Small Impedance Research Articles

Comparative analysis of two liner acoustic impedance characterization techniques

This study presents the comparison of two methodologies of small size liner acoustic impedance characterization. The first one is based on a normal incidence broadband acoustic excitation up to 160 dB inside a 30-mm diameter circular tube, and uses the two microphones method, with microphones flush-mounted inside the waveguide. This bench, called NTMM and developed at Airbus, allows to directly compute the acoustic impedance at the surface of the sample. The second one lies on a measurement inside the B2A wind tunnel at ONERA, where the sample is mounted as one of the vein walls, leading to a grazing aero-acoustic excitation, up to Mach 0.3 and 155 dB with a broadband excitation. The impedance is then educed by an inverse method. During the MAMBO research project, dedicated samples have been designed and tested with the two benches as well as on the CANNELLE multimodal test rig developed by Airbus. The full paper will analyze the results and offer a cross comparison of the methodologies, highlighting the advantages and limitations of each approach.

Trace RuO2 nanoparticles loaded nickel-coated multi-walled carbon nanotubes to boost hydrogen evolution reaction under acidic and alkaline media

Developing low-cost catalysts with high activity for the Hydrogen Evolution Reaction (HER) is a main challenge to reduce the dependence on precious metals while maintaining the catalytic activity. In this study, nickel-plated multi-walled carbon nanotubes (Ni-MWCNTs) with a large number of active sites were selected, and Ni-MWCNTs electrocatalysts loaded with trace amounts of RuO2 nanoparticles were prepared by annealing treatment, which exhibited excellent HER performances in both acidic and alkaline media. The RuO2 nanoparticles loaded nickel-coated multi-walled carbon nanotubes (RuO2@Ni-MWCNTs) had a small electrochemical impedance spectrum (EIS) and a large electrochemically active surface area (ECSA). Notably, RuO2@Ni-MWCNTs with less than 1 % Ru content exhibited excellent catalytic activities in both acidic and alkaline solutions. The results showed that the overpotentials of RuO2@Ni-MWCNTs were 20.2 mV (alkaline) and 73.7 mV (acidic), respectively. After stabilization at 20 mA cm−2 for 90 h, the evaluation results showed that RuO2@Ni-MWCNTs could maintain their catalytic efficiency without significant degradation.

Vinyl-functionalized covalent organic framework via tuning π-conjugation effectively promotes photocatalytic hydrogen evolution

Covalent organic frameworks (COFs) show great potential in photocatalytic water splitting. However, it is still crucial to explore the effect of π-conjugation of COFs on photocatalytic performance. Here, a series of COFs with different degrees of conjugation (DHTA-BD COF, DHTA-STP COF, DHTA-AZO COF) have been investigated through the synergistic effect of varying the planarity and π electronic structures. The results show that the vinyl-functionalized DHTA-STP COF achieves an excellent photocatalytic hydrogen generation rate of 16.1 mmol g1h−1 under visible light conditions, 4.3 times higher than the DHTA-BD COF, and the hydrogen production of the DHTA-AZO COF is extremely low under the same test conditions. Moreover, the synergistic effect of the smaller dihedral angle and ordered π electronic structures with the introduction of vinyl structure in DHTA-STP COF leads to a higher degree of conjugation, facilitating π delocalization efficiency and promoting the redistribution of charges. Experimental and theoretical calculations have demonstrated that DHTA-STP COF is a promising photoactive semiconductor with the strongest photocurrent, the smallest impedance, the narrowest electronic bandgap, and the strongest separation ability of electron-hole pairs. This finding provides guidance for introducing appropriate conjugated units into COFs to improve the photocatalytic hydrogen production efficiency.

