Efficient Dissociation Research Articles

Impact of regio-isomeric monochlorinated end groups on packing mode, miscibility, and photovoltaic performance of asymmetric selenophene-fused M-series acceptors

Optimal bulk-heterojunction (BHJ) morphology is crucial for efficient charge transport and good photovoltaic performance in organic solar cells (OSCs). Yet, the correlation between chemical structures of nonfullerene acceptors (NFAs) and molecular interaction in the BHJ blends remains opaque. Herein, we study three isomeric NFAs referred to as MQ1-x (x = β, γ, or δ) that shared an asymmetric selenophene-fused heteroheptacene backbone end-capped by two monochlorinated end groups. Remarkably, miscibility between the polymer donor of PM6 and MQ1-x successively elevates as the chlorine atoms move from β-, to γ-, to δ-position of terminals. Combined with the varied molecular crystallinity of these NFAs, diverse BHJ morphologies are observed in their blend films. As a result, the MQ1-δ-based devices present the highest PCE of 12.08% owing to the efficient charge dissociation and transport induced by the compact molecular packing and optimal BHJ morphology. Our investigation provides a new insight in the material design that has a good balance in molecular packing and film morphology for high-performance OSCs.

Half-Planar-Half-Twisted Small Molecule Acceptors for Efficient Polymer Solar Cells

A series of asymmetric acceptor−π–donor−π′–acceptor-type (A-π-D-π′-A) non-fullerene acceptors (NFAs) were designed and synthesized, namely, h-IEICO, h-IEICO-2F, h-IEICO-4F, and h-IEICO-4Cl, which were prepared by simultaneously linking halogenated ending groups both at the 4-position of 3-ethylhexoxythiophene (π-segment) of one side and at the 5-position of 3-ethylhexoxythiophene (π′-segment) of another side. The asymmetric molecular structure, as well as the radically different steric hindrance caused by the two distinct π-bridged segments, successfully produced a wondrous half-planar-half-twisted backbone configuration. As a result of the special molecular structures of these materials, as well as the excellent electron-attracting properties of the fluorine and chlorine atoms attached to them, h-IEICO-4F and h-IEICO-4Cl are characterized by an absorption red-shift and a down-shifted molecular energy level among all four molecules. The J52:h-IEICO-4F device demonstrated preferable exciton dissociation and collection efficiency, suppressed charge recombination, a high and balanced charge transport ability, superior morphological properties, and better crystallinity, resulting in an efficiency of 11.65%. However, the efficiencies of the J52:h-IEICO-, J52:h-IEICO-2F-, and J52:h-IEICO-4Cl-based solar cells are 5.24, 9.96, and 10.43%, respectively. This work demonstrates the significant influence of the adjusting planarity of the conjugated backbone as well as the fine-tuning of the end-group halogenation substitution on the characteristic regulation and the photovoltaic performances of NFAs for efficient PSCs.

Over 17.4% Efficiency of Layer‐by‐Layer All‐Polymer Solar Cells by Improving Exciton Utilization in Acceptor Layer

AbstractLayer‐by‐layer all‐polymer solar cells (LbL all‐PSCs) are prepared with PM6 and PY‐IT by using sequential spin coating method. The exciton dissociation efficiency in acceptor layer near electrode is rather low due to the limited exciton diffuse distance and impossible energy transfer from narrow bandgap acceptor to wide bandgap donor. In this study, less PM6 is incorporated into PY‐IT layer to enhance exciton dissociation in PY‐IT layer near electrode. A power conversion efficiency (PCE) of 17.45% is achieved in the LbL all‐PSCs incorporating 10 wt% PM6 into PY‐IT layer, which is much larger than 16.04% PCE of PM6/PY‐IT‐based LbL all‐PSCs. Over 8% PCE enhancement can be realized by incorporating 10 wt% PM6 into PY‐IT layer, which is attributed to the enhanced exciton utilization efficiency in PY‐IT layers near electrode. The enhanced exciton utilization efficiency in PY‐IT layer can be confirmed from the quenched photoluminescence (PL) emission in PY‐IT:PM6 films. Meanwhile, charge transport in acceptor layers can be optimized by incorporating less PM6, as confirmed from the optimized molecular arrangement. This study indicates that the strategy of incorporating less donor into acceptor layer has great potential in fabricating efficient LbL all‐PSCs by improving exciton utilization efficiency in acceptor layer near electrode.

