Electrode Contact Resistance Research Articles

Effect of Silver Powder Microstructure on the Performance of Silver Powder and Front-Side Solar Silver Paste.

Silver powder, as the primary component of solar silver paste, significantly influences various aspects of the paste's performance, including printing, sintering, and conductivity. This study reveals that, beyond the shape and size of the silver powders, their microstructure is a critical factor influencing the performance of both silver powders and silver pastes in solar cell applications. The growth process leads to the formation of either polycrystalline aggregated silver powder or crystal growth silver powder. Analyzing the performance characteristics of these different microstructures provides guidance for selecting silver powders for silver pastes at different sintering temperatures. Polycrystalline aggregated silver powder exhibits higher sintering activity, with a sintering initiation temperature around 450 °C. The resulting silver paste, sintered at 750 °C, demonstrates a low sheet resistance of 2.92 mΩ/sq and high adhesion of 2.13 N. This silver powder is suitable for formulating silver pastes with lower sintering temperatures. The solar cell electrode grid lines have a high aspect ratio of 0.37, showing poor uniformity. However, due to the high sintering activity of the silver powder, the glass layer dissolves and deposits more silver, resulting in excellent conductivity, a low contact resistance of the silver electrode, a low series resistance of the solar cell of 1.23 mΩ, and a high photoelectric conversion efficiency of 23.16%. Crystal growth silver powder exhibits the highest tap density of 5.52 g/cm3. The corresponding silver paste shows improved densification upon sintering, especially at 840 °C, yielding a sheet resistance of 2.56 mΩ/sq and adhesion of 3.05 N. This silver powder is suitable for formulating silver pastes with higher sintering temperatures. The solar cell electrode grid lines are uniform with the highest aspect ratio of 0.40, resulting in a smaller shading area, a high fill factor of 81.59%, and a slightly higher photoelectric conversion efficiency of 23.17% compared to the polycrystalline aggregated silver powder.

Approaches to Reduce the Operating Temperature of Protonic Ceramic Electrochemical Cells to

Protonic ceramic electrochemical cells (PCECs) have been developed as a promising technology for efficient power generation and hydrogen production via steam electrolysis. However, the current operating temperature range of 450-600°C still limits their widespread application and adoption in ceramic electrochemical cell technology. To address this issue, lowering the operating temperature range to 250-450°C has been proposed, which would expand the range of materials for building PCEC systems and reduce their cost. In this presentation, I will discuss our group's series of approaches to redesign PCECs. These approaches include using readily fabricated single-grain thick, chemically homogeneous, and robust electrolytes, as well as newly developed positive electrode materials. Our innovations have simultaneously reduced the electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, while also improving durability. As a result, we have set several new records of using PCECs for both power generation and renewable hydrogen production.

High Performance Protonic Ceramic Electrochemical Cells Operating at

Protonic ceramic electrochemical cells (PCECs) can operate in both fuel cell and steam electrolysis modes for efficient power generation and green hydrogen production. Thanks to the low activation energy of proton conduction, PCECs are uniquely capable of operating at temperatures below 600°C. Although some intriguing demonstrations of intermediate-temperature (500-600°C) PCECs (IT-PCECs) have been made in the last decade, the operating temperature of PCECs is still too high to revolutionize ceramic electrochemical cell technology, which is ascribed to the high ohmic resistance and positive electrode polarization resistance. It has been also recognized the electrode polarization resistance dominates the total resistance at <500°C. These challenges suggest both the electrolyte and positive electrode should be redesigned to lower the PCEC operating temperature.In this work, we present two main approaches to reducing electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, which enables PCECs operation at <500°C. First, by using the ultrasonic spray coating system to coat the electrolyte layer on a negative electrode substrate with low Ba-deficiency, a bamboo-structured, ultrathin, and chemically homogeneous electrolyte can be fabricated. Second, a newly in-situ formed composite positive electrode was developed, which enhances the interfacial bonding between the positive electrode and electrolyte, further reducing ASRo , while improving both bulk oxygen-ion diffusion coefficient and surface oxygen exchange coefficientat <500°C.The newly developed LT-PCECs attain outstanding power densities in fuel cell mode (as high as 0.77 W cm-2 at 450°C), and exceptional current densities in electrolysis mode (over -1.28 A cm-2 at 1.4 V and 450°C). Furthermore, reducing the temperature does not sacrifice the fuel flexibility of these ceramic fuel cells. We demonstrated that the PCECs can directly utilize ammonia and methane for power generation at <500°C. Exceptional durability has been also demonstrated in both fuel cell and electrolysis modes at <500°C.These results further emphasize that through the PCEC scalable manufacturing processes and novel positive electrode materials presented here, PCECs can be employed for power generation and H2 production at <500°C, thereby transforming the architectures and removing previous operational constraints of ceramic electrochemical cells for scaled operation. PCECs can therefore be considered as one part of the growing hydrogen economy, while leveraging the existing fossil fuel infrastructure and achieving higher energy efficiency and lower CO2 emissions.

