An efficient strategy to boost the directed migration of photogenerated holes by introducing phthalocyanine as a hole extraction layer

Abstract

Although the sluggish water oxidation kinetics could be optimized by the decoration of cocatalysts, the transport of photogenerated charges in the bulk photoanodes is still a critical bottleneck in cocatalyst modified semiconductor photoanodes. Herein, we have firstly proposed the concept of modulating the photogenerated charge migration in the bulk photoanode by inserting phthalocyanine as the hole extraction layer between the semiconductor (Ti-Fe₂O₃) and the cocatalyst (CoPi). Benefitting from the gradient band structure of Ti-Fe₂O₃, metal-free 2,3,9,10,16,17,23,24-octacarboxy phthalocyanine (H₂Pc(COOH)₈) and CoPi, as well as the coplanar binding mode of Ti-Fe₂O₃ and H₂Pc(COOH)₈, the photogenerated holes of Ti-Fe₂O₃ would be migrated directionally to CoPi through H₂Pc(COOH)₈, hence more photogenerated holes arrive at CoPi and participate in the water oxidation reaction. As expected, the triphasic photoanode (CoPi/Pc/Ti-Fe₂O₃) exhibits not only a higher photocurrent density but also a more negative onset potential than CoPi/Ti-Fe₂O₃.