One-step synthesis of MnS/MoS2/C through the calcination and sulfurization of a bi-metal-organic framework for a high-performance supercapacitor and its photocurrent investigation.

Based on a Mn/Mo-metal organic framework (MOF) precursor, [Mn(4,4'-bipyridine)0.5 MoO4]·1.5H2O, a MnS/MoS2/C hybrid was synthesized through a calcination and sulfurization approach and it is mainly constituted by MoS2/C nanorods and MnS/MoS2/C nanoflakes. The MnS/MoS2/C hybrid delivers a high specific capacitance of 1162 F g-1 at 0.5 A g-1 in 2 M KOH electrolyte, and it possesses a good rate capacity with a retention of 75.7% (880 F g-1) at 10 A g-1, which is due to the synergetic effects of the components MnS, MoS2 and carbon matrix in the hybrid material. The carbon matrix in the hybrid material can not only anchor the active components of MnS and MoS2, but also transport electrons efficiently. The completely exposed Mo and S edges on the preferential 2H-(002) and 3R-(003) facets of MoS2 are beneficial for ion adsorption and electrochemical reaction. An asymmetric supercapacitor constructed by the MnS/MoS2/C hybrid (positive electrode) and activated carbon (AC) (negative electrode) exhibited a capacitance retention of 81% after 5000 galvanostatic charge-discharge cycles (GCD). During the GCD process, the metal sulfides were probably transformed into metal hydroxides in the presence of OH- electrolyte ions. In addition, the MnS/MoS2/C hybrid exhibits a visible light-driven photocurrent response, and DFT calculation proves that it is attributed to the semiconducting feature of MoS2 in the hybrid.

The photocurrent response in the perovskite device based on coordination polymers: structure, topology, band gap and matched energy levels.

Using a rigid ditopic ligand, 4,5-di(4'-carboxylphenyl)benzene (H2L), three coordination polymers (CPs) formulated as MnL(H2O)2 (1), CdL(H2O) (2) and Mn2L2(DMF)3 (3) have been synthesized and structurally characterized by single-crystal X-ray diffraction. These three CPs display 2D architectures but with different topologies. The experimental data and DFT calculation indicate that CP 2 is a semiconductor, and its CB/VB energy levels match with those of the perovskite CH3NH3PbI3. A FTO/TiO2/CH3NH3PbI3/CP 2 device is fabricated and the CP-based device shows much larger photoresponse under visible light illumination (650 nm > λ > 350 nm, 100 mW cm-2) than the individual CP 2. At 0 V vs. AgCl/Ag, the largest photocurrent density yielded by the CP-based perovskite device is ca. 200 times that of CP 2, which is due to the matched energy levels of all the materials in the device, leading the photogenerated electron-hole pairs to be separated effectively. Meanwhile, the coverage of the insoluble CP on the surface of the perovskite CH3NH3PbI3 can improve the stability of the perovskite against water.