Development of the oxygenated thermionic energy converters utilizing the sputtered metal oxides as a collector

Refractory metal oxides such as NbOx, WOx, MoOx, TaOx, PtOx and Silver oxide (AgOx) have been studied for an oxygenated thermionic converter and a low work function collector. The metal oxide materials were deposited on metal substrates by RF sputtering in the Ar/O2 gas mixture to fabricate collector electrodes. Work function values of the collector electrodes were evaluated by cesium plasma immersion technique. Very low work function values were obtained, for instance 1.25V as φC of AgOX. A research thermionic energy converter with a plane parallel type of a polycrystalline W emitter and the metal oxide collectors (AgOX, NbOX and PtOX), was set up and the power generation experiments were conducted. In the case of the W-AgOX thermionic converter, the barrier index VB was 2.05 V. Similarly VB=2.15 V for the W-NbOX converter, VB=2.25 V for the W-PtOX converter.