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2D metal monochalcogenides have recently attracted interest for photoelectrochemical (PEC) applications in aqueous electrolytes. Their optical bandgap in the visible and near‐infrared spectral region is adequate for energy conversion and photodetection/sensing. Their large surface‐to‐volume ratio guarantees that the charge carriers are photogenerated at the material/electrolyte interface, where redox reactions occur, minimizing recombination processes. However, solution‐processed photoelectrodes based on these materials exhibit energy conversion efficiencies that are far from the current state of the art expressed by established technologies. This work reports a systematic morphological, spectroscopic, and PEC characterization of solution‐processed films of photoactive InSe flakes for PEC‐type photodetectors. By optimizing the thickness and hybridizing InSe flakes with electrically conductive Sn:In2O3 (ITO) nanocrystals, photoanodes with a significant photoanodic response in both acidic and alkaline media are designed, reaching responsivity up to 60.0 mA W−1 (external quantum efficiency = 16.4%) at +0.4 V versus RHE under visible illumination. In addition, a strategy based on the use of sacrificial agents (i.e., 2‐propanol and Na2SO3) is proposed to improve the stability of the InSe and ITO/InSe photodetectors. Our data confirm the potential of 2D InSe for PEC energy conversion and sensing applications, remarking the challenges related to InSe stability during anodic operation. [ABSTRACT FROM AUTHOR]

Hollow structures made of nanoscale building blocks are of great interest as catalysts for electrochemical water splitting. Here we report a solution-phase synthesis of yolk–shell Co3O4/Co1−xRuxO2 microspheres (MSs) having a shell made of Co1−xRuxO2 nanorods and the core of Co3O4. Benefiting from the peculiar morphology and the synergy between the different materials present in the MSs, the latter exhibit enhanced electrochemical oxygen evolution activity and long-term stability in acidic media. The catalyst achieves a catalytic current density of 10 mA cm−2 at an overpotential of only 240 mV, a small Tafel slope of 70 mV dec−1, and a high mass activity of 600 A g−1 and maintains its activity throughout a 24 h chronopotentiometry tests at constant current densities of 10 and 20 mA cm−2. [ABSTRACT FROM AUTHOR]

Gallium selenide (GaSe), a layered semiconductor of Group‐III monochalcogenides, has been recognized by the scientific community in recent years as an appealing material in the fields of photonics and (opto)electronics. Thanks to its pseudodirect bandgap and its thickness‐dependent (opto)electronic properties, GaSe has emerged as a promising candidate for the implementation of thin‐film transistors (TFTs) and photodetectors with fast response and high sensitivity. Solution processing of 2D materials provides low‐cost inks that allow the design and realization of printed electronic devices, enabling this technology to move from the laboratory to the industry. In this work, a solution‐processed GaSe‐based light‐driven transistor is presented. Liquid phase exfoliation (LPE) is used to exfoliate bulk GaSe in isopropanol, formulating a functional ink that is subsequently deposited by spray coating onto Si/SiO2 substrates. The GaSe phototransistor exhibits a p‐channel behavior with a high on/off ratio (≈103) that is gate‐voltage dependent. Moreover, the device response also depends on the illumination with a maximum responsivity of 13 A W–1 to UV–visible light and a fast response time of 35 ms. This study demonstrates that liquid phase exfoliated GaSe is a promising candidate for the design and realization of next‐generation (opto)electronic devices. [ABSTRACT FROM AUTHOR]

