Electrochemical Conversion of CO2 to Fuels and Useful Chemicals over Metal Supported Solid Oxide Electrolyzers

Comparison of corrosion behaviour of zinc in NaCl and in NaOH solutions; Part II: Electrochemical analyses

Study on corrosion resistance and roughness of micro-plasma oxidation ceramic coatings on Ti alloy by EIS technique

The electrochemical impedance spectroscopy (EIS) technique was used to evaluate the water transport (diffusion and equilibrium water uptake) and the dielectric properties of freestanding polyimide (Kapton® and PMDA-ODA) and polyethyleneterephthalate (PET) membranes at 25 and 40°C, respectively, and in supported PMDA-ODA-coated metals. Permeability and diffusion coefficients of freestanding films were also obtained by using the Payne cup method and the MacBain quartz spring balance in order to assess the reliability of the EIS method when compared to other techniques. Results from this work show that the diffusivity of water in polyimide films varies from 1.42 x 10–9 to 3.53 x 10–9 cm2 s–1 for thickness between 2.4 and 125 μm, while the equilibrium water uptake varies from 2.31 to 4.63% by weight for the same range of thickness. The average calculated dielectric constant of the freestanding Kapton® films is 4.5. Water diffusion coefficient in PET varies from 2.11 x 10–9 to 12.61 x 10–9 cm2 s–1 for thicknesses between 22 and 205 μm, while the equilibrium water uptake varies from 0.50 to 0.95% by weight for the same range of thickness. The average calculated dielectric constant of the freestanding PET films is 3.6. Transport properties’ results obtained through the electrochemical technique are in reasonable agreement with those obtained with the classical gravimetric method. Capacitance data obtained with the EIS technique were interpreted in terms of a model in which the electrical analog of the film is composed of either a parallel RC or of a series of parallel RC circuits. Thick films are better described in terms of a series of parallel RC circuits. Theoretical analysis presented in this paper indicates that transport properties of water through freestanding and applied films (paints) can be obtained from EIS (capacitance data) only when specific requirements are met.

This article proposes a real-time electrochemical impedance spectroscopy (EIS) technique that can provide high accurate estimation of the impedance of each lithium-ion (Li-ion) cell of a battery (BT) stack, even for less than mΩ. Thus, the suggested EIS technique can be used in high demanding applications, such as nearly zero-energy buildings, microgrids, and electric vehicles. This is attained because a smooth cell excitation current is utilized that is provided by the proper control of the gate-source of each cell's parallel-connected MOSFET and thus, effective harmonic analysis can be accomplished. Since the circuit topology of the EIS is implemented without requiring expensive electronic equipment, it is affordable to be applied in the BT system of any application. The proposed EIS system can cooperate with a BT cell equalization (BCE) system that utilizes the same MOSFET control scheme to provide the excitation current. Thus, a combined EIS-BCE system is developed that can be used to improve the performance of a Li-ion BT management system. The accuracy of the EIS technique and its high performance by operating within a combined EIS-BCE system are experimentally validated.

Evaluation of Metal Corrosion under Defective Coatings by WBE and EIS Technique

Power for the small user : Golding, E. W., New Commonwealth37(2): 103–107, Feb. 1959. Illus.

Microbiologically Influenced Corrosion (MIC) and biofouling are major challenges to operators who manage water systems in the oil & gas and other sectors. Key to these threats is the formation and accumulation of biofilms in piping systems due to the agglomeration of both biotic components (e.g. microorganisms such as bacteria, archea and extracellular polymeric substances) and abiotic materials (e.g. inorganic solids). These biofilms adhere to inner pipe wall surfaces, and evolve over time depending on surrounding environmental conditions. Manual detection of biofilm formation and bio-fouling often occurs during routine inspection, or during an unexpected system shut down due to a corrosion failure or flow blockage. In this study, a novel in-situ method to detect the presence of biofilm forming bacteria in a fluid system has been proposed based on capacitance measurements using the Electrochemical Impedance Spectroscopy (EIS) technique. Two probe types were used to measure the growth of bacteria: 1) a parallel plate system to measure total bacteria concentration (planktonic and sessile), and 2) a small-scale Interdigitated Electrode (IDE) system to measure the formation of biofilms (sessile bacteria). In both series of tests, Pseudomonas.putida was used as the model bacteria due to its ability to grow rapidly as a biofilm. Upon introduction of the microorganism to the system, EIS patterns were correlated to the observed bacterial concentration which was determined using plating methods to quantify microbial counts over time. Surface areas and gap sizes of the various probes were also evaluated to determine their effect on measured sensitivities. Preliminary tests show that the EIS technique is capable of detecting and quantifying the bacterial counts (i.e. initiation and growth of biofilms). Furthermore, utilizing a model circuit, the effective capacitance at different concentrations of bacteria was determined. This “proof of concept” study demonstrates the potential for a viable, real-time detection method for systems susceptible to bio-fouling and/or MIC.

