Transition metal dichalcogenides (MX2, where M = Mo or W and X = S or Se) have been regarded as some of the best alternatives for noble metal-free electrocatalysts for the hydrogen evolution reaction (HER). A tremendous number of attempts have mainly focused on the maximization of the number of active edge sites and the conductivity of MX2-based electrocatalysts to enhance HER performance. However, for MX2-based electrocatalysts, the acceleration of the kinetic process to improve HER performance has been neglected until now. Here we report a colloidal epitaxial growth strategy for synthesizing MoSe2–NiSe nanohybrids with well-defined heterointerfaces that are constructed by in situ growth of metallic NiSe nanocrystallites on the MoSe2 nanosheets. These high-quality vertical heteronanostructures with band alignment give rise to the electrons being transferred from the metallic NiSe nanocrystallites to the MoSe2 matrix, achieving the electronic modulation of the MoSe2–NiSe nanohybrids for efficient electrocatalytic activity. The MoSe2–NiSe nanohybrids exhibit excellent HER catalytic properties with a low onset potential of −150 mV, a large cathodic current density (10 mA cm–2 at an overpotential of 210 mV), and a small Tafel slope of 56 mV per decade. The greatly enhanced electrocatalytic properties were attributed to the electronic structure modulation from the synergetic interactions between NiSe nanocrystallites and MoSe2 nanosheets. We anticipate that the construction of hybrid structures will be a powerful tool for creating high-performance electrocatalysts in solids.

MoSe2 nanosheets have been extensively pursued due to the outstanding properties of this typical layered transition metal dichalcogenide (LTMD). In this work, we report a facile, fast strategy to synthesize scalable hierarchical ultrathin MoSe2-x (x ∼ 0.47) nanosheets. The nanosheets possess 2-5 Se-Mo-Se atomic layers and were synthesised through a bottom-up colloidal route within 20 mins under mild conditions from the reaction of MoO2(acac)2 with dibenzyl diselenide. The as-obtained hierarchical ultrathin MoSe2-x nanosheets are Mo-rich with a Se vacancy and show excellent HER performance with a small overpotential of ∼170 mV, large cathodic currents, and a Tafel slope of 98 mV per decade. Such high performance has been attributed to the unique structure of the Se vacancy defect, large surface area, as well as the enhanced conductivity. Meanwhile, the pathway can be extended as a general strategy to prepare other metal selenides, such as ultrathin WSe2 and SnSe nanosheets, and PbSe nanocrystals. It will also pave a new way to synthesize scalable nanostructured materials for intriguing nanodevices and large-scale applications.

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Bilayer-and bulk-heterojunction solar cells based on liquid crystalline porphyrins ͑donors͒ were fabricated by solution processing. These porphyrins are ͑i͒ highly absorptive over the wavelengths of the solar spectrum, ͑ii͒ having energy levels matched well with the electron acceptors and anode materials to facilitate charge separation and transfer, and ͑iii͒ of a unique homeotropically aligned architecture for efficient charge transport and light harvesting. Thermal annealing of these solar cells induced alignments of porphyrins in the photoactive layers, leading to a factor of 4-5 higher power conversion efficiencies and short circuit current densities than their counterpart devices without postannealing.