An official website of the United States government
Most of the measurements of electrode polarization resistance are conducted using electrochemical impedance spectroscopy (EIS). The electrochemical devices, however, are typically used in a DC mode. The objective of the present work was to measure electrode polarization resistance using both EIS and DC techniques. A solid cylinder of 8YSZ of diameter ~1.17 cm and length ~5.00 cm was made by powder pressing followed by sintering. LSM + YSZ electrodes were applied on the two end surfaces of the cylinder upon which gold mesh was placed. Four Pt electrodes/probes were painted along the circumference. During DC measurements, DC voltage was applied across the end electrodes and potentials were measured at all four probes. The current was also measured. From these measurements electrode polarizations were estimated separately for the two electrodes as a function of current. EIS was conducted across the two end electrodes as well as across electrode-1 and probe-2, and across probe-2 and electrode-2. This allowed the determination of the polarization resistances of the two electrodes separately. Point by point additions of the electrode-1/probe-2 and probe-2/electrode-2 spectra matched the electrode-1/electrode-2 spectra. There was good agreement between the DC and the EIS measurements.
more »
« less
Detection of Microbes in Ice Using Microfabricated Impedance Spectroscopy Sensors
During the growth of a polycrystalline ice lattice, microorganisms partition into veins, forming an ice vein network highly concentrated in salts and microbial cells. We used microfabricated electrochemical impedance spectroscopy (EIS) sensors to determine the effect of microorganisms on the electrochemical properties of ice. Solutions analyzed consisted of a 176μS cm−1conductivity solution, fluorescent beads, andEscherichia coliHB101-GFP to model biotic organisms. Impedance spectroscopy data were collected at −10 °C, −20 °C, and −25 °C within either ice veins or ice grains (i.e., no veins) spanning the sensors. After freezing, the fluorescent beads andE. coliwere partitioned into the ice veins. The corresponding impedance data were discernibly different in the presence of ice veins and microbial impurities. The presence of microbial cells in ice veins was evident by decreased electrical characteristics (electrode polarization between electrode and ice matrix) relative to solid ice grains. Further, this electrochemical behavior was reversed in all bead-doped solutions, indicating that microbial processes influence sensor response. Linear mixed-effects models empirically corroborated the differences in polarization associated with the presence and absence of microbial cells in ice. We show that EIS has the potential to detect microbes in ice and differentiate between veins and solid grains.
more »
« less
- PAR ID:
- 10469836
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- ECS Sensors Plus
- Volume:
- 2
- Issue:
- 4
- ISSN:
- 2754-2726
- Format(s):
- Medium: X Size: Article No. 042801
- Size(s):
- Article No. 042801
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This paper addresses the use of Ce 0.8 Gd 0.2 O 2−δ (GDC) infiltration into the Ni–(Y 2 O 3 ) 0.08 (ZrO 2 ) 0.92 (YSZ) fuel electrode of solid oxide cells (SOCs) for improving their electrochemical performance in fuel cell and electrolysis operation. Although doped ceria infiltration into Ni–YSZ has recently been shown to improve the electrode performance and stability, the mechanisms defining how GDC impacts electrochemical characteristics are not fully delineated. Furthermore, the electrochemical characteristics have not yet been determined over the full range of conditions normally encountered in fuel cell and electrolysis operation. Here we present a study of both symmetric and full cells aimed at understanding the electrochemical mechanisms of GDC-modified Ni–YSZ over a wide range of fuel compositions and temperatures. Single-step GDC infiltration at an appropriate loading substantially reduced the polarization resistance of Ni–YSZ electrodes in electrolyte-supported cells, as measured using electrochemical impedance spectroscopy (EIS) at various temperatures (600–800 °C) in a range of H 2 O–H 2 mixtures (3–90 vol% H 2 O). Fuel-electrode-supported cells had significant concentration polarization due to the thick Ni–YSZ supports. A distribution of relaxation times approach is used to develop a physically-based electrochemical model; the results show that GDC reduces the reaction resistance associated with three-phase boundaries, but also appears to improve oxygen transport in the electrode. Increasing the H 2 O fraction in the H 2 –H 2 O fuel mixture reduced both the three-phase boundary resistance and the gas diffusion resistance for Ni–YSZ; with GDC infiltration, the electrode resistance showed less variation with fuel composition. GDC infiltration improved the performance of fuel-electrode-supported full cells, which yielded a maximum power density of 2.28 W cm −2 in fuel cell mode and an electrolysis current density at 1.3 V of 2.22 A cm −2 , both at 800 °C.more » « less