Enhanced alkaline water splitting on cobalt phosphide sites by 4d metal (Rh)-doping method

The construction of effective water-splitting electrocatalysts in alkaline conditions is challenging due to lower water dissociation efficiency than in acidic conditions. In this study, we investigated the effect of doping 4d and 5d metals into the 3d metal active site of cobalt phosphide (CoxP) on the water-splitting reaction. Introducing Ru slightly improved hydrogen evolution efficiency, but Rh doping significantly enhanced the catalytic parameters with an overpotential of 0.03 V at 10 mA/cm2. Rh regulated the electronic structure of CoxP to improve proton reduction. The Rh-CoxP electrode showed a comparable catalytic efficiency to that of a Pt/C standard. Ir doping slightly improved catalytic reactivity, but not as much as Rh. Our results showed that doping 4d metal from the same group as Co maximizes the doping effect during hydrogen evolution. A lab-scale water electrolyzer built with Rh-CoxP successfully demonstrated catalytic water splitting in alkaline electrolyte.

Facile construction of Z-scheme AgCl/Bi3TaO7 photocatalysts for effective removal of tetracycline under visible-light irradiation

A string of AgCl/Bi3TaO7 two-component composite was synthesized by hydrothermal and deposition-precipitation process initially. The photocatalytic activities of mixed-phase AgCl/Bi3TaO7 were evaluated toward the decomposition of tetracycline (TC). Among these as-prepared materials, AgCl/Bi3TaO7 nanocomposites when the molar ratio of baked materials between AgCl and Bi3TaO7 was 1:5 presented the optimal photocatalytic quantum efficiency for TC dissociation (86.82%) with visible-light exposure, which was 1.69 and 2.38 folders higher than that of single Bi3TaO7 and AgCl, respectively. What is more, it illustrated that the photo-generated carriers were markedly isolated on account of the formation of heterojunction confirmed by EIS analysis. Meanwhile, radical trapping experiments implied that the photo-induced holes (h+), hydroxyl radical (·OH), and superoxide radical (·O2-) were the major active species. The escalated photocatalytic activity could be ascribed to the unique construction of Z-scheme AgCl/Bi3TaO7 heterojunction, which could expedite charge separation and transmission, cement light absorption capability and retain the strong redox ability of photo-generated electrons and holes. Our finding suggests that AgCl/Bi3TaO7 nanocomposites possess great potential for photocatalytic oxidation of residual TC in the wastewater effluents and the reported strategy can contribute to the development of novel high-performance photocatalyst.

Conformational Regulation of Dielectric Poly(Vinylidene Fluoride)‐Based Solid‐State Electrolytes for Efficient Lithium Salt Dissociation and Lithium‐Ion Transportation

AbstractRestricted by the poor ability of polymers to dissociate lithium salts and transport ions, solid‐state polymer electrolytes (SPEs) show extremely low ionic conductivities (≈10−7–10−5 S cm−1) and transference number of lithium ions (tLi+ ≈0.2–0.4) at 25 °C. Here, a novel polymer matrix of SPEs that simultaneously promotes lithium salt dissociation and ion transportation based on a high dielectric poly(vinylidene fluoride‐trifluoroethylene‐chlorotrifluoroethylene) (TerP) and an all‐trans conformational poly(vinylidene fluoride‐trifluoroethylene) (CoP), is developed. The high dielectric constant increases the polarity of CH2CF2 polar groups; then, brings a strong electronegative end that dissociates Li+ from lithium salts. The all‐trans conformation assures all fluorine atoms locate on one side of the chain, constructing ion hopping highways. As a result, the TerP/CoP (TC) SPE exhibits a high ionic conductivity (2.37 × 10−4 S cm−1) and a quite large tLi+ of 0.61 at 25 °C. The Li/TC SPE/Li symmetric cells cycle stably for more than half a year (>4500 h) and the LiNi0.8Co0.1Mn0.1O2/TC SPE/Li cell cycles steadily for 1000 and 600 cycles at 1 C and 2 C at 25 °C, respectively. This work paves a new way to prepare high‐performance SPEs by simultaneously modulating dielectric constants and conformation of polymers.

