Electrochemical Flow Reactor Research Articles

Assessment of pillar-array electrodes for electrochemical flow reactors using a novel hydrodynamic electrode performance factor

This work introduces and validates a Hydrodynamic Electrode Performance Factor (HEPF) for flow reactors. Traditional approaches to electrode optimization often rely on separated mass transfer and pressure drop metrics, hindering comparisons. We address this issue by combining electrochemical and hydrodynamic parameters through a new mathematical expression. This formulation draws inspiration from established equations in heat transfer and the widely recognized Chilton-Colburn analogy, aiming to develop a quantification method independent of the experimental arrangement. The HEPF is complementary to the well-established volumetric mass transfer coefficient and to Storck’s energetic effectiveness postulates for electrochemical reactors. Additionally, this study validates the proposed equation experimentally and then applies it to evaluate pillar array electrodes using 2D computational fluid dynamics simulations for laminar flow conditions. Both experimental and simulation approaches are used to analyze the hydrodynamic behaviour of the electrodes, utilizing the Forchheimer and Hagen-Poiseuille numbers. Notably, preliminary turbulence effects are observed at Reynolds numbers as low as 50 to 125. Visualization of velocity streamlines revealed distinct wake formation behind the pillars at these low Reynolds numbers. This study also explores how reactor inlets, outlets, and tubing pressure losses affect electrode performance. Results emphasize the importance of considering pressure drop, which is integral to the new hydrodynamic performance factor. Analysis of pillar array electrodes demonstrates that reducing both interpillar distance and pillar radius leads to improved electrochemical performance.

3D printed optimized electrodes for electrochemical flow reactors

Recent advances in 3D printing have enabled the manufacture of porous electrodes which cannot be machined using traditional methods. With micron-scale precision, the pore structure of an electrode can now be designed for optimal energy efficiency, and a 3D printed electrode is not limited to a single uniform porosity. As these electrodes scale in size, however, the total number of possible pore designs can be intractable; choosing an appropriate pore distribution manually can be a complex task. To address this challenge, we adopt an inverse design approach. Using physics-based models, the electrode structure is optimized to minimize power losses in a flow reactor. The computer-generated structure is then printed and benchmarked against homogeneous porosity electrodes. We show how an optimized electrode decreases the power requirements by 16% compared to the best-case homogeneous porosity. Future work could apply this approach to flow batteries, electrolyzers, and fuel cells to accelerate their design and implementation.

An Analytical Model for Electrochemical Tubular Flow Reactors

This paper introduces the first analytical model designed for tubular electrochemical flow reactor, enabling a detailed examination of how reactor geometry and material selection impact performance. The model revealed that certain conditions, such as high electrode resistance relative to charge transfer, electrolyte, and separator resistance, can lead to uneven current distributions and reduced electrode utilization. The model highlights a critical electrode radius, dependent on reactor geometry and material properties, that minimizes the Area Specific Resistance (ASR) while minimizing reactor size. Additionally, it was found that the ASR increases with reactor length, but this effect can be mitigated by using highly conductive electrodes, thus allowing for enhanced power output. These insights provide a foundation for future research and the development of more efficient tubular reactor designs.

