Chemistry Letters, Ahead of Print.
Recent Progresses on Dopant‐Free Organic Hole Transport Materials toward Efficient and Stable Perovskite Solar Cells
Comprehensive Summary
As the third generation new battery, the power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs) has increased from 3.8% in 2009 to 25.8% currently certified, which fully shows that they have great research value and development prospect. As one of the main components of high-efficiency PSCs, hole transport materials (HTMs) play an important role in extracting and transporting holes and inhibiting charge recombination. However, commonly used HTMs require doping, and the hygroscopicity and corrosiveness of the dopants will destroy the stability of PSCs and hinder their commercialization. Therefore, it is of great significance to develop dopant-free HTMs. In this review, the dopant-free HTMs in recent six years are reviewed and summarized systematically, including organic small molecules, polymers and cross-linkable materials. We focus on the design of the molecular cores and discuss their structure–property correlation, conductivity, and photovoltaic performance. Finally, how to design an ideal HTM is summarized. We hope that this review can provide reference for the development of low-cost and dopant-free HTMs to prepare efficient and stable PSCs.
Phase‐space relative Rényi entropy in density functional theory
The phase-space relative Rényi entropy is introduced using the information theoretical and thermodynamic view of density functional theory. In the special case of constant inverse temperature the phase-space relative Rényi entropy is a sum of the position-space relative Rényi entropy and a term arising from the momentum space. This quantity can be considered as a measure of similarity. It includes more information than the position-space measures, it also incorporates momentum-space knowledge.
Abstract
The phase-space relative Rényi entropy is introduced using the information theoretical and thermodynamic view of density functional theory. In the special case of constant inverse temperature the phase-space relative Rényi entropy is a sum of the position-space relative Rényi entropy and a term arising from the momentum space. This quantity can be considered as a measure of similarity. It includes more information than the position-space measures, since it also incorporates momentum-space knowledge.
Toward a correct treatment of core properties with local hybrid functionals
We report new DFT functionals following the local hybrid approach. In these local hybrid functionals (LHs), a local mixing function (LMF) determines the position-dependent exact-exchange admixture. The suggested new pt-LMFs are based on a Padé form and modify the previously used ratio between von Weizsäcker and Kohn–Sham local kinetic energy densities by different powers of the density to enable flexibly improved approximations to the correct high-density and iso-orbital limits relevant for the innermost core region.
Abstract
In local hybrid functionals (LHs), a local mixing function (LMF) determines the position-dependent exact-exchange admixture. We report new LHs that focus on an improvement of the LMF in the core region while retaining or partly improving upon the high accuracy in the valence region exhibited by the LH20t functional. The suggested new pt-LMFs are based on a Padé form and modify the previously used ratio between von Weizsäcker and Kohn–Sham local kinetic energies by different powers of the density to enable flexibly improved approximations to the correct high-density and iso-orbital limits relevant for the innermost core region. Using TDDFT calculations for a set of K-shell core excitations of second- and third-period systems including accurate state-of-the-art relativistic orbital corrections, the core part of the LMF is optimized, while the valence part is optimized as previously reported for test sets of atomization energies and reaction barriers (Haasler et al., J Chem Theory Comput 2020, 16, 5645). The LHs are completed by a calibration function that minimizes spurious nondynamical correlation effects caused by the gauge ambiguities of exchange-energy densities, as well as by B95c meta-GGA correlation. The resulting LH23pt functional relates to the previous LH20t functional but specifically improves upon the core region.
Photoreforming for Lignin Upgrading: A Critical Review
The refinement of biomass, particularly lignin, for the production of chemicals as a solution to the energy crisis, has been substantiated as a potentially promising technology. The effective amalgamation of photocatalytic technology with biomass refining has received considerable attention recently. Nonetheless, the current research landscape is heavily concentrated on lignin molecular models, with little attention being paid to the study of actual lignin. This Review highlights recent progress in the photoreforming of actual lignin for the production of energy or chemicals.
Abstract
Photoreforming of lignocellulosic biomass to simultaneously produce gas fuels and value-added chemicals has gradually emerged as a promising strategy to alleviate the fossil fuels crisis. Compared to cellulose and hemicellulose, the exploitation and utilization of lignin via photoreforming are still at the early and more exciting stages. This Review systematically summarizes the latest progress on the photoreforming of lignin-derived model components and “real” lignin, aiming to provide insights for lignin photocatalytic valorization from fundamental to industrial applications. Considering the complexity of lignin physicochemical properties, related analytic methods are also introduced to characterize lignin photocatalytic conversion and product distribution. We finally put forward the challenges and perspective of lignin photoreforming, hoping to provide some guidance to valorize biomass into value-added chemicals and fuels via a mild photoreforming process in the future.
Sustainable Syntheses of Paracetamol and Ibuprofen from Biorenewable β‐pinene
Scalable chemical processes have been used to convert biorenewable β-pinene into 4-isopropenylcyclohexanone (4-IPEC), which is then used as a feedstock to prepare bioderived versions of the commonly prescribed painkillers, paracetamol and ibuprofen.
