Recent Developments in Reversible CO₂ Hydrogenation and Formic Acid Dehydrogenation over Molecular Catalysts

Carbon dioxide (CO₂), a valuable feedstock, can be reutilized as a hydrogen carrier by hydrogenating CO₂ to formic acid (FA) and releasing hydrogen by FA dehydrogenation in a reversible manner. Notably, FA is liquid at room temperature and can be stored and transported considerably more safely than hydrogen gas. Herein, we extensively reviewed transition-metal-based molecular catalysts explored for reversible CO₂ hydrogenation and FA dehydrogenation. This Review describes different approaches explored for carbon-neutral hydrogen storage and release by applying CO₂ hydrogenation to FA/formate and the subsequent release of H₂ by the dehydrogenation of FA over a wide range of molecular catalysts based on noble and non-noble metals. Emphasis is also placed on the specific catalyst-to-substrate interaction by highlighting the specific role of the catalyst in the CO₂ hydrogenation-FA dehydrogenation pathway.