Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial Visible Light-Induced Photocatalytic H2and O2Evolution over BaTaO2N

Abstract

The doping of foreign cations and anions is one of the effective strategies for engineering defects and modulating the optical, electronic, and surface properties that directly govern the photocatalytic O2 and H2 evolution reactions. BaTaO2N (BTON) is a promising 600 nm-class photocatalyst because of its absorption of visible light up to 660 nm, small band gap (Eg = 1.9 eV), appropriate valence band-edge position for oxygen evolution, good stability under light irradiation in concentrated alkaline solutions, and nontoxicity. Although the photocatalytic and photoelectrochemical water-splitting efficiencies of BaTaO2N have been progressively improved, it is still far from the requirements set for practical applications. Here, we employ a 5% B site-selective doping of aliovalent metal cations (Al3+, Ga3+, Mg2+, Sc3+, and Zr4+) to enhance sacrificial visible light-induced photocatalytic H2 and O2 evolution over BaTaO2N. The results of physicochemical characterizations reveal that no significant change in crystal structure, crystal morphology, and optical absorption edge is observed upon cation doping. Therefore, the difference observed in O2 and H2 evolution during the photocatalytic reactions over pristine and doped BaTaO2N photocatalysts is explained by examining optical, electronic, and surface properties. Also, molecular dynamics (MD) is used to gain insights into the respective effect of cation doping on adsorption energy of water molecules and formed intermediates (H∗ for H2 evolution and HO*, O*, and HOO∗ for O2 evolution) on the BaTaO2N surfaces terminated with TaO6, TaN6, and TaO4N2 octahedra. Finally, the experimental reaction rates for H2 and O2 evolution are correlated well using a linear energy-performance relationship, elucidating the doping and surface-termination trends observed in the BaTaO2N photocatalysts.