Machine Learning-Driven Prediction of DLD Chip Throughput

Abstract The microfluidic chip technology, capable of manipulating fluids at the micrometer-scale, is increasingly being applied in the fields of cell biology, molecular biology, chemistry, and life sciences. The densely integrated microfluidic chip devices enable high-throughput parallel experiments and integration of various operational units. However, the development of densely integrated microfluidic chips also comes with high demands on driving equipment. Due to manufacturing processes and inherent design limitations, the driving capability of the equipment is restricted. To address potential challenges faced by microfluidic chips in the development towards integrated biological microsystems and to maximize their high-throughput performance, improvements are required not only in selecting appropriate driving equipment but also in design aspects. This study focuses on the DLD chip and delves into the complexity of microfluidic chip design. By combining Bézier curves to characterize arbitrarily shaped micropillars and conducting finite element analysis to compute the pressure field of DLD chips, we explore methods utilizing random forest, XGBoost, LightGBM, and ANN machine learning algorithms to predict the impedance of DLD chips. Our objective is to guide engineers in designing chips with smaller impedance (lower pressure drop) and larger throughput more quickly and efficiently during the design phase. Ultimately, through evaluating the predictive capabilities of the four models on new data, we select the ANN algorithm model to predict the pressure drop under different designs of DLD chips. This offers possibilities for enhancing the efficiency and integration of microfluidic technology in biomedical applications.

Electrodeposition fabrication of graphene oxide/α-MnO2/polyaniline hierarchical porous electrodes with large hybrid specific capacitance for efficient U(VI) electrosorption

The radioactive pollution caused by the excessive discharge of uranium-containing wastewater generated from nuclear industry posed harmful effect to the ecological environment and human health. Herein, the electrodeposition of polyaniline on graphene oxide/α-MnO2 surface was conducted to fabricate novel hierarchical porous graphene oxide/α-MnO2/polyaniline (GMP) electrodes with large specific capacitance for U(VI) electrosorption through hybrid capacitance deionization (HCDI). As expected, the prepared GMP have high specific capacitance, small electrochemical impedance, and excellent electrosorption performance. Among the different GMP composites, GMP-2 presents the highest specific capacitance (303.85 F/g) and largest electrosorption capacity of U(VI) (330.41 mg/g at 0.9 V and pH4.0), indicating that its electrosorption capacity is closely related to the specific capacitance. Moreover, GMP-2 showed good selectivity for U(VI) electrosorption through pseudocapacitive mechanism. The XPS and FTIR characterization indicated that apart from hybrid capacitance (EDL and pseudocapacitance) mechanism, complexation and electrostatic interactions were also involved for U(VI) capture. The GMP-2 electrode is facile to fabricate and has excellent electrosorption performance, which could be used in HCDI for radioactive wastewater treatment.

Asymmetric capacitive deionization based on pore structures of biochar

Biochar is an affordable and sustainable material for the application of capacitive deionization. Although the desalination capability of biochar is significantly impacted by its pore size distribution, the correlation between them is challenging to explore due to the uncontrollable pore size. This study exclusively utilizes different activation mechanisms to regulate the pore size distribution of carbon derived from the same biomass precursor, and explores the role of pore structures in capacitive deionization. The specific capacitance of microporous biochar (MiB) can reach up to 319.1 F/g (0.2 A/g), with an Epzc of 0.11 V and high oxygen content, while mesoporous biochar (MeB) has a specific capacitance of only 170.4 F/g, an Epzc of 0 V, and a small charge transfer impedance. The MeB//MiB desalination cell is designed based on these characteristics and demonstrates a higher salt adsorption capacity of 17.04 mg/g at 1.2 V, compared to MiB//MiB (15.72 mg/g) and MeB//MeB (6.07 mg/g), alongside a stability of 81 % after 50 cycles. These capabilities can be attributed to the expanded voltage range resulting from the different Epzc, and the high ion storage capacity of MiB, as well as the fast ion transport capability of MeB. The oxygen/carbon ratio of the anode in MeB//MiB increased by only 42 %, whereas that in MiB//MiB increased by 370 %, confirming the oxidation inhabitation ability of the asymmetric structure and the oxidation resistance of MeB. Therefore, constructing ideal pore structures and more importantly reasonable deployment is an effective strategy for improving desalination capacity and stability.

