5 research outputs found
Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch PolymerāMetal Oxide Hybrid Solar Cells
For
efficient solar cells based on organic semiconductors, a good
mixture of photoactive materials in the bulk heterojunction on the
length scale of several tens of nanometers is an important requirement
to prevent exciton recombination. Herein, we demonstrate that nanoporous
titanium dioxide inverse opal structures fabricated using a self-assembled
monolayer method and with enhanced infiltration of electron-donating
polymers is an efficient electron-extracting layer, which enhances
the photovoltaic performance. A calcination process generates an inverse
opal structure of titanium dioxide (<70 nm of pore diameters) providing
three-dimensional (3D) electron transport pathways. Hole-transporting
polymers was successfully infiltrated into the pores of the surface-modified
titanium dioxide under vacuum conditions at 200 Ā°C. The resulting
geometry expands the interfacial area between hole- and electron-transport
materials, increasing the thickness of the active layer. The controlled
polymer-coating process over titanium dioxide materials enhanced photocurrent
of the solar cell device. Density functional theory calculations show
improved interfacial adhesion between the self-assembled monolayer-modified
surface and polymer molecules, supporting the experimental result
of enhanced polymer infiltration into the voids. These results suggest
that the 3D inverse opal structure of the surface-modified titanium
dioxide can serve as a favorable electron-extracting layer in further
enhancing optoelectronic performance based on organic or organicāinorganic
hybrid solar cell
Self-Terminated Artificial SEI Layer for Nickel-Rich Layered Cathode Material via Mixed Gas Chemical Vapor Deposition
Because of the higher specific capacity,
nickel-rich layered cathode
material has received much attention from the lithium-ion battery
community. However, its cycle life is desired to improve further for
practical applications, and unstable interface with electrolyte is
one of the main capacity fading mechanisms. Here, we report a facile
chemical vapor deposition process involving mixed gases of CO<sub>2</sub> and CH<sub>4</sub>, which yields thin and conformal artificial
solid-electrolyte-interphase (SEI) layer consisting of alkyl lithium
carbonate (LiCO<sub>3</sub>R) and lithium carbonate (Li<sub>2</sub>CO<sub>3</sub>) on nickel-rich active cathode powder. The coating
layer protects from side reactions and improves the cycle life and
efficiency significantly. Remarkably, the coating process is self-terminated
after the thickness reaches ā¼10 nm, leading to the coating
layer to account for only 0.48 wt %, because of the growing binding
energy between the gas mixture and the surface products. The self-termination
is characterized by various analytical tools and is well-explained
by density functional theory calculations. The current gas phase coating
process should be applicable to other battery materials that suffer
from continuous side reactions with electrolyte
Enhanced Electrochemical Stability of a Zwitterionic-Polymer-Functionalized Electrode for Capacitive Deionization
In
capacitive deionization, the salt-adsorption capacity of the electrode
is critical for the efficient softening of brackish water. To improve
the water-deionization capacity, the carbon electrode surface is modified
with ion-exchange resins. Herein, we introduce the encapsulation of
zwitterionic polymers over activated carbon to provide a resistant
barrier that stabilizes the structure of electrode during electrochemical
performance and enhances the capacitive deionization efficiency. Compared
to conventional activated carbon, the surface-modified activated carbon
exhibits significantly enhanced capacitive deionization, with a salt
adsorption capacity of ā¼2.0 Ć 10<sup>ā4</sup> mg/mL
and a minimum conductivity of ā¼43 Ī¼S/cm in the alkali-metal
ions solution. Encapsulating the activated-carbon surface increased
the number of ions adsorption sites and the surface area of the electrode,
which improved the charge separation and deionization efficiency.
In addition, the coating layer suppresses side reactions between the
electrode and electrolyte, thus providing a stable cyclability. Our
experimental findings suggest that the well-distributed coating layer
leads to a synergistic effect on the enhanced electrochemical performance.
In addition, density functional theory calculation reveals that a
favorable binding affinity exists between the alkali-metal ion and
zwitterionic polymer, which supports the preferable salt ions adsorption
on the coating layer. The results provide useful information for designing
more efficient capacitive-deionization electrodes that require high
electrochemical stability
Enhanced Selectivity for CO<sub>2</sub> Adsorption on Mesoporous Silica with Alkali Metal Halide Due to Electrostatic Field: A Molecular Simulation Approach
Since
adsorption performances are dominantly determined by adsorbateāadsorbent
interactions, accurate theoretical prediction of the thermodynamic
characteristics of gas adsorption is critical for designing new sorbent
materials as well as understanding the adsorption mechanisms. Here,
through our molecular modeling approach using a newly developed quantum-mechanics-based
force field, it is demonstrated that the CO<sub>2</sub> adsorption
selectivity of SBA-15 can be enhanced by incorporating crystalline
potassium chloride particles. It is noted that the induced intensive
electrostatic fields around potassium chloride clusters create gas-trapping
sites with high selectivity for CO<sub>2</sub> adsorption. The newly
developed force field can provide a reliable theoretical tool for
accurately evaluating the gas adsorption on given adsorbents, which
can be utilized to identify good gas adsorbents
CO<sub>2</sub> Enhanced Chemical Vapor Deposition Growth of Few-Layer Graphene over NiO<sub><i>x</i></sub>
The use of mild oxidants in chemical vapor deposition (CVD) reactions has proven enormously useful. This was also true for the CVD growth of carbon nanotubes. As yet though, the use of mild oxidants in the CVD of graphene has remained unexplored. Here we explore the use of CO<sub>2</sub> as a mild oxidant during the growth of graphene over Ni with CH<sub>4</sub> as the feedstock. Both our experimental and theoretical findings provide in-depth insight into the growth mechanisms and point to the mild oxidants playing multiple roles. Mild oxidants lead to the formation of a suboxide in the Ni, which suppresses the bulk diffusion of C species suggesting a surface growth mechanism. Moreover, the formation of a suboxide leads to enhanced catalytic activity at the substrate surface, which allows reduced synthesis temperatures, even as low as 700 Ā°C. Even at these low temperatures, the quality of the graphene is exceedingly high as indicated by a negligible D mode in the Raman spectra. These findings suggest the use of mild oxidants in the CVD fabrication as a whole could have a positive impact