3D interconnected nanoporous Ta3N5 films for photoelectrochemical water splitting: thickness-controlled synthesis and insights into stability

Abstract

Solar-driven photoelectrochemical (PEC) water splitting is a promising technology for sustainable hydrogen production, which relies on the development of efficient and stable photoanodes for water oxidation reaction. The thickness and microstructure of semiconductor films are generally crucial to their PEC properties. Herein, three-dimensional (3D) interconnected nanoporous Ta3N5 film photoanodes with controlled thickness were successfully fabricated via galvanostatic anodization and NH3 nitridation. The porous Ta3N5 nanoarchitectures (NAs) of 900 nm in thickness showed the highest PEC performance due to the optimal light-harvesting and charge separation. Compared with the hole-induced photocorrosion, the electrochemical oxidation at high anodic potentials resulted in severer performance degradation of Ta3N5. Although the surface oxide layer on deteriorated Ta3N5 photoanodes could be removed by NH3 re-treatment, the PEC performance was only partially recovered. As an alternative, anchoring a dual-layer Co(OH)x/CoOOH co-catalyst shell on the porous Ta3N5 NAs demonstrated substantially enhanced PEC performance and stability. Overall, this work provides reference to controllably fabricate 3D nanoporous Ta3N5-based photoanodes for efficient and stable PEC water splitting via optimizing the light absorption, hole extraction, charge separation and utilization.