Exploring the role of carbon nitrides (melem, melon, g-C3N4) in enhancing photoelectrocatalytic properties of TiO2 nanotubes for water electrooxidation

Carbon nitrides (CNs), synthesised from melamine at temperatures 400 degrees C or 525 degrees C with their derivatives prepared by acidic protonation and oxidation using H2SO4 are tested as co-catalysts for oxygen evolution reaction (OER) modifying anodic Titania nanotubes (TiO2-NTs) surface. Materials exhibit crystalline structures and contain tri-s-heptazine rings with different terminal groups (-NH2, -NHOH, -NO2, -OH, =O), which are important for their catalytic and photoelectrocatalytic performance. These materials exhibit p-type semiconductor behaviour. Heterojunctions formed by n-type TiO2 and p-type carbon nitrides were tested using linear sweep voltammetry (LSV) in the dark and under illumination in the potential range allowing the water oxidation reaction to proceed. It is demonstrated, that the presence of -NH2 functional groups play a considerable role in OER kinetics in the dark. Changes in photocurrent at the anodic potential range are discussed considering Z-scheme heterojunction formation promoted with the catalytic activity of -NH2/- NHOH pending groups. Acidtreated melem in junction with Titania nanotubes emerges as the best co-catalyst for anodic water oxidation in the dark, with a Tafel slope of 83 mV/dec. This research encourages further exploration of melem and melon cocatalysts for improved electro- and photoelectrocatalytic applications.