Reactions between alkali metal hydrides MH (M = Li, Na, or K) and carbon dioxide (CO2) at room temperature were systematically investigated for the first time. It was found that the raw alkali metal hydrides did not react with CO2 under static-pressure conditions at room temperature, but the mechanically activated alkali metal hydrides reacted with CO2 and released large amounts of hydrogen (H-2). Under the same ball-milling conditions, the order of reactivity of the alkali metal hydrides with CO2 was KH > NaH > LiH. The particle size of the activated alkali metal hydrides had a large influence on the reactivity of the alkali metal hydrides with CO2. During the reactions, CO2 was reduced by alkali metal hydrides, generating elemental carbon, alkali metal oxides and H-2, and it was consumed by alkali metal oxides, forming carbonates. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.