Good Electron Transport Research Articles

The Structural, stability, electronic and optoelectronics properties of Y2AgBiX6 (Y = K, Na, li; X = I, Br, Cl) halide double Perovskites: A First-Principles study

The crystal structure, electronic and optoelectronic properties of halide double perovskites Y2AgBiX6 (Y = K, Na, Li; X = I, Br, Cl) have been studied by first principles (FPs) in this paper. According to the elastic modulus and formation energy of crystal Li2AgBiX6, its structural stability is poor. In addition, the dependence of their electronic and mechanical properties, the effective mass of carriers and light absorption on elemental composition has been analyzed, and it is inferred that these materials have good electron transport properties. The photovoltaic characteristics of halide perovskite materials (PMs) based on potassium and sodium are studied. The photovoltaic properties of perovskite films with thickness of 1 μm, 5 μm and 10 μm were further analyzed, and it was found that the absorption was the highest when the film thickness was 10 μm. The current–voltage curve of the solar cell with above perovskite as absorbing material is calculated and analyzed by first principles. The result shows that Na2AgBiBr6, Na2AgBiCl6, K2AgBiI6 and K2AgBiCl6 are predicted to have excellent photovoltaic properties. Compared to other commonly used PMs, perovskite Y2AgBiX6 (Y = K, Na, Li; X = I, Br, Cl) has a smaller effective mass, which may contribute to good carrier transport and high performance of its optoelectronic devices. The absorption curves of K2AgBiBr6, K2AgBiCl6, Na2AgBiBr6, Li2AgBiBr6, and Li2AgBiCl6 matched well with the spectral irradiance of AM 1.5. Taken together, K2AgBiBr6 and Na2AgBiBr6 are the most suitable candidates for solar cell absorption layers because of their appropriate band gap and good stability.

Improving Microbial Fuel Cell Performance Using Porous Capacitive Composite Bioanode Materials with Energy Storage Function

Microbial fuel cells (MFCs) have shown promise in solving energy and environmental problems, but their practical application is limited by their low power output. In this study, carbon nanotubes/polypyrrole composite anode materials were prepared on a porous sponge matrix. By combining the porous characteristics of sponge, the good conductive properties of carbon nanotubes, and the energy storage ability of polypyrrole capacitive materials, the prepared anode exhibited a large specific capacity, high porosity, large specific surface area, good electron transport ability, and good biocompatibility. The results showed that the maximum power density of the modified anode MFC reached 7.46 W m−3, which was 2.53 times higher than that of the control anode. The stored energy Qs released by the modified anode was 235.6 C m−2, 6.5 times higher than that of the control electrode. In addition, the transfer impedance Rct of the S/CNT/PPy electrode (5.5 Ω) was much lower than that of the control anode (16.8 Ω). The research presented in this paper demonstrates a new approach to improving the power generation ability and energy storage performance of MFCs.

Bone-inspired (GNEC/HAPAAm) hydrogel with fatigue-resistance for use in underwater robots and highly piezoresistive sensors

A novel bone-inspired fatigue-resistant hydrogel with excellent mechanical and piezoresistive properties was developed, and it exhibited great potential as a load and strain sensor for underwater robotics and daily monitoring. The hydrogel was created by using the high edge density and aspect ratio of graphene nanosheet-embedded carbon (GNEC) nanomaterials to form a three-dimensional conductive network and prevent the expansion of microcracks in the hydrogel system. Multiscale progressive enhancement of the organic hydrogels (micrometer scale) was realized with inorganic graphene nanosheets (nanometer scale). The graphene nanocrystals inside the GNEC film exhibited good electron transport properties, and the increased distances between the graphene nanocrystals inside the GNEC film caused by external forces increased the resistance, so the hydrogel was highly sensitive and suitable for connection to a loop for sensing applications. The hydrogels obtained in this work exhibited excellent mechanical properties, such as tensile properties (strain up to 1685%) and strengths (stresses up to 171 kPa), that make them suitable for use as elastic retraction devices in robotics and provide high sensitivities (150 ms) for daily human monitoring.

