Pristine Ta 3 N 5 Nanotubes: Trap-Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

• Published in: Chemistry : a European journal Vol. 22; no. 51; pp. 18501 - 18511
• Main Authors: Khan, Sherdil, Santos, Marcos J L, Malfatti, Célia F, Dupont, Jairton, Teixeira, Sérgio R
• Format: Journal Article
• Language: English
• Published: Germany 19-12-2016
• Subjects: nanotechnology; applied biasing; trapping states; photoelectrochemistry; thermal nitridation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201603246

Ta
N
is a promising photoelectrode for solar hydrogen production; however, to date pristine Ta
N
electrodes without loading co-catalysts have presented limited photoelectrochemical (PEC) performance. In particular, large external biasing has been required to run water oxidation, the origin of which is investigated herein. Ta
N
nanotubes (NTs) prepared by nitridation were characterized by a wide range of techniques. The bandgap was confirmed by a novel PEC technique. Nondestructive synchrotron-excited XPS has shown the presence of reduced Ta species deeper in the Ta
N
surface. Lower photocurrent and transient spikes that were intense at lower applied biasing were observed under water oxidation; however, spikes were inhibited in the presence of a sacrificial agent and photocurrent was improved even at low biasing. It was observed for the first time that the lower PEC performance under water oxidation can be attributed to the presence of interband trapping states associated with pristine Ta
N
NTs/electrolyte junction. These states correspond to the structural defects in Ta
N
, devastate PEC performance, and present the necessity to apply higher biasing. The key to circumvent them is to use a sacrificial agent in the electrolyte or to load a suitable co-catalyst to avoid hole accumulation under water oxidation, thereby improving the phootocurrent. The findings on the interband states could also provide guidance for the investigation of PEC properties of new types of semiconducting devices.