Modelling post-plasma quenching nozzles for improving the performance of CO2 microwave plasmas

Given the ecological problems associated to the CO2 emissions of fossil fuels, plasma technology has gained interest for conversion of CO2 into value-added products. Microwave plasmas operating at atmospheric pressure have proven to be especially interesting, due to the high gas temperatures inside the reactor (i.e. up to 6000 K) allowing for efficient thermal dissociation of CO2 into CO and O2. However, the performance of these high temperature plasmas is limited by recombination of CO back into CO2 once the gas cools down in the afterglow. In this work, we computationally investigated several quenching nozzles, developed and experimentally tested by Hecimovic et al., [1] for their ability to quickly cool the gas after the plasma, thereby quenching the CO recombination reactions. Using a 3D computational fluid dynamics model and a quasi-1D chemical kinetics model, we reveal that a reactor without nozzle lacks gas mixing between hot gas in the center and cold gas near the reactor walls. Especially at low flow rates, where there is an inherent lack of convective cooling due to the low gas flow velocity, the temperature in the afterglow remains high (between 2000 and 3000 K) for a relatively long time (in the 0.1 s range). As shown by our quasi-1D chemical kinetics model, this results in a important loss of CO due to recombination reactions. Attaching a nozzle in the effluent of the reactor induces fast gas quenching right after the plasma. Indeed, it introduces (i) more convective cooling by forcing cool gas near the walls to mix with hot gas in the center of the reactor, as well as (ii) more conductive cooling through the water-cooled walls of the nozzle. Our model shows that gas quenching and the suppression of recombination reactions have more impact at low flow rates, where recombination is the most limiting factor in the conversion process.

Dual P-doped-site modified porous g-C3N4 achieves high dissociation and mobility efficiency for photocatalytic H2O2 production

Organic semiconductor under photoexcitation could generate abundant strong-binding Frenkel excitons and inevitably suffer from low dissociation efficiency (<1%) and poor mobility ability, which severely suppresses the efficient utilization of photogenerated charges and corresponding activity. Herein, a dual P-doping strategy is proposed in bay and corner sites implanted polymeric carbon nitride (PCN-D) for visible-driven H2O2 production. The dual P doping breaks localized electron state around original symmetric heptazine units and weakens the binding energy between electrons and holes, increasing dissociation efficiency to reach 11.9% with 20-fold improvement. In addition, the conductivity ability of PCN-D, including formed carrier charge concentration and mobility, achieves 13-fold and 7-fold improvement, which facilitates the charge transfer and separation. The proposed dual doped-P-site strategy, with the blessing of porous structure, provides plentiful active center for effective adsorption and activation of O2 molecule, further accelerating reaction progress and achieving six-times increase of photocatalytic H2O2 production rate. This work provides in-depth insight into the importance of dual P-doping to optimize kinetic behavior of photogenerated charges and opens an avenue to the multiscale doping-modulation of semiconductor with high efficiency solar energy conversion.