A unique redox active ion-electron conductor enabled 5C fast-charging graphite anode for lithium-ion batteries

Enhancing the charging rate of lithium-ion batteries is poised to accelerate the rapid promotion of electric vehicles, decrease greenhouse gas emissions, and reduce the energy crisis worldwide. However, during the fast-charging process, the slow transport of ions and electrons in the graphite anode makes it challenging to achieve a high capacity and good reversible capability. A multifunctional binder that can realize redox reactions with excellent ionic/electronic conduction is reported herein. The electronic/ionic conductance composition is analyzed for the Li-SPODs binder. Thereinto, the total conductivity of Li-SPODs (0.82 mS cm−1) is divided into three parts: lithium sulfonate ionic conductivity (0.54 mS cm−1) in the eigenstate state, electronic conductivity (1.7 × 10−4 mS cm−1) in the doped state, and doping lithium ionic conductivity(0.27 mS cm−1) in the doped state. The conductivity splitting of Li-SPODs binder can reveal the distinct effect of both conductances on graphite electrodes. Benefiting from the high conductive Li-SPODs binder, the contact resistance of the graphite electrode decreased by 54.4 % compared to the carboxymethyl cellulose/butadiene styrene rubber (CMC/SBR) binder. Meanwhile, the full cell based on the lithium iron phosphate cathode and graphite anode (the areal capacity of 2 mAh cm−2) exhibits an extraordinary capacity and outstanding cycling stability (0.04 % capacity decay per cycle during 500 cycles) even at 5C. More importantly, this novel design strategy provides new insight into preparing a multifunctional binder for fast-charging electrodes with high power and energy.

High Performance GaN-Based Ultraviolet Photodetector via Te/Metal Electrodes.

Photodetectors (PDs) based on two-dimensional (2D) materials have promising applications in modern electronics and optoelectronics. However, due to the intralayer recombination of the photogenerated carriers and the inevitable surface trapping stages of the constituent layers, the PDs based on 2D materials usually suffer from low responsivity and poor response speed. In this work, a distinguished GaN-based photodetector is constructed on a sapphire substrate with Te/metal electrodes. Due to the metal-like properties of tellurium, the band bending at the interface between Te and GaN generates an inherent electric field, which greatly reduces the carrier transport barrier and promotes the photoresponse of GaN. This Te-enhanced GaN-based PD show a promising responsivity of 4951 mA/W, detectivity of 1.79 × 1014 Jones, and an external quantum efficiency of 169%. In addition, owing to the collection efficiency of carriers by this Te-GaN interface, the response time is greatly decreased compared with pure GaN PDs. This high performance can be attributed to the fact that Te reduces the contact resistance of the metal electrode Au/Ti to GaN, forming an ohmic-like contact and promoting the photoresponse of GaN. This work greatly extends the application potential of GaN in the field of high-performance photodetectors and puts forward a new way of developing high performance photodetectors.

Investigating the Electromechanical Sensitivity of Carbon-Nanotube-Coated Microfibers.

The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30-60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5-30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors.

Titanium Nitride Nanorods Array-Decorated Graphite Felt as Highly Efficient Negative Electrode for Iron-Chromium Redox Flow Battery.