PEG-PVP-Assisted Hydrothermal Synthesis and Electrochemical Performance of N-Doped MoS2/C Composites as Anode Material for Lithium-Ion Batteries.

Molybdenum disulfide shows promise as an anode material for lithium-ion batteries. However, its commercial potential has been constrained due to the poor conductivity and significant volume expansion during the charge/discharge cycles. To address these issues, in this study, N-doped MoS2/C composites (NMC) were prepared via an enhanced hydrothermal method, using ammonium molybdate and thiourea as molybdenum and sulfur sources, respectively. Polyethylene glycol 400 (PEG400) and polyvinylpyrrolidone (PVP) were added in the hydrothermal procedure as soft template surfactants and nitrogen/carbon sources. The crystal structure, morphology, elemental composition, and surface valence state of the N-doped MoS2/C composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that the NMC prepared by this method are spherical particles with a nanoflower-like structure composed of MoS2 flakes, having an average particle size of about 500 nm. XPS analysis shows the existence of C and N elements in the samples as C-N, C-C, and pyrrolic N. As anodes for LIBs, the NMC without annealing deliver an initial discharge capacity of 548.2 mAh·g-1 at a current density of 500 mA·g-1. However, this capacity decays in the following cycles with a discharge capacity of 66.4 mAh·g-1 and a capacity retention rate of only 12% after 50 cycles. In contrast, the electrochemical properties of the counterparts are enhanced after annealing, which exhibits an initial discharge capacity of 575.9 mAh·g-1 and an ultimate discharge capacity of 669.2 mAh·g-1 after 70 cycles. The capacity retention rate decreases initially but later increases and elevated afterward to reach 116% at the 70th cycle, indicating an improvement in charge-discharge performance. The specimens after annealing have a smaller impedance, which indicates better charge transport and lithium-ion diffusion performance.

Controlled synthesis of X (X = Mo, Cr and W) doped NiCoP nanostructures as efficient and environmentally friendly urea electrolysis catalyst

Urea electrolysis is an effective way to replace water splitting for H2 generation, which is expected to achieve carbon neutralization. However, problems such as high energy consumption and slow urea oxidation kinetics have hindered its rapid development. In this study, a series of foreign element modified NiCoP-based catalysts were in-situ grown on Ni foam through hydrothermal process, solvothermal method and low temperature phosphating method. The morphology of the electrode was regulated by changing the impregnation elements. It was found that Mo3P@NiCoP/NF has rich active sites and small impedance, which makes it have excellent urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) property. At a current density of 10 mA cm−2, the potential of UOR is 1.206 V, and the overpotential of HER is 90 mV. The assembled Mo3P@NiCoP/NF / / Mo3P@NiCoP/NF cell demands only a potential of 1.285 V to drive a current density of 10 mA cm−2, and presents good durability within 12 h, which is one of the best electrochemistry activity and stability reported to date. Density functional theory suggests that NiCoP improves the reaction rate of this Mo3P@NiCoP/NF catalyst, and Mo3P enhances the metallicity of this catalyst, thereby enhancing the catalytic performance of Mo3P@NiCoP/NF.

Mechanism analysis of photocatalytic activity on Semiconductor-Type-Modulated heterojunctions

The construction of heterojunction is one of the most popular strategies to improve the performance of photocatalysts, but the influence of heterojunction types on their photocatalytic behaviors is rarely investigated. Here, the p-n and n-n type heterojunctions were constructed through combining p-type BiOBr (p-BOB) or n-type BiOBr (n-BOB) with n-type g-C3N4 (CN), and their photocatalytic performances were evaluated through RhB degradation and production of H2 in comparison with that of pure n-/p- BiOBr semiconductor. The n-n type heterojunction n-BOB/CN exhibits more excellent photocatalytic performance than that of p-n type heterojunction p-BOB/CN though the latter presents more efficient separation of photogenerated carriers with the strongest photocurrent response and the smallest impedance under the driven of strong built-in electric field. The step-scheme (S-scheme) charge transfer mechanism in n-BOB/CN heterojunction was proposed based on the calculation of work functions and the corresponding valance or conduction band potential, which is responsible for the more excellent photocatalytic performance of n-BOB/CN than that of p-BOB/CN.