Enhancing protonic ceramic fuel cell performance through nanomilling of BCZY electrolyte powder

To obtain dense, high-quality electrolytes, sintering of the proton-conducting electrolyte BaCe0.6Zr0.2Y0.2O3 (BCZY) in protonic ceramic fuel cells (PCFCs) should be conducted at relatively high temperatures. However, in the co-sintering of a porous anode substrate and electrolyte thin film, high sintering temperatures often cause the coarsening of the NiO-BCZY anode, thus reducing the number of electrocatalytic active sites for H2 oxidation as well as degrading cell performance. A scalable nanomilling process is proposed to reduce electrolyte sintering temperature to maintain triple phase boundary, good electron and proton transport in PCFC anode. By using the nanomilling process, BCZY nanoparticles more than halved the original diameter (from 297 nm to 131 nm) were produced. The co-sintering temperature can be lowered. The cell sintered at 1400 °C exhibited the highest peak power density of 490 mW/cm2, 38% higher than that of un-nanomilled process. The substantial improvement in cell performance can be attributed to the lower co-sintering temperature, which caused less coarsening of the NiO anode. This preserved a greater number of electrocatalytic active sites for H2 oxidation by Ni in cell operation, as evidenced by the 50% decrease in charge transfer resistance from electrochemical impedance measurements.

Thick Electrodes of a Self‐Assembled MXene Hydrogel Composite for High‐Rate Energy Storage

Supercapacitors based on two‐dimensional MXene (Ti3C2Tz) have shown extraordinary performance in ultrathin electrodes with low mass loading, but usually there is a significant reduction in high‐rate performance as the thickness increases, caused by increasing ion diffusion limitation. Further limitations include restacking of the nanosheets, which makes it challenging to realize the full potential of these electrode materials. Herein, we demonstrate the design of a vertically aligned MXene hydrogel composite, achieved by thermal‐assisted self‐assembled gelation, for high‐rate energy storage. The highly interconnected MXene network in the hydrogel architecture provides very good electron transport properties, and its vertical ion channel structure facilitates rapid ion transport. The resulting hydrogel electrode show excellent performance in both aqueous and organic electrolytes with respect to high capacitance, stability, and high‐rate capability for up to 300 μm thick electrodes, which represents a significant step toward practical applications.

Elimination of Interface Energy Barriers Using Dendrimer Polyelectrolytes with Fractal Geometry.

In this work we study conjugated polyelectrolyte (CPE) films based on polyamidoamine (PAMAM) dendrimers of generations G1 and G3. These fractal macromolecules are compared to branched polyethylenimine (b-PEI) polymer using methanol as the solvent. All of these materials present a high density of amino groups, which protonated by methoxide counter-anions create strong dipolar interfaces. The vacuum level shift associated to these films on n-type silicon was 0.93 eV for b-PEI, 0.72 eV for PAMAM G1 and 1.07 eV for PAMAM G3. These surface potentials were enough to overcome Fermi level pinning, which is a typical limitation of aluminium contacts on n-type silicon. A specific contact resistance as low as 20 mΩ·cm2 was achieved with PAMAM G3, in agreement with the higher surface potential of this material. Good electron transport properties were also obtained for the other materials. Proof-of-concept silicon solar cells combining vanadium oxide as a hole-selective contact with these new electron transport layers have been fabricated and compared. The solar cell with PAMAM G3 surpassed 15% conversion efficiency with an overall increase of all the photovoltaic parameters. The performance of these devices correlates with compositional and nanostructural studies of the different CPE films. Particularly, a figure-of-merit (Vσ) for CPE films that considers the number of protonated amino groups per macromolecule has been introduced. The fractal geometry of dendrimers leads to a geometric increase in the number of amino groups per generation. Thus, investigation of dendrimer macromolecules seems a very good strategy to design CPE films with enhanced charge-carrier selectivity.

