Enhancement of the photoelectrochemical conversion efficiency of nanotubular TiO2 photoanodes using nitrogen plasma assisted surface modification

A synergistic combination of nanostructure synthesis and plasma surface modification was used to enhance the photoelectrochemical activity of titania (TiO2) anodes. Titania nanotubular photoanodes were synthesized by electrochemical anodization of Ti thin foils. Nitrogen plasma was used to dope N at the surface of the photoanodes while removing chemisorbed species. X-ray photoelectron spectroscopy analysis showed an increase in the surface concentration of nitrogen. The photocurrent density of plasma treated samples was approximately 80% higher than that of the control. The open circuit potential of the plasma treated samples was more negative compared to that of the control, implying a favorable energetics for water splitting. This increase in photoactivity could be ascribed to: (1) increased absorption of visible light due to bandgap reduction, (2) minimization of charge carrier traps, (3) optimal oxygen vacancies, and (4) increased surface area for enhanced optical absorption and improved charge carrier generation.