Two-Dimensional Metal–Organic Framework Acts\nas a Hydrogen Evolution Cocatalyst for Overall Photocatalytic Water\nSplitting

Abstract

Water-splitting\nsemiconductor photocatalysts require hydrogen evolution\nreaction (HER) cocatalysts, the majority of which are robust metals\nand metal oxides. Metal complexes feature designability and reaction\nselectivity. This feature should be appreciated in the application\nas HER cocatalysts by suppressing unfavorable back reactions; however,\nlow stability hampers their application. In this research, we demonstrate\nthat a fully π-conjugated and conductive two-dimensional metal–organic\nframework (2D MOF), which possesses both virtues of metals/metal oxides\nand metal complexes, serves as an ideal HER cocatalyst candidate.\nNiBHT, a kind of 2D MOF, is deposited on the photocatalyst SrTiO₃:Al with CoO<i>_x</i> as an oxygen evolution\ncocatalyst to show long-term overall one-step water splitting with\nan apparent quantum efficiency (AQE) of 6.5% at 350 nm. In comparison\nto Pt as a representative HER cocatalyst, NiBHT turns out to be a\nsuppressor of back reactions related to oxygen reduction reactions,\nwhich is proven both experimentally and theoretically.