Abstract
Scalable processes have been developed to convert β-pinene into 4-isopropenylcyclohexanone, which is then used as a feedstock for the divergent synthesis of sustainable versions of the common painkillers, paracetamol and ibuprofen. Both synthetic routes use Pd0 catalysed reactions to aromatize the cyclohexenyl rings of key intermediates to produce the benzenoid ring systems of both drugs. The potential of using bioderived 4-hydroxyacetophenone as a drop-in feedstock replacement to produce sustainable aromatic products is also discussed within a terpene biorefinery context.
Calculation of Ionization, Excitation and Electron Capture Cross Sections for Be4++H(2s, 2p) Collisions
Collisions between (excited) hydrogen atoms and beryllium impurity ions are expected to occur inside fusion reactors and the cross sections of all inelastic processes are then needed. A comparative study of H(2s) and H(2p) targets in collision with Be4+ ions at fusion-relevant energies is presented.
Abstract
A computational study of Be4++H(2s, 2p) collisions has been carried out employing the Classical Trajectory Monte Carlo (CTMC) method for the impact energy range from 20 keV/u to 1000 keV/u. The integral n partial cross sections for H(n) excitation and Be3+(n) electron capture and, the total ionization and electron capture cross sections are calculated and compared to recent semiclassical results. A general good agreement is observed for the n partial and total electron capture and ionization cross sections. The comparative study of the three inelastic processes show no significant differences between both excited targets.
First‐Principles Microkinetic Study of the Catalytic Hydrodeoxygenation of Guaiacol on Transition Metal Surfaces
Catalytic Hydrodeoxygenation of Guaiacol: By constructing a first-principles microkinetic model from over 300 DFT models of the intermediates, we report that guaiacol HDO exhibits highly desirable deoxygenation and hydrogenation kinetics over Ni(111) at industrial temperatures.
Abstract
The mechanism behind the hydrodeoxygenation (HDO) of guaiacol on Co(0001), Ni(111), Cu(111), Pd(111), and Pt(111) was investigated by constructing a first-principles microkinetic model from density functional theory (DFT) models for 68 possible intermediates over each surface. We report that the most energetically favorable pathway for this process is the demethylation of guaiacol to catechol over Ni(111), which exhibits highly desirable deoxygenation and hydrogenation kinetics at industrial temperatures. Guaiacol readily undergoes hydrogenation over Pt(111) and Pd(111), but the products exhibit slow desorption from the surfaces at standard operation temperatures. Furthermore, the deoxygenation pathway is hindered by the high energy barrier associated with the scission of the Calkyl−O bond.
Au(III) π‐Allyl Complexes: Synthesis, Structure, Reactivity, and Catalytic Applications
Au(III) π-allyl complexes have recently been shown to be readily accessible and stable, as well as highly reactive towards nucleophiles, including in catalytic transformations. They display structural features and reactivity profiles that differ noticeably from the related Pd(II) π-allyl complexes, making them complementary and attractive for synthesis.
Abstract
π-Allyl complexes of transition metals are key species in organometallic chemistry and homogeneous catalysis. Palladium(II) π-allyl complexes in particular, have gained a lot of attention, but their isoelectronic gold(III) counterparts long remained elusive. However, this situation changed during the last few years. This concept article describes the preparative routes, characterization, structure and reactivity of such species, together with their catalytic applications. The influence of the ancillary ligand at gold, either (P,C)/(N,C)-cyclometalated or (P,N)-hemilabile, is analysed in detail. The Au(III) and Pd(II) π-allyl complexes are also compared to highlight the similarities and differences.
Exploring the Synergistic Effects of Dual‐Layer Electrodes for High Power Li‐Ion Batteries
A Li-ion battery electrode architecture which uses two different active materials in a layered configuration is investigated. The results surprisingly show that layered electrodes are superior to their blended (mixed) counterparts during high-rate (dis)charge. The mechanism of this synergistic effect is elucidated using a newly minted synchrotron fluorescence technique to map the concentration of Li+ throughout an operating cell.
Abstract
The electrification of the transport sector has created an increasing demand for lithium-ion batteries that can provide high power intermittently while maintaining a high energy density. Given the difficulty in designing a single redox material with both high power and energy density, electrodes based on composites of several electroactive materials optimized for power or capacity are being studied extensively. Among others, fast-charging LiFePO4 and high energy Li(Ni x Mn y Co z )O2 are commonly employed in industrial cell manufacturing. This study focuses on comparing different approaches to combining these two active materials into a single electrode. These arrangements were compared using standard electrochemical (dis)charge procedures and using synchrotron X-ray fluorescence to identify variations in solution concentration gradient formation. The electrochemical performance of the layered electrodes with the high-power material on top is found to be enhanced relative to its blended electrode counterpart when (dis)charged at the same specific currents. These findings highlight dual-layer lithium-ion batteries as an inexpensive way of increasing energy and power density of lithium-ion batteries as well as a model system to study and exploit the synergistic effects of blended electrodes.