With rapid development of the global economy, increasing environmental pollution and the depletion of fossil fuels, there is a vital need for clean, sustainable and efficient sources of energy as well as new technologies allied with energy conversion and storage (1). Among many application fields, some of the most practical and efficient technologies for electrochemical energy conversion and storage are fuel cells, batteries and electrochemical supercapacitors. In recent years, these devices have attracted significant attention, each with recognized advantages. Driven by this need and the promise of the technology, significant progress in practical and theoretical research and development of these devices has taken place. One of the challenges of developing these electrochemical energy conversion and storage technologies is the use of low cost and readily available materials that possess complex requirements of different applications. To overcome obstacles of high costs of raw materials and avoid usage of depleting sources, bio-based carbon materials are believed to lead the next generation of many industries including aerospace, sports equipment and electrochemical devices due to their abundance, high chemical stability, electrical conductivity, low cost and non-toxicity, high specific surface area and wide operating temperature range (2). The feasibility of the carbon precursors in different electrochemical devices for practical applications including hybrid power sources in electrical vehicles, burst-power generation in electronic devices, back-up power sources, portable and stationary equipment has been demonstrated. Cellulosic fibers in nano and micro scale, the green and most abundant material, have eco-friendly attributes that are economically and technically feasible to replace man-made fibers (3). Carbonization of cellulose yields carbons, including charcoal, activated carbon and graphite fibers. The process comprises of introducing the fibers in an inert atmosphere, preheating and drying the fibers, treating the dried fibers up to a certain temperature at which they carbonize by evolution of a purging gas and finally cooling the carbonized residues (4). The produced carbon materials have been investigated as a potential material in different electrochemical devices and have proved to have prospect as electrode materials for supercapacitors, catalyst supports in fuel cells and membrane separators in lithium-ion batteries. In this project, bio-based cellulosic starting materials have been investigated as a candidate for supercapacitor electrode materials. The produced activated carbon materials upon carbonization of the cellulose fibers have been functionalized and characterized by different techniques to study the effect of the morphology and surface area of the carbonaceous residues on their performance in the electrochemical device. This work has been coupled with a range of electrochemical tests in two and three-electrode systems including cyclic voltammetry, electrochemical impedance spectroscopy and charge-discharge loop tests. The work highlights the importance of relating the different characterization techniques of the raw and produced materials and the effect of each on the performance of the activated carbons as electrode materials in supercapacitors.

