This article aims to investigate the mechanochemical hydrogen desorption reactions of alkali hydrides (XH: X = Li, Na, or K) with carbon dioxide. The result of this investigation shows that CO2 can be efficiently reduced by XH (X = Na or K), generating COx-free hydrogen under room-temperature mechanical ball milling condition in the absence of a catalyst. The mole percentage and production rate of hydrogen in the gaseous product, which can reach 98.72% and 95.37%, respectively, depend on the milling time, rotation rate of milling and the mole ratio of XH/CO2. During the mechanochemical reactions, carbon dioxide is fast and wholly consumed by XH, producing element carbon, alkali carbonates, and H-2. This work establishes a new, simple and efficient means for the room-temperature preparation of COx-free hydrogen and the elimination of COx contaminant in hydrogen. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.