CO₂-mediated hydrogen storage and release cycles realized by a bimetallic ruthenium complex in pure water

CO₂-mediated liquid H₂ storage is a promising technology; however, it typically requires additives such as bases, which increase both cost and energy consumption. Herein, a bimetallic Ru complex is fabricated that catalyzes reversible cycles of CO₂ hydrogenation to formic acid (FA) and FA dehydrogenation in pure water without any additives. The H₂ storage and release cycles are controlled simply by varying the H₂ pressure at 80 °C. Moreover, the system maintains its activity over at least 15 cycles (240 h), achieving a cumulative H₂ storage of nearly 2000 μmol. Labeling experiments using ¹³CO₂ and D₂ confirm the origins of the C and H atoms in FA. This efficient, green, and mild system demonstrates potential for sustainable hydrogen energy applications.