The effect of boron species from borosilicate glass sealant on the electrocatalytic activity and microstructure of La0.8Sr0.2MnO3 (LSM) oxygen electrodes is studied for the first time under accelerated solid oxide electrolysis cell (SOEC) operation conditions at 800 degrees C. The presence of volatile boron species has remarkable detrimental effect on the electrochemical activity of LSM oxygen electrode for the O-2 evolution reaction (OER). After polarization at 200 mA cm(-2) for 2 h, the electrode polarization and ohmic resistances increase rapidly from similar to 40 and 1.2 Omega cm(2) to 614 and 33 Omega cm(2), respectively. Under the anodic polarization conditions, there is an accelerated Sr segregation and boron deposition preferentially occurs at the electrode/electrolyte interface, forming lanthanum borates and manganese oxide. Boron deposition and reaction is driven to the interface region due to the increased activity and energetics of lanthanum at LSM lattice sites at the electrode/electrolyte interface under anodic polarization conditions, accelerating the disintegration and delamination of the LSM electrode. The results indicate the potential detrimental effect of volatile boron on the electrochemical activity and stability of LSM oxygen electrodes of solid oxide electrolyzers. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.