Conversion of CO2 into value-added chemicals has attracted considerable attention as an important method to reduce greenhouse gas emissions and also to alleviate the current dependence on fossil fuels. Traditional reducing agent for CO2 reduction relies heavily on gaseous hydrogen from high-pressure cylinder, which meets storage and transportation problem. Moreover, the elaborately prepared and noble-metal involved catalysts are required commonly. Thus, new safe and facile hydrogen source is needed urgently. Hydrous hydrazine, which possesses high hydrogen capacity (7.9%), is regarded as a promising liquid hydrogen storage material. Herein, hydrous hydrazine was employed as an in situ hydrogen source which possesses high reactive activity for reduction of CO2 under hydrothermal conditions. A 62% yield of formic acid with 99% selectivity was achieved by using a common Ni and ZnO powder catalyst. The proposed method is facile and safe because it requires neither elaborately prepared catalysts, nor high-purity hydrogen and hydrogen storage. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.