RESUMEN

Resonance Raman (rR) spectroscopy has been applied to study the nature of the iron-oxo (Fe=O) moiety of oxoiron(IV) porphyrin π-cation radical complex (CompI). While the axial ligand effect on the nature of the Fe=O moiety has been studied with rR spectroscopy, the porphyrin ligand effect has not been studied well. Here, we investigated the porphyrin ligand effect on the Fe=O moiety with rR spectroscopy. The porphyrin ligand effect was modulated by the electron-withdrawing effect of the porphyrin substituent at the meso-position. This study shows that the frequency of the Fe=O stretching band, ν(Fe=O), hardly change even when the electron-withdrawing effect of the porphyrin substituent changes. This result is further supported by theoretical calculation of CompI. The natural atomic charge analysis reveals that the oxo and axial ligands work to buffer the electron-withdrawing effect of the porphyrin substituent. The electron-withdrawing porphyrin substituent shifts an electron population from the ferryl iron to the porphyrin, but the decreased electron population on the ferryl iron is compensated by the shift of the electron population from the oxo ligand and the axial ligand. The shift of the electron population makes the Fe-axial ligand bond length short, but the Fe=O bond length unchanged, resulting in the invariable ν(Fe=O) frequency.

Asunto(s)

RESUMEN

Although the electron-withdrawing effect of gold (Au) is highlighted in catalytic reactions, its enhancement mechanism for electron transport, especially in the electrochemical process, is still unclear. Herein, Au-decorated Bi2 O3 (Au-Bi2 O3 ) is proposed as a proof-of-concept to investigate the electron-withdrawing effect in the electrocatalytic CO2 reduction reaction (eCO2 RR) process. Evidence from in situ Raman spectra and in situ XRD tests reveals that, compared to Bi2 O3 , Bi species in Au-Bi2 O3 can be reduced to metallic Bi more rapidly and more easily driven by the electron-withdrawing effect of Au. The XPS tests after eCO2 RR further validates the transformation from Bi3+ to Bi0 in Au-Bi2 O3 is more complete. Meanwhile, in the in situ Fourier transform infrared (FTIR) spectra, the key intermediates (CO2 *- and OCHO*- ) appear at the more positive potential, indicating that metallic Bi is favorable for eCO2 RR due to the lower energy barrier as corroborated by density function theory (DFT) calculations. Au don't directly participate in the conversion from CO2 to formate as the reaction sites, but utilize the electron-withdrawing effect to motivate Bi-sites to deliver higher catalytic activity and higher selectivity to formate at a lower applied potential. This study not only has an insight into the electron-withdrawing effect of Au on the eCO2 RR process, but also develops a new perspective for engineering electron-withdrawing effect in electrocatalysts for high-efficient CO2 -to-formate conversion.

RESUMEN

Aqueous zinc-ion batteries are emerging as one of the most promising large-scale energy storage systems due to their low cost and high safety. However, Zn anodes often encounter the problems of Zn dendrite growth, hydrogen evolution reaction, and formation of by-products. Herein, we developed the low ionic association electrolytes (LIAEs) by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl2 electrolyte. Owing to the electron-withdrawing effect of -CF3 groups in TFE molecules, in LIAEs, the Zn2+ solvation structures convert from larger aggregate clusters into smaller parts and TFE will construct H-bonds with H2O in Zn2+ solvation structure simultaneously. Consequently, ionic migration kinetics are significantly enhanced and the ionization of solvated H2O is effectively suppressed in LIAEs. As a result, Zn anodes in LIAE display a fast plating/stripping kinetics and high Coulombic efficiency of 99.74%. The corresponding full batteries exhibit an improved comprehensive performance such as high-rate capability and long cycling life.

RESUMEN

Modulation of the carrier concentration and electronic type of monolayer (1L) MoS2 is highly important for applications in logic circuits, solar cells, and light-emitting diodes. Here, we demonstrate the tuning of the electronic properties of large-area 1L-MoS2 using graphene oxide (GO). GO sheets are well-known as hole injection layers since they contain electron-withdrawing groups such as carboxyl, hydroxyl, and epoxy. The optical and electronic properties of GO-treated 1L-MoS2 are dramatically changed. The photoluminescence intensity of GO-treated 1L-MoS2 is increases by more than 470% compared to the pristine sample because of the increase in neutral exciton contribution. In addition, the A1g peak in Raman spectra shifts considerably, revealing that GO treatment led to the formation of p-type doped 1L-MoS2. Moreover, the current vs voltage (I-V) curves of GO-coated 1L-MoS2 field effect transistors show that the electron concentration of 1L-MoS2 is significantly lower in comparison with pristine 1L-MoS2. Current rectification is also observed from the I-V curve of the lateral diode structure with 1L-MoS2 and 1L-MoS2/GO, indicating that the electronic structure of MoS2 is significantly modulated by the electron-withdrawing functional group of GO.

RESUMEN

The regioselective carbon-carbon bond formation was studied using 5,5,5-trifluoro-1-phenylpent-3-en-1-yne as a model substrate, and predominant acceptance of electrophiles ß to a CF3 group as well as a deuterium trap experiment of the lithiated species led to the conclusion that the obtained regioselectivity is kinetically determined for the reactions with electrophiles, under equilibration of the possible two anionic species.