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

Abstract

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 TiO2 photocatalysts with unique and specific coordination environments, 2,2'‐bipyridine‐Ni‐O‐TiO2 (T‐Ni Bpy) and 2‐Phenylpyridine‐Ni‐O‐TiO2 (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‐TiO2. 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, are corresponding 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 TiO2 is one of the determining factors for achieving the excellent HER activity.