Bifunctional hierarchical NiCoP@FeNi LDH nanosheet array electrocatalyst for industrial-scale high-current-density water splitting

Aiming to design and prepare non-noble metal electrocatalysts for hydrogen production at high current density (HCD), NiCoP@FeNi LDH hierarchical nanosheets were deposited on nickel foam progressively using a hydrothermal-phosphorization-electrodeposition process. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), NiCoP@FeNi LDH/NF requires only 195 and 230 mV overpotentials to reach 1000 mA cm−2, respectively. For overall water splitting, only 1.70 V is required at 1000 mA cm−2. This is the largest value for non-noble metal-based electrocatalysts reported so far at HCD. The hierarchical structure exhibits good electron transport capability and the porous-macroporous structure enhances the gas release rate, resulting in enhanced hydrogen production at HCD. Especially, the synergistic effect of NiCoP and FeNi LDH contributes to the adsorption-desorption equilibrium of intermediate radicals during the reaction process and ultimately enhances the catalytic activity. This work provides useful direction for industrial-scale hydrogen production applications at HCD.

Schottky construction of bimetallic Au-Cu alloy@TiO2 hollow nanoboxes embedded optical switch for enhancing photocatalytic and selective adsorption activities via one-pot deposition-precipitation strategy

One-pot soft integration strategy based on wet chemistry via a simple in situ deposition-precipitation approach has been developed to fabricate series of bimetallic Au-Cu alloy@TiO2 hollow nanoboxes (THB) embedded optical switch. The bimetallic Au-Cu alloys were embedded into the nanodevice through Schottky junctions. This embedded optical switch could exhibit excellent photocatalytic performance. Under simulated sunlight irradiation, Au-Cu4:3 @THB nanodevice exhibited the photodegradation rate of RhB was of 99.4 % in 150 min, which was 3.0 times higher than that of THB. The oxidation rate of NO reached 27.0 %, 2.3 times that of THB. The enhanced photocatalytic activity could mainly be attributed to Au-Cu alloy SPR effects; the photoreactivity of the nanodevice was greatly improved after modification with bimetallic Au-Cu. Under dark conditions, the RhB adsorption rate of bimetallic Au-Cu4:3 @THB nanodevice reached 98.6 %, which was 6.1 times higher than that of THB. As the adsorption effect test of mixed dyes (MB/MO and RhB/MO), after 5 h of adsorption, the adsorption capacity of cationic dyes was 3.1 times that of anionic dyes, it was concluded that the bimetallic Au-Cu4:3 @THB optical switch had an excellent selective adsorption effect. This was due to the large surface area and mesoporous structure of the adsorbent, good electron transport structure, and the formation of a galvanic cell after adding dyes. This research provides a promising catalytic material with optical switch for environmental restoration and protection. It has broad application prospects in photocatalytic degradation, photocatalytic oxidation and adsorption of organic pollutants.

TaOx electron transport layers for CO2 reduction Si photocathodes

TaOx electron transport layers used in photocathodes for light-driven CO2 reduction have good electronic transport, are stable, and are catalytically inert for the competing hydrogen evolution reaction.

A controllably fabricated polypyrrole nanorods network by doping a tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt for enhanced ammonia sensing at room temperature.

The morphology adjustment and functional doping optimization of polypyrrole (PPy) are of great significance in improving its gas sensing performance. Here, the PPy-0.5TcCoPc nanorods with a uniform dispersed 3-D network were prepared using one-step in situ polymerization using the electrostatic interaction between dopant counterion substituents in tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt (TcCoPcTs) with larger space structure and pyrrole (Py) molecules, in which TcCoPcTs is not only used as a dopant molecule crosslinking PPy chains to obtain a 3-D network, thus improving the conductivity, but also as a sensor accelerator to improve the gas-sensing performance. The resulting PPy-TcCoPc hybrid exhibits superior NH3-sensing properties than PPy and tetra-β-carboxylate cobalt phthalocyanine (TcCoPc) under the same test conditions, especially the PPy-0.5TcCoPc sensor shows ultrafast response/recovery time to 50 ppm NH3 (8.1 s/370.8 s), low detection limit of 8.1 ppb and excellent gas selectivity at room temperature (20 °C). Besides, the PPy-0.5TcCoPc sensor also maintains superior response (49.3% to 50 ppm NH3), humidity resistance and conspicuous stability over 45 days. The excellent NH3-sensing performance of the PPy-0.5TcCoPc hybrid arises from the excellent gas selectivity of TcCoPc, the remarkable response mechanism between PPy and NH3, the high electrical conductivity, abundant active sites and good electron transport ability of the unique 3-D network with large specific surface area. The morphology regulation and functional doping optimization strategy of TcCoPcTs doped PPy broaden the research direction of ideal gas sensor materials.