Novel ternary metals-based telluride electrocatalyst with synergistic effects of high valence non-3d metal and oxophilic Te for pH-universal hydrogen evolution reaction

Electrocatalyst designs based on oxophilic foreign atoms are considered a promising approach for developing efficient pH-universal hydrogen evolution reaction (HER) electrocatalysts by overcoming the sluggish alkaline HER kinetics. Here, we design ternary transition metals-based nickel telluride (MoWNiTe) catalysts consisting of high valence non-3d Mo and W metals and oxophilic Te as a first demonstration of non-precious heterogeneous electrocatalysts following the bifunctional mechanism. The MoWNiTe showed excellent HER catalytic performance with overpotentials of 72, 125, and 182 mV to reach the current densities of 10, 100, and 1000 mA cm−2, respectively, and the corresponding Tafel slope of 47, 52, and 58 mV dec−1 in alkaline media, which is much superior to commercial Pt/C. Additionally, the HER performance of MoWNiTe is well maintained up to 3000 h at the current density of 100 mA cm−2. It is further demonstrated that the MoWNiTe exhibits remarkable HER activities with an overpotential of 45 mV (31 mV) and Tafel slope of 60 mV dec−1 (34 mV dec−1) at 10 mA cm−2 in neutral (acid) media. The superior HER performance of MoWNiTe is attributed to the electronic structure modulation, inducing highly active low valence states by the incorporation of high valence non-3d transition metals. It is also attributed to the oxophilic effect of Te, accelerating water dissociation kinetics through a bifunctional catalytic mechanism in alkaline media. Density functional theory calculations further reveal that such synergistic effects lead to reduced free energy for an efficient water dissociation process, resulting in remarkable HER catalytic performances within universal pH environments.

Defect suppression of a perovskite film with In2O3 quantum dots for improved solar cell performance

Solution-processable indium oxide quantum dots (In2O3) were introduced into a MAPbI3 film to solve the problem of low MAPbI3 film quality caused by inherent defects. Compared with the MAPbI3 film, the MAPbI3:In2O3 film exhibited an optimized time-resolved photoluminescence component ratio and improved carrier dissociation and transport efficiency. When the MAPbI3:In2O3 film was used to fabricate solar cells instead of the MAPbI3 film, the fill factor enhanced from 76.32% to 80.63%, the short circuit current density increased from 20.18 mA cm−2 to 21.32 mA cm−2, and the power conversion efficiency improved from 13.96% to 16.18% in the standard AM 1.5 illuminated condition, respectively.

Vanadium Oxide Nanosheet-Infused Functionalized Polysulfone Bipolar Membrane for an Efficient Water Dissociation Reaction.

A high-performing bipolar membrane (BPM) was fabricated using functionalized polysulfones as the ion-exchange layers (IELs) and two-dimensional (2D) V2O5-nanosheets blended with polyvinyl alcohol (PVA) as the water dissociation catalyst (WDC) at the interfacial layer. The composite BPM showed a low resistance of 0.79 Ω cm2, confirming the good contact between the IEL and WDC, much needed for the ionic conductivity. It also demonstrated high water dissociation performance with a water dissociation voltage of 1.11 V corresponding to a current density of 1.02 mA/cm2 in the presence of a 1 M NaCl electrolytic solution. The functionalization of the polysulfone with -SO3- and R4N+ groups successfully resulted in the increase of hydrophilicity of the polymer, thereby increasing the water uptake capacity of the membranes. The blending of 2D V2O5 nanosheets with PVA proved to be an effective WDC, as confirmed by the increased conductivity and efficiency of the water dissociation (WD) reaction. The 2D V2O5-ns have great potential toward water adsorption onto its surface, thereby interacting with the water molecules, weakening the bonding force of water, and dissociating it into H+ and OH-. The transportation of coions across the membranes and generation of protons and hydroxyl ions at the interfacial layer are correlated with the change in the pH of the catholyte and anolyte as a function of current density during the WD reaction. The high performance of the composite BPM (BPM_VO-ns) was demonstrated at a higher current density of 100 mA/cm2 with a WD resistance of 0.027 Ω cm2. The durability was tested by subjecting it to 45 h of run at lower (1.02 mA/cm2) and higher (100 mA/cm2) current densities which display a negligible change in the interlayer voltage. Thus, the fabricated composite BPMs pave the way to be utilized for efficient and durable WD reactions under neutral electrolytic conditions.

