Electrode Structure Research Articles

Influence of nanocolumnar electrode geometry on electrochemical sensor performance

The concentration of glucose in sweat recently has been measured with high sensitivity, selectivity, and reproducibility by nanostructured NiO electrodes manufactured by the glancing angle deposition (GLAD) technique. The GLAD technique allows electrode morphological properties such as porosity and film thickness to be tightly controlled, providing ample opportunity to enhance the sensor performance. Currently, the selection of optimal GLAD parameters is determined experimentally by trial and error, at high costs in time and resources. Numerical simulation allows the effects of various parameters on sensor performance to be investigated at a much lower cost compared to experimental studies. In this work, a 2D reaction–diffusion model for the surface-catalyzed reactions in the nanostructured GLAD electrodes is developed, which are then solved using the finite element method. Parametric studies on the nanocolumn thickness and nanocolumn separation of the GLAD structures are then conducted to optimize GLAD-based electrode structures with different adsorption and catalytic rates. This research offers new guidance for rapidly designing highly effective sensors with higher sensitivity and lower limits of detection.

High performance Al anode for Al-air battery enabled by coordinating In and Sb additions with discharge parameters

High performance of Al anode for Al-air battery was achieved via coordinating minor In and Sb additions with discharge parameters. The electrochemical behaviors, discharge performance and surface structures of aluminum electrodes are systematically investigated to understand the alloying chemistry coordination of indium and antimony. The results show that coordinating indium and antimony can significantly activate the Al electrode without aggravating the hydrogen evolution. The assembled Al-air cell with Al-0.05In-0.05Sb electrode exhibits a desirable specific capacity and energy density of 2638 Ah·kg−1 and 3166 Wh·kg−1, respectively. Furthermore, antimony has better activating effect than indium, especially at discharge current density over 40 mA·cm−2. The activating mechanisms are discussed in detail.

Self-mixing anti-corrosive Zn-In powder composite anode with ultra-long lifespan for aqueous zinc-ion battery

Appropriate design of electrode structure and chemistry for Zn metal anode is important to the kinetics and electrochemical stability of Zn in aqueous batteries. Herein, In modified Zn powder electrode with carbon nanofibers as the stable electric conductive matrix provides an effective approach to simultaneously enhance reaction kinetics and inhibit H2 generation reactions. The designed Zn–In powder electrode presents self-mixing In distribution within the electrode during cycling thus enabling superior anti-corrasion and stable conductive network that significantly alters the Zn deposition behavior. Instant 3D Zn deposition with super-fast interfacial kinetics is achieved due to favorable Zn nucleation and growth as well as suppressed side reactions. Stable cycling of over 6300 h is achieved, which is 30-fold longer lifespan than Zn foil anode. Even at 5 mA cm−2, 5 mAh cm−2 (depth of discharge: 31.1%), Zn–In powder anode still presents stable cycling of over 500 h and low polarization voltage. Ultra-long cycle life of over 20,000 cycles can be achieved for full cells using Zn–In powder electrode paired with V2O5 cathode. Modified composite Zn powder electrode provides an effective and practical approach to address the electrochemical stability of Zn-based anodes in rechargeable cells.

A fast response time gas ionization chamber detector with a grid structure.

The time response characteristic of the detector is crucial in radiation imaging systems. Unfortunately, existing parallel plate ionization chamber detectors have a slow response time, which leads to blurry radiation images. To enhance imaging quality, the electrode structure of the detector must be modified to reduce the response time. This paper proposes a gas detector with a grid structure that has a fast response time. In this study, the detector electrostatic field was calculated using COMSOL, while Garfield++ was utilized to simulate the detector's output signal. To validate the accuracy of simulation results, the experimental ionization chamber was tested on the experimental platform. The results revealed that the average electric field intensity in the induced region of the grid detector was increased by at least 33%. The detector response time was reduced to 27% -38% of that of the parallel plate detector, while the sensitivity of the detector was only reduced by 10%. Therefore, incorporating a grid structure within the parallel plate detector can significantly improve the time response characteristics of the gas detector, providing an insight for future detector enhancements.

