Edge vs. basal plane electrochemistry of layered pnictogens (As, Sb, Bi): Does edge always offer faster electron transfer?

Materials with layered structure are at the forefront of material research. Graphite, MoS₂ and black phosphorus, as layered materials, exhibit, in general, fast heterogeneous transfer at the edge planes and slow at the basal plane for many electroactive molecules. There is a fundamental question whether this is general behaviour of layered materials. Here, we examined fundamental electrochemistry of layered pnictogens (As, Sb and Bi) using single crystal edge- and basal-plane electrodes. Significant differences in behaviour of edge and basal plane surface for the electrochemical properties were found. The surface morphology of electrodes was examinated in detail. The electrochemical activity was investigated by both, inner and outer sphere probes. Several trends related to the pnictogen position in periodic table were observed. Importantly, an increasing activity of basal plane with atomic number was observed and attributed to the decreasing degree of anisotropy. However, catalytic activity towards hydrogen evolution reaction (HER) was observed only for the edge-planes of the electrodes.