Ultrathin metal−organic layers/carbon nitride nanosheet composites as 2D/2D heterojunctions for efficient CO2 photoreduction

Metal−organic layers (MOLs), with well-defined, abundant active sites and good electron transport capabilities, are ideal platforms for studying the photoreduction of CO2 to value-added chemicals feedstocks in 2D/2D assembled materials.

Controllable engineering of intrinsic defects on carbon nanosheets enables fast and stable potassium storage performance

Defect-enriched carbon nanomaterials possess high potassium storage capacity and rapid ion transport capability; nevertheless, their rate performance is restricted by the deteriorated electronic conductivity induced by over-broken sp2-C conjugated structure. Herein, intrinsic defect-enriched carbon nanosheet (DCS) with controllable defect density is reported for the high-efficiency anode of potassium-ion batteries (PIBs). The DCS constructed by internal sp2-C configuration and external sp3-C defects can ensure good electron transport ability and afford abundant active sites for K+ storage. As PIBs anode, DCS-24 obtained by ball-milling for 24 h with optimized defect density delivers a high specific capacity of 270.9 mAh g−1 at 0.5 C, an excellent rate performance (189 mAh g−1 at 10 C), as well as long cycle durability (255.1 mAh g−1 over 3000 cycles at 1 C). Electrochemical results and density functional theory simulations indicate that the intrinsic defects of carbon materials improve the capacitive K+ storage capacity, speed up the K+ diffusion, and lower the K+ adsorption energy.

Fabrication of Li, Na and K electrolytes with doping elements for improved efficiency based on MOT and symmetry

This work is focused on finding a more effecient electrolyte to enhance the lithium-ion battery's overall characteristics and performance under Molecular Ortbital Theory (MOT) approach. As lithium-based electrolytes are now widely employed in all battery-operated portable devices, their use must be done with caution owing to a number of issues, including their toxicity, limited ionic conductivity, explosiveness, corrosiveness and hydrolysability creating harmful gasses. Using computational tools, a solution for these kinds of issues has been evaluated. The core idea is to simulate and evaluate by changing molecular symmetries. The molecular descriptors used include non-covalent interactions, band structure, density of states, electrostatic potential and fukui indices. Following our findings, a soft molecule with a smaller energy gap will be more polarizable and capable of charge transfer, making it more chemically reactive and less non-corrosivity than lithium hexafluoroarsenate (LiAsF6) and lithium hexafluorophosphate (LiPF6). For comparison, we also examined the electronic properties of electrolytes using first-principles calculations based on the DFT in the material design software MedeA® computational environment and also carried out Band structure and DOS calculation, which indicate the significance of band gap of between 1.41 to 2.91 eV. Since, soft molecules lead to good conductivity, chemically reactive and electron transport. A relative study with sodium and potassium-based electrolytes was also performed.

Spirobifluorene-based hole-blocking material with enhanced efficiency through hole and exciton confinement in blue fluorescent OLEDs

A new hole-blocking material, 2-(9,9′-spirobi[fluoren]-5-yl)-4-phenylbenzo [4,5]thieno[3,2-d]pyrimidine (SBF-BTPym), was designed and synthesized using spirobifluorene and electron transport moieties. The high triplet energy and high thermal stability of the spirobifluorene moiety were suitable for designing the hole-blocking material for blue fluorescent organic light-emitting diodes (OLEDs). The electron deficiency of benzothienopyrimidine allowed good electron transport properties, and a deep highest occupied molecular orbital energy level of −6.55 eV suppressed leakage of the holes from the emitting layer (EML) to the adjacent layer. Blue fluorescent OLEDs consisting of a triplet-triplet annihilation–induced host were fabricated using SBF-BTPym. The maximum external quantum efficiency of the blue fluorescent device was 7.2%, which was higher than that of the device without a hole-blocking layer by 10%. According to transient electroluminescence analysis, exciton confinement in the EML is mainly responsible for the improved efficiency.

