Charge Transfer Speed Research Articles

In-situ growth of FeCo layered double hydroxide nanorods on MXene for high-performance supercapacitor electrodes

In the pursuit of clean energy solutions, supercapacitors have gained attention due to their exceptional energy storage capabilities. Layered double hydroxide (LDH), a notable material in this field, faces some challenges such as slow charge transfer speed and volumetric expansion. To tackle these issues, a novel FeCo-LDH/MXene composite was synthesized through in-situ hydrothermal growth of FeCo layered double hydroxide (FeCo-LDH) nanorods on MXene using ionic self-assembly, forming a three-dimensional (3D) composite with enhanced rate capability and cycling stability due to the synergetic coupling of MXene and LDH. The FeCo-LDH/MXene electrode significantly improves surface capacitance control performance and exhibits exceptional electrochemical performance, achieving a specific capacitance of 2058.2 F g−1 at 1 A g−1 and maintaining 1732.7 F g−1 at 10 A g−1, with 82.4 % capacity retention. Furthermore, the assembled supercapacitor delivers an energy density of 48.8 Wh kg−1 at 750 W kg−1 and 25.7 Wh kg−1 at 15000 W kg−1, demonstrating excellent rate performance, as well as 80.3 % capacitance after 5000 cycles at 2 A g−1, highlighting its durability. This advancement not only overcomes the specific capacitance challenge of MXene electrodes but also enhances the conductivity and cyclic stability of LDH, making FeCo-LDH/MXene a promising candidate for future high-performance energy storage applications.

Interface Engineering of Flower-like Co 2 P/WO 3-x /Carbon Cloth Catalysts with Oxygen Vacancies for Efficient Oxygen Evolution Reaction.

The Constructing an efficient and low-cost oxygen evolution reaction (OER) electrocatalyst is critical for improving the performance of electrolysis in alkaline water. In this study, a self-supported electrocatalyst of flower-like cobalt phosphide and tungsten oxide (Co2P/WO3-x/CC) was prepared on carbon cloth (CC)surface by hydrothermal reaction with solution immersion etching and phosphorization annealing under H2/Ar atmosphere. This strategy can generate oxygen vacancies (OV), improving the speed of charge transfer between cobalt phosphide (Co2P) and tungsten oxide (WO3-x) components. The catalyst greatly increases the electrochemical active surface area, which is beneficial for efficient oxygen evolution. Electrochemical testing studies show that in 1.0 M KOH solution, Co2P-WO3-x/CC catalyst exhibits good OER activity, with a low overpotential of 254 mV at 10 mA cm-2, a small Tafel slope of 58.32 mV dec-1. The synergistic effect of oxygen vacancies and Co2P with WO3-xcan regulate electronic structures, expose more active sites, and cooperatively enhancing the OER activity. This study provides a workable strategy for preparing efficient non-noble metal OER electrocatalysts on engineered interfaces and OV.

Unlocking Unexpected Charge Transfer Pathways in Interconnected Nanostructures.

Accurate control of charge transfer pathways is critical to unlocking the full potential of charge transfer proteins (CTPs) and exploring their diverse applications. We show that the intentional manipulation of junctions in Al nanocrosses on graphene induces asymmetry, unlocking unexpected charge transfer pathways and facilitating the generation of coupled resonators. The junction asymmetry, which is induced by nanotrench formation facilitated by focused electron beam irradiation, provides a versatile means to achieve precise and controlled interconnect manipulation. We find that tuning the nanotrench dimensions in nanocrosses allows for the tailored modulation of the charge transfer speed and the energies of CTPs. Furthermore, CTPs excited in our experimental nanocrosses, featuring nanotrenches, exhibit weak coupling. This crucial insight underscores the importance of controlled trench formation in unlocking various functionalities of CTPs for use in sensing, catalysis, and energy conversion applications. The controlled manipulation of interconnects in Al nanocrosses thus emerges as a promising avenue for advancing the device performance in these fields.

Balancing Carrier Dynamics in Oxygen-Vacancy-Tuned Amorphous Ga2O3 Thin-Film Self-Powered Photoelectrochemical-Type Solar-Blind Photodetector Arrays for Underwater Imaging.

