Reduced graphene oxide encapsulated octahedral NiSe2 nanocrystals with dominant {111} crystal facets for efficient hydrogen evolution reaction

•Octahedral NiSe2 nanocrystals with dominant {111} crystal facets were prepared.•Crystal facets effect of NiSe2 in electrocatalytic HER was studied.•A strong crystal facets dependent effect was demonstrated.•Further improvement in HER activity could be achieved by rGO encapsulation.•The electrocatalytic mechanism was studied through theoretical calculation. Regulating the exposed crystal facets of electrocatalysts is an effective means to enhance their electrocatalytic activity. However, related studies have focused mainly on traditional noble metals or metal oxides based electrocatalysts, while the research on crystal facets dependent electrocatalytic activity of metal selenides is still very rare. Here, crystal facets effect of cubic NiSe2 in electrocatalytic HER was studied. It was shown that octahedral NiSe2 nanocrystals dominated by active {111} crystal facets exhibited significantly enhanced HER activity. Moreover, by encapsulating the octahedral NiSe2 nanocrystals into reduced graphene oxide (rGO) nanosheet networks, further improvement in their HER activity could be achieved. First principles calculations and experimental characterization indicated that {111} crystal facts of NiSe2 had abundant surface active sites and ideal catalytic reaction energy barriers. This study not only expands the research on crystal facets-dependent HER activity, but also gains a deep understanding of the electrocatalytic mechanism. Reduced graphene oxide encapsulated octahedral NiSe2 nanocrystals with dominant {111} crystal facets was designed for efficient hydrogen evolution reaction. [Display omitted]