Within a tight-binding electron-phonon interacting model, we investigate the dynamics of photoexcitations to address the generation mechanism of charged polarons in conjugated polymers by using a nonadiabatic evolution method. Besides the neutral polaron exciton which is well known, we identify a novel product of lattice dynamic relaxation from the photoexcited states in a few hundreds of femtoseconds, which is a mixed state composed of both charged polarons and neutral excitons. Our results show that the charged polarons are generated directly with a yield of about 25%, which is independent of the excitation energies, in good agreement with results from experiments. Effects of the conjugation length are also discussed.
Exploiting
efficient electrocatalysts for hydrogen peroxide (H2O2) electroproduction by oxygen reduction reaction
(ORR) is highly desired in practical application. Herein, nitrogen-
and fluoride-codoped carbon nanocages (NF-Cs) are successfully synthesized
through a simple and scalable template method. With the aid of a porous
structure, a large surface area, and the introduction of N and F atoms,
NF-Cs show excellent electrocatalytic performance for H2O2 electroproduction in alkaline solution (pH 13) with
a faradaic efficiency of 89.6% at very positive applied potential
(0.74 V). In acid solution (pH 0.35), the faradaic efficiency of H2O2 electroproduction stably maintains at 85%–88%
in the range of 0.4–0.72 V potential. The experimental and
theoretical results reveal that the strong synergistic effect between
the doped N and F atoms facilitate the H2O2 electroproduction
through 2e ORR. That is, the doped N atoms promote O2 molecule
adsorption on the catalyst surface, and the F atoms facilitate the
desorption of the *OOH intermediate, which is the key factor for the
NF-Cs efficiently catalyzing H2O2 electroproduction.
These results provide beneficial references for reasonably designing
effective carbon-based electrocatalysts for H2O2 electroproduction.
By considering a metal/polymer/metal structure within a tight-binding one-dimensional model, we have investigated the polaron formation in the presence of an electric field. When a sufficient voltage bias is applied to one of the metal electrodes, an electron is injected into the polymer chain, then a self-trapped polaron is formed at a few hundreds of femtoseconds while it moves slowly under a weak electric field (not larger than 1.0 × 10 4 V/cm). At an electric field between 1.0 × 10 4 V/cm and 8.0 × 10 4 V/cm, the polaron is still formed, since the injected electron is bounded between the interface barriers for quite a long time. It is shown that the electric field applied at the polymer chain reduces effectively the potential barrier in the metal/polymer interface.
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