Conductivity Switching of N-Doped Ta Oxide Nanotubular Arrays

Abstract

Ta oxynitride (TaO x N y ) nanotubes (NTs) were synthesized by the anodization of Ta in an aqueous H 2 SO 4 + HF solution, forming Ta oxide NTs, followed by the high temperature conversion of Ta oxide to TaO x N y in ammonia. The electrochemical behavior of these nanotubular arrays was then investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), revealing a wide range of interesting properties. The Ta oxynitride NTs, which are shown to contain evenly spaced holes along their length, undergo a reversible redox process involving cation intercalation in both aqueous solutions and dry acetonitrile at potentials negative of 0.5 V, while above this, the nanotubular array is nonconducting. From the CV charges, it is possible that this reaction occurs only on the exposed TaO x N y NT surfaces, although the nanotubular array does undergo conductivity and colour switching. EIS analysis has confirmed the pseudocapacitive properties of the TaO x N y NTs at < 0.5 V, while at potentials above this, Mott-Schottky analysis shows that they are n-type semiconductors having a donor density of ca. 6  10 21 cm -3 .

Pristine Ta3N5 Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

“…[35,44,45] The reversible peaks, peaks II and IV,s eem to be attributed to the redox mechanism of the Ta-reduced species that appeared due to ion intercalation/deintercalation related to the Ta 5 + /Ta 4 + redox process as has recently been suggested by Abhayawardhana et al fort antalum-based oxynitride (TaO x N y )N Ts obtained from the nitridation of Ta 2 O 5 NTs. [66] The presenceo fr educed tantalum speciesh ad already been discussed in the XPS analyses ( Figure 2). In addition, the appearance of aw ide absorption mode above the absorption edge in UV/Vis (Figure 3c)isani ndirect indication of their presence.…”

Ta-Based Catalyst Support for Proton Exchange Membrane Fuel Cell Applications

“…Further, these NPs show voids in their structures, a unique feature that can be seen when converting Ta 2 O 5 to TaO x N y . As explained in our previous work, involving the conversion of Ta 2 O 5 nanotubes to TaO x N y (26), this is the result of changing the material density by substituting 3 oxide ions with 2 nitride ions, while keeping the primary Ta cation oxidation state unchanged. From these TEM images, it remains uncertain if the NPs are residing inside the pore or just on the outer surface of the CICs, but it can clearly be seen that they are well dispersed.…”

Electrochemically anodized one-dimensional semiconductors: a fruitful platform for solar energy conversion

“…Incorporation of N into WO 3 reduces the bandgap from 2.9 to 2.2 eV, thereby lowering the onset potential and increasing the photocurrent density at fixed potential for oxygen evolution reaction under visible light illumination. In another work, N-Doped Ta oxide NTs were fabricated by anodization of Ta foil in an aqueous H 2 SO 4 +HF solution forming Ta oxide NTs, followed by hightemperature transformation of Ta oxide to TaO x N y in an ammonia atmosphere [125]. The N-doped TaO x N y NTs have been demonstrated to be the most efficient photocatalyst under visible light irradiation among various non-metal-element-doped photocatalysts, which is mainly ascribed to the fact that p states of nitrogen places just above the VB maximum of most metal oxides, thereby contributing to the bandgap narrowing without substantial increase of charge recombination [116].…”