In this work, the fabrication of electrochemical fluidic fused filament fabricated devices (eF4D) was accomplished using a polyethylene terephthalate glycol (PETg) non-conductive filament for the ...fluidic and insulating parts and a polylactic acid/carbon black (PLA-CB) composite filament for the electrodes. For the first time, it is demonstrated that 3D conductive filaments can be chemically and/or electrochemically activated inside microchannels without affecting channel dimensions and keeping their structural integrity intact. eF4Ds were morphologically and electrochemically characterized under static and hydrodynamic conditions allowing us to explore their analytical potential in both approaches. Interestingly, the electrodes activated using a combination of chemical and electrochemical activation exhibited the best electrochemical performance in static conditions whereas under hydrodynamics the electrochemically activated electrodes (without any previous chemical pretreatment) exhibited a better performance. Indeed, electrochemically activated 3D-printed electrodes integrated into eF4Ds followed the behavior predicted by the Levich model for channel electrodes and were employed for the determination of dopamine in cell culture media with excellent analytical performance. This work paves the way for the fabrication of tailored monolithic electrochemical (micro)fluidic devices with tremendous potential for the (real-time) analysis of biological samples.
•Functional fully 3D printed electrochemical microfluidic devices (EMDs).•Efficient in-channel (electro)chemical electrode activation.•Fully 3D-printed EMDs followed the Levich model for channel electrodes.•EMDs were challenged towards dopamine determination in cell culture media.
The present research provides a study of carbon-supported intermetallic Pt-alloy electrocatalysts and assesses their stability against metal dissolution in relation to the operating temperature and ...the potential window using two advanced electrochemical methodologies: (i) the in-house designed high-temperature disk electrode (HT-DE) methodology as well as (ii) a modification of the electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) methodology, allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. While the rate of carbon corrosion follows the Arrhenius law and increases exponentially with temperature, the findings of the present study contradict the generally accepted hypothesis that the kinetics of Pt and subsequently the less noble metal dissolution are supposed to be for the most part unaffected by temperature. On the contrary, clear evidence is presented that in addition to the importance of the voltage/potential window, the temperature is one of the most critical parameters governing the stability of Pt and thus, in the case of Pt-alloy electrocatalysts, also the ability of the nanoparticles (NPs) to retain the less noble metal. Lastly, but also very importantly, results indicate that the rate of Pt redeposition significantly increases with temperature, which has been the main reason why mechanistic interpretation of the temperature-dependent kinetics related to the stability of Pt remained highly speculative until now.
The oxygen evolution reaction (OER) is the limiting step in splitting water into its constituents, hydrogen and oxygen. Hence, research on potential OER catalysts has become the focus of many ...studies. In this work, we investigate capable OER catalysts but focus on catalyst stability, which is, especially in this case, at least equally as important as catalyst activity. We propose a specialized setup for monitoring the corrosion profiles of metal oxide catalysts during a stability testing protocol, which is specifically designed to standardize the investigation of OER catalysts by means of differentiating between catalyst corrosion and deactivation, oxygen evolution efficiency, and catalyst activity. For this purpose, we combined an electrochemical flow cell (EFC) with an oxygen sensor and an inductively coupled plasma–optical emission spectrometry (ICP-OES) system for the simultaneous investigation of catalyst deactivation, activity, and faradaic efficiency of catalysts. We tested various catalysts, with IrO2 and NiCoO2 used as benchmark materials in acidic and alkaline environment, respectively. The scalability of our setup will allow the user to investigate catalytic materials with supports of higher surface area than those which are typical for microelectrochemical flow cells (thus, under conditions more similar to those of commercial electrolyzers).
Renewable energy has rapidly advanced in the global energy system, triggering the visible development of energy storage technologies in recent decades. Among them, the electricity-fuel-electricity ...approach is an effective way for the storage and utilization of renewable power. In this work, a bifunctional electrochemical flow cell integrating both ammonia production and electricity generation modes is developed for renewable energy conversion and storage. Ammonia, a hydrogen carrier having a high hydrogen content of 17.6 wt %, is relatively easier to convert to liquid phase for large-scale storage. The long-distance ammonia transport can reliably depend on the established infrastructure. In addition, as a carbon-free fuel beneficial for achieving the goal of carbon-neutrality, ammonia is considered as an environmentally benign and cost-effective mediator fuel. This flow cell is able to operate via two modes, i.e., an ammonia-production mode for energy storage in the form of ammonia (via nitrogen reduction reaction) and an electricity-generation mode for energy conversion in the form of electricity (via ammonia oxidation reaction). This flow cell is constituted by a PtAu/C-coated nickel-foam electrode for nitrogen and oxygen reduction reactions, a Pt/C-coated nickel-foam electrode for water and ammonia oxidation reactions, and an alkaline anion exchange membrane for charge-carrier migration. Charging this flow cell with the supply of nitrogen results in a Faradaic efficiency of 2.70% and an ammonia production rate as high as 9.34 × 10−10 mol s−1 cm−2 at 23 °C. Moreover, energizing this flow cell with ammonia results in an open-circuit voltage of 0.59 V and a peak power density of 3.31 mW cm−2 at 23 °C. A round-trip efficiency of 25.7% is realized with the constant-electrode mode.
