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

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 mu mol . 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, similar to 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 TiO2 is one of the determining factors for achieving the excellent HER activity.

Automated summary

This study demonstrates the efficient photocatalytic hydrogen evolution reaction (HER) by constructing well-defined single-site Ni-grafted TiO2 photocatalysts with unique coordination environments. The T-Ni Bpy catalyst exhibits high catalytic activity, with a rate and turnover frequency 260 times higher than those of Ni-O-TiO2. The electron paramagnetic resonance and femtosecond transient IR absorption measurements indicate that the presence of fewer electron trapped oxygen vacancies and a larger portion of long-lived photogenerated electrons are essential for achieving excellent HER activity.