(Best Student Presentation Award) Ppb-Level Detection on Formaldehyde By Phase-Engineered 2D-WSe2 Layers Grown By Plasma-Assisted Chemical Vapor Reaction

Layered transition metal dichalcogenides (TMDs) have attracted increasing attention for semiconducting applications owing to their distinctive properties, such as high surface-to-volume ratio, good electronic transport and phase-engineered. However, most of the methods for fabricating thermodynamic metastable phase have so far been induced by conventional CVD process. The high synthesis temperature may cause damages to the substrate and also the processing time is extended. In this concept, here, we incorporated a plasma function into a typical selenization process, which is then applied to metal oxides, namely, a plasma-assisted chemical vapor reduction (PACVR) process, to overcome the disadvantage of CVD process since the presence of high-energy Se ions under plasma treatment lower the energy barrier for a reaction and facilitate the formation of TMDCs at lower temperature. In this work, we developed a facile method to achieve phase control and report a ppb-level detection gas sensor on formaldehyde. Tunable phase synthesis of WSe2 can be achieved by varying conditions such as temperature, carrier gas flow rate and plasma power in a low-temperature PACVR system. Through the detailed investigation of chemical bonding in WSe2 by Raman and XPS, it was found that 100% 2H phase and hybrids of 1T’ and 2H phases can be achieved, and the ratio of 1T’/2H is tunable, relying on substrate temperatures under plasma treatment. By investigating the sensing behavior towards HCHO gas, the performance is highly associated to the ratio of 1T’/2H. The responsivity of 33 % can be achieved with the ratio of the hybrids around 0.46 in WSe2. The phase-engineered 2D-WSe2 layers grown by plasma-assisted chemical vapor reaction with tunable performance can be applied to detect other VOCs efficiently. Figure 1

Upcycling of cattle manure for simultaneous energy recovery and supercapacitor electrode production

Organic waste, such as cattle manure, is a serious matter of concern because of its disruptive impact on the environment. Even though disposal and reclaim of cattle manure represent the first lines of intervention to solve this problem, upcycling strategies should eventually be essential to reconvert huge amounts of the waste. In the present study, a pyrolysis process was used to reclaim value from cattle manure. Through the process, cattle manure was transformed into pyrolytic gas, pyrolytic liquid, and porous carbon material. The porous carbon material was further carbonized followed by an activation step to make a supercapacitor electrode. The electrode of a hierarchical porous carbon (termed as CMPC) is formed via carbonization and activation processes of solid residue derived from the pyrolysis of cattle manure. The bicontinuous structure of CMPC provide good ion and electron transport pathways, enabling fast charge-discharge. Specifically, in a basic solution electrolyte, CMPC electrode exhibits significant specific capacitance of 161 F g−1 at 0.4 A g−1, comparable to or even larger than other biomass-derived carbon electrodes, and high rate-performance (62% of low-capacitance). It also shows long cycle lives for at least 10,000 charge-discharge cycles at a constant current of 2.7 A g−1. As the pyrolytic gas and pyrolytic liquid had higher heating values of 7.6 MJ kg−1 and 8 MJ kg−1, respectively, they can potentially be used as fuels to supply heat and energy to the pyrolysis process. The cattle manure upcycling process could greatly contribute to the reduction in greenhouse gas emissions.