High efficiency holographic impedance metasurface for dual circular polarized OAM waves

AbstractThis paper proposes a high aperture efficiency (AE) small size tensor holographic impedance metasurface (THIMS), which has the ability to create circular polarized (CP) high purity orbital angular momentum (OAM) multi‐beams with flexibly independent control of the individual beam direction, polarization and OAM mode. The tensor unit cell is a cross‐slotted circular patch. We design a THIMS at 14.6 GHz for dual CP OAM beams: Beam‐I (LHCP, l = 1, θ1 = 30°, φ1 = 0°), Beam‐II (RHCP, l = −1, θ2 = 30°, φ2 = 180°). The developed tensor dual CP THIMS has the following advantages: high purity in xoy plane at z = 9.73 λ (λ wavelength, measured purity 88.4% for Beam‐I, and 93.5% for Beam‐II), high AE 25.1%, and small size 5.986 λ × 5.986 λ × 0.0618 λ. The calculated, simulated and measured results agree well. The generated dual CP OAM beams have potential applications for high‐capacity wireless communication, radar high resolution imaging, and rotation velocity measurement.

Self-Assembly of Ultrathin, Ultrastrong Layered Membranes by Protic Solvent Penetration.

Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 μm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 μm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 μm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.

Biodegradable, Bifunctional Electro-acoustic Transducers Based on Cellular Polylactic Acid Ferroelectrets for Sustainable Flexible Electronics.

Nowadays, humans rely increasingly on smart electronics to address grand challenges and to improve life conditions in the era of digitalization and big data. However, electronics often have a limited lifespan, and they may bring electronic waste problems after their service. To mitigate this problem, environmentally sustainable methods of electronic device production and disposal are highly recommended, where advanced functional materials should be redesigned with improved sensing performance over the entire operational life while also being naturally degradable at the end. Herein, a biodegradable and flexible bifunctional electroacoustic transducer was fabricated with the utilization of cellular polylactic acid (PLA) ferroelectret films, possessing a small acoustic impedance of ∼0.02 MRayl which is quite close to that of air and a high figure of merit (FOM: d33·g33) of ∼11 GPa-1. Such devices have a prominent signal-to-noise ratio (SNR) of ∼23.5 dB @1 kHz and can work either as a microphone by direct piezoelectric effect or a loudspeaker by reverse piezoelectric effect in air medium. When used as a microphone, the flexible device exhibits a prominent receiving sensitivity up to 4.2 mV/Pa (∼-47.5 dB/ref. 1 V/Pa) at 1 kHz. When served as a loudspeaker, it is capable of yielding high sound pressure levels (SPLs) ranging from 60 to 103 dB (ref. 20 μPa) in a broad frequency range of 1-80 kHz with an active area of 3.14 cm2. Additionally, the electrical response curve of the device is very flat in a wide frequency range from 300 to 3000 Hz. With the high-performance acoustic-electric conversion capacity, the PLA ferroelectret-based flexible and filmlike electroacoustic transducer was used to realize accurate speech recognition and control, providing a strong impetus for its advanced and eco-friendly applications in the era of the internet of things (IoT) and artificial intelligence.

Machine learning for deconstructing contributions of atomic characterizations to achieve hybridization-determined electron transfer in a perovskite catalyst

Machine learning deconstructed the atomic contribution of a perovskite to catalytic toluene decomposition and found that wider hybridization resulted in smaller impedance, faster electron transfer speed, and enhanced catalytic activity.

