RESUMEN
In this work, to make out the aryl-fusion effect on the photophysical properties of boron-pyridyl-imino-isoindoline dyes, compounds 1-5 were theoretically studied through analyses of their geometric and electronic structures, optical properties, transport abilities, and radiative (k r) and non-radiative decay rate (k nr) constants. The highest occupied molecular orbitals of aryl-fused compounds 2-5 are higher owing to the extended conjugation. Interestingly, aryl fusion in pyridyl increases the lowest unoccupied molecular orbital (LUMO) level, while isoindoline decreases the LUMO level; thus, 4 and 5 with aryl fusion both in pyridyl and isoindoline exhibit a similar LUMO to 1. Compounds 4 and 5 show relatively low ionization potentials and high electron affinities, suggesting a better ability to inject holes and electrons. Importantly, the aryl fusion is conducive to the decrease of k IC. The designed compound 5 exhibits a red-shifted emission maximum, low λh, and low k IC, which endow it with great potential for applications in organic electronics. Our investigation provides an in-depth understanding of the aryl-fusion effect on boron-pyridyl-imino-isoindoline dyes at molecular levels and demonstrates that it is achievable.
RESUMEN
A systematic mechanistic investigation of CO2 reduction on a Ni-modified Cu(111) surface is performed based on an extensive set of density functional theory (DFT) calculations by focusing on the hydrocarbon CH4 formation pathways. By carefully analyzing reduction pathways on the Ni-modified Cu(111) surface, some important mechanistic information is deduced. The presence of Ni stabilizes all reaction intermediates, and thus reduces the activation barrier for almost all CO2 reduction steps. Most importantly, it can considerably lower than the activation barrier of CO2 hydrogenative dissociation into CO, which is the rate-determining step of CO2 reduction on a pure Cu(111) surface. Thus, the doping of Ni atom is able to activate CO2, leading to enhanced surface activity of CO2 reduction into hydrocarbons. Notably, the activation barriers that are required for CH4 and CH3OH formation are almost all easily overcome through the thermoactive process at ambient temperatures after doping of Ni atom. Thus, a higher CH4 and CH3OH yield may be expected in the presence of the doped Ni atom. Thermodynamic analyses indicate that doping of Ni may reduce the overpotential of CO formation through CO2 hydrogenative dissociation. On this basis, two decriptors may be proposed in order to describe the catalytic activity of Cu-based catalysts for CO2 reduction, and a perfect Cu-based alloy in CO2 reduction should moderately bind CO and form and reduce CO more easily. Simutaneously, CO hydrogenation occurs more easily on the (111) facet of Ni-modified Cu than dimerization, thereby the selectivity of (111) facet of Cu on production CH4 is further confirmed to some degree. The present study reveals a rich reaction chemistry and provides new insights to guide the rational design of Cu-based alloy catalysts for hydrocarbons formation from CO2 reduction. Graphical Abstract Reduction pathways of CO2 into hydrocarbonsá .
RESUMEN
The effects of alloying Pt with transition metal Ni on oxygen reduction reaction (ORR) mechanisms was investigated based on a systematic density functional theory (DFT) calculation explored in the present work. New insights into the ORR mechanisms were reported at the atomic level on Pt-segregated Pt3Ni(111). Only one molecular chemisorption state with the end-on OOH configuration was identified through geometry optimization and minimum energy path (MEP) analysis; top-bridge-top configuration as observed on pure Pt(111) was not identified on Pt-segregated Pt3Ni(111), indicating that alloying Pt with Ni influences the intermediates of ORR, and leads to only the dissociation mechanism of chemisorption state OOH species being involved in acid medium on Pt-segregated Pt3Ni(111). By contrast, the dissociation mechanisms of chemisorbed O2 molecule with top-bridge-top configuration and OOH species both were involved on pure Pt(111). The rds of the entire four-electron ORR was changed after Pt alloying with Ni. The rds of the entire ORR is the proton and electron transfer to O2 to form OOH on Pt-segregated Pt3Ni(111), whereas it is the reaction of O atom protonation to form OH species on pure Pt(111), indicating that sublayer Ni strongly influences the rds of ORR. The comparison of the ORR mechanisms explained that Pt3Ni alloy enhanced the ORR electrocatalytic activity more than pure Pt. The effect of electrode potential on ORR pathway on the pure Pt and Pt3Ni alloy was considered to obtain further insights into the electrochemical reduction of O2. Results showed that the proton and electron transfer becomes difficult at high potential. The ORR can easily proceed when the electrode potential lowers. For pure Pt- and Pt-based alloys, this phenomenon may imply the origin of the overpotential.