Charge Accumulation Research Articles

Challenges in Accurate Calculation of Electrochemical Reactions Using First Principles Calculations: Water Adsorption on Pt(111) Surface Under Applied Potential

Modelling of chemical reactions controlled by an applied external potential could greatly enhance technological developments in the fields like electrochemical synthesis, fuel cells, water electrolysis and etc. Such modelling could be used for in silico search for more active and more stable catalysts, avoiding time consuming and costly experiments. However, a key prerequisite for reliable and successful modelling should be a close agreement between evaluated properties and their experimental observations.In this presentation the fundamental reaction of water interactions with a surface of Pt electrode is discussed. We chose this reaction as a useful illustrative example where available experimental measurements, such as potentials of water adsorption and dissociation on Pt surface could be directly compared to the modelling for benchmarking of a computational accuracy. Herein, the ability of an employed DFT-based method with implicit model of solution is tested, addressing challenges such as limitations in accurate evaluation of materials work functions, approximate model of solution and difficulties in total energy evaluation under the constant potential.As a first step, we point out to the problem of employing an experimental range of a potential of the standard hydrogen electrode (SHE), used as a reference in theoretical calculations in view of an inability of DFT to provide sufficiently accurate evaluation of materials work function and hence an operating potential. Secondly, we also show that upon hydration of a Pt surface there exists a peculiar non-monotonic change of a potential upon charging of a slab in contrast to monotonic relation for a clean Pt surface, which we explain by modification of water binding mechanism (presence of a dual charge in certain voltage range) with changing of a charge state of Pt surface (Fig. 1).To characterise the binding mechanism of a water molecule to Pt(111) surface we analysed the partial density of states, Fukui function and density matrices of p-states of an oxygen atom of a water molecule upon adsorption. Based on our calculations we conclude that greater binding upon application of a higher potential is accounted for by a charge accumulation in the Pt-O interatomic space, in spite of an overall total charge decrease.In summary our work provides a reliable methodology, that could be applied for analysis of reaction steps of electrochemical reactions on Pt surface under the applied external potential.This presentation is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

(Invited) Organic Photoelectrochemical Cells for Overall Solar Water Splitting

Solar-driven water splitting to produce hydrogen and oxygen offers a promising avenue for reducing reliance on fossil fuels as hydrogen can be converted into electrical energy using a fuel cell or transformed into useful chemical feedstocks. Despite its potential, the search for cost-effective light harvesting semiconductors suitable for industrial-scale deployment remains a challenge. Organic photoelectrochemical cells (OPECs) utilizing organic semiconductors (OSs) coupled with co-catalysts have recently attracted great attention as alternative photoelectrodes for solar water splitting, considering the unique features of OSs such as precisely tunable optoelectrical properties and solution-processability at low temperatures. However, the conversion efficiency and stability of OPECs (both photocathode and photoanode) have remained particularly poor. Herein, I present high-performance and robust organic photoelectrochemical cells by employing a bulk heterojunction (BHJ) blend of semiconducting polymers as a photoactive layer. The in-depth study using sacrificial agents for photoreduction and photooxidation unveils critical parameters that significantly affect the performance and operational stability of OPECs: (i) rational selection of semiconducting polymer donor and acceptor to generate free charges efficiently and ensure chemical stability upon illumination, (ii) large surface roughness of interlayers to improve interfacial adhesion, and (iii) mitigation of charge accumulation at the interfaces. By leveraging these findings, the optimized polymer BHJ photocathode and photoanode show outstanding performance and robustness compared to previous OPECs, demonstrating a new benchmark of OPECs in solar water splitting. Consequently, this advancement, combined with the simplicity of the polymer blending process, establishes the use of polymer BHJs as a promising route for efficient and scalable solar-driven water splitting technology.

Enhancing the Efficiency and Stability of Perovskite Solar Cells Via Hybrid Electron Transport Layer Strategy.