Synthesis of nanoporous solid polymer electrolyte AuNiCe/NC hydrogenation membrane electrode

In this study, using graphite fiber cloth as the support, gold-based solid polymer electrolyte (SPE) membrane electrodes were synthesized by high-vacuum ion beam sputtering, nitrogen doping of the support, combined electrochemical dealloying, and hot-pressing technology. The application of the SPE membrane electrode to couple hydrogen evolution and liquid organic hydrogen storage is of significant importance for sustainable hydrogen energy and efficient carbon dioxide conversion. Using various characterization techniques, we systematically analyzed the phase structure, surface morphology, porous structure, and electrocatalytic performance of the membrane electrode for the hydrogenation of cyclohexene. The results indicated that doping the carbonaceous support with nitrogen (NC), doping with cerium as catalyst promoter, and combined electrochemical dealloying can all enhance the activity of the catalyst. Cerium doping provides the catalyst with oxygen vacancies for accelerated electron transfer. After combined electrochemical dealloying, AuNiCe/NC formed a three-dimensional bicontinuous porous structure. The electrochemically active surface area increased by 23.94 times, the energy consumption of catalytic cyclohexene hydrogenation decreased by 35.7%, and current efficiency and the formation rate of cyclohexane increased by 54.9% and 29.4%, respectively.

Novel Binder with Cross-Linking Reconfiguration Functionality for Silicon Anodes of Lithium-Ion Batteries.

Silicon is expected to be used as a high theoretical capacity anode material in lithium-ion batteries with high energy densities. However, the huge volume change incurred when silicon de-embeds lithium ions, leading to destruction of the electrode structure and a rapid reduction in battery capacity. Although binders play a key role in maintaining the stability of the electrode structure, commonly used binders cannot withstand the large volume expansion of the silicon. To alleviate this problem, we propose a PGC cross-linking reconfiguration binder based on poly(acrylic acid) (PAA), gelatin (GN), and β-cyclodextrin (β-CD). Within PGC, PAA supports the main chain and provides a large number of carboxyl groups (-COOH), GN provides rich carboxyl and amide groups that can form a cross-linking network with PAA, and β-CD offers rich hydroxyl groups and a cone-shaped hollow ring structure that can alleviate stress accumulation in the polymer chain by forming a new dynamic cross-linking coordination conformation during stretching. In the half cell, the silicon negative prepared by the PGC binder exhibited a high specific capacity and capacity maintenance ratio, and the specific capacity of the silicon negative electrode prepared by the PGC binder is still 1809 mAh g-1 and the capacity maintenance ratio is 73.76% following 200 cycles at 2 A g-1 current density, indicating that PGC sufficiently maintains the silicon negative structure during the battery cycle. The PGC binder has a simple preparation method and good capacity retention ability, making it a potential reference for the further development of silicon negative electrodes.

Zn2SnO4@Ti ceramic film anode preparation by microarc oxidation for 2e– WOR degradation of unsymmetrical dimethylhydrazine (UDMH)

The main challenge facing the anodic electro-Fenton through the 2e– water oxidation reaction (WOR) for toxics degradation lies in the electrode's stability, because the anodic oxygen evolution (OER) generated O2 will inevitably exfoliate the electro-active components loaded on the electrode substrate. To address this point, two aspects need attention: 1) Identifying a catalyst that exhibits both excellent electrocatalytic activity and selectivity can improve the faradaic efficiency of hydrogen peroxide (H2O2); 2) Employing novel methods for fabricating highly stable electrodes, where active sites can be firmly coated. Consequently, this study utilized microarc oxidation (MAO) to prepare a ceramic film electrode Zn2SnO4@Ti at 300 V. Zn2SnO4 acts as an WOR electrocatalyst and further improved the generation of H2O2 for treating real wastewater containing Unsymmetrical Dimethylhydrazine (UDMH). From the perspective of characterization of electrode structure, Zn2SnO4@Ti forms a stable active coating, the electrochemical yield of H2O2 is high up to 78.4 μmol h−1 cm−2, and the selectivity of H2O2 is over 80% at 3.3 V vs. RHE, which can be fully applied to scenarios where it is inconvenient to transport H2O2 and need in-situ safe production. Additionally, the prepared electrodes exhibit significant stability, suitable for various applications, providing insightful preparation strategies and experiences for constructing highly stable anodes.

