Carbon quantum dots modified anatase/rutile TiO2 photoanode with dramatically enhanced photoelectrochemical performance

[Display omitted] •The CQDs modified A/R-TiO2 is prepared with greatly enhanced PEC performance.•The A/R-TiO2 heterojunction suppresses the bulk recombination of photoinduced carriers.•The CQDs dramatically improve the OER kinetics and UV–vis light harvesting.•The charge transfer mechanism of ternary CQDs/A/R-TiO2 heterojunction is proposed. TiO2 is a promising photoanode material for photoelectrochemical (PEC) water splitting, but its severe bulk recombination of photogenerated carriers, sluggish oxygen evolution reaction (OER) kinetics and poor visible light response are the main bottleneck problems. Here, the carbon quantum dots (CQDs) modified anatase/rutile TiO2 photoanode (CQDs/A/R-TiO2) was designed by growth of anatase TiO2 nanothorns on rutile TiO2 nanorods and further surface modification of CQDs. The results revealed that the A/R-TiO2 heterojunction significantly suppressed the bulk recombination of photogenerated carriers. With further incorporation of CQDs into A/R-TiO2, dramatical improvement of OER kinetics and ultraviolet-visible (UV–vis) light harvesting were obtained. The bulk charge separation efficiency (ηbulk) and surface charge injection efficiency (ηsurface) of CQDs/A/R-TiO2 are 1.69 and 5.74 times higher than that of the pristine TiO2 at 0.6 V vs. RHE, respectively. Meanwhile, the photocurrent is increased by 11.72 times and the onset potential is negatively shifted by 240 mV for CQDs/A/R-TiO2.