Tin oxide (SnO2) is extensively employed as the electron transport layer (ETL) for perovskite solar cells, but the presence of unsaturated Sn dangling bonds and oxygen vacancy defects at surface hinders effective carrier transport. Herein, we present an effective strategy for constructing a hybrid ETL by doping ZnF2 into the SnO2, effectively addressing the oxygen vacancy defects at both the bulk and interface of SnO2, thus markedly minimizing nonradiative recombination losses. Additionally, the process-induced strong bonding between F and Sn atoms facilitates the establishment of electron transfer pathways, leading to an increased electron cloud density within SnO2 and enhanced electron transfer capability, thus further suppressing charge accumulation at the interface. The hybrid ETL strategy can be adaptable to perovskites with various cations. The MAPbI3 and Cs0.1FA0.9PbI3 perovskite solar cells achieved remarkable PCEs of 21.31% and 24.91%, respectively. Moreover, the hybrid ETL design significantly enhances device stability. After 600 h of ambient storage, the unencapsulated optimized devices retained approximately 90% of their initial efficiency.

A Hypothesis on the Function of High‐Valent Fe in NiFe (Hydr)oxide in the Oxygen‐Evolution Reaction

AbstractThis study investigated the dynamic changes in NiFe (hydr)oxide and identified the role of high‐valent Fe in the oxygen‐evolution reaction (OER) within alkaline media via in situ techniques. Several high‐valent Fe ions were found to remain considerably stable in the absence of potential in NiFe (hydr)oxide, even 96 hours after the OER. For Ni2+ hydroxide treated with 57Fe ions, where Fe sites are introduced onto the surface of Ni2+ hydroxide, no Fe4+ species were detected at the rate‐determining step (RDS). The findings of this study suggested that the oxidation of bulk Fe ions, similar to Ni ions, to high valent forms, is charge accumulation without a direct role in OER; these results offered a novel perspective on manipulating Fe states to optimize OER efficacy. The prevailing hypothesis suggested that trace amounts of high‐valent Fe ions, notably those on the surface, directly participate in OER.

A Hypothesis on the Function of High-Valent Fe in NiFe (Hydr)oxide in the Oxygen-Evolution Reaction.

This study investigated the dynamic changes in NiFe (hydr)oxide and identified the role of high-valent Fe in the oxygen-evolution reaction (OER) within alkaline media via in situ techniques. Several high-valent Fe ions were found to remain considerably stable in the absence of potential in NiFe (hydr)oxide, even 96 hours after the OER. For Ni2+ hydroxide treated with 57Fe ions, where Fe sites are introduced onto the surface of Ni2+ hydroxide, no Fe4+ species were detected at the rate-determining step (RDS). The findings of this study suggested that the oxidation of bulk Fe ions, similar to Ni ions, to high valent forms, is charge accumulation without a direct role in OER; these results offered a novel perspective on manipulating Fe states to optimize OER efficacy. The prevailing hypothesis suggested that trace amounts of high-valent Fe ions, notably those on the surface, directly participate in OER.

BCN-driven interfacial effect: A novel strategy to remarkably enhance the capacitance of Co3O4/NiO for supercapacitor

A BCN/Co3O4/NiO (BCN/CNOs) hetero-interface was developed to introduce a novel strategy that remarkably enhances the specific capacitance of transition metal oxides (TMOs). The engineered hetero-interface driven by BCN was characterized by plentiful electrons accumulation and effectively increased the specific capacitance of the as-prepared BCN/CNOs electrode to 8533 mF cm−2 at 2 mA cm−2, obtaining 154 % improvement compared to acid-treated carbon cloth loaded CNOs (ACC/CNOs). DFT theoretical calculations indicated that the BCN-driven interfacial effect primarily accelerates the charge transfer due to charge accumulation at interface between BCN and CNOs. Due to charge rearrangement at the interface, the reduced diffusion barrier of OH− on the surface of CNOs significantly improved the charge storage capacity. This research provides a universal reference basis for remarkably improving the capacitance of TMOs.