Unlocking the Potential of Li–Ag Alloys: Phase Selection and Practical Application

Dendrite formation, contact loss, and continuous formation of the solid electrolyte interphase (SEI) preclude the practical use of the energy-dense lithium (Li) metal. Li–Ag alloys have the potential to address these issues due to their exceptional lithiophilicity, outstanding mechanical stability, and moderate chemical stability. This study evaluates all phases in the Li–Ag phase diagram based on lithiation capacity, Li insertion, mechanical property, and chemical stability. Our findings suggest that Li 4 Ag is the most promising phase, and the Gibbs free energy of nucleation (∆ G nucle ) for Li–Ag alloys is 3 to 5 orders of magnitude smaller compared to pure Li, resulting in uniform nucleation and deposition behavior. We proposed practical applications within the Li 4 Ag phases or from the Li 9 Ag 4 to the Li 4 Ag phases, which may provide a usable capacity of 409 to 696 mAh/g, respectively. Experiments indicate that Li 4 Ag exhibits not only the smallest impedance but also the highest capacity retention compared to Li 9 Ag 4 and pure Li. The study provides valuable guidance for the selection and application of Li-containing alloys in future battery development.

Hysteresis in memristors produces conduction inductance and conduction capacitance effects.

Memristors are devices in which the conductance state can be alternately switched between a high and a low value by means of a voltage scan. In general, systems involving a chemical inductor mechanism as solar cells, asymmetric nanopores in electrochemical cells, transistors, and solid state memristive devices, exhibit a current increase and decrease over time that generates hysteresis. By performing small signal ac impedance spectroscopy, we show that memristors, or any other system with hysteresis relying on the conductance modulation effect, display intrinsic dynamic inductor-like and capacitance-like behaviours in specific input voltage ranges. Both the conduction inductance and the conduction capacitance originate in the same delayed conduction process linked to the memristor dynamics and not in electromagnetic or polarization effects. A simple memristor model reproduces the main features of the transition from capacitive to inductive impedance spectroscopy spectra, which causes a nonzero crossing of current-voltage curves.

Regular polyhedron α-Fe2O3 nanocrystals prepared from hot rolled sludge for photocatalytic degradation of organic pollutants: Optimization and mechanism

Herein, a photocatalyst with the micromorphology of regular polyhedron (RP-α-Fe2O3 nanocrystals) was prepared via hot rolled sludge (HRS), and its preparation mechanism was investigated. The optical property test and DFT calculations exhibited the RP-α-Fe2O3 nanocrystals has strong visible light absorption and small electrochemical impedance, which indicated that it has excellent catalytic performance under visible light. The degradation efficiency of 100 mg/L Rhodamine B (RhB) solution could reach 99.2% within 60 min. Furthermore, the RP-α-Fe2O3 nanocrystals exhibited excellent reusability and stability. Meanwhile, hydroxyl radicals (·OH), superoxide radicals (·O2−) and photogenerated holes (h+) were the most significant active substances that affect the photocatalytic efficiency, due to they would synergically degrade RhB in the photocatalytic reaction system. Particularly, the diffraction peak of N1s was detected in the RP-α-Fe2O3 nanocrystals after reaction, and the intensity of CO and CO peaks increased, which proved that the photocatalyst has adsorption for RhB.

Iontronic Nanopore Model for Artificial Neurons: The Requisites of Spiking.

Brain-inspired neuromorphic computing is currently being investigated for effective artificial intelligence (AI) systems. The development of artificial neurons and synapses is imperative to creating efficient computational biomimetic networks. Here we propose the minimal configuration of an effective iontronic spiking neuron based on a conical nanofluidic pore ionic diode. The conductance is composed of a Boltzmann open channel probability and a blocking inactivation function, forming the structure of a memristor. The presence of a negative resistance and the combination of activation-deactivation dynamics cause a Hopf bifurcation. Using the characteristic frequencies of small perturbation impedance spectroscopy, we discuss the conditions of spiking, in which the system enters a limit cycle oscillation. We arrive at the conclusion that an excitable neuron-like system can be made with a single active channel instead of the more complex combination of multiple channels that occurs in the Hodgkin-Huxley neuron model.