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•A flow cell integrating ammonia production and electricity generation is developed.•It produces NH3 at a rate of 9.34 × 10−10 mol s−1 cm−2 with an efficiency of 2.70%.•It exhibits a voltage of 0.59 V and a peak power density of 3.31 mW cm−2 at 23 °C.•A round trip efficiency of 25.7% is realized with the constant-electrode mode.
•Pt and Ni dissolution mechanisms are morphology-independent.•Pt and Ni dissolution rates are morphology-dependent.•Increased Pt and Ni dissolution rate above 1 V versus RHE.•In situ ICP-MS evidence ...of Pt-skeleton nanostructure formation.•Long AST needed for steady state dissolution and catalyst's lifetime prediction.
An electrochemical flow cell combined with inductively coupled plasma mass spectrometry (FC-ICP-MS) is a powerful tool to understand the mechanisms of metal dissolution and to develop mitigation strategies. Herein, we quantified in situ the amount of Pt and Ni atoms dissolved from PtNi/C nanocatalysts employed to electrocatalyze the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cell cathode. The nanocatalysts feature similar crystallite size and Pt:Ni atomic ratio but different morphologies (spheres, octahedra, sponges). The FC-ICP-MS results reveal that the nanocatalyst morphology affects the dissolution rate of Pt and Ni but not the dissolution mechanism. They also provide analytical evidence that dissolution of Pt atoms is consistently accompanied by the dissolution of Ni atoms exceeding the stoichiometric composition. Furthermore, we demonstrate that ex situ acid leaching mitigates, but does not entirely prevent, the electrochemical dissolution of Ni atoms. Stabilized Pt and Ni dissolution rates were achieved after a one hour long accelerated stress test (AST). We provide evidence that the Pt dissolution rate remains constant before and after the AST. In contrast, the dissolution rate of Ni decreases by a factor of 10 following the AST. Among various nanoparticle shapes, spherical PtNi/C nanoparticles offer the best solution regarding the Pt and Ni retention compared to other nanoparticle shapes.
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A sequential injection analysis device has been developed and applied for the automated determination of Mn(II) in environmental water samples. Differential pulse cathodic stripping voltammetry is ...selected as the electrochemical detection method. The device consists of several electronic equipment. The electrochemical flow cell was designed for replacing the traditional three-electrode system and introducing high reproducibility. An electrochemical analyzer saddled with laboratory-programmed software written by Embarcadero Delphi 10.2. For higher current response, various determination parameters such as the flow rate, the medium pH, the deposition potential and the thickness of gasket in the electrochemical flow cell have been optimized. Under the optimal conditions, the detection limit (3σ/slope) of 0.63 μg L−1 and a calibration curve (R2 = 0.9987) of current response and Mn(II) concentration from 2.5 μg L−1 to 200 μg L−1 could be achieved. The device was successfully applied to the determination of trace Mn(II) in environmental water samples, and in continuous real-time monitoring of Mn(II) variations in tap water for 14 days. The results are consistent with the reference method and the average recovery is found to be 95.2%–101.4%. The device shows high sensitivity and reproducibility in the determination of Mn(II), and presents a great potential for on-site and real-time detection of metal ions where rapid, low-cost and low-volume analysis is required.
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•A portable sequential injection analysis device has been developed.•An electrochemical flow cell is designed for introducing higher reproducibility.•The detection limit for Mn(II) was as low as 0.63 μg L−1•The sequential injection analysis device has been applied in real-time monitoring of Mn(II) of tap water for 14 days.
