One-step water splitting and NaHCO3 reduction into hydrogen storage material of formate with Fe as the reductant under hydrothermal conditions

In this paper, we give an overview of recent advances in the production of formic acid, as a hydrogen carrier, from CO₂ and water by using the earth-abundant metal of Fe as the reductant under hydrothermal conditions, which mainly includes: 1) hydrogen production from water with Fe; 2) reduction of HCO₃^– to formic acid in the presence and absence of catalysts; 3) proposed reaction mechanisms. The novel options under this study are mainly the use of water as a hydrogen source with metal Fe as a reductant, and the formed Fe_xO_y as an auto-catalyst. Such a process possesses several benefits: (i) water acts not only as a hydrogen source but also as an environmentally benign solvent; (ii) there are no hydrogen requirements, including pumps or storage, because hydrogen is derived from water and reacts with CO₂in situ; (iii) no exotic catalysts or harsh reagents are used; and (iv) the method is simple and highly efficient. This technology can provide a one-step, sustainable and highly efficient way to reduce CO₂ into formic acid using the hydrogen directly from water.