Selective electrooxidation of methane to formic acid by atomically dispersed CuOx and its induced Lewis acid sites on V2O5 in a tubular electrode

Electrocatalytic oxidation of methane (CH4) to value-added chemicals is an attractive approach to directly use natural gas. Herein, we synthesize CuOx/V2O5 composite catalysts in the hollow porous titanium tubes for selective electrooxidation of CH4 to formic acid (FA). The complexed Cu2+ ions achieve atomic-level dispersion on the V2O5 surface, and then transform into atomically dispersed CuOx during heat treatment, forming Cu-O-V bonds. Interestingly, atomically dispersed CuOx simultaneously induces the generation of abundant oxygen vacancies with strong Lewis acid activity. Moreover, the porous tubular electrode realizes the directional transmission of CH4 gas and create rich gas-liquid-solid three-phase reaction interfaces. The optimized active components and electrode structure achieve the Faradaic efficiency of FA up to 92 % at the current density of 14.4 mA cm−2. Mechanism research indicates that atomically dispersed CuOx and its induced Lewis acid sites promote the electrooxidation of H2O and the adsorption-activation of CH4 to produce *OH and *CH3.

Multiphase Reset Induced Reliable Dual-Mode Resistance Switching of the Ta/HfO2/RuO2 Memristor.

Higher functionality should be achieved within the device-level switching characteristics to secure the operational possibility of mixed-signal data processing within a memristive crossbar array. This work investigated electroforming-free Ta/HfO2/RuO2 resistive switching devices for digital- and analog-type applications through various structural and electrical analyses. The multiphase reset behavior, induced by the conducting filament modulation and oxygen vacancy generation (annihilation) in the HfO2 layer by interacting with the Ta (RuO2) electrode, was utilized for the switching mode change. Therefore, a single device can manifest stable binary switching between low and high resistance states for the digital mode and the precise 8-bit conductance modulation (256 resistance values) via an optimized pulse application for the analog mode. An in-depth analysis of the operation in different modes and comparing memristors with different electrode structures validate the proposed mechanism. The Ta/HfO2/RuO2 resistive switching device is feasible for a mixed-signal processable memristive array.

A composite electrode of stabilized lithium metal powder and lithiophilic Ag-coated Cu powder for lithium metal batteries

In this study, we fabricate a composite electrode of lithium metal powder (LMP) and Ag-coated Cu powder (Li/Cu@Ag) for lithium metal battery simply by Ag-coating on Cu powder through galvanic replacement and pelletizing their mixture. Due to the structure of the composite electrode and high surface area of LMP, local current density can be reduced. The lithiophilic Ag particles on the Cu powder lower lithium nucleation overpotential and enable uniform lithium plating. The Li/Cu@Ag electrode shows superior electrochemical performance with this synergetic effect and the reason for the improvement has been investigated. Specifically, a long lifespan of 400 h at a current density of 1 mA/cm2 is achieved with a Li||Li symmetric cell when using the Li/Cu@Ag electrode in a corrosive carbonate electrolyte. In addition, LiFePO4||Li/Cu@Ag cell shows excellent cycling stability and high-capacity retention (over 74 % after 400 cycles at 3C).

From 2D to 3D: WS2/MoS2 heterostructure in-situ anchored on Ti3C2Tx MXene with enhanced ion/electron migration and sodium storage at −20 ℃

Layered transition metal dichalcogenides (TMDs), featuring robust electrochemical activity, high capacity, and large interlayer spacing, have attracted widespread interest in research on sodium storage. However, the limitations in dynamics and structure expansion lead to degraded cycling life and rate capability, especially in cold climate with low temperatures. Generally, heterostructure engineering, combined with conductive matrix, gives a promise towards enhancing electronic transportation, accelerating ionic diffusion, and alleviating large structure change of layered TMDs upon sodium storage. Herein, a robust WS2/MoS2 heterostructure, rendering ultrafast charge transfer, is presented, and further hybridization with layered conductive Ti3C2Tx MXene results in three-dimensional crosslinked nanoarchitectonics, leading to electrochemical performance at 25 °C and -20 °C, which shows only 0.03 % capacity degradation per cycle up to 2800 cycles at 2.0 A g−1 (25 °C). Strikingly, the desired WS2/MoS2/Ti3C2Tx exhibits a high capacity of 293.7 mAh g−1 (100 cycles) at 0.1 A g−1 even at −20 °C. Besides, density functional theory calculations further manifest the decreased sodium diffusion barrier and facilitated charge-transfer dynamics in the designed heterostructure with Ti3C2Tx. More importantly, this work not only represents the correlation between structure and performance for target electrode, but also provides a deep insight for the rational design of heterostructure/Ti3C2Tx MXene for next-generation high-performance electrode materials.

