Imidazole substituted Zinc(II) phthalocyanines for co-catalyst-free photoelectrochemical and photocatalytic hydrogen evolution: influence of the anchoring group.

Novel zinc phthalocyanine derivatives, ZnPc-1 and ZnPc-2, consisting of one and four imidazole units, respectively, have been synthesized and utilized as panchromatic photosensitizers for photocatalytic and photoelectrochemical H2 evolution. The effect of the imidazole-anchoring group on the photocatalytic H2 production has been compared with ZnPc-3, which possesses a carboxylic acid unit as the anchoring group. ZnPc-1/TiO2 shows the best photoactivity with the highest H2 evolution rate of 0.4006 mmol g-1 h-1, which is much higher than that of ZnPc-2/TiO2 and ZnPc-3/TiO2 (0.3319 mmol g-1 h-1 and 0.3555 mmol g-1 h-1, respectively). After 20 h of irradiation, ZnPc-1 produces an H2 production rate of 3.4187 mmol g-1 with a turnover number (TON) of 14863 and a solar-to-hydrogen energy (STH) conversion efficiency of 1.03%, without using a co-catalyst.

Subphthalocyanine-sensitized TiO2 photocatalyst for photoelectrochemical and photocatalytic hydrogen evolution.

A series of SubPcs comprising a carboxylic acid anchoring group at the peripheral (SubPcs 1, 2) or axial position (SubPc 3) were synthesized and used as sensitizers for photocatalytic H2 production, for the first time. SubPc 3/TiO2 shows the best photocatalytic activity with a hydrogen evolution rate of 1396 µmol h-1, which is much higher than that of SubPcs 1 and 2 (771 and 658 µmol g-1, respectively). This work clearly shows that considering their optical and redox properties, SubPcs are promising candidates for light-driven water splitting systems.