Iron-chromium redox flow batteries have attracted widespread attention because of their low cost. However, the performance of these batteries is still lower than that of vanadium redox flow batteries due to the poor electrochemical activity of Cr3+ /Cr2+ redox couples on graphite felt electrodes. Herein, binder-free TiN nanorods array-decorated 3D graphite felt composite electrode-is demonstrated. The dendrite-like TiN nanorods array increases the specific surface area of the electrode. The nitrogen and oxygen elements on the surface provide more adsorption sites and electrochemically active sites for Cr3+ /Cr2+ . The contact resistance of the composite electrode is effectively reduced and its homogeneity and stability are improved by avoiding the use of a binder and mixing process. A battery prepared using the TiN nanorods array-decorated 3D graphite felt electrode has enabled the maximum power density to be 427 mW·cm-2 , which is 74.0% higher than a battery assembled with TiN nanoparticles bonded to graphite felt. At a current density of 80 mA·cm-2 , the TiN nanorods battery exhibits the highest coulombic efficiency of 93.0%, voltage efficiency of 90.4%, and energy efficiency of 84.1%. Moreover, the battery efficiency and composite electrode structure remains stable during a redox flow battery cycle test.

Determination of the tortuosity and contact resistances in thick graphite anodes via electrochemical impedance spectroscopy

Developing thick electrodes is vital to achieving the requirement of next-generation of lithium-ion batteries (LIBs) with high energy density. However, the thick electrode suffers from severe polarization, which makes the investigation of its internal impedance and dynamics crucial. Herein, the three types of resistances (ionic transmission resistance, ohmic resistance, and contact resistance) dominated by the composition and microstructure of thick graphite anodes are systematically explored by utilizing electrochemical impedance spectroscopy measurements on the symmetrical cell. Firstly, the relationship between tortuosity (τ) calculated from ionic transmission resistance and porosity (ε) of electrodes is studied, which conforms to the deformed Bruggeman equation (τ=fε−α). And the effect of different morphologies of mesocarbon microbeads (MCMB) and flake graphite (FG) on tortuosity is analyzed, then the mechanism of improving the dynamics of thick graphite anodes through constructing vertical electrolyte channels is clarified. Secondly, the ohmic resistance produced by electronic transmission and by ionic transmission are quantitatively characterized separately. Thirdly, the factors affecting the contact resistance of electrodes are also discussed in detail, revealing that the contact area and electronic resistivity govern the contact resistance. This work contributes to preparing the thick electrodes with low resistances.

Poly(3-hexylthiophene)-Based Organic Thin-Film Transistors with Virgin Graphene Oxide as an Interfacial Layer.

We fabricated and characterized poly(3-hexylthiophene-2, 5-diyl) (P3HT)-based Organic thin-film transistors (OTFTs) containing an interfacial layer made from virgin Graphene Oxide (GO). Previously chemically modified GO and reduced GO (RGO) were used to modify OTFT interfaces. However, to our knowledge, there are no published reports where virgin GO was employed for this purpose. For the sake of comparison, OTFTs without modification were also manufactured. The structure of the devices was based on the Bottom Gate Bottom Contact (BGBC) OTFT. We show that the presence of the GO monolayer on the surface of the OTFT's SiO2 dielectric and Au electrode surface noticeably improves their performance. Namely, the drain current and the field-effect mobility of OTFTs are considerably increased by modifying the interfaces with the virgin GO deposition. It is suggested that the observed enhancement is connected to a decrease in the contact resistance of GO-covered Au electrodes and the particular structure of the P3HT layer on the dielectric surface. Namely, we found a specific morphology of the organic semiconductor P3HT layer, where larger interconnecting polymer grains are formed on the surface of the GO-modified SiO2. It is proposed that this specific morphology is formed due to the increased mobility of the P3HT segments near the solid boundary, which was confirmed via Differential Scanning Calorimetry measurements.