Electrocatalytic Conversion of Plasma-Activated CO2 Toward Multicarbon Products

Renewable electricity-powered CO2 reduction reaction (CO2RR) toward chemicals and fuels has been gaining significant attention not only for achieving net-zero carbon emissions but also for enabling long-term energy storage. In electrochemical conversion, CO2 can be upgraded into single- or multicarbon products such as carbon monoxide, formate, and ethylene with remarkable selectivity. However, challenges still exist in terms of high overpotential, limited product range, and low production rates. Moreover, most reported CO2RR to multicarbon products which used Cu as catalysts have predominantly generated C2 products like ethylene or ethanol. However these systems require further performance improvement to target C3+ products which have higher energy density and market price. Another electrified conversion technique involves non-thermal plasma, which can activate CO2 into radical, ionized, and vibrationally excited species at atmospheric pressure and near-ambient temperature. However, plasma processes are non-selective, which poses limitations for controlling reaction pathways and necessitates H2 or light alkanes as co-reactants to produce hydrocarbons.We synergized plasma and electrocatalytic conversion to demonstrate a combined CO2RR process that overcomes the limitations of each individual method. Through the integration of a dielectric barrier discharge plasma and an electrochemical flow reactor, pre-activated CO2 was electrochemically converted on a Cu electrode to produce multicarbon products. The combination enhanced the faradaic efficiency and reaction rate of desirable products and opened new reaction pathways by increasing the activity of CO2 prior to adsorption. The production rates of ethanol, propanol, and acetaldehyde were significantly increased, and new products such as methanol, acetylene, and ethane that were formed only in the combined reaction were detected. The product distribution was studied according to plasma-activated states of CO2 and the electrochemical applied potential. To elucidate the synergistic effects in the combined system, the selectivity and production rates were compared with those in the plasma-only and electrochemical-only reactions. Further control experiments using ground-state reactants were conducted, and the excited states during plasma activation were identified by optical electron spectroscopy. This work represents not only electrocatalysis of pre-activated reactants for enhanced generation of multicarbon products during electrified conversion of CO2, but also demonstrates synergistic convergence of plasma and electrocatalysis for converting reactants possessing strong chemical bonds.

Leveraging Flow-Assisted Electrochemistry Toward Decarbonization of Cement Manufacturing

In an effort to decarbonize the global economy by 50% in 2030 and achieve net-zero carbon emissions by 2050, there is a dire need to electrify industrial processes [1]. Approximately 8% of global carbon emissions comes from cement production [2]. Considering the rising demand for cement due to infrastructure expansion, it is critical to develop new concepts for the decarbonization of cement production. With this goal in mind, our work explores the effectiveness of flow-assisted cement electrolysis as a replacement to conventional fossil fuel based high-temperature kilns in cement manufacturing plants [3].In this study, we employ a scalable 3-channel flow-reactor with acidic anolyte, basic catholyte, and a neutral chemical flush in between to generate calcium hydroxide, Ca(OH)2 [4, 5], which is the key ingredient in cement manufacturing. The central channel is separated from either half cells by a cation exchange and an anion exchange membrane. The electrochemical performance of the proposed cement electrolyzer under a variety of operating conditions is investigated by considering the key variables in reactor design, including flow rate, temperature, catalyst choice and feed concentrations, to shed light into the practical challenges of running a 3-channel flow reactor. Our preliminary study indicates that membranes are possibly responsible for a significant fraction of the limited yields of Ca(OH)2. Specifically, the anion exchange membranes tested are susceptible to degradation in alkaline conditions displaying poor ionic conductance, whereas the cation exchange membranes allow significant water crossover. The findings from this study pave the way in understanding key components for cement electrolysis and other electrochemical systems employing 3-channel flow reactors. References DeAngelo, J., et al., Energy systems in scenarios at net-zero CO2 emissions. Nature Communications, 2021. 12(1): p. 6096. Ellis, L.D., et al., Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams. PNAS, 2019. 117(23): p.12584. Rissman, J., et al., Technologies and policies to decarbonize global industry: Review and assessment of mitigation drivers through 2070. Applied Energy, 2020. 266: p. 114848. Perego, A., et al., Electrochemical Flow Reactor for Cement Clinker Production. ECS Meeting s, 2021. MA2021-02(27): p. 840. Olsson, J.A., S.A. Miller, and M.G. Alexander, Near-term pathways for decarbonizing global concrete production.Nature Communications, 2023. 14(1): p. 4574.