Rational Design of Ferroelectric 2D Perovskite for Improving the Efficiency of Flexible Perovskite Solar Cells Over 23.

Despite the great progress of flexible perovskite solar cells (f-PSCs), it still faces several challenges during the homogeneous fabrication of high-quality perovskite thin films, and overcoming the insufficient exciton dissociation. To the ends, we rationally design the two-dimensional (2D) perovskite based on pyridine heterocyclic ring as the organic interlayer. Through regulating its dipole moment by attaching the ammounium cation on different positions of the pyridine ring, we succeed to realize the ferroelectricity of the 2D perovskite. We uncover that incorporation of the ferroelectric 2D material into 3D perovskite induces an increased built-in electric field (BEF), which enhances the exciton dissociation efficiency and suppresses the nonradiative recombination in the device. Moreover, the 2D seeds could assist the 3D crystallization process by forming more homogeneous and highly-oriented perovskite crystals, and releasing the tensile stress in the film. As a result, an impressive power conversion efficiency (PCE) over 23% has been achieved by the 2D/3D based f-PSCs with outstanding ambient stability. Moreover, the ferroelectric 2D perovskite shows piezoelectricity as well, which intrigues an upshifted band-bending at the ITO/perovskite interface and decreased hole transport barriers. The device thus presents higher PCE under tensile-stresses, which opens new possibilities for developing highly-efficient f-PSCs.

Rational Design of Ferroelectric 2D Perovskite for Improving the Efficiency of Flexible Perovskite Solar Cells Over 23 %

AbstractDespite the great progress of flexible perovskite solar cells (f‐PSCs), it still faces several challenges during the homogeneous fabrication of high‐quality perovskite thin films, and overcoming the insufficient exciton dissociation. To the ends, we rationally design the ferroelectric two‐dimensional (2D) perovskite based on pyridine heterocyclic ring as the organic interlayer. We uncover that incorporation of the ferroelectric 2D material into 3D perovskite induces an increased built‐in electric field (BEF), which enhances the exciton dissociation efficiency in the device. Moreover, the 2D seeds could assist the 3D crystallization by forming more homogeneous and highly‐oriented perovskite crystals. As a result, an impressive power conversion efficiency (PCE) over 23 % has been achieved by the f‐PSCs with outstanding ambient stability. Moreover, the piezo/ferroelectric 2D perovskite intrigues a decreased hole transport barriers at the ITO/perovskite interface under tensile stress, which opens new possibilities for developing highly‐efficient f‐PSCs.

0D/2D Schottky junction synergies with 2D/2D S-scheme heterojunction strategy to achieve uniform separation of carriers in 0D/2D/2D quasi CNQDs/TCN/ZnIn2S4 towards photocatalytic remediating petroleum hydrocarbons polluted marine

The inherent advantages of 2D/2D S-scheme heterojunction contribute well to the photocatalysis due to efficient carriers’ separation kinetics and maintained redox ability. However, single 2D/2D S-scheme heterostructure fails to realize a perfect energy band alignment since the material contact interface is not perfectly contacted in real circumstance because of surface roughness and flexibility of 2D material. Herein, the 0D/2D Schottky junction synergies with S-scheme (S-S strategy) is proposed to improve weak links above. 0D Quasi CNQDs are utilized in 2D/2D S-scheme TCN/ZnIn2S4 to optimize the carriers’ separation kinetics in some area without 2D/2D close contact for TCN/ZnIn2S4. SI-XPS, UPS, and KPFM etc confirms such electron state. The CNQDs/TCN/ZnIn2S4 photocatalysts exhibits high degree of dissociation efficiency of photoinduced excitons due to S-S strategy. The results testify construction of S-S heterostructure would be an effective strategy for carriers’ modulation, and it will be a promising candidate for “green” elimination of oil spill on water surface.

Boosting charge transfer in Au-decorated B/K co-doped CN nanosheets towards enhanced photocatalytic CO2 reduction

A synergistic strategy to promote exciton dissociation and charge transfer efficiency of a CN catalyst for photocatalytic CO2 reduction via Au nanoparticle decoration and B/K co-doping simultaneously is reported.

