ABSTRACT: The efficient and safe decomposition of formic acid, as a promising energy carrier, has become increasingly important. Herein, we report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. A turnover frequency (TOF) of 12,000 h-1 and a turnover number (TON) of 350,000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure gas of 24.0 MPa (3480 psi) through the decomposition of formic acid, without formation of CO, was achieved. Mechanistic studies by NMR and DFT indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.