Large zero bias peaks and dips in a four-terminal thin InAs-Al nanowire device

We report electron transport studies of a thin InAs-Al hybrid semiconductor-superconductor nanowire device using a four-terminal design. Compared to previous works, thinner InAs nanowire (diameter less than 40 nm) is expected to reach fewer sub-band regime. The four-terminal device design excludes electrode contact resistance, an unknown value which has inevitably affected previously reported device conductance. Using tunneling spectroscopy, we find large zero-bias peaks (ZBPs) in differential conductance on the order of $2e^2/h$. Investigating the ZBP evolution by sweeping various gate voltages and magnetic field, we find a transition between a zero-bias peak and a zero-bias dip while the zero-bias conductance sticks close to $2e^2/h$. We discuss a topologically trivial interpretation involving disorder, smooth potential variation and quasi-Majorana zero modes.

Effect of Electrode Contact Resistance on Electrical Field Measurements

Effect of Electrode Contact Resistance on Electrical Field Measurements

Key factors affecting contact resistance in coplanar organic thin-film transistors

We present a comprehensive numerical analysis of contact resistance in coplanar organic thin-film transistors. A large number of hole-transporting organic transistors are investigated through two-dimensional finite-element simulation, by deliberately changing the channel length, source/drain electrode thickness, and hole-injection energy barrier heights. Gate-field-dependent terminal contact resistances of these devices are fully estimated and electrostatic distributions inside the organic semiconductor film are visualized for the understanding of physical mechanisms. It is found that the relationship between source/drain electrode thickness and contact resistance does not follow any simple trend and is also strongly associated with the injection energy barrier. Moreover, the origin of negative contact resistance in organic transistors featuring a minimal charge-injection barrier is elaborated. Finally, a direct impact of the semiconductor charge-carrier mobility on contact resistance is addressed, revealing a linear dependence of contact resistance on inverse mobility over a broad parameter range.

High Mass Loading, Binder-Free Carbon Nanotubes Matrix on Ni Foam for High Areal Capacitance Supercapacitors

Supercapacitors (SCs) have excellent merits of high power density, rapid charge/discharge rates, and long cycle stability [1]. However, their relatively low energy density hampers the practical applications [2]. In general, the energy density of SCs strongly depends on their intrinsic properties of active materials and related inactive indispensable components such as current collector, electrolyte, separator, tabs, and package. Usually, the weight of these inactive components can reach around 50~70% of total mass [3]. In most literature, active materials are evaluated at a relatively low areal mass loading (<5 mg/cm2) to pursue the maximum performance by fully exposing the active sites and shortening the charge and ion transport pathways as much as possible [4]. However, these evaluation methods show limited guidance to design commercial SCs based on such active materials. Low areal mass loading of active materials results in excessive utilization of the current collector. In general, the density of current collector (Al foil: 2.7 g/cm3) is several times larger than that of active materials (compacted density of activated carbons (ACs): 0.4~0.6 g/cm3), hindering the development for high-energy, lightweight and low-cost SCs [5]. ACs are the most promising material for commercial SCs owing to their high surface area, robust electrical conductivity, good chemical stability, and low cost. In commercial SCs, the ACs electrode is fabricated with an optimized mass loading of >10 mg/cm2 and a thickness of 100-200 µm [6]. However, the capacitance of SCs is not linear with the mass loading or electrode thickness. Simultaneously, the increased mass loading or electrode thickness results in inferior performances due to the decreased accessible surface area, enlarged electrical resistance, prolonged ion transport channels, and poor electrolyte wetting. Therefore, it is still needed to design a novel active materials-current collector system with high mass loading for the practical applications of SCs.In this work, we report using carbon nanotubes (CNTs) matrix with high mass loading embedded in Ni foam (NF) to develop high areal capacitance electrodes for SCs. The CNTs matrix was directly grown on the NF (the size of 1×1×0.05 cm) by CVD method at the temperature of 650-800 °C without any other catalysts. Acetylene (C2H2) was used as the carbon source at a flow rate of 5 sccm, and the balance gases were H2 and Ar with flow rates of 100 and 300 sccm, respectively. The mass loading of the CNTs matrix reaches up to 60 mg/cm2. Figure 1 (a) and (c) show the top and bottom surface morphologies of CNT-NF electrode. Two electrodes with the mass loading of 60.2 and 59.5 mg/cm2 were packaged into a coin cell for evaluating the performances. The glass fiber and 1mol/L MeEt3NB4 in Acetonitrile were used as the separator and electrolyte, respectively.Figure 2 (a) shows the cyclic voltammetry (CV) of SCs at the scan rates of 100 mV/s and 2 mV/s. The calculated capacitance of SCs is 1214 mF. Given that, the corresponding areal, gravimetric, and volumetric capacitance of CNTs matrix active material are calculated as 2.428 F/cm2, 40.4 F/g, and 48.6 F/cm3, respectively. Figure b (a) presents the electrochemical impedance spectroscopy (EIS) of SCs in the frequency range from 100 kHz to 100 mHz. The impedance at high frequency is the contact resistance between the active material and current collector, indicating that the contact resistance of the CNT-NF electrode is 0.187 Ω·cm2 because the CNTs matrix grows on NF directly without using any binders. After 600 cycles, the capacitance of SCs reaches 1442 mF by an increase of 18.8% and because CNTs matrix has a poor wetting ability in the organic solvents, as shown in Figure 2(c). In figure 2(d), the corresponding contact resistance is 0.205 Ω·cm2 after 600 cycles, showing CNT-NF electrode has excellent rate stability.In conclusion, we have successfully used Ni foam as the scaffold structure and current collector for growing high mass loading CNTs matrix as the active material for high areal capacitance application. Importantly, this 3D CNTs matrix electrode system could offer a promising strategy to simultaneously improve the areal capacitance and energy density (gravimetric or volumetric) of SCs.