Underwater imaging technology plays a pivotal role in marine exploration and reconnaissance, necessitating photodetectors (PDs) with high responsivity, fast response speed, and low preparation costs. This study presents the synergistic optimization of responsivity and response speed in self-powered photoelectrochemical (PEC)-type photodetector arrays based on oxygen-vacancy-tuned amorphous gallium oxide (a-Ga2O3) thin films, specifically designed for solar-blind underwater detection. Utilizing a low-cost one-step sputtering process with controlled oxygen flow, a-Ga2O3 thin films with varying oxygen vacancy (VO) concentrations are fabricated. By balancing the trade-offs among electrocatalytic reactions, charge transfer, carrier recombination, and trapping, both the responsivity and response speed of a-Ga2O3-based self-powered PEC-PDs are simultaneously improved. Consequently, the optimized PEC-PDs demonstrated exceptional performance, achieving a responsivity of 33.75mA W-1 and response times of 12.8ms (rise) and 31.3ms (decay), outperforming the vast majority of similar devices. Furthermore, a pronounced positive correlation between anomalous transient photocurrent spikes and the concentration of VO defects is observed, offering compelling evidence for VO-mediated indirect recombination. Finally, the proof-of-concept solar-blind underwater imaging system, utilizing an array of self-powered PEC-PDs, demonstrated clear imaging capabilities in seawater. This work provides valuable insight into the potential for developing cost-effective, high-performance a-Ga2O3 thin-film-based PEC-PDs for advanced underwater imaging technology.

Excellent Electrochromic Properties of Ti4+-Induced Nanowires V2O5 Films

Ti4+-doped V2O5 films with nanowires on top and a dense, long nanorod layer on the bottom were successfully fabricated using the spin-coating route. During the electrochromic cycling, charge transfer resistance (Rct) decreases while ion-diffusion ability (KΩ) rapidly drops in the first ten cycles and then levels off. Low Rct and morphology of nanowires collaboratively improved the electrochromic behavior of Ti4+-doped V2O5 films by enhancing the charge transfer speed and minimizing polarization and dissolution. The obtained Ti4+-doped V2O5 film shows better electrochromic properties than the undoped V2O5 film, with a coloration efficiency (CE) of 34.15 cm2/C, coloration time of 9.00 s, and cyclic retention of 82.6% at cycle 100. In contrast, the corresponding values for the undoped V2O5 film were 23.57 cm2/C, 13.16 s, and 43.6%.

One-Step Synthesis of Heterostructured Mo@MoO2 Nanosheets for High-Performance Supercapacitors with Long Cycling Life and High Rate Capability.

Supercapacitors have gained increased attention in recent years due to their significant role in energy storage devices; their impact largely depends on the electrode material. The diversity of energy storage mechanisms means that various electrode materials can provide unique benefits for specific applications, highlighting the growing trend towards nanocomposite electrodes. Typically, these nanocomposite electrodes combine pseudocapacitive materials with carbon-based materials to form heterogeneous structural composites, often requiring complex multi-step preparation processes. This study introduces a straightforward approach to fabricate a non-carbon-based Mo@MoO2 nanosheet composite electrode using a one-step thermal evaporating vapor deposition (TEVD) method. This novel electrode features Mo at the core and MoO2 as the shell and demonstrates exceptional electrochemical performance. Specifically, at a current density of 1 A g-1, it achieves a storage capacity of 205.1 F g-1, maintaining virtually unchanged capacity after 10,000 charge-discharge cycles at 2 A g-1. The outstanding long-cycle stability is ascribed to the vertical two-dimensional geometry, the superior conductivity, and pseudocapacitance of the Mo@MoO2 core-shell nanosheets. These attributes significantly improve the electrode's charge storage capacity, charge transfer speed, and structural integrity during the cycling process. The development of the one-step grown Mo@MoO2 nanosheets offers a promising way for the advancement of high-performance, non-carbon-based supercapacitor nanocomposite electrodes.

