Rough Electrode Research Articles

Theory for influence of uncompensated solution resistance on EIS of diffusion limited adsorption at rough electrode

Theory is developed for the electrochemical impedance spectroscopy (EIS) of the diffusion-limited adsorption process coupled with reversible charge transfer at rough electrodes under the influence of ubiquitous uncompensated solution resistance. This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness. The fractal nature of roughness is characterized in terms of fractal dimension, lower cut-off length and topothesy length. The high-frequency regime is controlled by the uncompensated solution resistance whereas the low-frequency regime is governed by the adsorption process. The magnitude of impedance as well as phase decreases with rise in adsorption isotherm (length) parameter. The intermediate frequency regime is controlled by the coupling of adsorption and uncompensated solution resistance with the diffusion process. The fractal roughness parameters has quantitative influence on the magnitude of impedance over whole frequency regime while the phase plot shows qualitative difference in the intermediate frequency regime. The governing length scales which controls the characteristic crossover frequencies are: diffusion length, adsorption-ohmic coupling length and topothesy length (or width of interface). The three emergent crossover frequencies are: (i) ohmic reduced inner crossover frequency (ii) adsorption roughness topothesy dependent pseudo-quasireversibility characteristic frequency (iii) outer crossover frequency. Synopsis: This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness.

25 Years of Light-Emitting Electrochemical Cells: A Flexible and Stretchable Perspective.

Light-emitting electrochemical cells (LECs) are simple electroluminescent devices comprising an emissive material containing mobile ions sandwiched between two electrodes. The operating mechanism of the LEC involves both ionic and electronic transport, distinguishing it from its more well-known cousin, the organic light-emitting diode (OLED). While OLEDs have become a leading player in commercial displays, LECs have flourished in academic research due to the simple device architecture and unique features of its operating mechanism, inviting exploration of new materials and fabrication strategies. These explorations have brought LECs to an exciting frontier in advanced optoelectronics: flexible and stretchable light-emitting devices. Flexible and stretchable LECs are discussed herein, presenting the LEC system as a robust and fault-tolerant development platform. The engineering of emissive composites is highlighted to control mechanical properties, and how the tolerance of LECs to electrode work function and roughness has enabled the incorporation of new electrode materials to achieve flexibility and stretchability. As part of this story, the solution processability of LECs has led to exciting demonstrations of flexible and printed LECs. An outlook is provided for LECs that builds on these strengths, potentially leading to flexible, stretchable, low-cost devices such as illuminated tags, smart packaging, flexible signage, and wearable illumination.

Controlling the Surface Roughness of Surface-Electrode Ion Trap Based on Micro-Nano Fabrication

The surface-electrode ion trap is one of the most promising devices to realize large-scale and integrated quantum information processing. However, a series of problems are faced in the micro-nano fabrication of surface-electrode ion traps. A prominent one is the difficulty to control the thick film surface roughness. A rough electrode surface could produce excessive radio frequency (RF) loss and deteriorate trapping ability of the surface-electrode ion trap. In this paper, a thick film micro-nano fabrication technology to control the surface roughness is presented, which can reduce the roughness of thick film surface-electrode down to 6.2 nm, while being controllable between 6.2 nm and 45 nm. Therefore, it can also provide a basis for studying the influence of electrode surface roughness on trap performance. The micro-nano fabrication technology is not only suitable for surface-electrode ion traps with various configurations, but also be further applied to researches of MEMS, solar cells and surface science.

Optimizing CO Coverage on Rough Copper Electrodes: Effect of the Partial Pressure of CO and Electrolyte Anions (pH) on Selectivity toward Ethylene

