Towards the application of fast Fourier transform - scanning electrochemical impedance microscopy (FFT-SEIM)

Laser-driven ultrafast impedance spectroscopy for measuring complex ion hopping processes

Superionic conductors, or solid-state ion-conductors surpassing 0.01 S/cm in conductivity, can enable more energy dense batteries, robust artificial ion pumps, and optimized fuel cells. However, tailoring superionic conductors requires precise knowledge of ion migration mechanisms that are still not well understood due to limitations set by available spectroscopic tools. Most spectroscopic techniques do not probe ion hopping at its inherent picosecond timescale nor the many-body correlations between the migrating ions, lattice vibrational modes, and charge screening clouds-all of which are posited to greatly enhance ionic conduction. Here, we develop an ultrafast technique that measures the time-resolved change in impedance upon light excitation, which triggers selective ion-coupled correlations. We also develop a cost-effective, non-time-resolved laser-driven impedance method that is more accessible for lab-scale adoption. We use both techniques to compare the relative changes in impedance of a solid-state Li+ conductor Li0.5La0.5TiO3 (LLTO) before and after UV to THz frequency excitations to elucidate the corresponding ion-many-body-interaction correlations. From our techniques, we determine that electronic screening and phonon-mode interactions dominate the ion migration pathway of LLTO. Although we only present one case study, our technique can extend to O2-, H+, or other charge carrier transport phenomena where ultrafast correlations control transport. Furthermore, the temporal relaxation of the measured impedance can distinguish ion transport effects caused by many-body correlations, optical heating, correlation, and memory behavior.

Non-Faradaic Impedimetric Detection of Heavy Metal Ions via a Hybrid Nanoparticle-DNAzyme Biosensor

Due to rapid industrialization, novel water-quality monitoring techniques for the detection of highly toxic and hazardous heavy metal ions are essential. Herein, a hybrid noble nanoparticle/DNAzyme electrochemical biosensor is proposed for the simultaneous and label-free detection of Pb2+ and Cr3+ in aqueous solutions. The sensor is based on the combination of a two-dimensional naked-platinum nanoparticle film and DNAzymes, whose double-helix configuration disassembles into smaller fragments in the presence of target-specific heavy metal ions. The electrochemical behavior of the fabricated sensor was investigated with non-faradaic electrochemical impedance spectroscopy (EIS), resulting in the successful detection of Pb2+ and Cr3+ well below their maximum permitted levels in tap water. So far, there has been no report on the successful detection of heavy metal ions utilizing the non-faradaic electrochemical impedance spectroscopy technique based on advanced nanomaterials paired with DNAzymes. This is also one of the few reports on the successful detection of chromium (III) via a sensor incorporating DNAzymes.

Efficient water-related failure detection in PEM fuel cells: Combining a PEMFCs fractional order impedance model with FFT-PWM techniques and artificial neural network classification

Water management and early detection of faults in proton exchange membrane fuel cells (PEMFCs) are among the most critical constraints that limit the optimal spread of this type of energy. Consequently, it is necessary to enhance the reliability and durability of PEMFCs by developing an approach to diagnose and identify water failure modes. This paper proposes an effective and simple method to detect, diagnose, and classify various water failure modes in PEMFCs using a hybrid diagnostic approach. This approach combines the PEMFC fractional order impedance model (FOIM) with fast Fourier transform pulse width modulation (FFT-PWM) techniques and artificial neural network pattern recognition (ANN-PR) classification. The results show an accurate match between the electrochemical impedance spectroscopy (EIS) experimental data, the Nyquist impedance spectra of FOIM, and the FFT-PWM algorithm as a proposed alternative technique to EIS measurements. Learning of ANN-PR was performed using the frequency spectrum amplitude (FSA) database of the voltage and current signals produced by the PEMFCs FOIM DC/DC boost converter, which was generated using the FFT-PWM algorithm. The ANN-PR achieved low values for error accuracy, with the Low Square Error and Learning Error reaching 6.676 × 10-19 and 1.888 × 10-16, respectively. The elements inside the confusion matrix and the rest of the matrices confirm that the proposed model's accuracy, precision, recall, and high F1 score reached 100%. Furthermore, all predictions made by the ANN-PR model were consistently accurate across all areas of failure detection. Overall, the proposed method helps in analyzing, diagnosing, and classifying fuel cell failure modes such as flooding and drying, which may simplify the health assessment of PEMFC.