Iron dopant in zinc oxide nanorods-based photoanode using chemical bath deposition method for photoelectrochemical water-splitting

Utilization of zinc oxide as a photoanode in photoelectrochemical (PEC) water splitting is cost-effective and environmentally friendly choices compared to noble metals, although some enhancements are required to address the limited light absorption and significant charge recombination. Iron as metal doping and nanorod structure, on the other hand, offers solutions to overcome these limitations. An in-depth study employing iron-doped zinc oxide nanorods using various concentrations of iron fabricated through a chemical bath deposition (CBD) method due to its high-quality results and scale-up feasibility, shows enhanced structures, electrical characteristics, optical properties, charge transfer speed, and overall effectiveness in converting solar energy to hydrogen. This dopant was effectively integrated into the photoanode, resulting in a reduction of the bandgap to 3.19 eV and the creation of nanorods that are both thinner and longer. The photocurrent density for the oxygen evolution reaction (OER) is 6 mA/cm2, and for the hydrogen evolution reaction (HER), it is 1.3 mA/cm2. Electrochemical Impedance Spectroscopy shows lower resistance and an improved diffusion coefficient, resulting in reduced energy requirements for hydrogen production. The solar-to-hydrogen efficiency is also reported at 4.7%. This method shows potential for future progress and possible performance improvements.

Construction of MOF-74 derived CuFe/C alloy highly dispersed on ultrathin single layered reduced graphene for electrochemical determination of paracetamol

Paracetamol (PAT) is a widely used drug for fever reduction and pain relief, but its accumulation due to overuse can lead to detrimental effects on human health and environment. Here, a novel composite material CuFe/C@rGO with excellent electrochemical properties was successfully constructed by loading carbon-encapsulated CuFe alloy (CuFe/C) on ultrathin single layered reduced graphene oxide (rGO) surface for PAT detection. Firstly, the CuFe/C nanoparticles was derived from MOF-74 as bimetallic ‘preassembly platform’ to obtain high dispersiveness, huge accessible surface area, and uniform pore structure of the resulted material. And then the CuFe/C was uniformly dispersed on rGO to effectively avoid the aggregation of CuFe/C and increase the conductivity of composite material. In virtue of the synergistic effect of CuFe/C and rGO, the composite material modified glassy carbon electrode CuFe/C@rGO/GCE would be endowed with abundant electrocatalytic acitive sites and fast charge transfer speed between electrode surface and analyte. Expectedly, the CuFe/C@rGO/GCE shows outstanding sensing performance with wide linear ranges of 0.006–110 μM, low detection limit of 0.0015 μM (S/N=3), together with superior reproducibility, stability and anti-interference. This developed composite material as a flexible sensing platform can be used to detect PAT in real samples with a satisfactory recovery.

Metal-free thiophene-based covalent organic frameworks achieve efficient photocatalytic hydrogen evolution by accelerating interfacial charge transfer

Photocatalysis is widely recognized as an efficient and environmentally friendly pathway for the conversion of solar energy into chemical energy. In recent years, designing efficient hydrogen evolution to obtain green clean energy has been one of the major challenges faced by researchers. Covalent organic frameworks (COFs) are considered as new and effective photocatalyst due to the inherent porosity, high crystallinity and structural adjustability. In this study, two metal-free thiophene-based covalent organic frameworks (JLNU-308 and JLNU-309) were constructed by solvothermal method through effective modulation sites. Because JLNU-COFs has a narrow band gap and good absorption capacity in the spectral range, the interfacial charge transfer speed is accelerated to solve the problem of low charge separation efficiency. Remarkably, JLNU-309 displays an impressive hydrogen evolution rate of 2868.57 μmol g−1 h−1 under visible light irradiation (λ > 420 nm). The superior hydrogen evolution reaction (HER) activity is due to the triazine units, which have high visible light absorption capacity, one-dimensional nanochannels of two-dimensional COFs and synergy with charge mobility. The photoelectrochemical measurements and calculation of density functional theory (DFT) supports the accuracy of the experiment. This work opens an avenue for constructing functional covalent organic frameworks for environmentally relevant critical applications. In addition, the simple synthesis process, excellent activity and high chemical stability indicate that JLNU-COFs are promising photocatalytic hydrogen production materials.