The conversion of the initial intermediate CO in the electrochemical reduction reaction of CO2 on the surface of oxide-derived Cu electrodes has been investigated as a function of partial pressure and pH, manipulated by the composition of the electrolyte. We show that in inert gas, an increase in partial pressure of CO results in a continuous increase in Faradaic efficiency (FE) for ethylene, at various potentials ranging from −0.7 to −1.1 V versus RHE, with the highest FE of ∼28% obtained using 1 bar CO at −0.8 V. When the partial pressure of CO is increased in a mixture of CO and CO2, an optimum in the ethylene FE was found for the partial pressure of CO in the range from 0.5 bar (at −1.1 V, FE is ∼45%) to 0.8 bar (at −0.9 V, FE is ∼35%). At lower negative potentials (−0.8 to −0.7 V), the presence of CO2 has negligible influence, and similar data to reduction of CO in inert gas were obtained. Variation of the anion in solution (0.1 M concentration) shows that the optimized FE toward ethylene increases from 5.2% in KH2PO4 to 43.2% in KOH. The observed differences in selectivity are attributed to anion buffering capacity and the associated local pH near the surface of the electrode. Using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), it was determined that the CO coverage increases as a function of increasing pH, confirming that CO coverage and pH correlate. Collectively, the data herein outline the critical role of reactant partial pressures and the significant effect of anion composition (pH) on the surface coverage of CO and concomitant selectivity in electrochemical reduction of CO2 to ethylene.

Selective electrooxidation of acetaldehyde in aqueous ethanol alkaline solutions on silver-containing electrodes

Selective electrochemical oxidation of acetaldehyde in aqueous alkaline ethanol solutions on the silver-containing electrodes has been presented. Several types of silver-containing electrode were used: the smooth silver disk electrode, rough silver electrode and the glassy carbon electrode modified with the silver-polypyrrole composite ink. Silver-polypyrrole (Ag-PPy) composite was synthesized via single-step chemical oxidation with the use of diluted aqueous solutions of silver nitrate and pyrrole in molar ratio 1:50. It has been shown that acetaldehyde is oxidized selectively on silver in the presence of ethanol in alkaline solutions. The influence of various factors (pH, the presence of molecular oxygen, ethanol and acetate anions, surface area extension and polypyrrole presence) on the aldehyde electrooxidation process has been studied. It was shown that for the silver-polypyrrole composites the aldehyde electrooxidation peak potential is shifted to negative direction in comparison with the silver electrode. However, the sensitivity of the silver-polypyrrole composite modified electrode is lower than for smooth or rough silver electrode. The addition of nitrate anions in alkaline solution permits to increase the peak currents for Ag-PPy modified electrode.

Printed resistive switching memory operated by screen-printed microbattery via shared electrode

The combination of printed electronic devices has a pivotal role in establishing intelligent designs in fields such as smart labels for logistics or miniaturized health monitoring. Research to date has tended to focus on individually printed components rather than on their integration. The switching behaviour of inkjet-printed, resistively switching memory cells driven by a screen-printed Zn-MnO2 microbattery, is investigated. Both components have a shared screen-printed Ag electrode that is printed on a low-cost, flexible, and transparent polyethylenterephthalat (PET) substrate. The rough electrode is covered by inkjet printed Spin-on-Glass and contacted by a second Ag electrode after packaging. This resistive memory cell exhibits non-volatile switching behaviour comparable to cells fabricated with standard semiconductor thin film technology. The battery delivers a high gravimetric capacity of 130 mAh/g. The memory cells exhibt clear resistive switching behaviour with switching voltages of Vset = − 0.15V, Vreset = 0.1V and a resistance ratio Roff/Ron ≈ 5 at a write current of Icc = 0.5mA. We demonstrate the potential of printed electronics by the printed integration of a memory with mobile power supply by achieving a retention duration of the battery triggered ON state of more than 2.5 h.

Study of Methanol Electro-Oxidation on Thin Nickel Films by Sampled Current Voltammetry

Nickel-based electrocatalysts have shown good catalytic activity for the electrochemical oxidation of alcohols in alkaline media, which has generated significant interest in using nickel films and nickel oxides in alcohol fuel cells. In this work, Ni films were deposited by the galvanostatic method on gold electrodes. The electrocatalytic activity for the electro-oxidation of methanol from these deposits was evaluated by cyclic voltammetry (CV) and sampled current voltammetry (SCV). Cyclic voltammetry measurements showed that depending on the Au electrode roughness, the position NiOOH formation peak of the electrodeposited Ni deposits could differ. The deposits were divided depending on whether the NiOOH formation peak was below or above 0.39 V vs. Ag|AgCl reference electrode. Sampled current voltammograms showed that the former presented greater specificity for the oxidation of methanol, and the latter, showed electrocatalytic activity for both the oxidation of methanol and for the oxygen evolution reaction.

