Comparison of Mono- and Multi-Layer MoS₂ within Non-Aqueous Reactive Carbon Capture and Conversion (RCC) Conditions

With a need to reduce global emissions and scale up alternative energy sources to fossil fuels, RCC integrates CO₂ capture and conversion into a singular electrochemical, thermal, or biological process as a feedstock for value added chemicals. Despite significant progress in CO₂ electrocatalyst design to improve efficiency, reproducibility, and selectivity in aqueous media, achieving the same milestones within non-aqueous media under RCC conditions remains a challenge. However, preliminary results show that single crystal molybdenum disulfide (MoS₂) exhibits high efficiency (~65%) towards CO production under non-aqueous RCC with ionic liquids. The electrocatalytic behavior of MoS₂ can be controlled by exposing edge and terrace active sites through surface defects or by modulating its structure through compositions such as thin film monolayers and multi-layer nanosheets. It is hypothesized that by decreasing MoS₂ layers, further efficiency and selectivity of CO₂ reduction products under relevant non-aqueous RCC conditions will be observed due to increased surface area of active sites. Two different synthetic pathways are detailed in this work, shear exfoliation of bulk MoS₂ to yield dispersions of nanosheets and metal organic chemical vapor deposition (MOCVD) of monolayer MoS₂ thin films. The shear exfoliation process is a combination of mechanical and liquid-phase techniques, utilizing a homogenizer along with chemical exfoliation from different surfactants. Exfoliating agents such as sodium cholate resulted in MoS₂ nanosheets with large terraces while polyvinylpyrrolidone (PVP) resulted in small nanoparticle MoS₂ sheets. Therefore, size distribution of MoS₂ sheets may be controlled with the type of exfoliating agent. Our MOCVD process utilizes Mo(CO₆) and diethyl sulfide (DES) as metal organic precursors flown in a vapor phase with Ar and H₂ gas for deposition onto Si/SiO₂ wafers. At optimal chamber pressure and temperature as well as precursor/gas flow rates, deposition of nucleation zones, monolayers, and few layered structures occur as a function of time. Shear exfoliated nanosheets and MOCVD deposited monolayers will be tested against single crystal MoS₂ under relevant non-aqueous RCC conditions with ionic liquids.