Construction of electrochemical flow reactor: static mixing and micro-cell for dehydrogenation oxidation from TNT to 2,2’,4,4’,6,6’-hexanitrostilbene

From the electrochemical synthesis in beakers to the application of electrochemical reactors, flow electrosynthesis has become more and more prominent in the field of organic synthesis. But for multi-feed reactions, the problem of efficient mixing in the electrochemical reactor remains unresolved. A novel electrolytic cell was devised to facilitate thorough mixing of various feedstocks during electrochemical oxidation. With structural optimization guided by computational fluid dynamics (CFD) simulations, the choice of reaction channels was deliberated upon, alongside an elucidation of the mixing mechanism. The reactor's performance was assessed based on both mixing efficiency and electrochemical oxidation capability with the synthesis of 2,2’,4,4’,6,6’-hexanitrostilbene (HNS) serving as a model. The high efficiency of the electrochemical reactor was verified by the enhanced yield, purity, and faradaic efficiency of HNS. It is environmentally friendly and easy to realize industrial production.

Hardness Removal by A Continuous Flow Electrochemical Reactor from Different Types of Water

The present study focuses on the technique of hardness removal by using a novel reactor performing an electrocoagulation (EC) process. The variation of alkalinity is also recorded. Continuous flow experiments were conducted for Total Hardness (TH) removal using a transparent plastic reactor using aluminum plate electrodes that have holes so that the water flows through the plates in a zigzag way. The influence of various operating parameters such as the number of plates (two and four), flow rate (600, 1000 L/h), and water type (Tigris River & rejected water from Reverse Osmosis system RO) was investigated. The results showed that an increase in the number of electrodes led to an increase in the total hardness removal efficiency. In addition, the increase in the flow rate led to a decrease in the removal efficiency. For the rejected RO water type, the highest hardness removal rate was 16.16% for 4 plates electrodes and 600 L/h flow rate while for the river water was 29% for 4 plates electrodes and 1000 L/h.

Selective electrochemical oxidation of organic compounds in a mass transfer-enhanced electrochemical flow reactor (e[sbnd]NETmix)

eNETmix stands as an electrochemical flow reactor engineered to enhance mass transfer. This study aimed at assessing the performance of the eNETmix reactor in the realm of organic electrosynthesis. Specifically, the research focused on the selective electrochemical oxidation of 4-methoxybenzyl alcohol (4-MBA) to p-anisaldehyde (PAA) using a bare fluorine-doped tin oxide (FTO) anode. The efficiency of the process was assessed for distinct current densities (j), Reynolds numbers (Re), supporting electrolyte contents, and substrate initial contents. The eNETmix reactor was extensively compared to a commercial electrochemical flow reactor (MicroFlowCell from ElectroCell, Denmark). eNETmix facilitated the use of a broader range of j (0.8–2.0 mA cm−2versus 0.8 mA cm−2) together with smaller Re (≥190 versus >1750), supporting electrolyte contents (≥1 mM versus ≥30 mM), and substrate initial contents (≥2.0 mM versus ≥3.0 mM) with no loss of PAA production or energy consumption. These findings underscore a remarkable suitability of eNETmix as a reactor for organic electrosynthesis.

Sequential Paired Electrochemical Transformation of Styrene Oxide via Anodic Meinwald Rearrangement and Cathodic Nitro­methylation in an Electrochemical Flow Reactor with Catalytic Electrical Input

AbstractPaired electrosynthesis, which utilize both anodic and cathodic events in electrolysis, enables attractive transformations with higher current efficiency than conventional electrosynthesis. The electrochemical flow technique has been widely employed to ensure stable reaction conditions and mitigate issues stemming from mass transfer. In this study, the electrochemical Meinwald rearrangement of styrene oxides was investigated, yielding aldehydes as intermediates, followed by the nitromethylation of aldehydes to produce β-nitro alcohols. These reactions were achieved with catalytic electrical input, enabling the conversion of various styrene oxides into the corresponding β-nitro alcohols.

