Single-Site Ni-Grafted TiO2 with Diverse Coordination Environments for Visible-Light Hydrogen Production

Graphical With the combination of surface organometallic chemistry and post-synthetic ligand exchange or calcination, the coordination environments of Ni sites were precisely manipulated to achieve a splendid improvement in hydrogen evolution reaction (HER) under visible-light irradiation. Thereinto, the 2,2′-bipyridine bonded Ni catalyst showed the optimum HER ability, 260 folds as Ni without ligand and 2.5 folds as 2-phenylpyridine bonded Ni catalyst. Solar hydrogen production at a high efficiency holds the significant importance in the age of energy crisis, while the micro-environment manipulation of active sites on photocatalysts plays a profound role in enhancing the catalytic performance. In this work, a series of well-defined single-site Ni-grafted TiO 2 photocatalysts with unique and specific coordination environments, 2,2′-bipyridine-Ni−O−TiO 2 (T−Ni Bpy) and 2-Phenylpyridine-Ni−O−TiO 2 (T−Ni Phpy), were constructed with the methods of surface organometallic chemistry combined with surface ligand exchange for visible-light-induced photocatalytic hydrogen evolution reaction (HER). A prominent rate of 33.82 μmol ⋅ g −1 ⋅ h −1 and a turnover frequency of 0.451 h −1 for Ni are achieved over the optimal catalyst T−Ni Bpy for HER, 260-fold higher than those of Ni−O−TiO 2 . Fewer electrons trapped oxygen vacancies and a larger portion of long-lived photogenerated electrons (>3 ns, ~52.9 %), which were demonstrated by the electron paramagnetic resonance and femtosecond transient IR absorption, correspond to the photocatalytic HER activity over the T−Ni Bpy. The number of long-lived free electrons injected from the Ni photoabsorber to the conduction band of TiO 2 is one of the determining factors for achieving the excellent HER activity.