In　this　work,　flexible　graphene　supercapacitor　electrodes　were　prepared　from　biomass-derived　carbon　dots/graphene　composite　film　(CDGF)　and　hydrogel　(CDGH)　with/without　an　electrodeposited　NiCo2S4　layer.　Results　showed　that　the　dispersive　CDs　with　abundant　heteroatoms　effectively　inhibited　the　aggregation　of　graphene　sheets　and　increased　the　number　of　active　sites.　By　combining　CDs　modification　and　NiCo2S4　electrodeposition,　the　electrochemical　performance　of　the　prepared　ternary　composite　electrodes　is　significantly　enhanced.　In　particular,　the　CDGF-NiCo2S4　electrode　has　a　specific　capacitance　of　up　to　1348　F　g(-1)　at　a　current　density　of　0.5　A　g(-1).　The　resultant　CDGF-NiCo2S4　flexible　symmetric　supercapacitor　using　1.0　M　H2SO4　as　aqueous　electrolyte　shows　a　large　specific　capacitance　(313　F　g(-1)　at　0.5　A　g(-1))　and　a　high　energy　density　of　85.1　Wh　kg(-1)　at　a　power　density　of　353　W　kg(-1).　By　contrast,　the　CDGH-NiCo2S4　flexible　solid-state　supercapacitor　using　polyvinyl　alcohol　(PVA)/H2SO4　as　gel　electrolyte　has　improved　cycling　stability　(83.1%　capacitance　retention　after　10000　charging/discharging　cycles)　and　a　better　mechanical　flexibility　(96.8%　capacitance　retention　after　1000　bending　cycles).　This　work　demonstrates　the　importance　of　CDs　and　metal　sulfides　in　modifying　graphene-based　composite　electrodes　for　flexible　supercapacitor.　(C)　2019　Elsevier　B.V.　All　rights　reserved.