The maximum efficiency enhancement of a solar-driven graphene-anode thermionic converter realizing total photon reflection

Abstract

Thermionic converters show highly efficient thermoelectric conversion performance. Compared to metals, graphene materials exhibit excellent optical and electrical properties. A novel solar-driven graphene-anode thermionic converter is proposed, in which a photon reflector is attached to the graphene-anode to reduce dissipation. Expressions for the power output density and efficiency of the system are derived by considering the major irreversible dissipation. The performance characteristics of the system are comprehensively evaluated, including the effects of the voltage output, current density, area ratio of the absorber to the cathode, and solar concentration factor. The results show that the solar-driven graphene-anode thermionic converter with a photon reflector achieves better performance than the case without reflectors, and outperforms the solar-driven metal-anode thermionic converter. Under the same conditions of 3000 solar concentrations, the maximum power output density and efficiency of the proposed system attain 777.2 Wcm−2 and 44.56%, which increase 24.33% and 115.2%, respectively, compared to those of the solar-driven metal-anode thermionic converter. Besides, the maximum efficiency and power output density of the system at different concentrations and corresponding optimal values of key parameters are calculated. The optimum operating region of the proposed system is determined and the optimum selection criteria of key parameters are provided.