-
Abstract Microbial biofilm contamination is a widespread problem that requires precise and prompt detection techniques to effectively control its growth. Microfabricated electrochemical impedance spectroscopy (EIS) biosensors offer promise as a tool for early biofilm detection and monitoring of elimination. This study utilized a custom flow cell system with integrated sensors to make real-time impedance measurements of biofilm growth under flow conditions, which were correlated with confocal laser scanning microscopy (CLSM) imaging. Biofilm growth on EIS biosensors in basic aqueous growth media (tryptic soy broth, TSB) and an oil–water emulsion (metalworking fluid, MWF) attenuated in a sigmoidal decay pattern, which lead to an ∼22–25% decrease in impedance after 24 Hrs. Subsequent treatment of established biofilms increased the impedance by ∼14% and ∼41% in TSB and MWF, respectively. In the presence of furanone C-30, a quorum-sensing inhibitor (QSI), impedance remained unchanged from the initial time point for 18 Hrs in TSB and 72 Hrs in MWF. Biofilm changes enumerated from CLSM imaging corroborated impedance measurements, with treatment significantly reducing biofilm. Overall, these results support the application of microfabricated EIS biosensors for evaluating the growth and dispersal of biofilm in situ and demonstrate potential for use in industrial settings. One-Sentence SummaryThis study demonstrates the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors for real-time monitoring and treatment evaluation of biofilm growth, offering valuable insights for biofilm control in industrial settings.more » « less
-
Lanthanum strontium cobalt iron oxide (LSCF) is commonly used as a cathode in solid oxide fuel cells (SOFCs), because it is a mixed ionic-electronic conductor with reasonable oxygen ion conductivity and high electronic conductivity. Yttria stabilized zirconia (YSZ) is used as an electrolyte in SOFCs with good oxygen ion conductivity. AC techniques are used to test the performance of SOFCs. But electrode processes at the cathode and the anode cannot be studied separately using 2-probe electrical impedance spectroscopy (EIS). To overcome this problem, 2-probe EIS with three probes and DC tests were conducted. An LSCF/8YSZ/LSCF symmetrical bar-shaped cell was made, and platinum strip electrodes were applied as probes for EIS and DC measurements. Impedance spectra across the cathode and the platinum strip electrode and across the anode and the platinum strip electrode were measured separately. The sum was evaluated to see if it matches the EIS spectra across the cathode and the anode. The polarity was switched to study how it affects the electrode processes. The polarization resistances of the electrodes were also measured by a DC method separately. EIS and DC measurements are in good agreement. Results indicate the two electrodes need not be identical.more » « less
-
Lignin is unique among renewable biopolymers in having significant aromatic character, making it potentially attractive for a wide range of uses from coatings to carbon fibers. Recent research has shown that hot acetic acid (AcOH)–water mixtures can be used to recover “ultraclean” lignins of controlled molecular weight from Kraft lignins. A key feature of this discovery is the existence of a region of liquid–liquid equilibrium (LLE), with one phase being rich in the purified lignin and the other rich in solvent. Although visual methods can be used to determine the temperature at which solid lignin melts in the presence of AcOH–water mixtures to form LLE, the phase transition can be seen only at lower AcOH concentrations due to solvent opacity. Thus, an electrochemical impedance spectroscopy (EIS) technique was developed for measuring the phase-transition temperature of a softwood Kraft lignin in AcOH–water mixtures. In electrochemical cells, the resistance to double-layer charging ( i.e. , polarization resistance R p ) is related to the concentration and mobility of free ions in the electrolyte, both of which are affected by the phases present. When the lignin–AcOH–water mixture was heated through the phase transition, R P was found to be a strong function of temperature, with the maximum in R P corresponding to the transition temperature obtained from visual observation. As the system is heated, acetate ions associate with the solid lignin, forming a liquefied, lignin-rich phase. This association increases the overall impedance of the system, as mobile acetate ions are stripped from the solvent phase and thus are no longer available to adsorb on the polarizing electrode surfaces. The maximum in R P occurs once the new lignin-rich phase has completely formed, and no further association of the lignin polymer with AcOH is possible. Except at sub-ambient temperatures, the phase-transition temperature was a strong function of solvent composition, increasing linearly from 18 °C at 70/30 AcOH/water to 97 °C at 10/90 wt% AcOH/water.more » « less
