Design Of Energy Conversion And Storage Devices Based On Low Dimensional Nanomaterials

The photoelectric conversion, hydrogen evolution reaction and supercapacitors that are both environmentally friendly and renewable energy conversion and storage systems hold great promise for alternative sustainable energies and that can positively influence the quality of our lives and the health of our environment. However, the performance of these energy systems needs to be further signicantly improved to satisfy increasing demands placed upon them. Nanostructured materials are advantageous in offering huge surface to volume ratios, favorable transport features, and attractive physicochemical properties, resulting in improved energy conversion and storage. The details are summarized briefly as follows:1. For the first time, the organolead halide perovskites photo detectors based on CH3NH3PbI3 film were fabricated through a low-cost, solution-processed and self-assembly strategy on flexible substrates. In the photocurrent measurement, the photodetector has a broad photoresponse range from 780 nm to 310 nm, far exceeding the performance of current photodetectors. Besides, the photodetector was characterized in terms of power intensity dependent photoresponse and time-resolved photocurrent. The photoresponse and external quantum efficiency of the CH3NH3PbI3 film-based flexible photodetectors were measured at different wavelengths and reached 3.49 AW-1,1.19×103%, respectively, at 365 nm. This demonstrates that the photodetector shows high sensitivity, fast response speed and excellent stability, indicating that the developed CH3NH3PbI3 film photodetector is a great candidate for applications in broadband light detection, and may be further extended to applications in optoelectronic devices.2. We firstly synthesize nanosheets of Ⅰ-Cu2WS4 with a thickness of only about 0.8 nm via ultrasonic exfoliation of lamellar LixCu2WS4 intermediate. Compared with the bulk counterpart,Ⅰ-Cu2WS4 ultrathin nanosheets possess more flexible feature, extremely high exposure of surface atoms and better interface contact with the substrate. The as-exfoliated nanosheet exhibits an extremely large cathodic current density of 74 mA cm-2, showing 74-fold enhancement compared with that of the bulk counterpart, confirming the excellent activity of the atomically-thin Ⅰ-Cu2WS4 nanosheets. Evidently, as displayed by the calculated density of states (DOS), the Ⅰ-Cu2WS4 slab shows an obviously increased DOS at the conduction band edge compared with the bulk counterpart, which indicates that more carriers can be effectively transferred to the conduction band minimum (CBM) of the atomically thin Ⅰ-Cu2WS4 sheets. Furthermore, the charge density distributions of the single-layered Ⅰ-Cu2WS4 slab and the bulk counterpart near the Fermi level also demonstrate that the slab possesses a higher degree of hybridization than the bulk counterpart, which can facilitate the charge transport during the HER process. The surface sulfur atoms are HER active sites was identified. The catalytic stability of our Ⅰ-Cu2WS4 nanosheet is characterized by continuous cyclic voltammetry performed for 2000 cycles. At the end of the cycling procedure, the current densities show that the catalyst affords similar to the initial cycle with negligible loss of the cathodic current, indicating that the Ⅰ-Cu2WS4 catalysts maintained its unique nanosheet structure over a long time in an acidic environment. In this chapter, the tenary chalcogenide compound not only enriches the application of nano electrocatalyst, but also offers the opportunity for designing highly efficient HER catalysts and determining the active sites for tenary compounds.3. Based on the understanding of the benefits of the semiconducting 2H phase to metallic IT structure electronic transition for WS2, we firstly report an inorganic graphene analogue, WS2(1-x)Se2X ultrathin nanosheets with only 1.0 nm thickness, as a promising material to construct a flexible all-solid-state thin-film supercapacitance device. Analyses indicate that the enhanced electrocatalytic activity of the nanosheet is correlated to the metallic transition state. The highly conductive WS2(1-x)Se2x ultrathin nanosheets guarantee the high specific capacitance as well as the excellent stability of this novel energy storage material. By employing the WS2(1-x)Se2x nanosheets as the active electrode material, the flexible all-solid-state thin-film double-layer capacitance exhibits a high surface specific capacitance of 660.8 F cm-3, and negligible degradation occurs even after 2000 charge-discharge cycles. Meanwhile, the ultrathin configuration of the nanosheets endows superior mechanical property for the as-fabricated nano-device, which can be regarded as a feasible energy supply for the exploitation of flexible electronics.