Experimental characteristics of thermionic energy converters employing barium-dispenser cathode and semiconductor anodes

Thermionic energy converter (TEC) is a promising direct energy conversion technology which is expected to attain high efficiency approaching the ideal Carnot cycle. The exploration for low work function electrode materials and the alleviation of space charge effect have long been significant topics. In this work, TEC prototypes with Mo, n-type GaAs (nGaAs) and graphene/n-type GaAs Schottky heterojunction (Gr/nGaAs) anodes were developed and measured, respectively. The influences of cathode temperature, work function and space charge effect were analyzed by varying the cathode temperature and electrode gap. The electronic barrier was calculated to evaluate the space charge effect and exhibits an upward tendency with the increase of temperature and electrode gap. The experimental results indicate that the TEC with nGaAs anode exhibits the best performance. Notably, the output power of TEC with nGaAs anode shows an enhancement of 8.5-fold and 1.8-fold compared to that of Mo anode and Gr/nGaAs anode at 1398 K, respectively. In addition, the open-circuit voltage of nGaAs anode TEC was 0.57 V higher than that of the Gr/nGaAs anode TEC at 1398 K. This work not only provides a reference for the selection of TEC anode materials, but also paves the way for future researches aimed at achieving high output power in TECs.