An amorphous diamond electrical generator having a cathode at least partially coated with amorphous diamond material and an intermediate member coupled between the cathode and an anode. The amorphous diamond material can have at least about 90% carbon atoms with at least about 20% of the carbon atoms bonded in a distorted tetrahedral coordination. The amorphous diamond coating has an energy input surface in contact with a base member of the cathode and an electron emission surface opposite the energy input surface. The electron emission surface can have an asperity height of from about 10 to about 1,000 nanometers and is capable of emitting electrons upon input of a sufficient amount of energy. The intermediate member can be coupled to the electron emission surface of the amorphous diamond coating such that the intermediate member has a thermal conductivity of less than about 100 W/mK and a resistivity of less than about 80 -cm at 20 C. The amorphous diamond electrical generator is a thermionic emission device having improved electron emission properties.