Constructing Sequential Type II Heterojunction CQDs/Bi2S3/TiNbO Photoanode with Superior Charge Transfer Capability Toward Stable Photoelectrochemical Water Splitting

Efficient charge transfer and light-trapping units are pivotal prerequisites in the realm of Ti-based photoanode photoelectrochemical (PEC) water splitting. In this work, we successfully synthesized a ternary carbon quantum dots/Bi₂S₃ quantum dots/Nb-doped TiO₂ nanotube arrays (CQDs/Bi₂S₃/TiNbO) composite photoanode for PEC water splitting. CQDs/Bi₂S₃/TiNbO composite photoanode exhibited a considerably elevated photocurrent density of 8.80 mA cm^-2 at 1.23 V vs the reversible hydrogen electrode, which was 20.00 times better than that of TiO₂ (0.44 mA cm^-2). Furthermore, the CQDs/Bi₂S₃/TiNbO composite photoanode attested to exceptional stability, maintaining 92.54% of its initial current after 5 h of stability measurement. Nb-doping boosted the electrical conductivity, facilitating charge transfer at the solid-liquid interface. Moderate amounts of Bi₂S₃ quantum dots (QDs) and CQDs deposited on TiNbO provided abundant active sites for the electrolyte-photoanode interaction. Simultaneously, Bi₂S₃ QDs and CQDs synergistically functioned as light-trapping units to broaden the light absorption range from 396 to 530 nm, stimulating increased carrier generation within the composite photoanode. In comparison with pristine TiO, CQDs/Bi₂S₃/TiNbO photoanodes possessed a superior ability to promote interfacial reactions. This study may provide a strategy for developing high-performance Ti-based photoanodes with efficient charge transfer and light trapping units for highly driving solar-to-hydrogen conversion.