Due to their unique electronic and optoelectronic properties, tin selenide nanostructures show great promise for applications in energy storage and photovoltaic devices. Despite the great progress that has been achieved, the phase-controlled synthesis of two-dimensional (2D) tin selenide nanostructures remains a challenge, and their use in supercapacitors has not been explored. In this paper, 2D tin selenide nanostructures, including pure SnSe2 nanodisks (NDs), mixed-phase SnSe-SnSe2 NDs, and pure SnSe nanosheets (NSs), have been synthesized by reacting SnCl2 and trioctylphosphine (TOP)-Se with borane-tert-butylamine complex (BTBC) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. Utilizing the interplay of TOP and BTBC and changing only the amount of BTBC, the phase-controlled synthesis of 2D tin selenide nanostructures is realized for the first time. Phase-dependent pseudocapacitive behavior is observed for the resulting 2D nanostructures. The specific capacitances of pure SnSe2 NDs (168 F g(-1)) and SnSe NSs (228 F g(-1)) are much higher than those of other reported materials (e.g., graphene-Mn3O4 nanorods and TiN mesoporous spheres); thus, these tin selenide materials were used to fabricate flexible, all-solid-state supercapacitors. Devices fabricated with these two tin selenide materials exhibited high areal capacitances, good cycling stabilities, excellent flexibilities, and desirable mechanical stabilities, which were comparable to or better than those reported recently for other solid-state devices based on graphene and 3D GeSe2 nanostructures. Additionally, the rate capability of the SnSe2 NDs device was much better than that of the SnSe NS device, indicating that SnSe2 NDs are promising active materials for use in high-performance, flexible, all-solid-state supercapacitors.

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As group III-nitride semiconductors are thinned to only a few atomic layers, regarding as 2D materials, it would lead to an ultrawide bandgap (E g ) due to the quantum confinement effect, [11,12] which can be used as ultraviolet optoelectronic devices needed ultrawide E g semiconductors. [13,14] Moreover, 2D group III-nitride semiconductors showing anomalously temperature-dependent thermal conductivity and orbitally driven ultra-low thermal conductivity have been predicted, [15,16] which make them prospective for applications in energy conversion, for example, thermos-electrics. [17] However, the experimental synthesis of 2D group III-nitride semiconductors is still meeting with tremendous difficulties due to the fact that group III-nitride semiconductors more easily orientate along c-axis than any other axis [18] and the lateral mobility for precursor atoms of group III-nitride materials, i.e., AlN, is very low, [19] which result in the formation of 3D crystal structure. Moreover, the surface energy constraint and large lattice mismatch between group III-nitride semiconductors and substrates would also lead to the formation of 3D island crystal. [11] In this work, we have successfully realized the epitaxial growth of 2D AlN layers sandwiched between graphene and Si substrates for the first time in the world by metal organic chemical vapor deposition (MOCVD). On the one hand, Si (111) surface with high symmetry [20] has stable adsorption sites for Al and N adatoms, Figure S1 in the Supporting Information. On the other hand, Si has a lattice mismatch with AlN(0001) of ≈19%, [21] Figure S2 in the Supporting Information, producing the tensile stress together with the effect of Gibbs free energy that drive the crystal structure of 2D AlN transforming from R3m structure to P6 3 MC structure. [22][23][24] During the growth process, hydrogenation for graphene/Si hetero-structures with hydrogen (H 2 ) guarantees the formation of 2D AlN layers. The 2D AlN layers are sandwiched between graphene and Si substrates after hydrogenation, while no interlayer can be found between graphene and Si substrates without hydrogenation. To further study the formation mechanism of 2D AlN layers and the effect of hydrogenation on the formation of 2D AlN layers, theoretical calculations with first-principles calculations based on density functional theory (DFT) have been carried out. We further predicted and determined the E g of the 2D AlN layers theoretically and experimentally by Hartree-Fock local density

Exploring low-cost, high-activity, and long-durability hybrid electrocatalysts for cathodic oxygen reduction reaction (ORR) is vital to advance fuel cells technologies. In this paper, a series of graphene (G)-CuxPdy (Cu4Pd, Cu3Pd, CuPd, CuPd3, CuPd4) nanocomposites (G-CuxPdy NCPs) is obtained by assembly of CuxPdy alloy nanocrystals (NCs) with controlled component ratios on G nanosheets using the "dispersing-mixing-vaporizing solvent" strategy and used as electrocatalysts for ORR. Compared with pure CuxPdy NCs, greatly enhanced interfacial electron transfer dynamics are observed in G-CuxPdy NCPs, which show a strong correlation with the alloy compositions of the NCPs. The electrocatalytic experiments in alkaline solution reveal that the ORR activities of those G-CuxPdy NCPs are also strongly dependent on alloy components and exhibit a double-volcano feature with variations of alloy components. Among them, G-Cu3Pd NCPs possess the highest electrocatalytic activity, which is much better than some reported electrocatalysts and commercial Pd/C catalyst and close to Pt/C catalyst. By correlating the Pd 3d binding energies and the sizes of CuxPdy NCs with the mass-specific activities of G-CuxPdy NCPs and considering the interfacial electron transfer dynamics, the best catalytic activity of G-Cu3Pd NCPs may result from the unique electronic structure and the smallest size of Cu3Pd NCs as well as the strong synergistic effect between G and Cu3Pd NCs. Moreover, the durability of G-Cu3Pd NCPs is superior to that of Pt/C catalyst, indicating that they are promising cathodic electrocatalysts for using in alkaline fuel cells.

Following the extensive researches of graphene, 2D layered semiconductors have attracted widespread attention for their intriguing physical properties. 2D α‐Ga2S3 as an important member of group IIIA–VIA semiconductors has outstanding optoelectronic properties. However, the controllable large‐size synthesis of ultrathin α‐Ga2S3 nanosheets still remains a huge challenge. In this paper, a large‐size ultrathin nanosheets of hexagonal Ga2S3 is prepared via an improved chemical vapor deposition method. High‐performance photodetectors based on the ultrathin Ga2S3 nanosheets is demonstrated. The device shows a high photosensitivity/detectivity (9.2 A W−1/1.4 × 1012 Jones) and a fast response time (rise/fall time of <4/3 ms), respectively. Strikingly, wearable flexible photodetectors based on Ga2S3 nanosheets are fabricated accordingly and demonstrate great response performance and stability. This work provides a new direction for 2D semiconductors to apply in next‐generation nanoscale smart optoelectronics.