Correlating Electrolyte Infiltration with Accessible Surface Area in Macroporous Electrodes using Neutron Radiography

Carbon-based porous electrodes are commonly employed in electrochemical technologies as they provide a high surface area for reactions, an open structure for fluid transport, and enable compact reactor architectures. In electrochemical cells that sustain liquid electrolytes (e.g., redox flow batteries, CO2 electrolyzers, capacitive deionization), the nature of the interaction between the three phases - solid, liquid and gas - determines the accessible surface area for reactions, which fundamentally determines device performance. Thus, it is critical to understand the correlation between the electrolyte infiltration in the porous electrode and the resulting accessible surface area in realistic reactor architectures. To tackle this question, here we simultaneously perform neutron radiography with electrochemical measurements to correlate macroscopic electrode saturation/wetting with accessible surface area. We find that for untreated electrodes featuring neutral wettability with water, the electrode area remains underutilized even at elevated flow rates, both for interdigitated and parallel flow fields. Conversely, increasing the electrode hydrophilicity results in an order-of-magnitude increase in accessible surface area at comparable electrode saturation, and is less influenced by the electrolyte flow rate. Ultimately, we reveal useful correlations between reactor architectures and electrode utilization and provide a method that is broadly applicable to flow electrochemical reactors.

Optimization of Active Chlorine Production in a Filter-Press Type Electrochemical Reactor through Continuum Modelling and Response Surface Methodology

This study proposes a methodology to optimize the design of an electrochemical flow-by reactor to increase the active chlorine production. The performances of various reactor configurations were evaluated using Computational Fluid Dynamics, starting from the dimensions of the well-known FM01-LC reactor channel (B = 4 cm, L = 16 cm, and S = 1 cm), increasing or decreasing each component by 25%. These conditions were calculated using a Box-Behnken design of experiments, screening out the above dimensions as parameters in addition to the volumetric flow, which was operated at two different rates: 1 and 5 l min−1. A surface response methodology (RSM) was utilized to optimize the response variables, and determine the best design parameters. The combined computational study herein proposed suggests that the optimization of the flow electrochemical reactor design is a compromise between the flow uniform distribution, and mass transfer. It is found that the optimization method used is adequate at the experimental level, since the optimized channel (0.01 M) presents better performance than the conventional FM01-LC channel (0.002 M), after 60 min of experimental electrolysis. It is expected the current analysis will contribute to the development of new filter-press-type electrochemical reactors optimizing chlorine production for numerous applications.

A parallel line probe for spatially selective electrochemical NMR spectroscopy

In situ NMR is a valuable tool for studying electrochemical devices, including redox flow batteries and electrocatalytic reactors, capable of detecting reaction intermediates, metastable states, time evolution of processes or monitoring stability as a function of electrochemical conditions. Here we report a parallel line detector for spatially selective in situ electrochemical NMR spectroscopy. The detector consists of 17 copper wires and is doubly tuned to 1H/19F and X nuclei ranging from 63Cu (106.1 MHz) to 7Li (155.5 MHz). The flat geometry of the parallel line detector allows its insertion into a high electrode surface-to-volume electrochemical flow reactor, enabling a detector-in-a-reactor design. This integrated device is named “eReactor NMR probe”. Combined with B1-selective pulse sequences, selective detection of the nuclei at the electrode-electrolyte interface, that is within a distance of 800 μm from the electrode surface, has been achieved. The selective detection of 7Li and 19F nuclei is demonstrated using two electrolytes, LiCl and LiBF4 solutions, respectively. A good B1 homogeneity with an 810° to 90° pulse intensity ratio of 68–72 % was achieved. Using electrochemical plating of lithium metal as a model reaction, we further demonstrated the operando functionality of the probe. The new eReactor NMR probe offers a general method for studying flow electrochemistry, and we envision applications in a wide range of environmentally relevant energy systems, for example, Li metal batteries, electrochemical ammonia synthesis, carbon dioxide capture and reduction, redox flow batteries, fuel cells, water desalination, lignin oxidation etc.

