Edges are more electroactive than basal planes in synthetic bulk crystals of TiS2 and TiSe2

Layered materials and derived 2D material couples such as graphite/graphene, layered and single layer pnictogens (i.e., black phosphorus and phosphorene) and transition metal dichalcogenides (TMDs) have gained a lot of attention due to their electrocatalytic properties and as potential materials for energy storage. Previous studies have shown that electrochemical reactions at graphite, MoS2 and pnictogens mainly occur at the edges and steps of crystals rather than on the basal plane. The persisting question is if this is a general trend in nature within bulk crystals of 2D materials. To come closer to the answer to this question, we studied the surface of artificially grown TiS2 and TiSe2 crystals regarding their local electrochemical activity via scanning electrochemical microscopy (SECM). Both TMDs have shown increased electrochemical activity near crystal steps/edges. For correlation, optical and topographical analysis were performed via scanning electron microscopy (SEM) and atomic force microscopy (AFM). We show that the increased electrochemical activity at edges is persistent for these layered crystalline materials, thus expanding the knowledge their properties, which is important for future application in the energy sector.