Exploring the Living Cell: Applications and Advances of Scanning Electrochemical Microscopy

A living cell is a complex network of molecular, biochemical and physiological processes. Cellular activities, such as ion transport, metabolic processes, and cell-cell interactions can be determined electrochemically by detecting the electrons or ions exchanged in these processes. Electrochemical methods often are noninvasive, and they can enable the real-time monitoring of cellular processes. Scanning electrochemical microscopy (SECM) is an advanced scanning probe electroanalysis technique that can map the surface topography and local reactivity of a substrate with high precision at the micro- or nanoscale. By measuring electrochemical signals, such as redox reactions, ion fluxes, and pH changes, SECM can provide valuable insights into cellular activity. As a result of its compatibility with liquid medium measurements and its nondestructive nature, SECM has gained popularity in living cell research. This review aims to furnish an overview of SECM, elucidating its principles, applications, and its potential to contribute significantly to advancements in cell biology, electroporation, and biosensors. As a multidisciplinary tool, SECM is distinguished by its ability to unravel the intricacies of living cells and offers promising avenues for breakthroughs in our understanding of cellular complexity.

Fast electrochemical impedance spectroscopy of lithium-ion batteries based on the large square wave excitation signal

Electrochemical impedance spectroscopy (EIS) is a technique for electrochemical characterization that is sensitive to the battery state and can uncover multidimensional electrochemical evolution information within the battery. Lithium-ion batteries usually need to be used in conjunction with power conversion circuits, while conventional EIS testing is conducted offline and is time-consuming, which cannot effectively monitor the battery characteristics during use. To match the characteristics of the square wave signal during power switching, a rapid EIS measurement method for lithium-ion batteries based on the large square wave excitation signal is proposed in this paper, and develops a testing device with a response time of microseconds. The proposed method and device are applied to estimate the state of health (SOH) of the battery. In conclusion, we proposed method enhances the capabilities of EIS testing technology and has a good application prospect in real-time online impedance monitoring.

Scanning electrochemical microscope as a tool for the electroporation of living yeast cells

In this study, a scanning electrochemical microscope (SECM) was for the first time adapted to perform the electroporation process of living yeast cells. We have demonstrated that relatively low voltage pulses of 1-2 V vs. Ag/AglCl,Cl^-_sat applied to gold-based ultramicroelectrode (Au-UME) are performing reversible electroporation of yeast cells immobilized on fluorine-doped tin oxide (FTO)/glass surface. SECM and electrochemical impedance spectroscopy (EIS) were used for the determination of quantitative electrochemical characteristics before and after the electroporation. The electrochemical impedance spectroscopy (EIS) illustrated significant electrochemical changes of electroporated yeast cells, while SECM feedback mode surface vertical scan current-distance curves showed that the diameter of the area affected by the electrical pulse is about 25 times larger than the diameter of the Au-UME used for the electroporation process. The results presented in this research open up a possibility to develop a targeted electroporation system which will affect only the selected area of tissue or some other cell-covered surface. Such model is promising for the selective treatment of selected cells in tissues and/or other sensitive biological systems while selecting the location and size of electroporated areas.

Scanning Probe Microscopy Facility for Operando Study of Redox Processes on Lithium ion Battery Electrodes

An Atomic Force Microscope (AFM) is combined with a special designed glovebox system and coupled to a Galvanostat/Potentiostat to allow measurements on electrochemical properties for battery research. An open cell design with electrical contacts makes it possible to reach the electrode surface with the cantilever so as to perform measurements during battery operation. A combined AFM-Scanning Electro-Chemical Microscopy (AFM-SECM) approach makes it possible to simultaneously obtain topological information and electrochemical activity. Several methods have been explored to provide the probe tip with an amount of lithium so that it can be used as an active element in a measurement. The “wet methods” that use liquid electrolyte appear to have significant drawbacks compared to dry methods, in which no electrolyte is used. Two dry methods were found to be best applicable, with one method applying metallic lithium to the tip and the second method forming an alloy with the silicon of the tip. The amount of lithium applied to the tip was measured by determining the shift of the resonance frequency which makes it possible to follow the lithiation process. A FEM-based probe model has been used to simulate this shift due to mass change. The AFM-Galvanostat/Potentiostat set-up is used to perform electrochemical measurements. Initial measurements with lithiated probes show that we are able to follow ion currents between tip and sample and perform an electrochemical impedance analysis in absence of an interfering Redox-probe. The active probe method developed in this way can be extended to techniques in which AFM measurements can be combined with mapping electrochemical processes with a spatial resolution.