Advances in efficient homogeneous catalytic hydrogenation of CO₂ to formic acid: Bridging carbon utilization with renewable hydrogen storage

The rising concentration of atmospheric carbon dioxide (CO₂), primarily resulting from the large-scale combustion of fossil fuels, has triggered severe environmental consequences, including global warming and ocean acidification. These challenges highlight the urgent need for innovative and sustainable CO₂ mitigation strategies. Among the promising approaches, the catalytic hydrogenation of CO₂ to formic acid (FA) has garnered significant interest as a dual-purpose solution for carbon utilization and renewable hydrogen storage. FA is particularly appealing due to its high volumetric hydrogen capacity (53 g H₂ per liter) and its stability as a liquid under ambient conditions, making it an excellent candidate for hydrogen carrier applications in fuel cells and decentralized energy systems. This review highlights recent advances in homogeneous transition metal–catalyzed hydrogenation of CO₂ to FA and formate salts, with a focus on highly active systems achieving turnover numbers (TONs) above 100,000. While noble metals such as iridium and ruthenium remain benchmark catalysts owing to their superior activity and selectivity, increasing attention has been directed toward earth-abundant alternatives including chromium, manganese, copper, and nickel, which offer enhanced sustainability and scalability. Key factors influencing catalytic efficiency—such as ligand design, solvent effects, reaction conditions, and thermodynamic constraints—are systematically analyzed. Furthermore, mechanistic insights from both experimental and computational studies are discussed to elucidate the fundamental pathways of CO₂ activation and hydrogenation. Overall, this review aims to provide guidance for the rational design of next-generation catalytic system that combine high efficiency with long term sustainability.