Few-layer MoS2nanosheets coated onto multi-walled carbon nanotubes as a low-cost and highly electrocatalytic counter electrode for dye-sensitized solar cells

Abstract

In the current study, the nanocomposite of molybdenum disulfide and multi-walled carbon nanotubes (MWCNT@MoS₂) was proposed for the first time as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I₃⁻) to iodide (I⁻). This novel catalyst was synthesized by simply mixing MWCNTs and MoS₂ in an acidic solution and then converting the solid intermediate into the MWCNT@MoS₂ nanocomposite in a H₂ flow at 650 °C. X-ray powder diffraction, Raman and X-ray photoemission spectroscopy confirmed the composition and the structure of the MWCNT@MoS₂ nanocomposite. The microstructure details of the nanocomposite were studied by transmission electron microscopy, showing that only a few-layers of the MoS₂ nanosheets were formed on the MWCNT surface. This unique structure is beneficial to the improvement of the catalytic activity of MWCNT@MoS₂ towards the reduction of I₃⁻. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MWCNT@MoS₂ CE was higher than those of MoS₂, MWCNT and sputtered Pt CEs due to the increased active surface area of the former. Moreover, the peak current densities of the MWCNT@MoS₂ CE showed no sign of degradation after consecutive 100 CV tests, suggesting the great electrochemical stability of the MWCNT@MoS₂ CE. Furthermore, the MWCNT@MoS₂ CE demonstrated an impressive low charge-transfer resistance (1.69 Ω cm²) for I₃⁻ reduction. Finally, the DSSC assembled with the MWCNT@MoS₂ CE showed a high power conversion efficiency of 6.45%, which is comparable to the DSSC with Pt CE (6.41%).