Study of the image motion compensation method for a vertical orbit dynamic scanning TDICCD space camera

In this study, a collaborative compensation method for low-dimensional attitude maneuvering and time delay integration charge-coupled device (TDICCD) line-frequency matching is proposed. The method is combined with the validation and analysis of the coordinate system transformation model to address the mismatch between the TDI charge transfer speed and the speed of the target. This mismatch is caused by the inconsistency between the rotational scanning direction of the double-sided mirror used for dynamic vertical orbit scanning imaging in low Earth-orbit satellites and the direction of the satellite along its orbit. The image motion per unit exposure time is decreased from 0.619µm to 0.023µm compared with the uncompensated maneuver mode, and the image quality is noticeably higher.

Interfacial engineering of hierarchical MoNi4/NiO heterostructure nanosheet arrays as bifunctional electrocatalysts for urea-assisted energy-saving hydrogen production

Employing urea oxidation reaction (UOR) to substitute slow oxygen evolution reaction (OER) is an effective technique to accomplish high-efficiency hydrogen production. The exploitation of inexpensive and highly active bifunctional catalyst still remains a considerable challenge. We report the hybrid nanosheet arrays constructed of MoNi4/NiO heterojunction with hierarchically crosslinked network architecture by hydrothermal reaction and subsequent annealing process under H2/Ar atmosphere. The special heterostructure with neoteric morphology can promote electron shift and interface interaction through the powerful coupling interface between MoNi4 and NiO, increasing charge transfer speed, intrinsic activity and electrolyte transport. Only 31 mV overpotential and 1.37 V potential are needed to arrive 10 mA cm−2 for hydrogen evolution reaction (HER) and UOR, respectively. For the two-electrode urea-assisted electrolyzer, the lower potential of 1.41 V is required to reach 10 mA cm−2. Moreover, it displays superior stability with unceasing working for 54 h at the cell voltage of 1.41 V without obvious activity degeneration. This research provides an insight on the construct of high-efficiently bifunctional catalyst by synergistic coupling of NiMo-based alloys with metal oxides.

Flexible electrochemical capacitor based NiMoSSe electrode material with superior cycling and structural stability

Constructing composited electrode material is considered to be an efficient strategy to improve their electrochemical performance. It can accelerate the charge transfer speed of ions and enhance the conductivity of electrode. Meanwhile, the formation of the hybrid structure can largely avoid the aggregation of two dimensional materials and increase the electrochemical active area of the electrode. In this work, we synthesize NiMoSSe electrode materials on nickel foam by a facile hydrothermal avenue. The prepared composite shows a specific capacitance of 1035 C/g at 1 A/g due to the synergistic effect between MoS2 and MoSe2 phases. In addition, the devices are assembled with NiMoSSe samples, which offers an energy density of 82.71 Wh/kg at a power density of 2700 W/kg.

Ultra-thin nanosheets of Ti3C2Tx MXene/MoSe2 nanocomposite electrode for asymmetric supercapacitor and electrocatalytic water splitting

Nanohybrid anode materials for highly efficient asymmetric supercapacitors are developed with a hydrothermal approach using organ-like (Ti3C2Tx) MXene as a main basis. The MoSe2/Ti3C2Tx hybrid supercapacitor has a high specific capacitance of 1531.2 Fg−1 at 1 Ag−1 and a low potential of 200 mV at 10 mAg−1. Additionally, the Tafel slope of 37.7 mV dec−1 for the hydrogen evolution reaction (HER) makes this supercapacitor an excellent electrochemical performer. The supercapacitor with Ti3C2Tx/MoSe2nanohybrid as the positive electrode shows excellent performance. Even after 10,000 cycles, it retains a capacitance of 94.1% with a high current density of 5 Ag−1, a high specific energy of 58.8 Whkg−1 and a high specific power of 800.3 Wkg−1. In comparison with unmodified MoSe2, it increases conductivity, speed of charge transfer, and active sites which is explained by the strong interfacial connection between MXene and Ti3C2Tx crystals.

