Surface defect passivation of Ta3N5 photoanode via pyridine grafting for enhanced photoelectrochemical performance

Abstract

Tantalum nitride (Ta₃N₅) is a promising photoanode material for photoelectrochemical (PEC) water splitting, while the Ta₃N₅/Ta photoanode synthesized via general thermal oxidation and nitridation on a Ta foil method usually has serious carrier recombination at the surface, which usually reduces the PEC activities. Herein, we demonstrate an efficient strategy of decorating pyridine, a small organic molecule at the surface of the Ta₃N₅/Ta photoanode, to alleviate the surface recombination. Such decoration yields a stable photocurrent density of 4.4 mA cm^-2 at 1.23 V_RHE under AM 1.5G (air mass 1.5 global, 100 mW cm^-2) simulated sunlight, which is about 1.4 times higher than that of Ta₃N₅/Ta without modification, and the photocurrent density still remained ∼100% of its original value after a 5 h stability test. Further characterization of the incident photon-to-current conversion efficiency and absorbed photon-to-current efficiency of the pyridine/Ta₃N₅/Ta photoanode showed a significant increase to 62% and 72% at 500 nm, respectively. The enhanced pyridine/Ta₃N₅/Ta PEC performance can be attributed to minimizing the density of nitrogen vacancies due to the passivation of pyridine grafting, which results in the decreased recombination centers and improved charge separation efficiency at the surface. We thus believe that our study of surface passivation by using small organic molecules provides an alternative to address the surface recombination of Ta₃N₅ based photoelectrodes.