Effect of carbon material and surfactant on ink property and resulting surface cracks of fuel-cell microporous layers

Ensuring the consistency of electrode structure in proton exchange membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer (MPL). The first thing is to evaluate the homogeneity of MPL with cracks quantitatively. This paper proposes the homogeneity index of a full-scale MPL with an area of 50 cm2, which has yet to be reported in the literature to our knowledge. Besides, the effects of the carbon material and surfactant on the ink and resulting MPL structure have been studied. The ink with a high network development degree produces MPL with low crack density, but the ink with high PDI produces MPL with low crack homogeneity. The polarity of the surfactant and the non-polarity of PTFE are not mutually soluble, resulting in the heterogeneous PTFE distribution. The findings of this study provide guidelines for MPL fabrication.

Large-scale production of graphene encapsulated silicon nanospheres as flexible anodes for lithium ion batteries

Silicon (Si) is regarded as the most promising anode candidate for the next high energy density lithium ion batteries (LIBs) owing to its highest theoretical specific capacity and low lithiation potential. However, the practical application of Si-based materials is severely limited due to their enormous volume expansion, which leads to the breakdown of the electrode structure and shortens the cycle life. Herein, we successfully fabricated a free-standing graphene encapsulated silicon nanospheres (Si/rGO) film through homogenizing nano-Si in the lyotropic liquid crystallinity of graphene oxide (GO), followed by coating on the PET substrate and hot pressing technology. For the first time during the preparation process, the dispersion of nano-Si in deionized water was quantitatively characterized through real-time measurements of zeta potential and average particle size. Benefiting from the highly ordered layer-to-layer stacking and dense framework, the as-prepared Si/rGO film shows a high initial discharge capacity of 1727.2 mAh/g at 200 mA/g and superior cycling stability (1024.2 mAh/g over 200 cycles). This straightforward and easy-to-implement method can be used for industrial-scale production through continuous feeding.

Rational Design of Organic Electrocatalysts for Hydrogen and Oxygen Electrocatalytic Applications.

Efficient electrocatalysts are pivotal for advancing green energy conversion technologies. Organic electrocatalysts, as cost-effective alternatives to noble-metal benchmarks, have garnered attention. However, the understanding of the relationships between their properties and electrocatalytic activities remains ambiguous. Plenty of research articles regarding low-cost organic electrocatalysts started to gain momentum in 2010 and have been flourishing recently though, a review article for both entry-level and experienced researchers in this field is still lacking. This review underscores the urgent need to elucidate the structure-activity relationship and design suitable electrode structures, leveraging the unique features of organic electrocatalysts like controllability and compatibility for real-world applications. Organic electrocatalysts are classified into four groups: small molecules, oligomers, polymers, and frameworks, with specific structural and physicochemical properties serving as activity indicators. To unlock the full potential of organic electrocatalysts, five strategies are discussed: integrated structures, surface property modulation, membrane technologies, electrolyte affinity regulation, and addition of anticorrosion species, all aimed at enhancing charge efficiency, mass transfer, and long-term stability during electrocatalytic reactions. The review offers a comprehensive overview of the current state of organic electrocatalysts and their practical applications, bridging the understanding gap and paving the way for future developments of more efficient green energy conversion technologies.