Single Potential Step Chronoamperometry for EC’ Reaction at Rough Electrodes: Theory and Experiment

The theory is developed for the chronoamperometry of first order homogeneous catalytic chemical reaction coupled with electron transfer ($\rm{EC^{\prime}}$) on a rough electrode. We obtained a solution for the diffusion problem on an arbitrary and random topography of the electrode to generalize Danckwerts' equation. Derived equation of random electrode roughness is used for developing theory of (statistically isotropic) self-affine fractal on limited length scales. The characteristics fractal morphological parameters, viz. $D_{H}$, $\ell$ and $\ell_{\tau}$, are varied for detailed analysis of current transient. The current transient shows anomalously enhanced response for a rough electrode. Our theoretical results explain both transient and steady-state behavior of the current response under the influence of roughness. Steady-state current response depends on the rate constant, the diffusion coefficient of electroactive species and width of roughness. Finally, the theory is compared and validated with experimental data of ferrocyanide and ascorbic acid coupled system on rough Pt electrodes.

Study on Dry-Ice Particle Jet Polishing Process of 316L Stainless Steel Electrode

Dry-ice particle jet technique has the advantages of rapid sublimation, easy drying, and without residues after striking onto the surface, which has been applied in the field of optical coating and the polishing and cleaning of integrated circuit. However, the process mechanism of this technique on stainless steel is not clear and the application research is not in-depth, which restricts the development and application of dry-ice particle jet technique in electrode polishing. In this work, the influence of the processing parameters such as spraying pressure, spraying angle, spraying distance, and spraying time on the micro-morphology and roughness of the stainless steel electrode surface was studied by single factor experiments. In addition, the characterization methods for the surface roughness, surface defects, surface micro-morphology, surface micro-unevenness, and surface chemical composition of the stainless steel electrodes were developed. Comprehensive characterization technology of the electrode surface was established.

Vertically and Horizontally Drawing Formation of Graphite Pencil Electrodes on Paper by Frictional Sliding for a Disposable and Foldable Electronic Device

The objective of this study is to fabricate an electrode by frictional sliding caused by a rough paper surface. The pressure exerted during drawing induces adsorption of the graphite particles by the rough paper and simultaneously reduces the surface roughness of the paper electrode. Repetitive drawing in one-way direction reduced the roughness of the paper surface, decreasing the grain boundaries of graphite. This increases the electron pathway at the electrode, thus reducing the resistance to less than 50 Ω. At the same time, repetitive drawing could confirm that unstable errors caused by the hand could help converge within a certain margin of error. We quantified the relationship between pressure and resistance when drawing on the electrode using a pencil hardness tester. In addition, the electrodes formed by repeated drawing generated a new surface grain and boundary, parallel to the drawing direction, and changed the electrode characteristics with respect to the drawing direction. The grain boundary difference based on the drawing direction was measured via a heating test of the foldable device, a sound pressure level, and laser scattering vibrometer measurements of a linear speaker. The fabricated graphite electrodes can be used in disposable foldable paper electronics because they are prepared using inexpensive materials.

Drop of Thermal Contact Resistance between Multi-Layer Graphene and Metals by Laser Annealing

Significant drop of thermal contact resistance between a graphene flake and metal electrodes was shown as a result of laser annealing. The improvement of thermal contacts of initially rough metal electrodes is attributed to local melting of the metal surface caused by laser heating followed by increasing of real metal-graphene contact area.

