Electrochemically reduced TiO2 photoanode coupled with oxygen vacancy-rich carbon quantum dots for synergistically improving photoelectrochemical performance

Severe bulk charge recombination, sluggish oxygen evolution reaction (OER) kinetics and poor visible light harvesting are still the technical bottlenecks of famous TiO2 photoanode for photoelectrochemical (PEC) water splitting. Here, a novel CQDs/E-TiO2 photoanode was designed based on the accurately electrochemical reduction of TiO2 (E-TiO2, Ti4+ + e(-) -> Ti3+) and further modification of oxygen vacancy (O-V)-rich carbon quantum dots (CQDs) for synergistically improving PEC performance. The electrochemical reduction creates moderate O-V in TiO2, which increase the majority carrier density and provide photoinduced charge traps for sharply increasing the bulk charge separation efficiency (eta(bulk)). The CQDs modification dramatically improves the surface charge transfer efficiency (eta(surface)) by serving as oxygen evolution catalysts (OECs), because the abundant O-V in CQDs greatly promote the interfacial OER kinetics. Additionally, the visible light harvesting of TiO2 is significantly improved after CQDs modification. Near-complete bulk charge separation (eta(bulk) = 94.7%) is achieved for E-TiO2 at 1.23 V vs. RHE (V-RHE), which is 4.0 times higher than that of TiO2. The CQDs/E-TiO2 shows the eta(surface) of 56.0% at 0.40 V-RHE,V- which is 7.2 times higher than E-TiO2. Therefore, the CQDs/E-TiO2 exhibits remarkable photocurrent densities of 1.50 mA cm(-2) at 0.60 VRHE and 2.55 mA cm(-2) at 1.23 V-RHE, which are 27.0 and 10.0 times higher than TiO2, 3.5 and 1.5 times higher than E-TiO2, respectively.

Automated summary

The novel CQDs/E-TiO2 photoanode is designed to synergistically improve the performance of photoelectrochemical water splitting by electrochemically reducing TiO2 and modifiying CQDs to enhance bulk charge separation efficiency, surface charge transfer efficiency, and oxygen evolution reaction kinetics. The CQDs/E-TiO2 exhibits significantly higher photocurrent densities compared to TiO2 and E-TiO2, demonstrating its potential for efficient water splitting applications.