Passivation strategies for enhancing sensitivity and repeatability of microelectrode electrochemical sensors

The sensitivity and repeatability are crucial for the practical application of electrochemical sensors. Many studies have focused on sensing materials and electrode structure to enhance sensitivity and repeatability rather than insulating layers. In this paper, polyaniline (PANI) microelectrode arrays were prepared to explore the influence of the insulating layer on sensitivity and repeatability of electrochemical sensors. The effects of different types of insulating layers, the sizes of the electrodes, and the thicknesses of the insulating layers were studied by experiment and simulation. The research findings indicated that the kind of organic insulating layers (Polyimide (PI) and SU-8) did not have a significant effect on the performance of the sensors. However, as the electrode area increased, the PANI film deposited on the electrode exhibited improved uniformity and density, leading to significant improvements in sensitivity and repeatability of the sensors. Additionally, the thickness of the insulating layer also had a significant impact on the performance of the device. The microelectrode with thinner insulating layers exhibited improved performance in sensitivity, repeatability and signal-to-noise ratio. The research findings indicated that increasing the electrode size and reducing the thickness of the insulating layer led to a more uniform and dense PANI film, resulting in an array electrode that exhibits excellent performance and remarkable repeatability.

Enhancing sodium storage through tri-phase heterointerfaces in Co–Fe–MoSe2@N-doped carbon nanocubes with self-generated rich phase boundaries

Transition metal selenides have received considerable research interest as conversion-type anodes owing to their impressive theoretical specific capacity and high conversion reaction efficiency. Nevertheless, the practical application of these materials is constrained by the low intrinsic conductivity and substantial volume changes during repetitive cycles, which leads to electrode structure deterioration, reduced cyclic stability, and poor rate performance. Herein, a trimetallic selenide Co–Fe–MoSe2@N-doped carbon composite with self-generated abundant phase boundaries was successfully designed using a straightforward co-precipitation method followed by a selenization process. The hybrid material, with its inherent self-generated electric field at the heterojunction surfaces, significantly improves the reaction kinetics. Moreover, the experimental results, complemented with density functional theory calculations, also illustrate that the enriched heterostructure boundaries provide ample electrochemical reaction active sites, thereby boosting charge transfer efficiency and mitigating the Na+ diffusion barrier. Remarkably, the composite exhibits excellent cyclic performance, achieving 322.4 mAh g−1 at 5 A g−1 after 1000 cycles, surpassing the performance of various other metal selenides. This innovative approach of creating abundant phase boundaries through the heterostructured ternary metal selenide presents a promising avenue for advancing the practical application of conversion-type anode materials.

Computational analysis of electrode structure and configuration for efficient and localized neural stimulation.

Neuromodulation technique using electric stimulation is widely applied in neural prosthesis, therapy, and neuroscience research. Various stimulation techniques have been developed to enhance stimulation efficiency and to precisely target the specific area of the brain which involves optimizing the geometry and the configuration of the electrode, stimulation pulse type and shapes, and electrode materials. Although the effects of electrode shape, size, and configuration on the performance of neural stimulation have individually been characterized, to date, there is no integrative investigation of how this factor affects neural stimulation. In this study, we computationally modeled the various types of electrodes with varying shapes, sizes, and configurations and simulated the electric field to calculate the activation function. The electrode geometry is then integratively assessed in terms of stimulation efficiency and stimulation focality. We found that stimulation efficiency is enhanced by making the electrode sharper and smaller. A center-to-vertex distance exceeding 100µm shows enhanced stimulation efficiency in the bipolar configuration. Additionally, the separation distance of less than 1mm between the reference and stimulation electrodes exhibits higher stimulation efficiency compared to the monopolar configuration. The region of neurons to be stimulated can also be modified. We found that sharper electrodes can locally activate the neuron. In most cases, except for the rectangular electrode shape with a center-to-vertex distance smaller than 100µm, the bipolar electrode configuration can locally stimulate neurons as opposed to the monopolar configuration. These findings shed light on the optimal selection of neural electrodes depending on the target applications.