Covalent organic framework modified carbon nanotubes for removal of uranium (VI) from mining wastewater

The wastewater containing uranium produced in the mining process is harmful to the environment and life safety due to the inherent biotoxicity and radioactivity of uranium. In this paper, 4,4′-diamino-[1,1′-biphenyl]-3,3′-diol and 2,4,6-triformylphloroglucinol were in situ synthesized β-ketoenamine covalent organic frameworks (COFs) on the surface of carbon nanotubes (CNTs) to obtain a composite of CNT/COF-OH for removal uranium in the rare earth tailings wastewater. Grafting COFs with a large number of specific uranium-binding groups and redox-active sites on the surface of CNTs, CNT/COF-OH can effectively enhance the uranium ion selectivity and adsorption capacity. Furthermore, CNTs have good electron transport capacity and π-conjugation properties, electrons can be effectively transferred from CNTs to COFs, which increases the electron density of the adsorption functional groups, resulting in an increase of the adsorption energy and reductive activity for U (VI), thus improving the removal efficiency. In addition, the skeleton of COFs can be supported by CNTs, thus reducing collapse. Through the synergistic effect of composite, CNT/COF-OH had a good uranium adsorption capacity of 518.2 mg g−1. The adsorption capacity of CNT/COF-OH was increased by 390.7 %, 54.6 %, and 84.5 % compared with those of single CNTs, COF-OH, and mixed CNT + COF-OH, respectively. The selective separation coefficient of CNT/COF-OH was 1.6 times higher than that of COF-OH. The experiment of uranium removal was carried out in the rare earth tailings wastewater using CNT/COF-OH, the removal rate reached 96.7 %. The COFs modified CNTs with synergistic effect have important theoretical and practical significance for the safety problems caused by harmful ions in wastewater.

Modulating the Electron Transporting Properties of Subphthalocyanines for Inverted Perovskite Solar Cells.

The lack of organic non-fullerene ETMs with good electron transport and device stability is an important problem for the further development and commercialization of perovskite solar cells. Herein, the use of SubPcs as ETMs in PSCs is explored. To this end, we analyze the influence of SubPc peripheral functionalization on the efficiency and stability of p-i-n PSCs. Specifically, ETMs based on three SubPcs (with either six or twelve peripheral fluorine and chlorine atoms) have been incorporated into PSCs with the perovskite layer deposited by solution processing (CsFAMAPbIBr). The device performance and morphology of these devices are deeply analyzed using several techniques, and the interfacial effects induced by the SubPcs are studied using photoluminescence and TR-PL. It is observed that the device stability is significantly improved upon insertion the SubPc layer. Moreover, the impact of the SubPc layer-thickness is assessed. Thus, a maximum power conversion efficiency of 13.6% was achieved with the champion device.

Electronic properties of Borophene/InSe van der Waals heterostructures

In this work, we investigate the electronic properties of the Van der Waals heterojunctions based on InSe and borophene (Δ and χ3) by the first principle calculations. The orbital hybridizations can affect the electronic structures of InSe and boropheneΔ in heterostructure. The calculated tunneling barriers and the Schottky barriers indicate that the designed devices have good electronic transport. It is found that the Ohmic contact can be achieved by changing the interlayer distance. In addition, the external electric field can modulate the Schottky contact type and Schottky barriers height. The results can provide useful insight in high-performance devices based on the Borophene/InSe heterostructure.

In situ-formed tetrahedrally coordinated double-helical metal complexes for improved coordination-activated n-doping

In situ coordination-activated n-doping by air-stable metals in electron-transport organic ligands has proven to be a viable method to achieve Ohmic electron injection for organic optoelectronics. However, the mutual exclusion of ligands with high nucleophilic quality and strong electron affinity limits the injection efficiency. Here, we propose meta-linkage diphenanthroline-type ligands, which not only possess high electron affinity and good electron transport ability but also favour the formation of tetrahedrally coordinated double-helical metal complexes to decrease the ionization energy of air-stable metals. An electron injection layer (EIL) compatible with various cathodes and electron transport materials is developed with silver as an n-dopant, and the injection efficiency outperforms conventional EILs such as lithium compounds. A deep-blue organic light-emitting diode with an optimized EIL achieves a high current efficiency calibrated by the y colour coordinate (0.045) of 237 cd A−1 and a superb LT95 of 104.1 h at 5000 cd m−2.