MoSe2 and WSe2 nanofilms with vertically aligned molecular layers on curved and rough surfaces.

Two-dimensional (2D) layered materials exhibit high anisotropy in materials properties due to the large difference of intra- and interlayer bonding. This presents opportunities to engineer materials whose properties strongly depend on the orientation of the layers relative to the substrate. Here, using a similar growth process reported in our previous study of MoS2 and MoSe2 films whose layers were oriented vertically on flat substrates, we demonstrate that the vertical layer orientation can be realized on curved and rough surfaces such as nanowires (NWs) and microfibers. Such structures can increase the surface area while maintaining the perpendicular orientation of the layers, which may be useful in enhancing various catalytic activities. We show vertically aligned MoSe2 and WSe2 nanofilms on Si NWs and carbon fiber paper. We find that MoSe2 and WSe2 nanofilms on carbon fiber paper are highly efficient electrocatalysts for hydrogen evolution reaction (HER) compared to flat substrates. Both materials exhibit extremely high stability in acidic solution as the HER catalytic activity shows no degradation after 15 000 continuous potential cycles. The HER activity of MoSe2 is further improved by Ni doping.