Ball-in-ball　hollow　nanostructures　(BHSs)　based　on　transition　metal　chalcogenides　hold　great　promise　as　electrocatalytic　materials　for　fundamental　studies.　In　this　work,　we　have　developed　a　moderate　method　to　realize　the　synthesis　of　transition　metal　sulfide　ball-in-ball　hollow　nanospheres　(Co-Cu-WSx,　Co-WSx　and　Co-CuSx　BHSs).　Importantly,　it　was　found　that　these　ball-in-ball　hollow　nanospheres　exhibited　superior　electrocatalytic　properties　for　dye-sensitized　solar　cells　(DSSCs)　and　the　hydrogen　evolution　reaction　(HER)　in　alkaline　medium.　Compared　with　the　ternary　Co-WSx　and　Co-CuSx　counterparts,　the　quaternary　Co-Cu-WSx　nanospheres　exhibited　excellent　behavior　in　accelerating　the　reduction　of　I3-　in　DSSCs　and　expediting　the　HER　in　water　splitting.　Specifically,　DSSCs　based　on　Co-Cu-WSx　BHSs　achieved　a　splendid　power　conversion　efficiency　(PCE)　of　9.61%　which　was　higher　than　that　of　Pt　(8.24%)　under　the　same　conditions.　Also,　a　lower　η10　of　82.5　mV　and　a　smaller　Tafel　slope　of　53.8　mV　per　decade　were　obtained　for　a　Co-Cu-WSx　electrocatalyst　for　the　HER　in　1.0　M　KOH.　The　present　approach　is　proposed　as　a　new　idea　for　the　design　of　transition　metal　sulfide　hollow　nanospheres　for　different　energy　conversion　applications.　©　2019　The　Royal　Society　of　Chemistry.