Sulfur vacancy-rich ZnS on ordered microporous carbon frameworks for efficient photocatalytic CO2 reduction

ZnS has garnered significant attention as a versatile photocatalyst in the field of CO2 reduction. However, its photocatalytic efficiency has been hindered by its high charge recombination rates and sluggish reaction kinetics. Herein, we demonstrate a highly efficient CO2 photoreduction on well-designed S-deficient ZnS nanoparticles within an ordered mesoporous N-doped carbon framework (Vs-ZnS/OMNC) through an in situ thermal treatment strategy. The fs-TA spectrum elucidated that introducing sulfur vacancy (Vs) effectively promoted the separation of photogenerated charges in ZnS/OMNC and significantly improved its reaction kinetics. In situ DRIFTS spectroscopy and DFT calculations revealed that these S vacancies led to charge accumulation on neighboring Zn atoms, enabling effective adsorption and activation of CO2 molecules. Particularly, the vacancy strategy also effectively lowered the energy barrier for forming the key intermediate *COOH. Therefore, the CO evolution rate of Vs-ZnS/OMNC reached 712.1 μmol·g−1·h−1, which is 2.84 times higher than that without sulfur vacancy (250.74 μmol·g−1·h−1). Its CO2 reduction performance surpassed most ZnS-based photocatalysts reported previously. Additionally, the Vs-ZnS/OMNC exhibited outstanding stability without obvious degradation after five reaction cycles. This study provides insights into developing advanced photocatalysts through vacancy defect engineering combined with ordered mesoporous carbon structures.

Memristor-based model of neuronal excitability and synaptic potentiation.

In this manuscript, we investigate the memristor-based implementation of neuronal ion channels in a mathematical model and an experimental circuit for a neuronal oscillator. We used a FitzHugh-Nagumo equation system describing neuronal excitability. Non-linearities introduced by the voltage-gated ion channels were modeled using memristive devices. We implemented three basic neuronal excitability modes including the excitable mode corresponding to a single spike generation, self-oscillation stable limit cycle mode with periodic spike trains and bistability between a fixed point and a limit cycle. We also found the spike-burst activity of mathematical and experimental models under certain system parameters. Modeling synaptic transmission, we simulated postsynaptic response triggered by periodic pulse stimulation. We found that due to the charge accumulation effect in the memristive device, the electronic synapse implemented a qualitatively bio-plausible synapse with a potentiation effect with increasing amplitude of the response triggered by a spike sequence.

Long‐Lasting, Steady and Enhanced Energy Harvesting by Inserting a Conductive Layer into the Piezoelectric Polymer

AbstractFlexibility, higher piezoelectric performance, and long‐lasting stability of devices have a great demand in next generation energy technologies. Polyvinylidene fluoride (PVDF) polymer has a greater mechanical flexibility, but it suffers from low piezoelectric performance. Herein, sandwich‐structured piezoelectric film (SS‐PF) is designed by inserting the conductive poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer between two PVDF layers. The SS‐PF based flexible piezoelectric energy harvester (f‐PEH) generates higher voltage and current of 3.73 times and 4.64 times than the pristine PVDF film type f‐PEH. Moreover, the SS‐PF based f‐PEH shows no degradation in the output voltage confirming the excellent long‐lasting stability over 6 months. DFT simulation shows the occurrence of intermolecular forces between the PVDF/PEDOT:PSS interface. The electric field‐dependent charges alignment in PEDOT:PSS may induce the charge accumulation at the PSS‐PVDF interface and charge depletion at the PEDOT‐PVDF interface leading to the change in orientation of molecular structure in PVDF. Next, the SS‐PF based f‐PEH is tested for a vibration sensor to monitor the vibrations of curvy pipes and machines, and its output voltages are comparable with the commercial PVDF vibration sensor to confirm the real‐time use. The results present a novel design strategy, indicating a new direction for investigating piezo‐polymer‐based f‐PEH.

