Influence Of Electrode Roughness Research Articles

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.

The mechanism of Li2O2-film formation and reoxidation – Influence of electrode roughness and single crystal surface structure

In this work, the role of the electrode surface structure on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium ion containing dimethyl sulfoxide (DMSO) was elucidated for Pt single crystal electrodes and deliberately roughened polycrystalline gold and platinum electrodes. Both rotating ring disk electrode (RRDE) measurements and results obtained by differential electrochemical mass spectrometry (DEMS) show that the amount of insoluble Li 2 O 2 formed is proportional to the roughness factor and corresponds to one or two monolayers if referenced to the true surface area. The amount of soluble LiO 2 is independent of roughness, although the formation of the passivating Li 2 O 2 layer takes longer. On gold electrodes less side products are formed as compared to platinum electrodes. It was furthermore found that ORR on single crystalline Pt(100) leads to two monolayers of Li 2 O 2 , while in case of Pt(111)/Pt(pc) only one monolayer was reoxidized. The shape of the reoxidation peaks in the anodic potential scan is independent of roughness, but it depends not only on the electrode material (Au or Pt) but also on the atomic surface structure. Since Tafelslopes cannot be determined directly by usual methods for such surface confined reactions, we used ac voltammetry to determine the apparent transfer coefficient ( α′ ) and gain some insight into the reoxidation mechanism; the obtained α ′ of 0.3 hints to a rate determining first charge transfer. This agrees well with the detection of superoxide during oxidation of Li 2 O 2 on the surface. • Strong effect of electrode surface structure on electrochemistry in Li + -containing DMSO. • Superoxide as intermediate during lithium peroxide oxidation in DMSO. • Apparent transfer coefficient of lithium peroxide oxidation in Li + -containing DMSO. • Direct correlation of lithium peroxide formation and surface roughness.

Impedance spectroscopy and membrane potential analysis of microfiltration membranes. The influence of surface fractality

In this work, the proper charge density of a microfiltration membrane has been determined by using two different methods. Firstly, the ionic transport of a KCl solution has been investigated by simultaneous measurements of saline flux and membrane potential (MP) resulting from a concentration gradient through the membrane. A simple model, including all the relevant contributions to the global electrical potential drop, allowed a calculation of transport numbers and membrane charge density.The response of ions inside the membrane to an oscillating electrical potential has been analyzed by impedance spectroscopy (or electrical impedance spectroscopy EIS). A quite simple experimental EIS design allowed, by taking into account MP measurements too, an easy assignation of an equivalent circuit. After a careful analysis of EIS results, it was possible to evaluate the electrical conductivity inside the pores and the charge density. Both were found to be quite similar to the values obtained from MP alone. This agreement of EIS results with the MP ones, that are much simpler to deal with, confirms the accuracy of EIS to study the electrical properties of microfiltration membranes.The influence of electrode roughness and, in our EIS cell, the membrane roughness, on the constant phase element (CPE) of the equivalent circuit has been proved. Within this frame, the roughness fractal dimension of the membrane surface could be determined from EIS measurements. It resulted in fair agreement with the atomic force microscopy (AFM) determination.

Dark current measurements in humid SF6: influence of electrode roughness, relative humidity and pressure

The measurement of ‘dark current’ in pressurized SF6 at high electric field is performed using electrodes with a coaxial geometry. To identify the main mechanisms involved in measured currents, the influences of electrode roughness, gas pressure and relative humidity have been investigated. The experimental results reveal that charge injection from the electrode constitute the predominant process responsible for the dark current. The latter is nearly identical in positive and negative polarities, and shows an exponential increase versus the relative humidity and the electric field. The analysis of results shows that under high electric field, the emission of charged water clusters from the water films adsorbed on electrodes probably constitutes the main mechanism of charge emission.

Influence of Electrode Roughness on Double Layer Formation in Ionic Liquids

We have used broadband electrochemical impedance spectroscopy for characterizing double layer formation at the interface between the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethane)sulfonimide [Py1,4]TFSI and three gold electrodes with different surface structure and roughness. Two alternative approaches for analyzing the data were compared: a) A fit in the complex impedance plane using a resistor and a constant phase element (CPE) connected in series; b) A fit in the complex capacitance plane using a Cole–Cole function. In the complex capacitance plane, a high-frequency semicircle due to double layer formation could be clearly distinguished from other capacitive or Faradaic processes detected at lower frequencies. The Cole–Cole fit of the high-frequency semicircle revealed that this semicircle is almost unsuppressed with α values close to unity, even for the rough polycrystalline Au electrode. In contrast, the CPE exponent depends much more strongly on electrode potential and electrode roughness. We show that this strong dependence is closely related to the existence of slower capacitive or Faradaic processes, and is not caused by nonideal double layer formation.

Steady-state electrical transport through block copolymer nanostructures deposited on smooth and rough electrodes

The influence of electrode roughness on formation of metallic nanostructures made via block copolymer nanotemplates was studied. Metallic nanostructures fabricated on electrodes with various roughnesses were prepared by sputtering the metals onto polystyrene-block-poly(4-vinylpyridine) nanotemplates. Their structure was characterized by atomic force microscopy and x-ray reflectivity. If the electrode roughness exceeds a critical value of about 1nm per 1×1μm2, an adhesion insulating thin film is formed between the electrode (substrate) and block copolymer nanotemplate. This insulating film strongly influences electrical contact with the substrate electrode. Steady-state current-voltage characteristics were studied for various configurations of the electrodes. They were analyzed and discussed in the frame of several injection and transport mechanism models.

Advanced Dram Cell Dielectric Films using Rapid Thermal Processing

ABSTRACTThe reliable operation of a dynamic random access memory (DRAM) device requires a minimum level of charge to be stored in the capacitor. The nonlinear dependence between the scaling of the minimum charge and the cell area for higher DRAM densities is the driving force in the development of exotic capacitor structures and advanced cell dielectric materials. The conventional option of reducing the thickness of the silicon nitride dielectric films for high density DRAM applications will eventually be constrained by the increase in the leakage current due to direct carrier tunneling or by the decrease in the oxidation resistance of the films.In this paper we discuss the use of rapid thermal processing to modify the interface between the polysilicon storage node of the capacitor and the silicon nitride to improve the electrical and structural characteristics without any loss in capacitance. The influence of electrode roughness on the electrical behavior will also be discussed for the various dielectric stack combinations.