Well-crystallized, layered, two-dimensional bismuth oxyhalide (BiOX; X = Cl, Br, or I) ultrathin nanosheets have been synthesized via a simple and low-cost hydrothermal method. The nanosheets are assessed as oxygen reduction reaction (ORR) catalysts for the air electrodes of aluminum-air batteries using linear polarization, constant-current discharge and rotating ring-disk electrode techniques. Electrochemical results show that the obtained BiOI with the highly reactive (001) facets demonstrates higher electrochemical activity than BiOCl and BiOBr under high discharge current density. Koutecky-Levich analysis of the ORR current densities of all compositions indicates that BiOCl and BiOI are mainly dominated by a four-electron pathway. (C) 2017 Elsevier Ltd. All rights reserved.