Modulating intermolecular interactions by collaborative material design to realize THF-processed organic photovoltaic with 1.3 V open-circuit voltage

Achieving efficient exciton dissociation and high power conversion efficiency (PCE) becomes a great challenge when the open-circuit voltage (VOC) of organic photovoltaics (OPVs) reaches an upper limit value of 1.3 V or higher.

Theoretical calculations and experimental investigation toward the π-conjugated modulation in arylamine derivative-based hole transporting materials for perovskite solar cells.

Excellent hole transporting materials (HTMs) are beneficial to promote the performance of perovskite solar cells (PSCs). Herein, starting from the modulation of the π-conjugated groups of carbazole-diphenylamine derivatives, HTMs CY1 and CY2 were designed and investigated using density functional theory and Marcus theory. Theoretical simulations show that CY1 and CY2 exhibit appropriate HOMO/LUMO energy levels, small recombination energy, good optical properties and molecular stability. Compared with CY1, CY2 with a larger π-conjugated group on its side chain can yield a higher hole mobility and better charge separation. The experimental results confirm that CY2 in PSCs exhibits superior properties such as good hole transporting ability, good film morphology, and efficient charge extraction and dissociation at perovskite/HTM inerfaces. Therefore, a PSC device with CY2 yields a higher efficiency than those of CY1- and Spiro-OMeTAD-based devices. Hence, the results demonstrate that the strategy of the extended π-π conjugation on a side chain is a practicable approach to design potential HTMs for application in PSCs.

Surface ionization of CsCl molecules in the learning process

The paper presents the results of studying the catalytic properties of “metal-carbon” systems using the method of surface ionization of CsCl molecules. Using the Ir-C system as an example, it was shown that the poisoning effect of the same poison (carbon) strongly depends on the structure of the layer formed on the catalyst. In metals that do not form bulk carbides, the carbon monolayer completely poisons the catalytic properties of these metals. It is shown that individual atoms and clusters of samarium deposited on iridium coated with a monolayer of graphite lead to efficient catalytic dissociation of CsCl molecules. The mechanism of formation of a carbon film on the surface of a metal obtained by diffusion from the volume, which differs from the mechanism of formation of a carbon film obtained on the surface of a metal by adsorption, has been elucidated.

Strategically designed trimetallic catalyst with minimal Ru addresses both water dissociation and hydride poisoning barriers in alkaline HER

A highly active alkaline HER electrocatalyst (CoMoRu/CC) is prepared to achieve efficient water dissociation and consequently proton discharge with minimal Ru-content.

Band-structure tunability via the modulation of excitons in semiconductor nanostructures: manifestation in photocatalytic fuel generation.

Understanding the energetics of electron transfer at the semiconductor interface is crucial for the development of solar harvesting technologies, including photovoltaics, photocatalysis, and solar fuel systems. However, modern artificial photosynthetic materials are not efficient and limited by their fast charge recombination with high binding energy of excitons. Hence, reducing the exciton binding energy can increase the generation of charge carriers, which improve the photocatalytic activities. Extensive research has been dedicated to improving the exciton dissociation efficiency through rational semiconductor design via heteroatom doping, vacancy engineering, the construction of heterostructures, and donor-π-acceptor (D-π-A) interfaces to extend the charge carrier migration, promoting the dissociation of excitons. Consequently, functionalized photocatalysts have demonstrated remarkable photocatalytic performances for solar fuel production under visible light irradiation. This review provides the fundamental aspects of excitons in semiconductor nanostructures, having a high binding energy and ultrafast exciton formation together with promising photo-redox properties for solar to fuel conversion application. In particular, this review highlights the significant role of the excitonic effect in the photocatalytic activity of newly developed functional materials and the underlying mechanistic insight for tuning the performance of nanostructured semiconductor photocatalysts for water splitting, CO2 reduction, and N2 fixation reactions.