4 research outputs found
First-principles investigation of aluminum intercalation and diffusion in TiO2 materials: Anatase versus rutile
Aluminum-ion batteries, emerging as a promising post-lithium battery solution, have been a subject of increasing research interest. Yet, most existing aluminum-ion research has focused on electrode materials development and synthesis. There has been a lack of fundamental understanding of the electrode processes and thus theoretical guidelines for electrode materials selection and design. In this study, by using density functional theory, we for the first time report a first-principles investigation on the thermodynamic and kinetic properties of aluminum intercalation into two common TiO 2 polymorphs, i.e., anatase and rutile. After examining the aluminum intercalation sites, intercalation voltages, storage capacities and aluminum diffusion paths in both cases, we demonstrate that the stable aluminum intercalation site locates at the center of the O 6 octahedral for TiO 2 rutile and off center for TiO 2 anatase. The maximum achievable Al/Ti ratios for rutile and anatase are 0.34375 and 0.36111, respectively. Although rutile is found to have an aluminum storage capacity slightly higher than anatase, the theoretical specific energy of rutile can reach 20.90 Wh kg −1 , nearly twice as high as anatase (9.84 Wh kg −1 ). Moreover, the diffusion coefficient of aluminum ions in rutile is 10 −9 cm 2 s −1 , significantly higher than that in anatase (10 −20 cm 2 s −1 ). In this regard, TiO 2 rutile appears to be a better candidate than anatase as an electrode material for aluminum-ion batteries
Hierarchically Structured Ni Nanotube Array-Based Integrated Electrodes for Water Splitting
The development of
high-performance nonprecious electrocatalysts
for overall water splitting has attracted increasing attention but
remains a vital challenge. Herein, we report a ZnO-based template
method to fabricate Ni nanotube arrays (NTAs) anchored on nickel foil
for applications in the hydrogen evolution reaction (HER) and oxygen
evolution reaction (OER). On the basis of this precursor electrode,
the three-dimensional NiSe<sub>2</sub> NTAs of unique sandwich-like
coaxial structure have been fabricated by electrodeposition of NiSe<sub>2</sub> on Ni NTAs, which exhibits high performance toward the HER
in both acidic and alkaline media. The method based on Ni NTAs can
be readily extended to fabricate Ni<sub>2</sub>P NTAs by gas–solid
phosphorization for the HER, and NiFeO<sub><i>x</i></sub> NTAs by anodic codeposition of Ni and Fe for the OER. Consequently,
an alkaline electrolyzer has been constructed using NiFeO<sub><i>x</i></sub> NTAs and NiSe<sub>2</sub> NTAs as anode and cathode,
respectively, which can realize overall water splitting with a current
density of 100 mA cm<sup>–2</sup> at an overpotential of 510
mV
Heterostructured Arrays of Ni<sub><i>x</i></sub>P/S/Se Nanosheets on Co<sub><i>x</i></sub>P/S/Se Nanowires for Efficient Hydrogen Evolution
The development of
efficient electrocatalysts for hydrogen evolution reaction (HER) is
of increasing importance in energy conversion schemes. The earth-abundant
transition-metal phosphides, especially CoP and Ni<sub>2</sub>P, have
emerged as promising catalysts for HER. We describe here the preparation
and characterization of a hybrid catalyst of Ni<sub>2</sub>P nanosheets@CoP
nanowires on a carbon cloth for the reaction. The heterostructure
and synergistic effects of the Ni<sub>2</sub>P and CoP components
result in an extremely low overpotential of 55 mV for achieving a
catalytic current density of 10 mA cm<sup>–2</sup>, which is
remarkable for transition-metal phosphide electrocatalysts. The synthetic
procedure could be readily extended to related, heterostructured bimetallic
sulfides or selenides for HER
A Highly Conductive COF@CNT Electrocatalyst Boosting Polysulfide Conversion for Li–S Chemistry
The
catalysis of covalent organic frameworks (COFs) in Li–S
chemistry is largely blocked by a weak chemical interaction and low
conductivity. Herein, a new kind of diketopyrrolopyrrole (DPP)-based
COF is in situ fabricated onto the carbon nanotube (CNT) surface (denoted
as COF@CNT) to uncover the electrocatalysis behavior by its strong
chemical interaction and highly conductive property. We declare that
the electrocatalytic activity of DPP-COF can be maximized by introducing
an appropriate content of CNT (66 wt %); the analyses including density
functional theory calculations, X-ray photoelectron spectroscopy,
Fourier transform infrared, and Raman show that the DPP moiety can
mediate the conversion of polysulfides contributed by a CO/C–O
bonding conversion. Hence, the modified battery shows a 0.042% decay
rate over 1000 cycles and achieves a desirable capacity of 8.7 mAh
cm–2 with 10 mg cm–2 sulfur loading
and lean electrolyte (E/S = 5). This work will inspire the rational
design of COF@support hybrids for various electrocatalysis applications