Boosting the zinc-ion storage ability of MnO2 cathode by depositing oxygen-deficient CuOx layer

MnO2 is subject to intensified examination as the foremost promising cathode material for aqueous zinc-ion batteries (AZIBs). However, achieving high stability and fast kinetics simultaneously is extremely challenging. Herein, an α-MnO2 cathode has been successfully engineered with an oxygen-deficient CuOx coating utilizing active screen plasma technology. The CuOx coating, abundant in oxygen vacancies (OVs), promotes the dissociation of adsorbed water molecules and the ensuing formation of hydroxyl groups, thereby bestowing several benefits on the electrochemical performance. At the atomic level, the OVs serve to markedly fortify electron transport and expedite charge transfer. At the molecular level, the introduction of negatively-charged hydroxyl groups augments surface wettability, which in turn improves the Zn2+ diffusion kinetics and promotes the aggregation of a higher concentration of Zn2+ in the vicinity of the cathode. Furthermore, the CuOx layer is instrumental in preserving the integrity of the electrode structure by inhibiting the Mn dissolution. The integration of these multifaceted advantages culminates in a cathode that manifests a remarkable specific capacity (345 mA h g-1 at 0.2 A g-1) and exemplary cyclic stability (240 mA h g−1 after 1200 cycles at 0.5 A g−1). Conclusively, pouch cells with a large area (5 × 7 cm2) have been fabricated, demonstrating extraordinary flexibility and practical utility.

A computational study of rectification behavior of doped α-graphyne nanotubes

α-graphyne is a carbon nanosheet with sp and sp2 hybridization. This sheet is a hexagonal semi-metal like graphene. In this paper, we roll α-graphyne sheet and build zigzag nanotubes with three different size (n = 5, 6, 7). We used density functional tight binding (DFTB) to compute the band structures of nanotubes. The results show that the gap energies for n = 5, 6, 7 are about 0.648, 0.115, 0.309 eV, respectively. We add impurity atoms such as boron (B) and nitrogen (N) to nanotube. We found that the band gap energy of these doped nanotubes decrease. In addition, the structures that carbon atoms with sp2 hybridization replaced by impurity atoms are more stable. For the first time, we build two doped nanotube diodes at low (M1 model) and high (M2 model) concentration and compute current-voltage (I–V) curves with non-equilibrium Green's functions (NEGF). The I–V curves of doped nanotubes show non-linear asymmetric behavior. Form I–V curves, we compute rectification ratio and negative differential resistance (NDR). The low doped zigzag nanotube with n = 5 (M1 model) shows the highest rectification ratio (about 12.236 × 104) at 0.3 V. In addition, the rectification ratio of this diode at high concentration (M2) is about 3.67 × 103 at 0.6 V. The I–V curve of M2 model illustrations a notably negative differential resistance (NDR) at reverse bias. The ratio of current at peak to current at valley is about 26.83. To describe the I–V curves, we used transmission spectrum, the band structures of electrodes and the density of states (DOS) of central scattering region. In general, transition occurs when the energy levels of three regions (left electrode, scattering and right electrode) overlap.

Thermodynamic Origin-Based In Situ Electrochemical Construction of Reversible p-n Heterojunctions for Optimal Stability in Potassium Ion Storage.

Heterojunctions in electrode materials offer diverse improvements during the cycling process of energy storage devices, such as volume change buffering, accelerated ion/electron transfer, and better electrode structure integrity, however, obtaining optimal heterostructures with nanoscale domains remains challenging within constrained materials. A novel in situ electrochemical method is introduced to develop a reversible CuSe/PSe p-n heterojunction (CPS-h) from Cu3 PSe4 as starting material, targeting maximum stability in potassium ion storage. The CPS-h formation is thermodynamically favorable, characterized by its superior reversibility, minimized diffusion barriers, and enhanced conversion post K+ interaction. Within CPS-h, the synergy of the intrinsic electric field and P-Se bonds enhance electrode stability, effectively countering the Se shuttling phenomenon. The specific orientation between CuSe and PSe leads to a 35° lattice mismatch generates large space at the interface, promoting efficient K ion migration. The Mott-Schottky analysis validates the consistent reversibility of CPS-h, underlining its electrochemical reliability. Notably, CPS-h demonstrates a negligible 0.005% capacity reduction over 10,000 half-cell cycles and remains stable through 2,000 and 4,000 cycles in full cells and hybrid capacitors, respectively. This study emphasizes the pivotal role of electrochemical dynamics in formulating highly stable p-n heterojunctions, representing a significant advancement in potassium-ion battery (PIB) electrode engineering.