Enhanced Charge Transport in Tantalum Nitride Nanotube Photoanodes for Solar Water Splitting

Abstract

In the present work we grow anodic self-organized Ta2O5 nanotube layers, which are converted by ammonolysis to Ta3N5 nanotubes, and then are used as photoanodes for photoanalytic water splitting. We introduce a two-step anodization process that not only improves order (reduced growth defects) and overall light absorption in the nanotube layers, but also provides a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx) formation. As a result, such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular Ta3N5 electrodes under AM 1.5 G simulated sunlight (100 mW cm-2) conditions. Catching a Ta3N5: Layers of Ta3N5 nanotubes grown by a two-step anodization process show not only improved order and enhanced overall light absorption in the nanotube layers, but also provide a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx) formation. Such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular tantalum nitride electrodes under simulated sunlight conditions.