The effect of central metal in phthalocyanine for photocatalytic hydrogen evolution via artificial photosynthesis

Phthalocyanines (Pcs) are promising sensitizers in photocatalytic hydrogen evolution reaction from water splitting owing to the unique absorption properties and familiar sensitizers for light phase of photosynthesis. In this paper, two phthalocyanines (Pcs) bearing tetra carboxylic acid at the peripheral position with Zn and Co atoms as a central metal have been prepared in order to investigate the effect of the central metal atoms on the performance of photocatalytic hydrogen evolution from water splitting for mimicking photosynthesis. The photoelectrochemical and photocatalytic hydrogen evolution experiments have been carried out by using Pcs sensitized TiO2 (TiO2, ZnPc/TiO2 and CoPc/TiO2) and Pt co-catalyst in the presence of triethanolamine (TEOA) as a sacrificial electron donor under visible light. The hydrogen production rate of ZnPc/TiO2 and CoPc/TiO2 have been determined as the 1146 and 1051 μmolg−1h−1, respectively. The hydrogen evolution rates of ZnPc/TiO2 and CoPc/TiO2 have been enhanced by in situ photodeposited Pt, which are reached by 3448 and 3328 μmolg−1h−1 for the ZnPc/TiO2/Pt and CoPc/TiO2/Pt, respectively. These results have been established that ZnPc sensitized TiO2 shows more photocatalytic activity than CoPc sensitized TiO2 in the both absence and presence of Pt. These obtained results can be attributed to the spectral response of Pc sensitizers.