Phase transformation and electrochemical properties of La0.6R0.15Mg0.25Ni3.5 (R = La, Pr, Nd, Gd) alloys with multiphase structure

As a promising Ni-MH battery electrode material, the La-Mg-Ni-based superlattice hydrogen storage alloys have attracted extensive attention due to their stable crystal structure, high energy density and good electrochemical properties. However, most of the existing studies are based on annealed alloys with simple phase compositions. In the present work, the effects of rare-earth elements and phase composition on the electrochemical properties and structure stability of a series of as-cast La0.6R0.15Mg0.25Ni3.5 (R = La, Pr, Nd, Gd) alloys are studied. The alloys contain (La, Mg)2Ni7, (La, Mg)5Ni19 and (La, Mg)Ni3 superlattice phases as well as LaNi5 and LaMgNi4 non-superlattice phases. As the atomic radius of the replacement element R decreases, the cell parameters of each phase in the alloys from large to small are: La> Pr> Nd> Gd. The activation cycle of alloys is one charge/discharge cycle, which demonstrate excellent activation property due to their multi-phase structure that offers many pathways and tunnels for the transfer of hydrogen atoms. Moreover, it is found that Pr enhances the cycling stability and structural stability as well as reduces the oxidation degree of the alloys owing to its function on suppressing LaNi5 non-superlattice phase which would cause an increase in internal stress and structure damage due to the continuous expansion and contraction of superlattice phase cell volume with the process of charge/discharge. Furthermore, the addition of Nd can accelerate the diffusion of hydrogen and increase the reaction speed of charge transfer at the electrode/electrolyte interface, resulting in an enhanced rate discharge performance.

Progress and Insight of Van der Waals Heterostructures Containing Interlayer Transition for Near Infrared Photodetectors

AbstractVan der Waals (vdWs) heterostructures enable bandgap engineering of different 2D materials to realize the interlayer transition via type‐II band alignment leading to broaden spectrum that is beyond the cut‐off wavelength of individual 2D materials. Interlayer transition has a significant effect on the optoelectronic performance of vdWs heterostructure devices, and strong interlayer transition in 2D vdWs heterojunction is always demandable for sufficient charge transfer and rapid speed response. Herein, a state‐of‐the‐art review is presented on recent progress on interlayer transition in vdWs heterostructures for near‐infrared (NIR) photodetectors. First, the general synthesis techniques for vdWs heterostructures, band alignments in the vdWs heterostructures are provided. Then, the mechanism of interlayer transition in vdWs heterostructure and recent progress on interlayer transition in vdWs heterostructures for NIR photodetectors are summarized. Afterward, some worthy applications of NIR photodetectors are reviewed in related areas of this topic. At the last, an outlook, challenges, and future research directions of vdWs heterostructures for photodetectors at broaden response spectrum are presented.

Synergetic Passivation of Metal‐Halide Perovskite with Fluorinated Phenmethylammonium toward Efficient Solar Cells and Modules

AbstractSurface passivation with organic halide salts is a powerful strategy to enhance the performance of perovskite solar cells. However, the inevitable formed in‐plane favored two‐dimensional perovskite layers with low carrier mobility and high binding energy inhibit the interfacial charge transfer within the device. Herein, a bulky fluorinated phenmethylammonium salt is designed and synthesized to passivate the perovskite film without forming 2D perovskites. A strong interaction which is induced by an electron donation from passivation agent to perovskite not only reduces the defects at the top surface of the perovskite, but also suppresses the recombination reaction at the buried surface due to a permeation of the organic halide salt. Moreover, the results of time resolved photoluminescence and confocal microscopy images suggest that the interfacial charge transfer speed and uniformity are enhanced. As a result, the efficiency of a small‐area device increases from 20.7 ± 0.9% to 22.8 ± 0.4% (aperture: 0.16 cm2). Moreover, a stabilized efficiency of 18.0% (aperture: 10.0 cm2) is achieved for larger‐area modules with 6‐series connected sub‐cells. Equally important, the non‐encapsulated modules show significantly improved stability at ambient conditions (ISOS‐D‐1). These significant improvements provided by a simple and reproducible procedure can be readily adopted in other types of devices.