Pt nanoparticles deposited on mesoporous carbon (Pt/C) represent a benchmark catalyst for the hydrogen evolution reaction (HER) in both acid and alkaline conditions. However, it shows an order of magnitude lower activity under alkaline media compared to acid media. Moreover, the activity of this catalyst decreases rapidly under operational conditions due to both migration and aggregation of the metal particles, leading to a rapid decline in the number of active sites. We show here a Cu and Ru-based catalyst fabricated by slow electrodeposition of Ru onto a nanostructured Cu layer grown, in turn, on the top of a Ti substrate. Our catalyst has a high and stable HER activity, outperforming the benchmark Pt/C catalyst under alkaline conditions. The high activity and prolonged stability are attributed to the peculiar structure of our electrode, in which Cu nanoplates are directly attached perpendicular to the Ti substrate, providing a high surface area support onto which Ru nanocrystals are bound. This makes the Cu–Ru/Ti electrode one of the most active (−10 mA cm2 of HER current at only −23 mV overpotential) and stable electrocatalysts (no activity degradation for 100 h at −0.2 V) reported to date for the alkaline hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Intercalation and deintercalation of Cu into and from Bi2Se3 and Bi2Te3 colloidal nanocrystals is demonstrated in solid state. For this purpose, the nanocrystals are deposited on a solid substrate and subjected to moderate heating in the presence of a Cu source or a Cu scavenger. The results of the solid state experiments are consistent with those produced by solution-based intercalation. At moderate levels of solid state intercalation above about 10 at%, Cu forms superlattice structures in both Bi2Se3 and Bi2Te3, while higher intercalation levels ultimately lead to cation exchange. This is particularly the case in Bi2Se3 which transitions to Cu2-xSe while maintaining the two-dimensional morphology of the starting nanocrystals. The solid state intercalation is reversible, and Cu can also be deintercalated from the Bi2Se3 and Bi2Te3 nanocrystals upon heating and utilized in other reactions on the solid substrate. The extent of intercalation and deintercalation, however, depends on any interaction between the intercalant and host nanocrystals in response to heating. The concepts explored here hold promise for future development of novel solid state based energy storage nanodevices or possibly NC-based devices whose properties and/or function could be reversibly modulated through a combination of solid state CE and intercalation/deintercalation. [ABSTRACT FROM AUTHOR]

Solution-processed few-layer MoS2 flakes are exploited as an active buffer layer in hybrid lead-halide perovskite solar cells (PSCs). Glass/FTO/compact-TiO2/mesoporous-TiO2/CH3NH3PbI3/MoS2/Spiro-OMeTAD/Au solar cells are realized with the MoS2 flakes having a twofold function, acting both as a protective layer, by preventing the formation of shunt contacts between the perovskite and the Au electrode, and as a hole transport layer from the perovskite to the Spiro-OMeTAD. As prepared PSC demonstrates a power conversion efficiency ( η) of 13.3%, along with a higher lifetime stability over 550 h with respect to reference PSC without MoS2 (Δ η/ η = −7% vs. Δ η/ η = −34%). Large-area PSCs (1.05 cm2 active area) are also fabricated to demonstrate the scalability of this approach, achieving η of 11.5%. Our results pave the way toward the implementation of MoS2 as a material able to boost the shelf life of large-area perovskite solar cells in view of their commercialization. [ABSTRACT FROM AUTHOR]

The structural and compositional stabilities of two-dimensional (2D) Bi2Te3 and Bi2Se3 nanocrystals, produced by both colloidal synthesis and by liquid phase exfoliation, were studied by in situ transmission electron microscopy (TEM) during annealing at temperatures between 350 and 500 °C. The sublimation process induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic {011̅0} type planes, and through the preferential sublimation of Te (or Se). The observed anisotropic sublimation is independent of the method of nanocrystal's synthesis, their morphology, or the presence of surfactant molecules on the nanocrystals surface. A thickness-dependent depression in the sublimation point has been observed with nanocrystals thinner than about 15 nm. The Bi2Se3 nanocrystals were found to sublimate below 280 °C, while the Bi2Te3 ones sublimated at temperatures between 350 and 450 °C, depending on their thickness, under the vacuum conditions in the TEM column. Density functional theory calculations confirm that the sublimation of the prismatic {011̅0} facets is more energetically favorable. Within the level of modeling employed, the sublimation occurs at a rate about 700 times faster than the sublimation of the {0001} planes at the annealing temperatures used in this work. This supports the distinctly anisotropic mechanisms of both sublimation and growth of Bi2Te3 and Bi2Se3 nanocrystals, known to preferentially adopt a 2D morphology. The anisotropic sublimation behavior is in agreement with the intrinsic anisotropy in the surface free energy brought about by the crystal structure of Bi2Te3 or Bi2Se3. [ABSTRACT FROM AUTHOR]