Critical review: hydrothermal synthesis of 1T-MoS2 – an important route to a promising material

Abstract

The unique anisotropy, polytypism, and abundance of molybdenum disulfide make it a singularly versatile material for a range of catalytic, electrochemical, and tribological applications. By employing a hydrothermal synthesis, a high surface area, optionally-supported, gas-repellent metallic MoS₂ (1T-MoS₂) has been reported to be produced from benign reagents at scale. This hydrothermally produced material has been shown to exhibit outstanding performance as a capacitor, and as an electrocatalyst (e.g. for the hydrogen evolution reaction). However, synthetic ambiguity and sample mischaracterisations are extremely common within the literature of reports of hydrothermally produced 1T-MoS₂, and these occur across a range of analysis techniques such as Raman spectroscopy, X-ray diffraction, magnetic susceptibility, and X-ray photoelectron spectroscopy. These oversights have led to significant inconsistencies in the prevalent understanding of 1T-MoS₂. In most cases in the literature it is unclear whether MoS₂ or an intercalated (Mⁿ⁺)_(1/n)Mo^IIIS_2⁻ variant is produced. Given the high potential of this material for many cutting-edge applications, it is important to clarify the literature to help facilitate rapid progress. In this context the review presents a way forward, by setting out to provide clear and unambiguous synthetic and analytical strategies.