Exploring the impact of partial pressure and typical compounds on the continuous electroconversion of CO2 into formate

Previous research in CO2 electroreduction primarily focused on cathodic electrocatalysts and electrode configurations using pure CO2. Few studies explored the impact of residence time and N2/O2 compounds, crucial for practical industrial implementation. In this study, the effect of residence time and the influence of N2 and O2 compounds on CO2 electroreduction to formate are investigated, employing Bi carbon-supported nanoparticles in the form of Gas Diffusion Electrodes within an electrochemical flow reactor with a single pass of the reactants. The results highlight the critical role of residence time and the impact of N2 and O2 compounds in the CO2 electroconversion process. On the one hand, the evaluation of residence time holds paramount significance for the potential establishment of a large-scale CO2 recycling plant, as it has the potential to significantly impact both the capital and operational costs of the integrated electrolyzer-separator system. Optimal results are obtained in the range of residence times between 1.8 and 2.9 seconds, corresponding to CO2 flow rates of 150 and 250 mL·min−1, respectively. On the other hand, the study resulted in a promising Faradaic Efficiency for formate of 75.0%, with similar values achieved at CO2 concentrations in the range of 75 – 100 vol%. These results are particularly noteworthy as they demonstrate that achieving a CO2 capture efficiency of 100% is not necessary, thereby reducing the costs associated with this process and, consequently, the overall cost of integrating both capture and utilization processes in a CO2 recycling plant.

Visualization of CO2 electrolysis using optical coherence tomography.

Electrolysers offer an appealing technology for conversion of CO2 into high-value chemicals. However, there are few tools available to track the reactions that occur within electrolysers. Here we report an electrolysis optical coherence tomography platform to visualize the chemical reactions occurring in a CO2 electrolyser. This platform was designed to capture three-dimensional images and videos at high spatial and temporal resolutions. We recorded 12 h of footage of an electrolyser containing a porous electrode separated by a membrane, converting a continuous feed of liquid KHCO3 to reduce CO2 into CO at applied current densities of 50-800 mA cm-2. This platform visualized reactants, intermediates and products, and captured the strikingly dynamic movement of the cathode and membrane components during electrolysis. It also linked CO production to regions of the electrolyser in which CO2 was in direct contact with both membrane and catalyst layers. These results highlight how this platform can be used to track reactions in continuous flow electrochemical reactors.

Electroreduction of divanillin to polyvanillin in an electrochemical flow reactor

The electrochemical conversion of biobased intermediates offers an attractive and sustainable process for the production of green chemicals. One promising synthesis route is the production of the total vanillin-based polymer polyvanillin, which can be produced by electrochemical pinacolization of divanillin (5–5´bisvanillyl). Divanillin can be easily enzymatically generated from vanillin, a renewable intermediate accessible from lignin on an industrial scale. This study investigates systematically the electrochemical production of polyvanillin in a divided plane parallel flow reactor in recirculation mode. Several analytic methods, such as online UV–VIS spectroscopy, size exclusion chromatography (SEC), 2D-NMR (HSQC, 13C/1H), TGA and DSC were used to monitor the reaction progress and to characterize the reaction products under different galvanostatic reaction conditions revealing new insights into the reaction mechanism and structural features of the polymer. Further, by using an electrochemical engineering-based approach determining the limiting current densities, we readily achieved high current densities over 50 mA cm−2 for the polyvanillin synthesis and reached averaged molecular weights up to Mw = 4100 g mol−1 and Mn = 2700 g mol−1. The cathodic polymerization to polyvanillin offers an innovative approach for the electrochemical production of biobased polymers presented on flow cell level.Graphical

A continuous flow electrochemical reactor using readily available metal wires and carbon fibers as electrodes: environmentally benign halogenations of alkenes, alkynes, and aromatics

We have developed a new continuous-flow electrochemical reactor using readily available metal wires and carbon fibers as electrodes. Environmentally benign halogenations were used as a proof of concept.

