Phthalocyanine Grafting Strategy Induces Strong Intrinsic Electric Fields and Molecule-Edge Carrier Transport Pathways for Photoelectrochemical Water Splitting

Abstract

Limited charge separation, slow charge mobility, and high electron-hole recombination rates remain critical challenges impeding the efficiency of photoelectrochemical (PEC) water splitting. More regrettably, the charge transfer pathways within bulk charge transport are not yet fully understood, and the development of effective strategies to design these pathways remains a significant challenge. Herein, by optimizing the anchoring sites of small molecular ligands, we developed a molecularly functionalized layer, 4-ethyl-carbazole copper phthalocyanine (4EtCz-Pc), which is characterized by a strong dipole moment, a large internal electric field, and surprisingly positive electrostatic potential at the edge. When integrated in conjunction with the oxygen evolution cocatalyst (OEC) and the semiconductor photoanode BiVO4 (BVO), it forms a Co(OH)2/4EtCz-Pc/BiVO4 composite photoanode system. This innovative photoanode demonstrates an exceptional performance with continuous output for a duration of 15 hours. Additionally, a variety of advanced characterization methods, especially scanning photoelectrochemical microscopy (SPECM) analyses, confirmed that 4EtCz-Pc significantly reduces the energy barrier for hole injection from the anode to the active layer during PEC catalysis. This study proposes an effective strategy to optimize the ligands grafted onto phthalocyanine, generating a strong internal electric field that facilitates the formation of new charge transport pathways within the photoanode.