The　waste　heat　released　by　molten　carbonate　fuel　cells　(MCFCs)　contains　considerable　energy　that　can　be　captured　for　electric　power　generation.　Nonetheless,　the　current　high-grade　heat　harvesting　devices　for　the　MCFC　cogeneration　of　electrical　power　are　still　constrained　by　low　power　output　or　energy　conversion.　To　address　this　challenge,　we　present　a　novel　hybrid　system　that　combines　an　MCFC　and　a　graphene-collector　thermionic　generator　(GCTG),　in　which　the　GCTG　can　efficiently　harness　the　exhaust　heat　released　from　the　MCFC　and　generate　additional　electricity.　The　results　show　that　the　hybrid　system＇s　maximum　power　density　reaches　0.298　W/cm2,　which　is　1.6　times　that　of　the　sole　MCFC　at　923　K,　demonstrating　that　the　hybrid　system　delivers　a　significant　boost　in　output　performance.　Furthermore,　finite-time　thermodynamics　estimates　the　hybrid　system＇s　optimal　operating　regions　and　key　parameter　designs.　The　optimal　performance　of　the　hybrid　system　can　be　further　improved　by　selecting　the　optimal　area　ratio,　raising　the　MCFC　operating　temperature,　strengthening　the　heat　transfer　coefficient,　lowering　the　thermal　emissivity　of　the　thermionic　emitter,　and　manufacturing　the　perfect　optical　reflector.　The　MCFC-GCTG　outperforms　other　MCFC-based　hybrid　systems　regarding　output　performance,　demonstrating　that　GCTG　can　more　effectively　exploit　the　waste　heat　released　from　MCFCs　than　other　heat　recovery　devices.　This　study　offers　valuable　theoretical　guidance　for　the　strategic　optimization　of　the　MCFC-GCTG　hybrid　system,　thereby　paving　a　constructive　strategy　towards　realizing　advanced,　high-performance　MCFC　cogeneration　systems.　©　2023　Elsevier　Ltd