantly, shows higher HER activity in the edge than the basal plane. In situ transport measurement demonstrates that the improved HER performance of P-MoS2 is derived from intrinsic catalytic activity rather than charge transfer. Density functional theory calculations manifest that the edge sites of P-MoS2 are energetically more favorable for HER. The finding guides the rational design of edge-dominant P-MoS2, reaching a minuscule onset potential of ∼30 mV and Tafel slope of 48 mV/dec that are benchmarked against other activation methods. Our results disclose the hitherto overlooked edge activity of 2D materials induced by heteroatom doping that will provide perspectives for preparing next-generation 2D catalysts.