Crystalline/Amorphous Interface Engineering and d-sp Orbital Hybridization Synergistically Boosting the Electrocatalytic Performance of PdCu Bimetallene toward Formic Acid-Assisted Overall Water Splitting.

Advanced electrocatalysts capable of bifunctional catalysis for formic acid oxidation (FAOR) and hydrogen evolution reaction (HER) have garnered significant attention due to their exceptional energy efficiency. In this research, we have meticulously designed a PdCu bimetallene characterized by numerous crystalline/amorphous (c/a) interfaces and robust d-sp orbital hybridization, achieved by integrating the p-block metalloid boron within the PdCu matrix (B-PdCu-c/a). The B-PdCu-c/a bimetallene revealed a multitude of surface atoms and unsaturated defect sites, offering abundant catalytic active sites and an optimized electronic structure. The B2-PdCu-c/a exhibited the best performance in FAOR and HER, achieving a mass activity of 1106 mA mgcat-1 and an overpotential of 52 mV, respectively. Significantly, the two-electrode configuration of B2-PdCu-c/a∥B2-PdCu-c/a attained a low cell voltage of 0.19 V at 10 mA cm-2 during formic acid-assisted overall water splitting. Density functional theory (DFT) calculations indicated that c/a interface engineering and d-sp orbital hybridization synergistically optimized the electronic configuration of pristine PdCu bimetallene. This led to an elevation of the d-band center and an accumulation of charge at the c/a interface, which enhanced the adsorption of intermediates, facilitated C-H bond cleavage, and balanced the adsorption-desorption of hydrogen, thereby improving electrocatalytic activities for FAOR and HER, respectively. This study not only presents a viable strategy for effectively tuning the electronic configuration of bimetallene but also offers valuable insights into the development of electrocatalysts.

Underlying Mechanism of Electrolyte Compositional Engineering Based on Additive Solvation-Structure Governing Solid Electrolyte Interphase Formation in Lithium-Ion Batteries.

Substantial efforts are dedicated to optimizing the additive dosage in the electrolyte and studying its effect on solid electrolyte interphase (SEI) formation in Li-ion batteries (LIBs). This study reveals that the decomposition characteristics of the additive based on its lithium-ion solvation nature significantly contribute to controlling SEI formation. During SEI formation, the strong lithium-ion solvating additive spontaneously migrates to the negative electrode due to negative charge accumulation on the surface, and SEI reinforcement is feasible by increasing the additive dosage. In contrast, population-based SEI formation occurs with a weaker solvating additive, so dosage-dependent modification of the SEI is not effective. These findings demonstrate that compositional electrolyte engineering based on the solvation properties of the additive can be more effective than empirical and experimental studies based on trial and error.

Fibrous Pb(II)‐Based Coordination Polymer Operable as a Photocatalyst and Electrocatalyst for High‐Rate, Selective CO2‐to‐Formate Conversion

AbstractA nonporous [Pb(tadt)]n (tadt = 1,3,4‐thiadiazole‐2,5‐dithiolate) coordination polymer, KGF‐9, with a 2D infinite (−Pb−S−)n structure has been previously reported as a precious‐metal‐free photocatalyst for selective CO2‐to‐formate conversion under visible light. In the present work, a microwave (MW)‐assisted solvothermal reaction is used to synthesize KGF‐9 with improved physicochemical properties and catalytic activity. Compared with KGF‐9 prepared by the previously reported methods, that prepared by the new synthesis route exhibited a greater specific surface area, greater crystallinity, and greater photoconductivity. These improved properties led to a drastic increase of the apparent quantum yield (AQY) for selective formate production, from 2.6 to 25% at 400 nm; this AQY represents a record‐high value among reported heterogeneous photocatalysts for CO2‐to‐formate conversion. Interestingly, the AQY for formate production is unchanged irrespective of the light intensity (0.04–14 mW cm−2), indicating little contribution of charge accumulation in the bulk during the reaction (i.e., indicating efficient charge transport to surface reactants). When composited with Ketjen Black, KGF‐9 enabled the electrochemical conversion of CO2 to formate in aqueous solution while maintaining a high selectivity. A high‐rate reduction of CO2 to formate with a total absolute current density of 200–300 mA cm−2 is achieved, with a Faradaic efficiency (FE) of >90%.

