Thermionic emission from potassium-intercalated carbon nanotube arrays for direct energy conversion

Vacuum and solid-state thermionic electron emission are potentially efficient means for converting heat or solar energy directly into electrical power. However, low work function materials must be developed before reasonable efficiency can be realized with a power generation device based on thermionic emission. In this work, carbon nanotube (CNT) arrays have been doped with potassium atoms using a two-zone vapor method to lower their work functions to 2-4 eV. We have previously shown that carbon nanotube emitters prepared in this way are stable in atmospheric air although undesirable oxide compounds can form on the carbon nanotube surface. Using a hemispherical electron energy analyzer to obtain thermionic emission energy distributions, we show that low work function emitters can be prepared from potassium-intercalated CNT mats at temperatures as low as 400°C and that emitters prepared in this way can be stable at temperatures up to 620°C.