FeOOH-polypyrrole-multiwalled carbon nanotube ternary nanocomposite fabricated by liquid-liquid co-extraction technique for supercapacitors application

FeOOH-polypyrrole-multiwalled carbon nanotube (FeOOH-PPy-MWCNT) ternary nanocomposite for supercapacitor negative electrodes are prepared by liquid-liquid co-extraction (LLCE) technique using decylphosphonic acid (DPPA) as efficient co-extractor. LLCE offers advantages of reduced agglomeration and facilitates mixing of the individual components. This technique allows direct particle transfer from the reaction medium to the electrode fabrication slurry. The mechanism of LLCE extraction is analyzed. The synergetic effect of FeOOH, PPy and MWCNT significantly enhances charge storage properties of the FeOOH-PPy-MWCNT ternary nanocomposite electrodes. The FeOOH-PPy-MWCNT ternary nanocomposite electrode shows an integral capacitance of 5.1 F cm−2 (137.9 F g−1) in a negative potential window, which is significantly higher than capacitances of binary FeOOH-MWCNT and PPy-MWCNT nanocomposites. Moreover, the ternary composite offers advantages of a larger voltage window. Testing results for the ternary composites at different electrode potentials show reduced AC impedance. The asymmetric supercapacitor device composed of FeOOH-PPy-MWCNT anode and MnO2-MWCNT cathode exhibits a high areal capacitance of 2.5 F cm−2 at scanning rate of 2 mV s−1 in a voltage window of 1.6 V at an extremely small impedance. This facile LLCE fabrication technique opens a door for fabrication of advanced nanocomposite materials for supercapacitor applications.

Optimal negative sequence current suppression strategy without phase‐locked loop based on the control of clustered new energy power stations

AbstractIn the context of extremely uneven sources and loads in China, several large‐scale power transmission systems have been established. Affected by the small equivalent impedance of the system, the increase of negative sequence currents during open‐phase operation has seriously threatened the stable operation of synchronous generators. The necessity of negative sequence current suppression is particularly prominent. To address the above issues, this paper analyzes the feasible negative sequence suppression capacity of the grid‐connected inverter under the principle of positive sequence priority. Using the geometric analysis method to determine the optimal suppression capacity. The none‐phase‐locked loop (PLL) control method is used to improve the response speed and form the negative sequence current suppression strategy adapted to the open‐phase operation period. A simulation model was built in PSCAD to verify the effectiveness of the proposed strategy. The result shows that the suppression strategy has a faster response than the conventional PLL control. In scenarios with large negative sequence currents to be suppressed, a maximum suppression effect of approximately 63% can be achieved. Compared with the traditional suppression capacity selection, the strategy in this paper can reduce the residual of negative sequence current by about 10% at most. The negative sequence currents intruding into the generator can be effectively suppressed without additional devices.

Self-Assembled 2D VS2 /Ti3 C2 Tx MXene Nanostructures with Ultrafast Kinetics for Superior Electrochemical Sodium-Ion Storage.

Constructing nanostructures with high structural stability and ultrafast electrochemical reaction kinetics as anodes for sodium-ion batteries (SIBs) is a big challenge. Herein, the robust 2D VS2 / Ti3 C2 Tx MXene nanostructures with the strong Ti─S covalent bond synthesized by a one-pot self-assembly approach are developed. The strong interfacial interaction renders the material of good structural durability and enhanced reaction kinetics. Meanwhile, the enlarged and few-layered MXene nanosheets can be easily obtained according to this interaction, providing a conductive network for sufficient electrolyte penetration and rapid charge transfer. As predicted, the VS2 /MXene nanostructures exhibit an extremely low sodium diffusion barrier confirmed by DFT calculations and small charge transfer impedance evidenced by electrochemical impedance spectroscopy (EIS) analysis. Therefore, the SIBs based on the VS2 /MXene electrode present first-class electrochemical performance with the ultrahigh average initial columbic efficiency of 95.08% and excellent sodium-ion storage capacity of 424.6mAhg-1 even at 10Ag-1 . It also shows an outstanding sodium-ion storage capacity of 514.2mAhg-1 at 1Ag-1 with a capacity retention of nearly 100% within 500 times high-rate cycling. Such impressive performance demonstrates the successful synthesis strategy and the great potential of interfacial interactions for high-performance energy storage devices.