Revealing the Heterogeneity of Large-Area MoS 2 Layers in the Electrocatalytic Hydrogen Evolution Reaction.

The electrocatalytic activity concerning the hydrogen evolution reaction (HER) of micrometer-sized MoS 2 layers transferred on a glassy carbon surface was evaluated by scanning electrochemical cell microscopy (SECCM) in a high-throughput approach. Multiple areas on single or multiple MoS 2 layers were assessed using a hopping mode nanocapillary positioning with a hopping distance of 500 nm and a nanopipette size of around 55 nm. The locally recorded linear sweep voltammograms revealed a high lateral heterogeneity over the MoS 2 sheet regarding their HER activity, with currents between -40 and -60 pA recorded at -0.89 V vs. reversible hygrogen electrode over about 4400 different measured areas on the MoS 2 sheet. Stacked MoS 2 layers did not show different electrocatalytic activity than the single MoS 2 sheet, suggesting that the interlayer resistance influences the electrocatalytic activity less than the resistances induced by possible polymer residues or water layers formed between the transferred MoS 2 sheet and the glassy carbon electrode.