4 research outputs found
Anionic Ligand Assisted Synthesis of 3‑D Hollow TiO<sub>2</sub> Architecture with Enhanced Photoelectrochemical Performance
Hollow structured materials have
shown great advantages for use
in photoelectrochemical devices. However, their poor charge transport
limits overall device performance. Here, we report a unique 3-D hollow
architecture of TiO<sub>2</sub> that greatly improves charge transport
properties. We found that citric acid (CA) plays crucial roles in
the formation of the 3-D hollow architecture. First, CA controls the
hydrolysis rate of Ti ions and facilitates surface hydrolysis on templates
during hydrothermal synthesis. Second, CA suppresses the growth of
the carbon template at the initial reaction stage, resulting in the
formation of comparatively small hollow fibers. More importantly,
a prolonged hydrothermal reaction with CA enables a hollow sphere
to grow into entangled hollow fibers via biomimetic swallowing growth.
To demonstrate advantages of the 3-D hollow architecture for photoelectrochemical
devices, we evaluated its photoelectrochemical performance, specifically
the electrolyte diffusion and electron dynamics, by employing dye-sensitized
solar cells as a model device. A systemic analysis reveals that the
3-D hollow architecture greatly improves both the electrolyte diffusion
and electron transport compared to those of the nanoparticle and hollow
sphere due to the elongated porous hollow morphology as well as the
densely interconnected nanoparticles at the wall layer
1‑D Structured Flexible Supercapacitor Electrodes with Prominent Electronic/Ionic Transport Capabilities
A highly efficient 1-D flexible supercapacitor
with a stainless steel mesh (SSM) substrate is demonstrated. Indium
tin oxide (ITO) nanowires are prepared on the surface of the stainless
steel fiber (SSF), and MnO<sub>2</sub> shell layers are coated onto
the ITO/SSM electrode by means of electrodeposition. The ITO NWs, which grow radially on the SSF,
are single-crystalline and conductive enough for use as a current
collector for MnO<sub>2</sub>-based supercapacitors. A flake-shaped,
nanoporous, and uniform MnO<sub>2</sub> shell layer with a thickness
of ∼130 nm and an average crystallite size of ∼2 nm
is obtained by electrodeposition at a constant voltage. The effect
of the electrode geometry on the supercapacitor properties was investigated
using electrochemical impedance spectroscopy, cyclic voltammetry,
and a galvanostatic charge/discharge study. The electrodes with ITO
NWs exhibit higher specific capacitance levels and good rate capability
owing to the superior electronic/ionic transport capabilities resulting
from the open pore structure. Moreover, the use of a porous mesh substrate
(SSM) increases the specific capacitance to 667 F g<sup>–1</sup> at 5 mV s<sup>–1</sup>. In addition, the electrode with ITO
NWs and the SSM shows very stable cycle performance (no decrease in
the specific capacitance after 5000 cycles)
Improved Quantum Efficiency of Highly Efficient Perovskite BaSnO<sub>3</sub>‑Based Dye-Sensitized Solar Cells
Ternary oxides are potential candidates as an electron-transporting material that can replace TiO<sub>2</sub> in dye-sensitized solar cells (DSSCs), as their electronic/optical properties can be easily controlled by manipulating the composition and/or by doping. Here, we report a new highly efficient DSSC using perovskite BaSnO<sub>3</sub> (BSO) nanoparticles. In addition, the effects of a TiCl<sub>4</sub> treatment on the physical, chemical, and photovoltaic properties of the BSO-based DSSCs are investigated. The TiCl<sub>4</sub> treatment was found to form an ultrathin TiO<sub>2</sub> layer on the BSO surface, the thickness of which increases with the treatment time. The formation of the TiO<sub>2</sub> shell layer improved the charge-collection efficiency by enhancing the charge transport and suppressing the charge recombination. It was also found that the TiCl<sub>4</sub> treatment significantly reduces the amount of surface OH species, resulting in reduced dye adsorption and reduced light-harvesting efficiency. The trade-off effect between the charge-collection and light-harvesting efficiencies resulted in the highest quantum efficiency (<i>i</i>.<i>e</i>., short-circuit photocurrent density), leading to the highest conversion efficiency of 5.5% after a TiCl<sub>4</sub> treatment of 3 min (<i>cf</i>. 4.5% for bare BSO). The conversion efficiency could be increased further to 6.2% by increasing the thickness of the BSO film, which is one of the highest efficiencies from non-TiO<sub>2</sub>-based DSSCs
Indium–Tin–Oxide Nanowire Array Based CdSe/CdS/TiO<sub>2</sub> One-Dimensional Heterojunction Photoelectrode for Enhanced Solar Hydrogen Production
For photoelectrochemical (PEC) hydrogen
production, low charge
transport efficiency of a photoelectrode is one of the key factors
that largely limit PEC performance enhancement. Here, we report a
tin-doped indium oxide (In<sub>2</sub>O<sub>3</sub>:Sn, ITO) nanowire
array (NWs) based CdSe/CdS/TiO<sub>2</sub> multishelled heterojunction
photoelectrode. This multishelled one-dimensional (1D) heterojunction
photoelectrode shows superior charge transport efficiency due to the
negligible carrier recombination in ITO NWs, leading to a greatly
improved photocurrent density (∼16.2 mA/cm<sup>2</sup> at 1.0
V vs RHE). The ITO NWs with an average thickness of ∼12 μm
are first grown on commercial ITO/glass substrate by a vapor–liquid–solid
method. Subsequently, the TiO<sub>2</sub> and CdSe/CdS shell layers
are deposited by an atomic layer deposition (ALD) and a chemical bath
deposition method, respectively. The resultant CdSe/CdS/TiO<sub>2</sub>/ITO NWs photoelectrode, compared to a planar structure with the
same configuration, shows improved light absorption and much faster
charge transport properties. More importantly, even though the CdSe/CdS/TiO<sub>2</sub>/ITO NWs photoelectrode has lower CdSe/CdS loading (i.e.,
due to its lower surface area) than the mesoporous TiO<sub>2</sub> nanoparticle based photoelectrode, it shows 2.4 times higher saturation
photocurrent density, which is attributed to the superior charge transport
and better light absorption by the 1D ITO NWs