56 research outputs found
Theoretical Basis of Electrocatalysis
In this chapter, we introduce the density functional theory (DFT)-based computational approaches to the study of various electrochemical reactions (hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR)) occurring on heterogeneous catalysis surfaces. A detailed computational approach to the theoretical interpretation of electrochemical reactions and structure-catalytic activity relationships for graphene-based catalysts will be discussed. The electrocatalytic activity of catalysis can be theoretically evaluated by overpotential value determined from free energy diagram (FED) of electrochemical reactions. By comparing electrocatalytic activity of systematically designed graphene-based catalysts, we will discuss the structure-catalytic activity relationships, especially the electronic and geometrical effects of heteroatom dopants
Type I interferon is critical for the homeostasis and functional maturation of type 3 γδ T cells
Iridium(III) cyclometalates (<b>1c</b> and <b>2c</b>) in which the two carborane units on
the 4- or 5-positions of 2-phenylpyridine
(ppy) ligands were tethered by an alkylene linker were prepared to
investigate the effect of free rotation of <i>o</i>-carborane
on phosphorescence efficiency. In comparison with the unlinked complex,
tethering the <i>o</i>-carboranes to the 5-positions of
ppy ligands (<b>2c</b>) enhanced phosphorescence efficiency
by over 30-fold in polar medium (Φ<sub>PL</sub> = 0.37 vs 0.011
in THF), while restricting the rotation of <i>o</i>-carborane
at the 4-positions (<b>1c</b>) negatively affected the phosphorescence
efficiency. The different effects of restricted rotation of <i>o</i>-carborane on phosphorescence efficiency were likely a
result of the different variations of the carboranyl C–C bond
distances in the excited state
A robust nonprecious CuFe composite as a highly efficient bifunctional catalyst for overall electrochemical water splitting
To generate hydrogen, which is a clean energy carrier, a combination of electrolysis and renewable energy sources is desirable. In particular, for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrolysis, it is necessary to develop nonprecious, efficient, and durable catalysts. A robust nonprecious copper–iron (CuFe) bimetallic composite is reported that can be used as a highly efficient bifunctional catalyst for overall water splitting in an alkaline medium. The catalyst exhibits outstanding OER and HER activity, and very low OER and HER overpotentials (218 and 158 mV, respectively) are necessary to attain a current density of 10 mA cm−2. When used in a two‐electrode water electrolyzer system for overall water splitting, it not only achieves high durability (even at a very high current density of 100 mA cm−2) but also reduces the potential required to split water into oxygen and hydrogen at 10 mA cm−2 to 1.64 V for 100 h of continuous operation
Aromatic cages B: unprecedented existence of octagonal holes in boron clusters
The cage-like structures containing octagonal holes are located as the lowest-lying isomers for the B. The presence of octagonal holes, which have been found for the first time, not only gives us new insight into the bonding motif, but also marks a breakthrough in the structural characteristics of boron clusters since they were never expected to be stable units for elemental clusters. These cages are composed of both delocalized σ and π electron systems that consequently make them aromatic and thermodynamically stable.status: publishe
<i>p</i>- and <i>n</i>‑type Doping Effects on the Electrical and Ionic Conductivities of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> Anode Materials
We systematically
investigated p- and n-type doping effects on
the electrical conductivity of spinel Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> (LTO) by designing theoretically stoichiometric Li<sub>11</sub>Ti<sub>13</sub>O<sub>32</sub> (p-type) and Li<sub>10</sub>Ti<sub>14</sub>O<sub>32</sub> (n-type) because LTO has a nonstoichiometric
(Li)<sub>8</sub>[Li<sub>8/3</sub>Ti<sub>40/3</sub>]O<sub>32</sub> formula
with the <i>Fd</i>3<i>m̅</i> space group.
In this work, we present evidence that the electronic modification
plays a fundamental role in the electrical conductivity of LTO, especially,
n-type Li<sub>10</sub>Ti<sub>14</sub>O<sub>32</sub>, which has superior
electrical conductivity compared to p-type Li<sub>11</sub>Ti<sub>13</sub>O<sub>32</sub>. We proposed a way to improve the electrical conductivity
of pristine LTO by halogen ion doping, Li<sub>4</sub>Ti<sub>5</sub>O<sub>12–<i>x</i></sub>Hal<sub><i>x</i></sub> (Hal: F, Cl, and Br), for an n-type doping effect. However,
the substitution of halogen ions can enhance the electrical conductivity
by mixing Ti<sup>4+</sup>/Ti<sup>3+</sup> and impede the Li ion diffusion
in the lattice. The larger size of Cl and Br increases the Li ion
diffusion energy barrier with van der Waals repulsion. Therefore,
our theoretical investigations of the effects of halogen doping on
the electrical and ionic conductivities anticipate that the smaller-sized
F may be the most promising dopant for improving the performance of
LTO
Substituent engineering in tertiary phosphine oxides for passivating defects of perovskite solar cells
Abstract Defect passivation based on Lewis acid–base chemistry has been regarded as an effective strategy to improve the photovoltaic performance and stability of perovskite solar cells (PSCs). Here, we report on tertiary phosphine oxides (R3PO) as materials for defect passivation, where photovoltaic performance was investigated depending on the substituents R. Electron‐donating ability of the substituents in R3PO was found to play an important role in passivation. Cyclohexyl substituent was better in achieving photovoltaic performance than linear hexyl substituent. The heterocyclic morpholine substituent bearing oxygen and nitrogen in cyclohexyl form further improved photovoltaic performance due to its enhanced electron‐donating ability. Compared with an untreated PSC, the trimorpholinophosphine oxide (TMPPO)‐treated PSC improved the power conversion efficiency from 21.95% to 23.72%. Additionally, the dark‐storage stability test with an unencapsulated device showed that the TMPPO‐treated device maintained 92.7% of its initial PCE after 1250 h, while 86.8% was maintained for the untreated device. Three hundred hour‐light‐soaking of the encapsulated devices revealed that the operational stability of the TMPPO‐treated PSC was superior to the untreated device
<i>o</i>‑Carboranyl–Phosphine as a New Class of Strong-Field Ancillary Ligand in Cyclometalated Iridium(III) Complexes: Toward Blue Phosphorescence
Heteroleptic
tris-cyclometalated Ir(III) complexes supported by
the <i>o</i>-carboranyl–phosphine ligand (<i>CBP</i>), (C<sup>∧</sup>N)<sub>2</sub>Ir(<i>CBP</i>) (C<sup>∧</sup>N = <i>ppy</i> (<b>1</b>), <i>dfppy</i> (<b>2</b>)), have been synthesized and characterized.
The PL spectra of <b>1</b> and <b>2</b> displayed substantially
blue shifted phosphorescence relative to the corresponding Ir(C<sup>∧</sup>N)<sub>3</sub> complexes. Electrochemical and theoretical
studies showed that the <i>CBP</i> ligand functioned as
a strong-field ancillary ligand, and the greater HOMO stabilization
in comparison to that of the LUMO by the <i>CBP</i> ligand
was responsible for the increase in band gap, leading to a large blue
shift in phosphorescence
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