Electron Transfer Reduction by Hydrogen Creates Porosity in Tantalate Crystals and Produce Multifunctionality

Contrary to partially substituted systems, WO₃ molecular sieves that exclusively comprise a d⁰ transition metal ion and do not possess template ions in the cavity are a new class of materials for photocatalysis owing to their framework structure. Because WO₃ thermodynamically lacks proton-reduction capability, exploring diverse synthetic approaches of other materials is desirable for facilitating utilization as H₂ evolution and water splitting systems. Herein, we report an efficient approach for the protonation of Ag₂Ta₄O₁₁ to afford H₂Ta₄O₁₁ for application as a H₂ molecular sieve. Hydrogen reduction of Ag₂Ta₄O₁₁ at 300 °C and post-treatment using HNO₃ afforded H₂Ta₄O₁₁. Characterizations of H₂Ta₄O₁₁, coupled with density functional theory (DFT) calculations, reveal that the intrinsic structure of Ag₂Ta₄O₁₁ is maintained. Moreover, H⁺ is generated from H₂ oxidation and forms OH, and the orientation of OH is parallel to that of the ab plane. Desorption and adsorption of H₂ within H₂Ta₄O₁₁ were achieved by heating H₂Ta₄O₁₁ to above 90 °C. This is attributed to positive thermal expansion, as confirmed by high-temperature X-ray diffraction. H₂Ta₄O₁₁ is an active heterogeneous photocatalyst for the half-reactions of water splitting. Moreover, deuteration experiments of H₂Ta₄O₁₁ in D₂O suggest its capability as a H₂-D₂ conversion catalyst. Furthermore, H₂Ta₄O₁₁ functions as an active synthetic precursor for new tantalate materials, the direct synthesis of which is challenging.