Ultrafast response of spontaneous photovoltaic effect in 3R-MoS 2 –based heterostructures

Rhombohedrally stacked MoS2 has been shown to exhibit spontaneous polarization down to the bilayer limit and can sustain a strong depolarization field when sandwiched between graphene. Such a field gives rise to a spontaneous photovoltaic effect without needing any p-n junction. In this work, we show that the photovoltaic effect has an external quantum efficiency of 10% for devices with only two atomic layers of MoS2 at low temperatures, and identify a picosecond-fast photocurrent response, which translates to an intrinsic device bandwidth at ∼100-GHz level. To this end, we have developed a nondegenerate pump-probe photocurrent spectroscopy technique to deconvolute the thermal and charge-transfer processes, thus successfully revealing the multicomponent nature of the photocurrent dynamics. The fast component approaches the limit of the charge-transfer speed at the graphene-MoS2 interface. The remarkable efficiency and ultrafast photoresponse in the graphene-3R-MoS2 devices support the use of ferroelectric van der Waals materials for future high-performance optoelectronic applications.

The effect of photodiode shape on pinning potential for charge transfer in CMOS image sensors

The effect of the pinned photodiode (PPD) shape on charge transfer has been investigated in this paper. By equating the change in pinning potential distribution due to PPD shape to the decrease in depth of the depletion region in the vertical direction, an analytical model of the PPD shape effect on the pinning potential is proposed. The model for a triangular-like PPD is validated by TCAD simulations and is in very good agreement with the simulation results. Based on the model results, a tower-shaped PPD shape that can obtain constant lateral electric field is given. Simulation results show that the tower-shaped PPD have good pinning potential variation linearity and much better charge transfer performance than rectangular and triangular PPDs. The model and analysis results in this paper provide theoretical support and design ideas for the shape design and optimization of PPD-based pixels to improve the charge transfer speed and reduce the image lag.

Synergistic enhancement on flexible solid-state supercapacitor based on redox-active Fe3+ions/natural spidroin modified vertically aligned carbon nanotube arrays

The conductive skeleton and aligned carbon nanotube array (CNTA) structure can greatly shorten the ion transfer path and promote the charge transfer speed, which makes the CNTA an ideal electrode material for energy storage application. However, poor mechanical stability and low specific capacitance greatly impede its practical utilization. Here, we introduce a promising flexible electrode material based on the natural spider silk protein (SSP) modified CNTA(SSP/CNTA) with improved hydrophilicity and mechanical flexibility. The redox-active Fe3+ doped SSP/CNTA flexible solid-state supercapacitor (FSSC) device with superior energy storage performance was assembled in a symmetric ‘sandwich-type’ structure. The synergetic interaction between Fe3+ ions and the SSP are proved to greatly enhance the electrochemical performance especially the long-term cyclic stability. The Fe3+ doped SSP/CNTA FSSCs device achieves an ultra-high volumetric capacitance of 4.92 F cm−3 at a sweep speed of 1 mV s−1. Meanwhile it exhibited an excellent cycling stability with an increased capacitance by 10% after 10 000 charge–discharge cycles. As a control, a Fe3+ doped CNTA composite device without SSP will lose over 74% of the capacitance after 10 000 cycles. The energy storage mechanism analysis confirms the dominated capacitive behavior of the device, which explained a considerable power density and rate performance. Our method thus provides a promising strategy to build up highly-efficient redox-enhanced FSSCs for next generation of wearable and implantable electronics.

Lever-inspired triboelectric nanogenerator with ultra-high output for pulse monitoring

Triboelectric nanogenerators (TENGs) have great potential to alleviate the energy crisis. The contact separation mode of TENGs is one of the most fundamental and common modes of working. For improving the output signal of contact separation TENGs, previous researchers have adopted strategies such as surface microstructure treatment, multilayer design, and additive pump design. All of these strategies aim to increase the surface charge. Here, we propose a new strategy aimed at increasing the charge transfer speed, provide new paths for improving the output signal, and develop a lever-inspired contact separation TENG (Li-TENG). The contact separation speed can be varied by changing the lever ratio. As the magnification increases from 22 to 50 times, the voltage of Li-TENG increases from 91 V to 232 V. As self-powered pulse sensor, the Li-TENG measured a pulse signal of 12.3 V without surface microstructure treatment. This work shows great potential for improving the signal of contact-separation TENG-based self-powered sensors and energy harvesting devices.