Alkali metal-assisted nucleation and growth of stable 1T/2H MoS2 for the hydrogen evolution reaction

Abstract

The present work investigates the extent of mixed phase 1T/2H MoS₂ formation as the same precursor solution was maintained for 0 to 8 days in an alkaline medium. To confirm the mixed phase of MoS₂, powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, and transmission spectroscopy measurements were performed. The major XRD peak of the 1T phase for the 2θ value was at 13.8° and was indexed as the (002) plane along with the 2H phase, and Raman spectra E¹_2g = 381 cm⁻¹ and A_1g = 405 cm⁻¹, including extra peaks J₁, J₂, E_1g, and J₃. The high-resolution transmission electron spectroscopy interplanar spacing of 1T-MoS₂ and 2H-MoS₂ was 0.246 nm and 0.688 nm, respectively. Our studies indicate that the alkali metal Na⁺ plays a crucial role via intercalation, which expanded the inter-layer spacing and increased the catalytic surface area and conductivity, hence affecting the hydrogen evolution reaction (HER) efficiency. The HER showed an overpotential @10 mA cm⁻², and Tafel slope of 260 mV, 65 mV dec⁻¹ for the instantly prepared 0-MoS₂ sample compared to longer duration samples of 2 to 8 days.