Ni particle surface descriptor to enhance roughness of Ni internal electrode in MLCCs

The uniform and continuous nickel internal electrode is crucial in high capacity and highly reliable multi-layer ceramic capacitors (MLCCs). However, the mechanism and the key factors that affect the roughness of the electrode have not been investigated thoroughly. Thus, seeking suitable descriptors that describe the most influential element which decides the roughness is required for the logical design of the Ni paste. In this study, we analyzed the surface of nickel powders and compared their electrode roughness in the aspects of the surface carbon species on nickel nanoparticles. As the increase in the relative C–O/C–C and C=O/C–C ratios, the relative electrode roughness of C-Ni-1, C-Ni-2, C-Ni-3, and C-Ni-4 increased from 1.00, 1.29, 1.54 to 2.51. Thus, low contents of C–O and C=O on the surface of Ni particles could improve the uniformity of the electrode. This study suggests a valuable perspective to reveal the decisive component to build the optimum surface of nickel nanoparticles for uniform internal electrodes in MLCCs.

Compositional Investigations on the Spin Thermoelectric Effect in Ta100–xCux/Yttrium Iron Garnet Thin Films

Herein, the performance of spin thermoelectric devices comprising Ta100–xCux/yttrium iron garnet (YIG) films is investigated. Metallic electrodes of Ta100–xCux (x = 2, 3, 4, 5, and 7) are fabricated on high‐quality YIG films by magnetron sputtering technique. On each film, an undoped Ta electrode is also fabricated for the sake of precise comparison of spin thermoelectric performance. The hybrid Ta100–xCux/YIG devices thus prepared are examined in a longitudinal geometry for the measurement of thermal voltages (Vt). The experiments show that the voltages generated across the Ta100–xCux films with x = 2, 3, and 4 are higher compared with the ones across pure Ta, whereas it is slightly lower for x = 7 film. Such improvement in Vt is ascribed to an increase in the resistivity of Ta100–xCux that strengthens the spin thermoelectric voltage. However, the surface of TaCu alloy films is observed to become rougher as the Cu ratio increases, which affects the injection of spin current across the interface. Due to the interplay between the resistivity and interfacial roughness of TaCu electrodes, the best thermoelectric response is obtained in the Ta97Cu3/YIG system, which is five times higher than the one obtained for undoped Ta/YIG.

MnCo2O4 coated carbon felt anode for enhanced microbial fuel cell performance

A highly efficient anode is very crucial for an improved microbial fuel cell (MFC) performance. In this study, a binder-free manganese cobalt oxide (MnCo2O4@CF) anode was synthesized using a conventional carbon felt (CF) by a facile hydrothermal method. A large electrochemically active and rough electrode surface area of MnCo2O4@CF anode improved the substrate fluxes and microbial adhesion/growth. Furthermore, the electrochemical tests on the synthesized anode confirmed the superior bioelectrochemical activity, reduced ion transfer resistance, and excellent capacitance. This resulted in an improved power density (945 mW/m2), which was 3.8 times higher than that of CF anode. The variable valence state, high stability and biocompatibility of MnCo2O4@CF resulted in continuous current density performance for five MFC cycles. High-throughput biofilm analysis revealed the enrichment of electricity producing phylum of Proteobacteria and Bacteroidetes (∼90.0%), which signified that the modified MnCo2O4 anode accelerated the enrichment of electro-active microbes.

In-Situ Electronic and Vibrational SERS Observation of Gold Electrodes Under Various pH Conditions

