The effect of electrochemical oxygen pumping on the emission of oxygen negative ions, O-, from the surface of yttria-stabilized zirconia (YSZ) was studied with a quadrupole mass spectrometer capable of detecting negative ions. It was found that O- ions are emitted into a vacuum from the YSZ surface with a porous platinum electrode. With a potentiostat, the voltage between an air electrode and the platinum electrode on the emission surface was varied during the emission of O- ions at 925degreesC: deviation from the rest potential ranged from -750 to +150 mV. Negative ion mass analysis demonstrated that electrochemical polarization affected the emission rate of O- ions. The effect of electrochemical polarization increased with the magnitude of the polarization. The emission of O- ions was enhanced with cathodic polarization, whereas it was reduced with anodic polarization. Although oxygen pumping by anodic polarization enhanced the mass flow of oxygen from air into the vacuum chamber, it did not enhance the emission of O- ions. The variation in the emission rate of O- ions is due to the variation in the work function of the emission surface by electrochemical polarization. (C) 2003 The Electrochemical Society.