Heterogeneous Catalysis for Carbon Dioxide Mediated Hydrogen Storage Technology Based on Formic Acid

In the context of global carbon dioxide increasing drastically, renewable energy is crucial maintain the economic growth of the world. Hydrogen has attracted considerable attention as a clean fuel, but the large-scale storage and controllable release of H-2 is still urgently needed, yet largely not yet accomplished. Through the reactions of CO2 hydrogenation to formic acid (FA) and FA dehydrogenation to hydrogen, a "carbon neutral" sustainable hydrogen storage system can be constructed. With advantages of excellent recyclability and facile separation for heterogeneous catalysis, developing efficient heterogeneous catalysts for hydrogen storage based on FA is the primary focus of this review, mainly involving metal catalysts from nanoscale to single-atom scale. Firstly, the effects of metal size on the catalytic activities are highlighted in detail. Additionally, special attention is paid to the relevant structure-activity relationships of various supported catalysts and the mechanistic insights, which can provide a theoretical foundation for rational catalyst design. This review brings new and systemic insights into innovative and efficient heterogeneous catalysts design and applications for the ultimate FA-based sustainable hydrogen storage system with a closed carbon loop.