Surface-enhanced Raman scattering (SERS) is a vibrational scattering spectroscopy that enables selective and sensitive observation of chemical species existing near a metal surface. In particular, SERS is capable of detecting chemical information with high sensitivity at a buried interface such as an electrode/electrolyte interface. Compared to vibrational absorption spectroscopies, SERS can detect low-frequency vibrations in the THz region in addition to high-frequency vibrations in the so-called fingerprint region. Therefore, one can expect to obtain useful chemical information on electrode/electrolyte interfaces from extramolecular vibrations in such a low frequency region [1]. Moreover, we have recently reported that SERS background continuum is ascribed to surface-enhanced electronic Raman scattering, i.e., electronic SERS. This suggests that the background signals can provide electronic information on the metal electrode [2]. In this study, we measured both electronic and vibrational SERS spectra of electrode/electrolyte interfaces under electrochemical potential applications in various pH conditions.A gold electrode was roughened by applying oxidation and reduction cycles in 0.1 M KCl aqueous solution. In-situ SERS spectra for the gold electrode surface were measured in Ar-bubbled aqueous solutions with three different pH conditions under application of electrochemical potentials. A He-Ne laser radiation of 632.8 nm was used to measure SERS signals.Figure shows SERS spectra for the gold surface measured at -0.6, +0.2, and +0.6 V vs. Ag/AgCl in 0.1 M KOH solution. (The measured signal intensities were converted to the susceptibility [2].) In this pH condition, OH⁻ adsorption and surface oxidation occur at around -0.4 V and +0.3 V, respectively, during the positive-going potential scan. For vibrational peaks, the stretching modes of Au-OH⁻ and Au-O clearly showed the potential dependent behaviors, as expected; among these three potentials, νAu-OH- and νAu-O were observed only at +0.2 V and +0.6 V, respectively. Moreover, we found vibrational features in the THz region, which can be attributed to water cluster vibrations. These features decreased in intensity at +0.6 V. On the other hand, for the electronic background continuum, the signal intensity decreased at the potentials of OH⁻ adsorption and surface oxidation during the positive-going scan. This result suggests that surface adsorption-induced electronic change can be detected using electronic SERS. In the poster, we will present a detailed analysis of pH-dependence or anion-dependence of in-situ electronic and vibrational SERS spectra of gold surface.[1] M. Inagaki, K. Motobayashi, K. Ikeda, Electrochemical THz-SERS Observation of Thiol Monolayers on Au(111) and (100) Using Nanoparticle assisted Gap-Mode Plasmon Excitation. J. Phys. Chem. Lett. 8, 4236-4240 (2017)[2] M. Inagaki, T. Isogai, K. Motobayashi, K.-Q. Lin, B. Ren, K. Ikeda, submitted.Figure. SERS spectra of a roughened Au electrode in Ar-bubbled 0.1 M KOH solution under applied potentials of -0.6 V, +0.2 V, and +0.6 V vs Ag/AgCl. Figure 1

Dendrite-free Al recycling via electrodeposition using ionic liquid electrolytes: The effects of deposition temperature and cathode surface roughness

In this paper, the electrodeposition of Al from aluminum scrap alloys (A2020) on copper cathode substrates with varied surface roughness under different deposition temperatures was studied using low-temperature AlCl3-1-butyl-3-methyl-imidazolium chloride (BMIC) ionic liquid electrolytes. The bulk electrodeposition of Al was carried out under a voltage of 1.5 V at a stirring rate of 120 rpm using a fixed ionic liquid electrolyte concentration (molar ratio AlCl3: BMIC = 2:1). The effects of deposition temperature (range from 80 °C to 140 °C) and surface roughness of Cu cathode substrates (polished by 320, 600, 800, 1200 grits SiC sandpapers and mirror polishing process) on the morphology of deposited Al, current density, current efficiency and energy consumption, were investigated. The Al deposits were characterized using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), profilometer, and electrochemical measurements for current density, current efficiency, and energy consumption. It is demonstrated that the deposition temperature and surface roughness of Cu electrodes play a critical role in the nucleation and growth of Al deposits. Higher deposition temperature promotes the diffusion and/or migration of Al2Cl7− ions and then enhances the current density and efficiency during the electrodeposition of Al. Smoother surface of Cu electrodes is preferred for the formation of dendrite-free Al deposits. Typically, on the mirror polished Cu electrode, no Al dendrite structure was observed, and only plate-like Al deposits were formed at the deposition temperature of 100 °C. Pure metallic Al was successfully deposited on Cu electrodes in AlCl3+BMIC ionic liquid electrolytes for all experiments with a current efficiency range from 72% to 99% and energy consumption of 4.6–6.3 kW h/kg Al.

Using ultrathin double-layer gas-permeable capping metal to form sensitive low-power gas sensors

In this work, we investigated a simple, sensitive, and low-powered ammonia (NH3) gas sensor using a thin bi-layered metal capped on an organic semiconductor chemoresistor to deliver a sensitive response to NH3 (ppb level) at room temperature. An optimized thin bi-layered Al/Ag metal (2 nm/10 nm) successfully forms a gas-permeable structure to realize ppb-regime gas sensing better than other single-layered thin Ag, Al, or Au (12 nm) metal electrodes. The performance of the simple metal-capped gas sensor is greatly dependent on the surface roughness of the thin metal electrodes, and the very rough thin bi-layered metal Al/Ag (2 nm/10 nm) allows high gas penetration. The optimized device exhibits more than 10% response to 100 ppb NH3 at only 0.5 V. The simple, low-cost, highly sensitive, and low-powered gas sensors are promising for Internet of things applications.

