In Situ Oxidation-Assisted Construction of Photothermal-Photocatalytic Synergistic Strategy: Achieving Reversible Hydrogen Storage in Formic Acid

Solar-driven formic acid-mediated hydrogen storage-production cycle is a promising path for the development of hydrogen energy. However, the heat-driven formic acid dehydrogenation currently used increases the energy consumption, and CO₂ hydrogenation requires an additional supply of hydrogen. Here, we proposed a strategy that utilizes formic acid as a medium and CO₂ recycling to achieve solar-driven hydrogen production and storage by coupling photothermal catalytic and photocatalytic materials. In detail, MXene achieved a bifunctional action of broad-spectrum light absorption and catalysis, resulting in a photothermal-driven dehydrogenation of formic acid with a dehydrogenation rate of 39.42 mmol g^-1 h^-1. Concurrently, the orbital hybridization of Ti was tuned by an in-situ oxidation strategy to grow TiO₂ on the Ti-C substrate, thereby preserving the light absorption and photothermal conversion properties while enhancing the electron transport and carrier migration efficiencies. Ultimately, this process led to the reduction of CO₂ and H₂O to formic acid at a rate of 42.4 μmol g^-1 h^-1. More importantly, because this strategy couples CO₂ recycling and hydrogen production by water splitting, the efficiency of hydrogen production is even improved by orders of magnitude compared to that of water splitting. Consequently, this strategy not only enhances the development of formic acid hydrogen storage but also provides a valuable reference point for the advancement of water splitting.