Heterojunction interface engineering enabling high transmittance and record efficiency in Sb2S3 semitransparent solar cell

Antimony sulfide (Sb2S3) is an auspicious contender for semitransparent and tandem solar cells owing to its exceptional optoelectronic characteristics. Yet, complex bulk and heterojunction defects hinder achieving optimal power conversion efficiency (PCE). Although CdS is an established electron transport layer (ETL) in Sb-chalcogenide solar cells benefitting from its exceptional electron mobility (350 cm2V–1s−1) and energy level alignments, its potential contribution has been deplorably overlooked in Sb2S3 semitransparent photovoltaics (STPV). Herein, an optimized TiO2/CdS double ETL strategy is embraced to counteract CdS absorption loss and mitigate the “deep cliff” conduction band off-set at TiO2/Sb2S3 heterojunction. Subsequently, an evolved chemical bath deposition strategy is proposed to deposit a uniform, faster, and comparatively more transparent Sb2S3 absorber layer. A systematic investigation of the absorber layer and in-depth analysis of carrier dynamics at heterojunctions advocate for the mitigation of charge accumulation and recombination at the interface, thereby pledging superior carrier transport. The advantageous gradient energy band alignment of TiO2/CdS/Sb2S3 realized a record PCE of 5.61 % for STPV. Furthermore, the semitransparent device is innovatively employed as a window, enabling transmitted light to be harvested by subsequent Sb2S3 solar cells. It maintains 18 % of its standalone PCE, thereby setting new benchmarks for its practical submissions.

Evolution laws of charge mobility of transformer oil and pressboard material with temperature and electric field strength

Abstract Charge mobility, a pivotal parameter in the space charge analysis model for oil-pressboard insulation of converter transformer under DC electric fields, predominantly relies on theoretical or empirical data. The prevalent omission of empirical, measurement-based evaluations, combined with the neglect of temperature and electric field intensity effects, introduces uncertainties in the calculation of electric field and charge dynamics. Grounded on the principles of the electroacoustic pulse technique for space charge measurements, our investigation established a temperature-controlled platform to determine the charge-charge mobility in oil and pressboard insulation mediums. Utilizing diverse oil-pressboard insulation systems, this study identified the temporal patterns of both positive and negative charge mobilities and unravelled the mechanisms modulated by temperature and electric field intensity: (1) with increasing temperatures (from 20 °C to 80 °C) and intensifying electric field strengths (from 5kV mm−1 to 25kV mm−1), the charge mobility within transformer oil and pressboard exhibits a rising trend. Notably, temperature variations exert the most significant influence, yielding amplifications up to 24.8 times. (2) The intrinsic properties of different transformer oils and oil-impregnated pressboards result in pronounced differences in their charge transport behaviors. Specifically, naphthenic-based oil demonstrates enhanced charge mobility relative to its paraffin-based counterpart. In contrast, transformer oils with higher kinematic viscosities exhibit diminished charge mobility compared to those with lower viscosities. (3) A linear relationship is observed between the oil absorption rate and electrical conductivity, aligning closely with the insulating pressboard’s charge mobility. The evaluation of electric field and interface charge dynamics in oil-pressboard insulation under both DC and polarity-reversed conditions revealed that the electric field decay in naphthenic-based oil is more rapid than in paraffin-based oils. Moreover, both the magnitude and rate of interface charge accumulation in naphthenic-based oils exceed those in paraffin-based variants, further validating the accuracy of our charge mobility measurements and ensuing analysis.