Quantification of Schottky barrier height and contact resistance of a Au electrode on multilayer WSe2

Quantification of Schottky barrier height and contact resistance of a Au electrode on multilayer WSe2

The Unusual Dielectric Response of Large Area Molecular Tunnel Junctions Probed with Impedance Spectroscopy

AbstractThe dielectric behavior of organic materials at molecular dimensions can be vastly different than their bulk counterparts and therefore it is important to investigate and control the dielectric response of molecular‐scale materials for a large variety of applications. Large‐area molecular junctions are explored to study the charge transport mechanisms with unprecedented detail and to demonstrate novel functionalities. Therefore, large‐area molecular junctions are, in principle, a promising platform to study the dielectric effects at the molecular scale. This review summarizes recent progress on the measurements and understanding of the dielectric behavior of molecular systems and how they behave differently from their bulk properties. This review introduces, briefly, the concepts of impedance spectroscopy (IS) and how this technique can be applied to study the dielectric response of solid‐state large‐area molecular junctions. This analysis gives new insights in the factors that determine the dielectric constant of monolayers (including collective electrostatic effects and how the dielectric constant increases with monolayer thickness), how IS gives new insights into the role of defects, and the factors that contribute to the molecule–electrode contact resistance. This review ends with an outlook highlighting interesting future directions.

Electrochemical characteristics of grain boundaries in gadolinium and aluminum co-doped ceria and ceria-alumina composites

The influence of 1, 2, 4 and 10 cat.% Al2O3 addition on the electrochemical characteristics of commercially available 10 cat.% Gd-doped ceria and a 1:1 cat.% mixture of CeO2:Al2O3 were evaluated in our study. Analysis of the electronic conductivity and polarization-relaxation behavior of the samples showed that an Ohmic contribution to the total electronic resistance cannot only be attributed to the electrode contact resistance but is a combined contribution from the electrode interface and decreased pO2 dependence of the grain boundary resistivity of the material. The average electrical potential barrier at the grain boundaries was calculated from impedance spectroscopy data at 50–300 °C. Kelvin probe force microscopy (KPFM) measurements were used to analyze the local Volta potential distribution at the grain boundaries of pure Ce0.9Gd0.1O1.95 and of samples with 4 and 10 cat.% Al addition at room temperature. KPFM measurements showed clear evidence for an increased Volta potential difference between bulk and grain boundary cores and for a considerable broadening of the Volta potential gradient at the grain boundaries with increasing Al concentration.

