Toward Scalable Electrochemical Exfoliation of Molybdenum Disulfide Powder through an Accessible Electrode Design.

ABSTRACT

Cathodic electrochemical intercalation/exfoliation of transition metal dichalcogenides (TMDs) with bulky tetraalkylammonium-based cations is gaining popularity as it avoids the semiconducting (2H) to metallic (1T) phase transformation in TMDs like molybdenum disulfide (MoS2) and, generally, produces sheets with a larger aspect ratio - important for achieving conformal sheet-to-sheet contact in optoelectronic devices. Large single crystals are typically used as the precursor, but these are expensive, often inaccessible, and result in limited quantities of material. In this paper, a 3D-printable electrochemical cell capable of intercalating gram-scale quantities of commercially available TMD powders is presented. By incorporating a reference electrode in the cell and physically restraining the powder with a spring-loaded mechanism, the system can probe the intercalation electrochemistry, for example, determining the onset of intercalation to be near -2.5 V versus the ferrocene redox couple. While the extent of intercalation depends on precursor quantity and reaction time, a high yield of exfoliated product can be obtained exhibiting average aspect ratios as high as 49 ± 44 similar to values obtained by crystal intercalation. The intercalation and exfoliation of a wide variety of pelletized commercial powders including molybdenum diselenide (MoSe2), tungsten diselenide (WSe2), tungsten disulfide (WS2), and graphitic carbon nitride (gCN) are also demonstrated.