Thermoelectric voltage triggered self-biased photoelectrochemical water splitting utilizing visible light active Ag/NaNbO3 nanocomposite photoanode

Abstract

Nanostructure semiconductor photoactive materials are often used as working photoelectrodes to absorb solar light in conventional photoelectrochemical (PEC) cells for water splitting to demonstrate enhanced PEC performance. However, an external bias is required to start PEC water splitting reactions for the generation of hydrogen. Here, we demonstrate a novel way of designing a self-biased hybrid system that combines a darkened thermoelectric device (TE) and a photoelectrochemical cell with a visible light-active n-type Ag/NaNbO3 photoanode to produce hydrogen via water splitting by utilizing the entire solar spectrum. This method can combine utilization of a visible light photon energy from the Ag/NaNbO3 photoanode with thermal energy from the darkened TE device to overcome the overpotential requirements. Upon light illumination, the photoactive behaviour of the Ag/NaNbO3 photoanode and the voltage generated from the darkened TE device in our hybrid system modifies the band positions of an Ag/NaNbO3 photoanode and spontaneously provide the external overpotential requirement for the PEC process and enhances the H2 production. Compared to the stand-alone PEC device, the TE-coupled PEC hybrid system exhibited ∼17 times enhancement in the photocurrent density and H2 production at zero bias. The electrochemical impedance spectroscopy analysis also shows that the charge transfer process gets significantly enhanced in the hybrid PEC system compared to the PEC cell alone. This finding indicates the synergistic coupling between TE and PEC cells, where a single light energy source can increase H2 production in the hybrid systems without needing an external bias.