Efficient hydrogen production is one of the most important issues in the future energy economy. Dehydrogenation of formic acid has been extensively investigated for safe and easy hydrogen production. Thereby, various catalysts have been developed for aqueous formic acid dehydrogenation (FAD) reaction to efficiently produce hydrogen. However, there is still a lack of understanding of the reaction mechanism. Herein, to fundamentally comprehend the aqueous FAD reaction mechanism, we prepared Pd/C catalyst and performed controlled catalytic tests. The results demonstrated that the aqueous FAD reaction occurs through the formate anion dehydrogenation pathway. DFT calculation explained this by the observation that the charge of formate anion significantly mitigates the activation barrier of HCOO bond cleavage. In addition, computational prediction combined with kinetic isotope effect experiments verified that combinative desorption of hydrogen is the rate-determining step of FAD. (C) 2020 Elsevier Inc. All rights reserved.