E–NETmix: A pioneering electrochemical flow reactor with enhanced mass transfer

e–NETmix is an innovative electrochemical continuous-flow reactor with a static mixer characterized by a network of cylindrical chambers interconnected by prismatic channels arranged at 45° angles. This study focuses on the proof-of-concept of e–NETmix as regards global mass transfer properties by applying the limiting current technique for the ferricyanide-ferrocyanide reaction at different Reynolds numbers (Re). For Re from 100 to 1750, the volumetric mass transfer coefficients (kmA) ranged from ∼1.3 × 10−1 s−1 to ∼5.1 × 10−1 s−1 and the mass transfer coefficients (km) ranged from ∼6.8 × 10−5 m s−1 to ∼2.7 × 10−4 m s−1. A comprehensive comparison of the e–NETmix reactor with a commercial electrochemical flow reactor, the MicroFlowCell from ElectroCell (Denmark), revealed kmA and km values ∼63-fold and ∼8.6-fold higher in the new reactor, respectively, for similar Re. Moreover, the novel reactor showed mass transfer superiority over most existing reactors reported in the literature, allowing the attainment of kmA values up to ∼54-fold higher for similar mean linear fluid velocities (νavg) and km values up to ∼24-fold higher for similar Re. The superior performance of e–NETmix can be mainly attributed to the static mixer, which promotes convective mixing and the development of a laminar chaotic flow regime. This novel electrochemical flow reactor can be used to enhance several electrochemical and photoelectrochemical reactions.

Uniformity of Electrodeposited Coatings Onto Additively Manufactured Graphite Lattice Electrodes

The ability to uniformly electrodeposit metallic coatings onto geometrically complex substrates plays a significant role in developing specialized applications from coating detailed RF components to depositing catalytic coatings onto ordered foams electrodes for electrochemical flow reactors. However, there presently lacks guidelines for electrodeposition in porous media due to the problem’s multi-scale complexity. We present a framework for deconvoluting this process through continuum-level modeling and experimental validation of electrodeposited copper onto additively manufactured conductive lattice structures. Through numerical simulations we can predict thickness profiles and validate the model prediction and coating quality through micro-computed tomography. We further devise scaling laws with the aim of facilitating control over deposition uniformities on different lattice architectures and dimensions under fluid flow. In extension, the manufacturing platform for functionalized electrodes is extended to battery applications as use in novel electrode geometries within rechargeable secondary batteries as well as plating thickness evolution in custom redox flow battery cathodes for grid scale energy storage.This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 within the LDRD program 20-ERD-056. LLNL-ABS-847849.

Catalytic Electricity Promoted Electrochemical Synthesis

Direct electron transfer from organic compounds has been used as a powerful catalyst to promote various chemical transformations. In particular, electrochemical organic synthesis enables both hole-catalyzed (anodic oxidation) and electron-catalyzed (cathodic reduction) transformations. We will present the catalytic cathodic reduction-promoted reactions and the application of an electrochemical flow reactor, which allows efficient transformations. Trimethylsilylcyanide (TMSCN), for example, could be reduced on a cathode, and the corresponding radical anion reacted with carbonyl compounds or imines. The addition reaction only required a small amount of electricity, and the catalytic transformation was achieved.In addition, the machine learning-assisted conditions optimization of the electrochemical flow synthesis has also been demonstrated. Gaussian process regression (GPR) could illustrate the relationships between the conditions and the reactivities on counter maps. The counter maps suggest that achieve a good yield or time-scale yield of the desired compounds.

Hydrothermal electrochemical flow reactor to independently control temperature, pressure, and potential for manganese oxide electrodeposition

Electrodeposition has been widely applied for the fabrication of functional materials; however, most previous deposition processes were limited to temperatures of less than 100 °C. Furthermore, reaction pressure was concomitantly determined with the reaction temperature, hindering the full exploration of synthetic conditions. Here, we developed a hydrothermal electrochemical flow reactor equipped with flowing system and that enables the independent control of temperature and pressure and applied this reactor to the synthesis of manganese oxides (MnOx) for electrochemical oxygen evolution reaction. Systematic investigation of temperature and pressure revealed that the crystallinity and morphology of MnOx was influenced by deposition temperature, with particle size decreasing under higher pressure (4 MPa). Electrodeposition at higher temperature (160 °C) at 1 MPa generated a mixed phase of ε- and γ- MnO2, which showed superior electrochemical water oxidation activity to samples prepared at lower temperature (80 and 100 °C, respectively), achieving a current density of 10 mA cm−2 for at least 100 h under acidic conditions (pH 2.3). Our results show that the hydrothermal electrochemical flow reactor allows expanding synthetic parameters for the synthesis of highly functional catalytic materials.