This paper highlights the potential of electrochemical flow cells for oxidative-stress testing of active pharmaceutical ingredients using canagliflozin as a model substance. Based on design of ...experiments, we developed our method through a reduced combinatorial design, optimizing the following independent variables: cell size, electrolyte flow rate, electrolyte concentration, and electrolyte pH. Using ammonium phosphate buffer with methanol in a 50/50 vol ratio as a working electrolyte, we electrochemically oxidized samples and analyzed them by high-performance liquid chromatography, considering the following dependent variables: peak area of each impurity, peak area of canagliflozin, and the percentage of the corresponding peak areas. Our results showed that the most significant independent variables were electrolyte pH and flow rate. By data optimization, we determined the most suitable conditions for electrochemical oxidation of canagliflozin, namely 50 µm cell size, 300 mM electrolyte concentration, 0.1 mL/h electrolyte flow rate, and electrolyte pH = 4. The repeatability of the method, expressed as the relative standard deviation of the canagliflozin peak area, measured in ten separately oxidized samples, was 1.64%. For comparison purposes, we performed a degradation experiment using hydrogen peroxide, identifying five identical impurities in both cases, as confirmed by mass spectrometry. The degradation products formed when using the chemical method after 1, 3, and 7 days totaled 0.09%, 0.75%, and 3.75%, respectively, and the degradation products formed when using the electrochemical method after 3 h totaled 3.11%. Oxidation with hydrogen peroxide required 7 days, whereas electrochemical oxidation was completed in 3 h. Overall, the electrochemical method significantly saves time and reduces the consumption of active ingredients and solvents thanks to the miniaturized size of the electrochemical cell, thereby minimizing the costs of forced degradation studies.
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•Innovative electrochemical approach to oxidation study of canagliflozin.•Electrochemical oxidation is faster than hydrogen peroxide oxidation.•Identical degradation products were formed by both methods.•Different effect of pH was observed in both methods.
•A novel porous copper electrode of high surface areas and low densities was prepared.•The copper cathode was examinated for electroreduction of nitrate to ammonium.•Selective and quantitative ...reductionof nitrate was obtained in neutral solution.•High chemical yields and current efficiencies toward ammonium formation was recorded.•Recycling of nitrates as an abundant and inexpensive source of ammonium.
The aim of this work was to set up a novel electrochemical system allowing an efficient transformation of concentrated nitrate solutions to ammonium and which can be subsequently implemented on a large scale application. First, this paper describes the preparation of a porous copper modified electrode by successive electrodeposition of nickel then copper on a graphite felt of large specific surface area. Homogeneous Cu coating of all fibers in the 3D porous structure was successfully obtained using low concentrations of copper salts and high applied current intensities. The porous copper electrode was then used in a flow electrochemical process to achieve a selective and quantitative transformation of concentrated nitrate into ammonium. Different electrolytic solutions, slightly acid (acetate buffer) or neutral (phosphate buffer), and flow rates were investigated. The nitrate solution was quantitatively reduced into NH4+ with high selectivity in only one pass through the electrode. When the applied current was similar to the theoretical one, the maximum selectivity (96%) and the best current efficiency (72%) for NH4+ formation were reached at pH 7.2 with a flow rate of 2mLmin−1. The obtained ammonium solution can be subsequently used either as a potential nitrogen source during microbial culture or simply as a fertilizer.
The electrocatalytic reduction of CO2 on gold cathodes was found to differ significantly between a standard batch electrochemical cell and a flow cell incorporating a porous gold cathode. While the ...well-known influence of KHCO3 concentration on product selectivity was observed in the batch cell, the selectivity of the CO2 reduction reaction was shown to be independent of KHCO3 concentration in the flow cell. The Faradaic efficiency for CO production was found to be 80–90% regardless of the KHCO3 concentration whereas in the batch cell it decreased from 75% to 35% as the KHCO3 concentration is increased from 0.05 to 0.5 mol L−1. The current density was found to be independent of the KHCO3 concentration and similar in both cells (−4 to −10 mA cm−2 at −1.3 V vs Ag|AgCl). As the KHCO3 concentration effect is normally attributed to changes in the local pH at the cathode–electrolyte interface brought about by the buffering action of the electrolyte, the results found in this work suggest that pH buffering can be suppressed or manipulated in some cell/electrode configurations. In the flow cell used in this work, it is suggested that poor transport of the KHCO3 through the porous cathode support to the active surface results in higher local pH than that found at the surface of a cathode immersed in a traditional batch cell.
•The direct comparison between a batch (H-cell) and a flow-cell has been made.•The influence of KHCO3 concentration on Faradaic efficiency is significantly different in the two cells.•Up to 90% Faradaic efficiency towards CO production can be obtained in the flow-cell.
Abstract
This paper presents the results of investigating the influence of design parameters of an electrochemical flow cell based on film interdigitated microelectrodes on its cell constant. This ...investigation is performed by the analytical method. To determine the cell constant the linear resistance between the adjacent fingers of the interdigitated microelectrodes is used. In its turn this resistance is found from the potential distribution in the unit subdomain of the interdigitated microelectrode system of the cell with the limited height. The dependencies of the cell constant on the cell height and the design parameters of the interdigitated microelectrode system (the spacing between fingers and the finger width) are determined. The cell height at which the change of the design parameters of the interdigitated microelectrode system has the least effect on the cell constant is found.
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