Green hydrogen, produced through water electrolysis driven by Renewable Energy Sources (RES), is a compelling solution for storing renewable energy. Directly coupling RES with water electrolyzers enhances system efficiency and cost-effectiveness. Alkaline water electrolysis, a mature and cost-effective technology, faces challenges operating under fluctuating RES conditions using AC/DC convertor , which supply rippled DC. A comprehensive understanding of electrolyzer performance in dynamic conditions is crucial for developing durable, efficient systems.In the present experimental study, we extensively explored the performance of alkaline water electrolyzers and the key factors influencing it under dynamic operational conditions. The electrolytic cell was constructed using a zero-gap configuration, comprising a NiCoOx-based anode deposited on a Ni-mesh and an Ln-doped RuOx cathode deposited on a fine mesh of Ni metal. The Zirfon Perl UTP500 membrane served as a separator between the two cell compartments [1]. A 7.0 Molar KOH electrolyte at a room temperature of approximately 30°C was employed. The cell underwent dynamic operational mode through the application of a square wave cell voltage, shown in Fig.1 (a), utilizing the NF BP4620 power supply. Square waves with different frequencies, specifically 1, 100, 1000, and 3000 Hz, were employed. Steady-state operations were conducted while applying various DC voltages, serving as a reference study. The resulting current and the actual cell voltage waveforms were monitored and recorded using a high-resolution oscilloscope (YOKOGAWA DL850E). The flow of H2 gas was measured using a film flow meter (HORIBA STEC, SF series VP-3). The apparent power, real power, and reactive power components were calculated using formulas from a previously published report [2]. Subsequently, the specific energy consumption was determined for each condition.The applied cell voltages were categorized into two groups. In the first category, the maximum cell voltage (Vmax) was set at 2.0 V, a value sufficiently high and suitable for industrial cell operation when applied in a DC mode. Within this category, the minimum cell voltage (Vmin) took various values, namely 1.8, 1.6, and 1.4 V. In the second category, the average cell voltage was maintained at a constant 2.0 V, while the amplitude of the waveform was adjusted to 0.2 and 0.4 V by modifying both Vmax and Vmin. Figure 1(b) depicts the resulting current of the voltage waveform at 100 Hz, illustrating three different Vmin values. The figure reveals that at a high Vmin of 1.8V, the current consistently maintained positive values during the voltage cycle, indicating that the double-layer capacitance remained charged throughout the operational period. However, with Vmin set at 1.6V, a relatively small capacitive current emerged, suggesting partial discharge of the double-layer capacitance. Moreover, at a lower Vmin of 1.4V, the cell voltage became insufficient to drive water electrolysis in the current cell. Consequently, a relatively large negative (capacitive) current manifested during the Vmin period, denoting a deep discharge of the double-layer capacitance.The obtained results revealed a profound influence of the charge and discharge status of the double-layer capacitance on the AWE cell's performance throughout the voltage cycles. Notably, when the double-layer capacitor remained fully charged during the voltage cycles, minimal impact of the frequency was observed on key performance parameters, including H2 flow rate that shown in figure 1 (c), specific energy consumption that shown in figure 1 (d), and power factor. However, under conditions of partial discharge within the cell voltage cycles, a noticeable correlation between the size and frequency of the voltage waveform and the AWE cell's performance emerged. Deep discharge of the double-layer capacitance led to a frequency-dependent reduction in H2 flow rate, attributed to incomplete charge/discharge cycles. Hence, the critical factor influencing the performance of the electrolytic cell during dynamic operation is the condition (charging/discharging) of the double-layer capacitance. These findings offer valuable insights into optimizing the dynamic operation of AWE cells for enhanced efficiency and performance. Acknowledgments: This research was partially supported by New Energy and Industrial Technology Development Organization (NEDO).

The electrochemical CO2 reduction reaction (CO2RR) presents the opportunity to produce chemical feedstocks and fuels directly from CO2. Recent achievements in energy efficiency and current density are approaching the targets required for commercial viability; however, stability remains more than two orders of magnitude below the required 80,000 h. In CO2RR there is a challenge to distinguish the cause of failure among many possibilities. Failure can result from initial setup (e.g. over or under compression of the membrane and electrodes), gradual degradation of components (e.g. cathode and anode catalyst restructuring and dissolution), accumulation of products or byproducts (e.g. alcohols or salt accumulation), or immediate failures (e.g. a hole in the membrane or a short circuit). These failure modes must be addressed to reach the targeted stability needed for the wide-scale adoption of this technology. Early identification and mitigation of these failures would increase the electrolyzer lifetime and the commercial viability of CO2RR electrolyzers.Current techniques to characterize failures of the electrolyzer rely on post-mortem analysis of cell components. The analysis of individual components after operation may not accurately reflect their state in operando. There are techniques that are capable of analyzing the cell in operation (e.g. XAS, Raman, and TEM), but these typically require modified cell architectures and are operated at lower reaction rates. To effectively diagnose failure, the analysis technique should be applied to electrolyzers operating under realistic conditions.Here we implement an in-line real-time electrochemical impedance spectroscopy (EIS) technique to monitor CO2RR electrolyzers during operation. EIS is a non-destructive technique that can provide continuous information on the performance of specific components within the electrolyzer. We characterize common failure modes, such as poor compression, salt formation, catalyst degradation, and short circuits, and their identifying changes to the EIS response. We extract key electrochemical parameters from the EIS response and use them to develop a framework to identify and prevent the most common failure modes. Among other applications, this framework allowed for the detection of anode catalyst degradation 11 h before other indicators, such as cell voltage or product selectivity. This technique and framework can be applied to monitor CO2 electrolyzers as they are scaled and stacked.