Experimental investigation of the effect of C‐rate, electrode gaps, and electrode surface roughness on the performance characterization of lead‐acid batteries

One of the leading challenges for researchers is meeting the industry's need for fast charging-discharging and high capacity batteries, increasing the Charge-discharge rate (C-rate) always followed by high temperatures due to thermoelectrochemical reactions and a drastic reduction in the capacity of batteries. Flooded lead-acid batteries (FLABs) as the most common batteries are provided power for different equipment such as forklifts, submarines, emergency power back up, and for many electrical and telecommunications applications in the industry, has been studied in this article. The effect of three critical parameters of FLAB includes the electrode gaps, roughness quality of electrode surfaces, and C-rate on the capacity and temperature rise (TR) rate are experimentally investigated. Using the response surface methodology based on the central composite design model, the effect of these parameters on the performance of the battery is also evaluated, and a new correlation is proposed. Analysis of variance of 40 tests performed in this study showed that the C-rates have the most effect while the surface roughness of electrodes has the least effect on the capacity increase and the reduction of TR rate. The experimental results showed that the C-rate of C5 with electrode gaps of 4 mm had the optimal response in reaching the maximum capacity and the minimum TR rate.

β-Cyclodextrin-PANI decorated pencil graphite electrode for the electrochemical sensing of morin in almonds and mulberry leaves

Morin (3,2,4,5,7-pentahydroxyflavone) is one of the natural flavonoids which is present in a variety of fruits and herbs. β-cyclodextrin (β-CD) and polyaniline (PANI) decorated Pencil graphite electrode (PGE) has been successfully used as a sensitive and conducting electrode for the determination of morin. The hydroxyl groups of β-CD attract the analyte towards the modified electrode through hydrogen bonding. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to study the electrochemical properties of the modified electrodes. The enhanced surface roughness of β-CD-PANI/PGE has resulted in the increase of electrocatalytic activity of electrode towards the analyte. Opitical profilometric studies were performed to evaluate the surface roughness of electrodes and differential pulse votammetry (DPV) was used for the quantitative analysis of morin. Scanning electron microscopy (SEM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy were carried out to know the physicochemical characteristics of the modified electrodes. The experimental conditions such as scan rate, pH and concentration were optimized. The electrochemical process was found to be adsorption controlled and irreversible from scan rate studies. Under optimal conditions, the linear dynamic range for the quantification of morin was found to be 1.17–32 nM. The low detection limit (0.38 nM) indicates ultrasensitivity of the proposed method. The suggested method has been effectively employed for the determination of morin in almonds and mulberry leaves.

Influence of electrode roughness on DC biased admittance of quasi-reversible charge transfer with uncompensated solution resistance

Abstract The theory is developed for the DC potential biased electrochemical impedance spectroscopy (EIS) of quasi-reversible charge transfer with uncompensated solution resistance developed for rough and fractal electrodes. Theory shows that the influence of the real and apparent kinetics is contained in DC bias dependent characteristic length called the diffusion-kinetics-ohmic coupling length (LQΩ). Theory characterizes fractal irregularities of an electrode through its power spectrum which is experimentally obtained from SEM or AFM recordings. EIS response of DC biased quasi-reversible systems is an interplay of phenomenological lengths, i.e., LQΩ, diffusion length (LD) and morphological characteristics (fractal dimension and lengths in roughness), manifesting themselves at different frequencies. High frequency regime, LD > LQΩ, electrode kinetics follows the Warburg response with the macroscopic area of the electrode. There is an emergence of anomalous intermediate region, LD ~ LQΩ, which is influenced by various fractal morphological characteristics. This regime has maximum in phase angle (ϕ > 450) as well as signature of the fractal roughness.