Ultra-high energy storage efficiency achieved through the construction of interlocking microstructure and excitation of depressor effects

Glass-ceramic capacitors struggle to balance high energy storage efficiency (η>90 %) and sufficient breakdown field strength (Eb), hindering their use in energy storage. Interface polarization, caused by the accumulation of free charge, reduces breakdown strength. We prepared glass-ceramic materials with varying contents of the glass phase using traditional melting techniques, adjusting the glass content to enhance an interlocking structure between the glass and crystal phases, reducing Interface polarization. Divalent metal oxide BaO in the glass stimulated a depressor effect, filling gaps and increasing resistivity. The optimal composition (x = 0.2) achieved a 95 % energy storage efficiency and an energy storage density of 4.4 J/cm3 at 680 kV/cm, while x = 0.25 reached an ultra-high energy storage efficiency of 99 %. Increasing glass content reduced activation energy for Interface polarization (Ei) from 1.27 eV to 1.08 eV. Samples with x = 0.2 exhibited low dielectric loss (∼0.005), high dielectric constant (∼142), ultra-high power density (∼52.8 MW/cm3), and ultra-fast discharge speed (∼26 ns), suggesting future potential for high-performance glass-ceramic materials.

Electrical Tree and Partial Discharge Characteristics of Silicone Rubber Under Mechanical Pressure

Silicone rubber (SIR) is a crucial insulating material in cable accessories, but it is also susceptible to faults. In practical applications, mechanical pressure from bending or shrinking can impact the degradation of SIR, necessitating the study of its electrical tree and partial discharge (PD) characteristics under such pressure. This work presents the construction of a test platform for electrical trees under varying pressures to observe their growth process. A high-frequency current transformer is used to measure PD patterns during tree growth, enabling analysis of the effect of PD on tree initiation and propagation under pressure. The experimental results demonstrate a significant decrease in tree inception probability and increase in PD inception voltage under pressure. The pressure also influences the tree structure and PD during the treeing process, where the longest tree with a branch-like structure appears under 800 kPa. The effect of pressure on electrical tree and PD characteristics can be attributed to changes in free volume, alterations in air pressure within the tree channels, and the affected charge accumulation.

Evaluation of degradation phenomena in the electric potential distribution inside organic light-emitting diodes by electron holography

Understanding the intrinsic degradation processes of organic light-emitting diodes is necessary to improve their lifetimes. This intrinsic degradation is typically caused by carrier injection at the interface between the hole transport layer (HTL) and the emissive layer (EML). However, revealing the charge behavior in this local region with a high spatial resolution remains challenging. Thus, this study employed electron holography, a transmission electron microscopy (TEM) technique, to measure the nanometer scale potential distribution inside an OLED composed of N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD) and tris-(8-hydroxyquinoline)aluminum (Alq3) that was degraded via continuous voltage application. The α-NPD and Alq3 functioned as the HTL and EML, respectively. The degraded OLED was found to exhibit several potential distributions, depending on the local positions from which the TEM samples were lifted out of the same bulk sample. The distributions included (i) formation of a potential valley at the α-NPD/Alq3 interface, (ii) disappearance of electric fields within the organic layers, and (iii) similar distribution to original before degradation. We suggest that the degradation was caused by charge accumulation, cationization of Alq3, and local failures. Thus, this study revealed the influence of electric degradation at the nanometer scale because of charge injection to the α-NPD/Alq3 interface. Electron holographic degradation analysis near the HTL/EML interface is expected to aid in the development of design guidelines for preventing device degradation and thus extend device lifetime.

