Intercalation of Potassium Ions in Molybdenum Sulfide as Catalyst for CO2 Reduction

Abstract

The increasing CO 2 emission during the last decades highly contributed to global warming and as a consequence, we are facing the disruption of nature and more and more extreme weather conditions nowadays [1]. One way of dealing with the emitted excess CO 2 is to create a synthetic carbon cycle, where the emitted CO 2 is captured and turned into fuel using electrocatalysis and green energy. However, in order to achieve this, the exploration of new electrocatalysts is needed for the sake of cost and process efficiency and environmental friendliness. Two dimensional materials have a promising future as catalysts due to their high surface-to-volume ratio. A potential catalyst material for CO 2 reduction is molybdenite (MoS 2 ), a cheap, layered semiconductor which already showed selectivity towards CO 2 reduction in non-aqueous media [2,3]. Its layered structure allows not only to have a high specific surface area but also makes the intercalation of different ions possible. These features enable us to enhance the conductivity of the material via electron donation by the intercalated species [4]. The improved conductivity and the changed band gap can contribute to a higher efficiency of electrochemical processes. Our research investigates the intercalation mechanism of potassium ions into MoS 2 layers and the effects of the intercalated potassium on the CO 2 reduction efficiency. The intercalation process is studied experimentally through electrochemical impedance spectroscopy (EIS) and confirmed by X-ray diffraction (XRD). Furthermore, the Gibbs free energy profile of the intercalation is obtained by Molecular Dynamics (MD) simulations using umbrella sampling. The electronic properties are measured with X-ray photoelectron spectroscopy (XPS) and the products of the CO 2 reduction reaction is measured with gas chromatography (GC). The results suggest that the potassium intercalation improves the conductivity of the MoS 2 and consequently the CO 2 reduction efficiency. [1] McCrystall et al. New climate models reveal faster and larger increases in Arctic precipitation than previously projected. Nat. Commun. 12:6765, 2021. [2] Asadi et al. Robust carbon dioxide reduction on molybdenum disulphide edges. Nature Communications, 5(1), 2014. [3] Asadi et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO 2 reduction in ionic liquid. Science, 353(6298):467–470, 2016. [4] Wang et al. Atomic-scale clarification of structural transition of MoS 2 upon sodium intercalation. ACS Nano, 8(11):11394– 11400, 2014.