Transition　metal　chalcogenides　with　yolk-shell　nanostructures　are　a　family　of　promising　electrocatalytic　materials　with　complex　interior　construction　and　remarkable　structural　tenability.　In　this　work,　a　sequence　of　yolk-shell　transition　metal　sulfide　nanospheres　(Co-Ni-MoSx,　Co-MoSx　and　Ni-MoSx)　are　prepared　as　superior　Pt-free　catalysts　for　dye-sensitized　solar　cells.　This　yolk-shell　structure,　consisting　of　a　thin　shell　and　an　inner　porous　core,　exposes　more　active　sites　and　provides　more　contact　regions　between　the　electrolyte　and　catalyst.　By　comparing　with　the　ternary　Co-MoSx　and　Ni-MoSx　nanospheres,　the　quaternary　Co-Ni-MoSx　nanospheres　have　advantages　of　the　relatively　larger　surface　area,　favourable　chemical　composition,　higher　conductivity　and　excellent　catalytic　performance　for　expediting　the　reduction　of　I3−　in　solar　cells.　Particularly,　as　for　Co-Ni-MoSx,　a　splendid　power　conversion　efficiency　of　9.76%　is　achieved　under　a　standard　irradiation,　which　is　much　better　than　that　of　Pt　(8.24%).　©　2018　Elsevier　B.V.