thermal emissivity Subscript a anode A ambient b boiling point c cathode C collector e electrolyte E emitter F fuel cell i H 2 , O 2 , H 2 O L limit I internal j in, out, R, E, C act activation overpotential con concentration overpotential lb low bound leak leakage resistance max maximum ohm ohmic overpotential P maximum power density point ub up bound R radiative Rev reversible voltage T热离子缩写GTEC石墨烯热能转换器FC燃料电池FFTC远场嗜热伏oltaic细胞NFTC NFTC近场嗜热伏oltaic Cell RD Richardson-Dushman Sofc Solid氧化物燃料电池TEC热能转换器