Morphological, Structural and Electrochemical Evaluation of Nano-Sized Carbon Supported MoS2 as Platinum Free Counter Electrode Materials for DSSC
Published on: 2019-11-04
It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such as MoS2 and carbon supported MoS2 composite nanomaterials are of considerable importance because they govern 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 with the relevant materials. Moreover, the surface area morphology, distribution of the nanomaterials, and stability of the electrostatic bonds between the MoS2 with the carbon support play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MoS2 and carbon supported MoS2 composite nanomaterials on the morphological, structural and electrochemical properties of the composite counter electrode materials. MoS2 nanoflakes have been synthesized by a hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work carbon supported MoS2 NFs were prepared by mixing different mole ratios of MoS2 NFs with MWCNTs and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials were investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis revealed the presence of large MoS2 nanoflakes (NFs). SEM analysis has also revealed a significant change in the surface morphology of the carbon supported MoS2 composite nanostructures as the ratio of composition is varied. Structural properties through HRTEM analysis revealed a d-spacing of 0.65 nm for the (002) lattice plane belonging to a trigonal crystalline phase of MoS2 . HRTEM analysis has also revealed a d-spacing of 0.291 nm corresponding to the 002 plane of MWCNTs. Raman spectroscopy revealed characteristic vibrational frequencies and symmetries at 264.6 cm-1 (Eg), 354.2 cm-1 (Ag) belonging to the trigonal phase of MoS2 (1T-MoS2). FTIR analysis showed a narrow peak at 457.6 cm-1 due to Mo-S vibration bands. This observation confirms the successful synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements confirmed that the MoS2 /MWCNT composite with ratio 6:3:1 performed at the optimum level which is attributed to its larger reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated reduction current densities for the carbon supported MoS2 NFs is in the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating that the composite with ratio of 3:6:1 had the highest reduction rate than the rest of the other materials. Consequently, this composite also attained the least ΔEpp than the rest of the other counter electrodes.