Semimetallic core-shell TiO 2 nanotubes as a high conductivity scaffold and use in efficient 3D-RuO 2 supercapacitors

Abstract

In the present work we report on TiO2 nanotube arrays (TNTAs) that were converted to a conductive scaffold established via an optimized reduction treatment in Ar/H2. These conductive TNTAs are then employed for RuO2 nanoparticle decoration. The effect of the Ar/H2 treatment is evaluated by electron energy loss spectroscopy (EELS) and electron paramagnetic resonance (EPR). The results show that, under ideal conditions, buried Ti 3+ states are formed, with a higher concentration in the inner shell of the nanotube. Together with the capacitive and conductive performance, investigated by solid-state conductivity and electrochemical measurements, we find that 20 µm long TNTAs, annealed at 550°C in Ar/H2, yield an optimized and stable structure that provides a remarkably low resistivity of 13.5 KΩ/tube (vs. 70.2 MΩ for non-treated nanotubes). In cycling experiment, with a loading of only 0.048 mg.cm-2 RuO2 a specific capacitance of 1297 F.g-1 can be reached. The reason for this highly efficient use of RuO2 is that the conducting core-shell scaffold provides a unique, well dispersed RuO2 nanoparticle structure (~2.8 nm), which is responsible for the high specific capacitance, and moreover yields an excellent long-term cycling stability.

Conductive Cu‐Doped TiO2 Nanotubes for Enhanced Photoelectrochemical Methanol Oxidation and Concomitant Hydrogen Generation

“…Crystallization of the as‐anodized amorphous tube layers was carried out by annealing in a Rapid Thermal Annealer (Jipelec JetFirst 100) at 450 °C for 1 hour in air with a heating/cooling rate of 5 °C min −1 , and the reduced layers were obtained by annealing in Ar/10 % H 2 at an optimized temperature of 550 °C ,…”

“…In previous work, we showed that optimized annealing of TiO 2 nanotubes in Ar/H 2 can not only drastically improve the conductivity of TiO 2 nanotubular structures but also preserve the semiconductor properties of TiO 2 , thus providing efficient photoelectrodes ,…”

On the Controlled Loading of Single Platinum Atoms as a Co‐Catalyst on TiO2 Anatase for Optimized Photocatalytic H2 Generation

“…To form in these reductive gases structural surface defects (Ti 3+ ‐O v ) it takes >300 °C (in Ar/H 2 atmosphere). Several works [ 25,46–48 ] show that annealing TiO 2 in H 2 or Ar/H 2 mainly leads to two types of defect centers that is, Ti 3+ centers located in regular lattice positions and surface exposed Ti 3+[ 25,46–48 ] . The density of these defects on the TiO 2 surface can be adjusted by the annealing conditions (namely by the annealing atmosphere and the temperature [ 49,50 ] )—this is also illustrated in Figure S1, Supporting Information.…”

“…The results show that by increasing the temperature up to 500 °C, the H 2 evolution rate increased and by further increasing the temperature to 600 °C and 700 °C, the activity drops—this is well in line with previous work showing that Ti 3+ states can act as mediators for photocatalytic H 2 generation. [ 25,46,47 ] Figure S10, Supporting Information compares the H 2 evolution rates from differently Pt deposited layers (using a variation of temperatures of the reduction treatment and different concentrations of Pt). The results show that by increasing the reduction temperature the amount of evolved hydrogen increased, which can be due to a higher loading of atomic Pt on the surface.…”

Photocatalytic H2 Evolution: Dealloying as Efficient Tool for the Fabrication of Rh‐decorated TiO2 Nanotubes

“…Several modification approaches with a suitable co‐catalyst have been reported in the last years . Typically these co‐catalytic metals are decorated uniformly on TiO 2 nanotubes with common deposition methods such as chemical deposition, electrochemical deposition, and sputter‐deposition …”