A new phototransistor based on the mechanically exfoliated single-layer MoS(2) nanosheet is fabricated, and its light-induced electric properties are investigated in detail. Photocurrent generated from the phototransistor is solely determined by the illuminated optical power at a constant drain or gate voltage. The switching behavior of photocurrent generation and annihilation can be completely finished within ca. 50 ms, and it shows good stability. Especially, the single-layer MoS(2) phototransistor exhibits a better photoresponsivity as compared with the graphene-based device. The unique characteristics of incident-light control, prompt photoswitching, and good photoresponsivity from the MoS(2) phototransistor pave an avenue to develop the single-layer semiconducting materials for multifunctional optoelectronic device applications in the future.

Hydrogen evolution reaction (HER) on earth-abundant molybdenum disulfide (MoS 2) in acidic media is a robust process, but is kinetically retarded in alkaline media. Thus, improving the sluggish kinetics for HER in alkaline media is crucial for advancing the performance of water-alkali electrolyzers. Here, we demonstrate a dramatic enhancement of HER kinetics in base by judiciously hybridizing vertical MoS 2 sheets with another earth-abundant material, layered double hydroxide (LDH). The resultant MoS 2 /NiCo-LDH hybrid exhibits an extremely low HER overpotential of 78 mV at 10 mA/cm 2 and a low Tafel slope of 76.6 mV/dec in 1 M KOH solution. At the current density of 20 mA/cm 2 or even higher, the MoS 2 /NiCo-LDH composite can operate without degradation for 48 hr. This work not only brought forth a cost-effective and robust electrocatalyst, but more generally opened up new vistas for developing high-performance electrocatalysts in unfavorable media recalcitrant to conventional catalyst design.

energy conversion and storage. [1,2] Developing efficient electrocatalysts that can effectively enhance the sluggish kinetic processes are particularly important to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at low overpotentials. [3,4] Platinum group metals and noble metal oxides (e.g., IrO 2 , RuO 2 ) are considered as pioneering HER and OER catalysts, respectively. However, the large-scale applications are limited by the scarcity and high cost of these materials. [5,6] Recently, a great deal of effort and progress has been made toward the development of earth-abundant, highly efficient, and durable HER and OER catalysts, such as transition metal chalcogenides, [7][8][9] phosphides, [10][11][12] nitrides, [13][14][15] and carbides [16][17][18] (for HER), and transition metal oxide, [19][20][21] hydroxide/oxyhydroxide, [22][23][24] phosphate, [25][26][27] and carbon materials [28][29][30] (for OER). Due to the thermodynamic convenience and practical application in proton-exchange membrane or alkaline electrolyzers, these HER and OER catalysts generally exhibit high activity in strongly acidic and basic conditions, separately; thus pairing the two type catalysts in an integrated electrolyzer with high efficiency and stability for overall water splitting is difficult due to the mismatch of electrolyte pH. [31,32] There is Developing efficient, durable, and earth-abundant electrocatalysts for both hydrogen and oxygen evolution reactions is important for realizing largescale water splitting. The authors report that FeB 2 nanoparticles, prepared by a facile chemical reduction of Fe 2+ using LiBH 4 in an organic solvent, are a superb bifunctional electrocatalyst for overall water splitting. The FeB 2 electrode delivers a current density of 10 mA cm −2 at overpotentials of 61 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) in alkaline electrolyte with Tafel slopes of 87.5 and 52.4 mV dec −1 , respectively. The electrode can sustain the HER at an overpotential of 100 mV for 24 h and OER for 1000 cyclic voltammetry cycles with negligible degradation. Density function theory calculations demonstrate that the boron-rich surface possesses appropriate binding energy for chemisorption and desorption of hydrogen-containing intermediates, thus favoring the HER process. The excellent OER activity of FeB 2 is ascribed to the formation of a FeOOH/ FeB 2 heterojunction during water oxidation. An alkaline electrolyzer is constructed using two identical FeB 2 -NF electrodes as both anode and cathode, which can achieve a current density of 10 mA cm −2 at 1.57 V for overall water splitting with a faradaic efficiency of nearly 100%, rivalling the integrated state-of-the-art Pt/C and RuO 2 /C.

This article provides an overview on the design, fabrication and characterization of the most widely used cathode buffer layers (CBLs) constructed with pristine zinc oxide (ZnO), doped-ZnO, and ZnO-based composites as well as the surface modified ZnO-based CBLs for the improvement of power conversion efficiency (PCE) and long-term device stability of inverted polymer solar cells (PSCs). To achieve high PCE in inverted PSCs, the selection of an appropriate material to form the high quality CBL so as to optimize the electron collection and transport is particularly important. Among the different materials for CBL in inverted PSCs, ZnO has attracted most extensive research in view of its relatively high electron mobility, optical transparency, ease synthesis with versatile morphologies via low cost solution methods at low temperatures, and being environmentally stable. The research has revealed that the electronic processes at the interface between ZnO CBL and polymer active layer play an important role in determining the solar cells performance, and such processes are related to the ZnO CBL in terms of its morphology, microstructure, doping and surface modification. This review attempts to give a general review to better understand the impacts of (1) morphology, (2) thickness, (3) nanostructures, (4) doping, (5) surface modification and (6) composition/hybrids of ZnO CBLs on the solar cells performance. The fundamental understanding of the rapid progress of interfacial engineering made in PSCs would also be beneficial to the development of perovskite solar cells due to similar energy level and device structures.Fig. 12 (a) Schematic illustration of device structure with ZnMgO CBL. (b) Energy levels of the components in the inverted PSCs with various ZMO CBLs. (c) Optical absorption spectra of ZMO films. The inset shows an increase in the bandgap of ZMO films with the increasing of Mg content (x). (d) J-V curve of the device with the ZMO ( x = 0.3) CBL. 48 Fig. 13 (a) Chemical structures of PTB7-Th, PC 71 BM and BisNPC60-OH, (b) Schematic illustration of the proposed cathode interlayer from XPS depth profile; (c) Energy levels diagram for ZnO, InZnO, ZnO-BisC60 and InZnO-BisC60 determined from ultraviolet photoelectron spectroscopy (UPS) and UV-Vis results and for all the components in the inverted PSCs.

Highly efficient and stable electrocatalysts, particularly those that are capable of multifunctionality in the same electrolyte, are in high demand for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this work, highly monodisperse CoP and Co P nanocrystals (NCs) are synthesized using a robust solution-phase method. The highly exposed (211) crystal plane and abundant surface phosphide atoms make the CoP NCs efficient catalysts toward ORR and HER, while metal-rich Co P NCs show higher OER performance owing to easier formation of plentiful Co P@COOH heterojunctions. Density functional theory calculation results indicate that the desorption of OH* from cobalt sites is the rate-limiting step for both CoP and Co P in ORR and that the high content of phosphide can lower the reaction barrier. A water electrolyzer constructed with a CoP NC cathode and a Co P NC anode can achieve a current density of 10 mA cm at 1.56 V, comparable even to the noble metal-based Pt/C and RuO /C pair. Furthermore, the CoP NCs are employed as an air cathode in a primary zinc-air battery, exhibiting a high power density of 62 mW cm and good stability.