[en] The results of experimental study of output parameters of a thermionic converter with electrodes of Nb polycrystal doped with oxygen ions are given. The samples are doped by a nonchanneled oxygen ion beam of 100 keV energy, 30-50μA/cm² current density and 10¹⁸ cm^-2 flux. The conclusion is made that the observed increase of the converter current density is caused by improvement of the emission-adsorption properties of electrodes. The output parameters of the converter under study are stable with the ± 7% accuracy during 200 hours