- Title
- Synthesis and characterization of MXS (M = Mo & V) and carbon supported MXS nanocomposites as Pt-free counter electrodes for electrode for DSSC application
- Creator
- Bede, Asanda
- Subject
- Voltammetry
- Date
- 2020
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10353/18599
- Identifier
- vital:42612
- Description
- It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials was of considerable importance because it governs the efficiency of many photon assisted chemical and physical reactions in dye sensitized solar cells (DSSCs). The efficiency of DSSCs with composite counter electrode materials is reliant on the stability of the photochemistry reactions which can be optimized by appropriate doping levels of the composite materials. Moreover, the microstructure such as surface area, distribution of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials, and the stability of the electrostatic bonds between the MxS (Mo, V) with the carbon support also play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials on the morphological, structural and electrochemical properties of the composite materials. MoS2 nanoflakes nanostructures have been synthesized by hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work Carbon supported MoS2 NFs have been prepared by physically/chemically mixing different mole ratios of MoS2 NFs with multi-walled carbon nanotubes (MWCNTs) and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials have been investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis has revealed the presence of large MoS2 nanoflakes (NFs) as synthesized. SEM analysis has also revealed significant change in the surface morphology of carbon supported MoS2 composite nanostructures with the change in the mole ratio of the MoS2 NFs and carbon support multi-walled carbon nanotubes. Structural analysis through HRTEM analysis revealed a d-spacing of 0.65 nm with a corresponding (002) lattice plane belonging to a trigonal crystalline phase of MoS2. Also, HRTEM analysis has revealed d-spacing of 0.291 nm corresponding to 002 plane of MWCNTs. Raman spectroscopy has revealed Characteristic Raman vibration frequencies and symmetries at 264.6 cm-1(Eg), 354.2 cm-1 (Ag ) belonging trigonal phase of MoS2 (1T-MoS2). FTIR analysis has revealed a narrow peak at 457.6 cm-1 due Mo-S vibration bond. This observation confirms the success of synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements have revealed that the ratio 6:3:1 have shown to be optimum ratio due to its large reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated Rreduction for the carbon supported MoS2 NFs is the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating the trend of ratio 3:6:1 appeared to have higher reduction rate than the rest of the material and it had far less ΔEpp than the rest of other ratios. All CV curves for both pristine MoS2 NFs and carbon supported MoS2 NFs confirmed a distinct Faradic characteristic. The VS2 nanosheets (NSs) and carbon supported VS2 NSs were also effectively synthesized via hydrothermal method. The SEM micrographs for VS2 NSs and carbon supported VS2 NSs samples reveals level increased. Furthermore, SEM-EDX analysis have confirmed the presence of V and S as well as C and O on carbon supported VS2 nanocomposites, and it clearly shown a gradually blending as the ratios increases. The structural studies through XRD analysis have revealed peaks at 2θ angles of 15.4◦, 28.2◦, 34.2◦, 36.2◦, 43.3◦,48.3◦, 54.4◦, 57.7◦ and 66.2◦ which correspond to the lattice planes (001), (002), (100), (011), (102), (003), (110), (103) and (201) belonging to hexagonal VS2 (H-VS2) crystalline phase as per JCPDS card 36-1139. The HRTEM have revealed that the VS2 NSs have an edge to edge length of ~ 0.294 – 1.248 µm. Also, HRTEM micrographs of VS2 NSs have revealed interplanar d spacing of 0.571 nm belonging to the (001) lattice plane of hexagonal VS2 (H-VS2) structure. FTIR analysis have shown a peak at 558 cm-1 attributed to V-S which is evident that sulfur has bonded with the metal (V) and is in agreement with EDS. CV, CD and EIS measurements have shown that the ratio 1:8:1 is more superior to VS2 NSs and other carbon supported VS2 NSs. Based on Rreduction for the carbon supported nanosheets VS2 nanosheets are ordered as 1:8:1>3:6:1>6:3:1>8:1:1. Carbon supported VS2 NSs of the mole ratio 1:8:1 showed a small resistance of 0.32 Ω. This is further evidence that the carbon supported VS2 NSs of the mole ratio 1:8:1 in addition to revealing excellent catalytic behaviour is also more chemically stable and has good conductivity properties._________
- Format
- 149 leaves
- Format
- Publisher
- University of Fort Hare
- Publisher
- Faculty of Science and Agriculture
- Language
- English
- Rights
- University of Fort Hare
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