Carbon Dot Loading and TiO2 Nanorod Length Dependence of Photoelectrochemical Properties in Carbon Dot/TiO2 Nanorod Array Nanocomposites

Photoelectrochemcial (PEC) properties of TiO2 nanorod arrays (TNRA) have been extensively investigated as they are photostable and cost-effective. However, due to the wide band gap, only the UV part of solar light can be employed by TiO2. To enhance the photoresponse of TNRA in the visible range, carbon dots (C dots) were applied as green sensitizer in this work by investigating the effects of C dot loading and length of TiO2 nanorod on the PEC properties of TNRA/C dot nanocomposites. As the C dot loading increases, the photocurrent density of the nanocomposites was enhanced and reached a maximum when the concentration of the C dots was 0.4 mg/mL. A further increase in the C dot concentration decreased the photocurrent, which might be caused by the surface aggregation of C dots. A compromise existed between charge transport and charge collection as the length of TiO2 nanorod increased. The incident photon to current conversion efficiency (IPCE) of the TNRA/C dot nanocomposites in the visible range was up to 1.2-3.4%. This work can serve as guidance for fabrication of highly efficient photoanode for PEC cells based on C dots.