Enhanced proton conductivity of Y-doped BaZrO3 (BZY) by molten carbonate (MC) has recently been reported. To understand the phenomenon, the present work investigates the pathways and energetics of proton migration along ZrO2-terminated (100) surface of BaZr(Y)O-3 without and with the presence of MC from a density functional theory (OFT) perspective. The calculations explicitly show that the proton migration on BaZrO3 prefers a curved pathway with an energy barrier of 0.567 eV. In the presence of carbonate-ion, the proton migration barrier is remarkably reduced to 0.332 eV, which is in excellent agreement with 0.33 eV of the experimental activation energy for conductivity in the BZY-MC electrolyte. Overall, the enhanced proton conductivity in the BZY-MC composite electrolyte is originated from facile interfacial proton migration between BZY and MC phase. (C) 2016 Elsevier B.V. All rights reserved.