The applicability of the Wenner method for resistivity measurement of concrete in atmospheric conditions

The Wenner probe method is an established, non-destructive method for the measurement of concrete resistivity. When testing is carried out for concrete in atmospheric conditions, electrode contact resistance is a major factor which can result in a measurement error, greatly influencing the accuracy and replicability of resistivity measurements. To achieve sufficient electrolytic contact between the Wenner Probe and concrete, surface wetting is commonly used. This is problematic as concrete resistivity is sensitive to changes in moisture content, resulting in variations in resistivity measurements. No resistivity testing Standards have been developed to achieve sufficient electrode contact without water saturation. This paper presents an innovative and practical method utilising existing Wenner Probe equipment, capable of eliminating and/or minimising the influence of these factors in atmospheric conditions. The new method minimises the impact of concrete surface variability by establishing an alternative, reliable electrolytic contact between the Wenner equipment probes and concrete.

Sensorized tissue analogues enabled by a 3D-printed conductive organogel

State-of-the-art tissue analogues used in high-fidelity, hands-on medical simulation modules can deliver lifelike appearance and feel but lack the capability to provide quantified, real-time assessment of practitioner performance. The monolithic fabrication of hybrid printed/textile piezoresistive strain sensors in a realistic Y/V plasty suture training pad is demonstrated. A class of 3D-printable organogels comprised of inexpensive and nonhazardous feedstocks is used as the sensing medium, and conductive composite threads are used as the electrodes. These organogels are comprised of a glycol-based deep-eutectic solvent (DES) serving as the ionic conductor and 3-trimethoxysilylmethacrylate-capped fumed silica particles serving as the gelating agent. Rheology measurements reveal the influence of fumed silica particle capping group on the mixture rheology. Freestanding strain sensors demonstrate a maximum strain amplitude of 300%, negligible signal drift, a monotonic sensor response, a low degree of hysteresis, and excellent cyclic stability. The increased contact resistance of the conductive thread electrodes used in place of wire electrodes do not make a significant impact on sensor performance. This work showcases the potential of these organogels utilized in sensorized tissue analogues and freestanding strain sensors for widespread applications in medical simulation and education.

Analysis of the Transient Contact Resistance of Composite Copper-Graphite Material Obtained Using Plasma Spraying Technology

The article is devoted to the analysis of the internal structure and properties of a copper-graphite coating applied to a copper electrode. The article provides a calculation of the transient contact resistance of electrodes with a coating obtained using plasma spraying technology. Copper-graphite powder with high arc resistance was used as a spraying substance. Coated electrodes were tested for erosion resistance by an arc at currents of several kiloamperes. The aim of the work is to determine the effect of the composition and internal structure of the coating on the transient processes in the contact gap.

Performance comparison of different electrode materials for electro-osmosis treatment on subgrade soil

During the service life of subgrade, the moisture content increase on compacted subgrade soil can lead to bearing capacity serious degradation of the soil and exaggerated deformation. Electro-osmosis drainage is an effective method in reducing the moisture content of soil, which also serves to improve the subgrade. However, in practice, the low corrosion resistance and poor contact condition of conventional electrode materials make their energy inefficient. And the insufficient understanding of unsaturated soil electro-osmosis also limits the further application of this method. In this paper, a new type of electro kinetic geosynthetics (EKG) electrode was designed and used in electro-osmosis tests on unsaturated soil which was sampled from a reconstruction field in comparison with graphite and iron electrodes. The energy consumption, effective voltage variations, current variations and change in moisture contents under different voltage gradients were analyzed. A one-month field mesoscale test was conducted to verify the feasibility and efficiency of the new EKG electrode. Test results indicated that electro-osmosis drainage performed well with three kinds of electrode materials and the moisture reduction had reached 8.5–15.4%. The contact resistance of iron electrode would reach 1.8–4.1 times that of the EKG and graphite electrodes due to material corrosion. The newly-designed EKG electrode could reduce contact resistance by 19.7–40.8% for the layered fiber structure could enlarge the contact area between soil and electrodes.