Position of the anchoring group determined the sensitization efficiency of metal-free D-π-A dyes: Combined experimental and TD–DFT insights

We report on the design and synthesis of new D-π-A organic sensitizers incorporating D35 as the electron donor unit and (benzyloxy)benzene as the π- linker. The structure and yield of the synthesized dyes were confirmed via The 1H NMR, 13C NMR, and mass spectrometry analyses. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to get insights on the electronic properties of the synthesized dyes, indicating their capability as photosensitizers. The photophysical characteristics, electrochemical properties, and photovoltaic performance of the sensitizers were investigated. The cyclic voltammetry measurements showed that the oxidation potentials of the excited states of the dyes are more negative than the conduction band edge of anatase TiO2 and their ground state oxidation potentials are more positive than the CoII/III redox shuttle, indicating their potential as photosensitizers. The dye containing benzyloxy group at the para position to the anchoring group showed higher power conversion efficiency (PCE), higher light harvesting efficiency (LHE), wider range of absorption, lower bandgap, higher incident photon-to-current conversion efficiency (IPCE), and higher excitation binding energy than the counterpart dye containing benzyloxy group in the ortho position

Optical and electronic properties of niobium oxynitrides with various N/O ratios: insights from first-principles calculations

The electronic and optical properties of niobium oxynitride (NbON) complexes as a function of the N/O ratio were examined using the Perdew–Burke–Ernzerhof exchange–correlation functional of density functional theory. The investigated NbON complexes (i.e., pristine NbON crystal and Nb16O16N16, Nb16O15N17, Nb16O14N18, Nb16O17N15, and Nb16O18N14 super crystals) were found to be indirect bandgap semiconductors. Varying the N/O ratio reallocates the band edges, giving rise to redshifts in the absorption spectra at higher N/O ratios. Partial density of states calculations showed valence band dependency on the N 2p orbital energy, with the conduction band predominantly composed of Nb 4d states. The dielectric constant and refractive index of pristine NbON are found to be comparable to those of isostructural TaON, and varying the N/O ratio leads to a significant improvement in the optical properties of the studied systems

Photoelectrochemical Water Splitting by Defects in Nanostructured Multinary Transition Metal Oxides

Point defects play a crucial role in the performance of functional materials. The most important extrinsic elements for point defects in titanium-based photocatalysts are oxygen, nitrogen, and hydrogen due to their large chemical affinity and substantial solubility with titanium. Therefore, understanding the nature of such defects will help designing high-performance photocatalysts for various applications. Herein, we make use of alloyed multipodal Ti-Nb-Zr-O nanotubes (MPNTs) annealed under different atmospheres: Air, O2, and H2 for enhanced photoelectrochemical water-splitting. Structural analysis using XRD, Raman spectroscopy, and XPS confirmed the formation of a single mixed oxide Ti-Nb-Zr-O in a strained-anatase crystal structure in both Air and Oxygen atmospheres. However, XPS fitting showed the presence of ZrTiO4 and Ti 3+ upon annealing in Hydrogen atmosphere. Valence band XPS analysis confirms the presence of valence band tail states causing band-gap reduction in the hydrogen-annealed samples, with an absorption tail reaching NIR/Vis region. Mott-Schottky analysis showed 4 orders of magnitude increase in the carrier density for the samples annealed in hydrogen atmosphere compared to those annealed in Air or O2, owing to the presence of Ti 3+ defects/oxygen vacancies, titanium substitution by niobium, and the valence band tail states. These synergistic effects resulted in almost 25-fold enhancement in the photocurrent compared to the performance of the samples annealed in Oxygen or Air. It is thus concluded that annealing in a reducing atmosphere produces disordered and defective structure. Accordingly, the optical and electronic properties of complex metal oxides exhibiting poor performance can be manipulated to produce promising candidates for enhanced photoelectrochemical water splitting

Unveiling the effect of the structure of carbon material on the charge storage mechanism in MoS2-based supercapacitors

MoS2 is a 2D material that has been widely used in supercapacitor applications because of its layered structure that provides a large surface area and allows for high electric double-layer charge storage. To enhance the cycling stability and capacitance of MoS2, it is usually mixed with carbon materials. However, the dependence of the charge storage mechanism on the structure of the carbon material is still unclear in literature. Herein, the effect of the structure of the carbon material on the charge storage mechanism in 2H flower-shaped MoS2 is investigated in detail. Specifically, 2H MoS2 was mixed with either 8 nm-diameter carbon nanotubes (CNTs) or graphene nanoflakes (GNFs) in different weight ratios. Also, a composite of MoS2, CNTs, and GNFs (1:1:1) was also studied. The charge storage mechanism was found to depend on the structure and content of the carbon material. Insights into the possible storage mechanism(s) were discussed. The MoS2/CNT/GNF composite showed a predominant pseudocapacitive charge storage mechanism where the diffusion current was ∼89%, with 88.31% of the resulted capacitance being due to faradic processes