Carbon dioxide conversion into useful products has been gaining considerable attention as a global‐warming‐mitigation technique. The electrochemical conversion of CO2 into high‐value chemicals involves the utilization of electrical energy in the presence of an effective catalyst. The process products depend on the number of transferred electrons during the reaction and the characteristics of the electrode. Recently, electrodes coupled with active catalysts have been used to convert CO2 into valuable products including formic acid, hydrocarbons, and syngas. This review offers an overview of the recent literature on the electrochemical conversion of CO2 to valuable products, with an emphasis on the production of formate/formic acid. In addition, it compares the main features of electrochemical conversion to other techniques and summarizes their key advantages. It also provides future perspective for research and development, such as the need for novel and selective catalysts to obtain high conversion and product yield with low energy consumption.

Carbon electrodes have the advantages of being chemically inert at negative potential ranges in all media and high offset potentials for hydrogen evolution in comparison to metal electrodes, and therefore are the most suitable electrodes for electrochemistry and electrochemical conversion of CO2 into valuable chemicals. Herein we summarize on carbon electrodes the voltammetry, electrochemical and electrocatalytic CO2 reduction, as well as electron synthesis using CO2 and carbon electrodes. The electrocatalytic CO2 reduction using carbocatalyts and the future activities about electrochemical CO2 conversion are highlighted.

Estimating the parameters of lithium-ion (Li-ion) batteries under dynamic working conditions is a critical challenge in the health management of electrical energy storage systems. This paper estimates the equivalent circuit model (ECM) parameters and analyzes the influence of different factors on the Li-ion batteries impedance using the electrochemical impedance spectroscopy (EIS) technique. Firstly, the influence of the temperature, state of charge (SOC) and number of charging/discharging cycles on the impedance spectrum was studied. Nyquist plots were used to perform this analysis. Subsequently, ECMs were used to characterize the Li-ion batteries under study at different operating conditions. Specifically, the ECM parameters were estimated using the gaining-sharing knowledge (GSK) metaheuristic algorithm, allowing the consequent estimation of the impedance spectra obtained by the EIS technique. Experimental results included 15 datasets measured experimentally at three temperature levels for five SOCs and different number of charging/discharging cycles. To investigate the variation of Li-ion battery parameters with cyclic aging 350 datasets from the literature were also used. The results showed that the impedance and model parameters depend considerably on the considered factors. The estimation of the ECM parameters demonstrated high accuracy and reliability (mean RMSE values of 4.32E-02 and 2.33E-02 and mean STD values of 3.38E-16 and 5.82E-13 with measured and literature datasets, respectively), allowing the robust determination of the numerous impedance spectra under study.

Tandem and Hybrid Processes for Carbon Dioxide Utilization

The effect of Mentha spicata L. extract on the corrosion behaviour of carbon steel in 1.0 M HCl solution was investigated using polarization, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques. The solution containing 250 ppm of the ethanolic solution of extract showed the highest inhibition efficiency (IE). The effect of temperature on the rate of corrosion in the absence and presence of inhibitor was also studied. Adsorption of extract on the carbon steel surface obeyed the Langmuir adsorption isotherm. Polarization measurements indicated that the inhibitor was of mixed type. The IE values from EN measurements showed a reasonable agreement with those obtained from polarization and EIS techniques. The EN method was applied as a complementary quantitative technique to study the corrosion behaviour of the inhibitor.