The effects of potential and solar input on Z-scheme C₃N₄-TiO₂ nanotubes @ Ti electrode in a broad potential window

Construction of Z-scheme graphitic carbon nitride-titanium dioxide nanotubes (C₃N₄-TNT) has been known useful to optimize the band structure for improving photon capture and for accelerating charge carrier separation and transfer rate in photoelectrochemical water splitting (PECWS) cells. However, the reported operating potential window in a PECWS cell, often in 0 – 1.23 V_RHE (volt versus reversible hydrogen electrode) plus its overpotential, is too narrow to understand the C₃N₄-TNT electrode. Herein, a broad potential window of −0.5 − 2.5 V_RHE is applied to C₃N₄-TNT@Ti and recorded via the polarization test under chopped sunlight to analyze the effect of both electrons from external electrical circuit and photons from simulated sunlight. In 0 – 2.5 V_RHE, the potential enhances the photocurrent density. For example, at 1.6 V_RHE, the C₃N₄-TNT sample exhibits 1.8-time higher photocurrent density than that of pure TNT. In −0.5 − 0 V_RHE, i.e., both samples do not give photo-current response. In addition, for advanced water oxidation/reduction beyond WS to oxygen/hydrogen, a large potential window will be expected. Further, the light capture ability, the charge carrier recombination rate, and the electron flow path through the C₃N₄-TNT junction without and with reverse/forward potentials are discussed to elucidate the effect of the applied potential.