Degeneration mechanism of 30 MeV and 100 MeV proton irradiation effects on 1.2 kV SiC MOSFETs

In this study, we evaluated and characterized the effects of various proton irradiation energies and fluences on the electrical characteristics of SiC MOSFETs using a proton accelerator. The devices under test (DUTs) were fabricated utilizing 1.2 kV SiC MOSFET processes. To assess the impact of total ionizing dose (TID) and displacement damage (DD) on SiC MOSFETs, the DUTs were exposed to protons irradiation at energies of 30 MeV and 100 MeV, under ambient temperature conditions. Additionally, we examined the radiation hardness of DUTs under varying proton fluences, including 1 × 1012 cm−2, 1 × 1013 cm−2, 5 × 1013 cm−2, and 1 × 1014 cm−2.The results demonstrate that the threshold voltage (Vth) of the irradiated devices exhibited a negative shift, attributable to radiation-induced positive oxide trapped charges. This negative shift in Vth, coupled with the accumulation of positive trapped charges in the field limiting ring (FLR) oxide, resulted in augmented output currents and diminished breakdown voltage (BV) values. A significant reduction in current, ranging from 70% to 99%, was observed in the DUT subjected to irradiation at of 30 MeV and 1 × 1014 cm−2, highlighting the influence of DD. Conversely, irradiation at 100 MeV primarily revealed TID effects, characterized by a negatively shifted Vth. The on-state current at a gate voltage of 10 V and a drain voltage of 5 V of the DUT with irradiation of 100 MeV and 1 × 1014 cm−2 was a higher than that of DUT without irradiation because of a reduction of Vth.

PH‐Tunable 3D Interconnected Network of Multiwalled Carbon Nanotubes /Polyacrylic Acid Hydrogel with Excellent Electromagnetic Radiation Shielding Capability

AbstractThe fabrication of durable and high anticorrosion hydrogel composite materials composed of multi‐walled carbon nanotubes (MCNTs) and crosslinked polyacrylic acid (PAA) for EMI shielding application is reported. The MCNTs contribute to the generation of 3D porous structures and enhance the mechanical properties of composite hydrogel. The 3D porous structure and high electrical conductivity inherited from ultrahigh electrically conductive MCNTs enable excellent EMI shielding properties with a total shielding efficiency EMI SE (SET) value of 32.8 dB (>99.9%) at only 3 wt% filler content of MCNTs. The MCNTs/PAA hydrogels also display superior EMI shielding performance under a strong acidic environment with SET > 99.99% while the 3D porous structure remained intact. The combination of electron–ion system in pH solution enriches the charge transfer and accumulation, enabling dipole orientation and polarization that are favorable for enhancing EMI attenuation. Moreover, the porous structure of MCNTs/PAA also contributes to partial trapping and dissipation of EM radiation energy via multiple scattering phenomena. This work thus paves the way toward applications of 3D hierarchical network materials for EMI shielding applications in both land and aqueous environments.

Surface chemistry characterization of AA2014 aluminum alloy powder through triboelectric charging

Traditional characterization techniques for powders primarily focus on bulk properties, often neglecting the critical role of surface chemistry variations that influence the performance in applications such as additive manufacturing. The method presented in this work addresses this gap by utilizing triboelectric charging concept to gain a comprehensive understanding of powder surface state under varying environmental conditions. In particular, the study investigates the detection of surface chemistry variations of AA2014 powder caused by an exposure to various relative humidity (RH) levels through a change in triboelectric charging behavior. The surface variations are analyzed in parallel with X-ray photoelectron spectroscopy (XPS). The findings reveal a direct correlation between elevated RH and increased hydroxide species content at the surface of the powder. The triboelectric charging experiments demonstrated a significant RH-dependent variations of charge accumulation, with higher humidity levels leading to reduced static charge buildup on the powder particles. The charge accumulation behavior in the powder was fitted with the compressed exponential relaxation model. The results showed that each surface chemical species exhibits a distinct correlation between charging rate and charge accumulation, confirming the effectiveness of the method to detect subtle variations in surface chemistry. The variations in the exponent of the fitted model were shown to be characteristics to the surface scale of the powder particles.