Flow Cell Experiments Research Articles

Framework Integrated with Flow Cell Experiments and Simulations for Understanding Etching in Chemical Conversion Treatments

In this study, a new framework integrates simulations and flow cell experimentation to quantitatively understand the mechanism of chemical treatment reactions. Using this framework, the mechanisms of etching reactions induced by weak and strong acids were specifically investigated. A flow cell system experiment was developed for the etching experiment. Two acids (HNO3 and HF) were used, along with HNO3 without electrolytes. Average flow velocities were measured, and the molar flux of Fe2+ ions was determined by sampling the solution passing through the flow cell and measuring the iron content by using inductively coupled plasma. A concentration field simulation of the etching reaction in the flow cell was conducted. The concentration field within the boundary layer was visualized to understand the mechanism of H+ ion supply to the metal surface. In the case of weak acid solutions, H+ ions are primarily supplied by dissociation. In contrast, they were supplied by diffusion in strong acid solutions. A boundary layer formed within 100 μm from the metal surface. The experimental and simulated molar flux of Fe2+ ions were compared. The molar flux attributed to weak acid etching was more than 10 times that attributed to strong acids. The reaction rate constant of the H+ reduction reaction was evaluated through a parameter study. The influence of spectator ions on the etching process was investigated. An experiment was conducted to compare the etching of iron plates using HNO3 solutions with different concentrations of spectator ion. The results confirmed that the higher the concentration of the spectator ion, the greater the etching amount. Numerical analysis revealed that the electric field in the electric migration term acts in a direction that impedes the movement of H+ ions to the metal surface. While it is already known that electric migration inhibits electrode reactions, this study enabled its quantitative visualization and evaluation.

Impact of Magnetic Graphene Nanofluidic Electrolytes for I3 -/I - in Zinc/Iodide Redox Flow Batteries

Redox flow batteries (RFBs) stand out as a highly promising technology to tackle the growing challenges of intermittent energy supply, known for their extended cycle life, low environmental impact, scalability, and design flexibility1 , 2. Among various RFBs, aqueous zinc-iodide redox flow batteries (ZIRFBs), have been gaining increasing attention, due to their low material costs, high solubility (ZnI2 ~ 7M), rapid kinetics, and impressive theoretical energy density (322 Wh/L)3 , 4. However, the redox reactions of I3 -/I- on the graphite felt cathode in ZIRFBs exhibit poor reversibility and electro-activity compared to the Zn/Zn2+ pair at the anode5. This discrepancy results in significant electrode polarization resistance, a major hindrance to achieving high energy efficiency and a primary obstacle to commercialize large-scale ZIRFBs. To address this issue, researchers typically enhance the cathode’s electrochemical activity or conductivity to promote the I3 -/I- reaction, thereby reducing polarization resistance, by modifying the cathode with materials such as graphene quantum dots6, metal-organic frameworks5, and conductive polymers7.Unlike electrode modifications, electrolyte nanofluids have been relatively underexplored in the RFBs field, despite several studies on carbon-based nanofluids in all vanadium RFBs and polysulfide/iodide RFBs. These nanofluidic electrolytes have demonstrated superior conductivity and higher surface area compared to carbon felt, thereby enhancing battery performance. In this study, a magnetic graphene composite was developed using a self-assembly method facilitated by electrostatic force. The graphene was prepared by electrochemical exfoliation of graphite, modified with poly(diallyldimethylammonium chloride) (PDDA) to provide a positively-charged.Material characterization with X-Ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) confirmed the successful synthesis of the composite. Flow cell experiments with a ZIRFB using a 3M solution revealed a notable improvement in the charge-discharge energy efficiency upon the addition of 0.3 mg/ml PDDA-graphene, from 72% to 82% at a current density of 30 mA/cm2, and from 47% to 60% at a current density of 70 mA/cm2. Performance improvements were also observed compared to unmodified graphene.This magnetic nanofluid holds promise for the easy separation of nanoparticles and electrolytes by a magnetic field, enabling the recovery and reuse of the nanoparticles. To endow nanoparticles with magnetism for cost-effective recovery, we further modified the PDDA-graphene with magnetite, using electrostatic self-assembly. The mass ratio of graphene to magnetite in the composite had a significant impact on the ZIRFB flow cell performance. At a mass ratio of 4:1, the nanofluid enhanced ZIRFB energy efficiency by 7.3% and 9.7% at current densities of 30 and 70 mA/cm2, respectively. Conversely, when the mass ratio was 1:1, adverse effects on battery performance were observed. In addition to the charge-discharge energy efficiency, the battery performance was also evaluated using polarization to determine the maximum power density, and electrochemical impedance spectroscope (EIS). Vinco, J. H., Domingos, A. E. E. da C., Espinosa, D. C. R., Tenório, J. A. S. & Baltazar, M. dos P. G. Unfolding the Vanadium Redox Flow Batteries: An indeep perspective on its components and current operation challenges. J. Energy Storage 43, 103180 (2021).Lourenssen, K., Williams, J., Ahmadpour, F., Clemmer, R. & Tasnim, S. Vanadium redox flow batteries: A comprehensive review. J. Energy Storage 25, (2019).Yang, Y., Liang, S. & Zhou, J. Progress and prospect of the zinc–iodine battery. Curr. Opin. Electrochem. 30, 100761 (2021).Khor, A. et al. Review of zinc-based hybrid flow batteries: From fundamentals to applications. Mater. Today Energy 8, 80–108 (2018).Li, B. et al. Metal-Organic Frameworks as Highly Active Electrocatalysts for High-Energy Density, Aqueous Zinc-Polyiodide Redox Flow Batteries. Nano Lett. 16, 4335–4340 (2016).Liu, Y. et al. Stable static zinc-iodine redox battery constructed with graphene quantum dots coated graphite felt. J. Power Sources 520, 230861 (2022).Yang, J., Song, Y., Liu, Q. & Tang, A. High-capacity zinc-iodine flow batteries enabled by a polymer-polyiodide complex cathode. J. Mater. Chem. A 9, 16093–16098 (2021).

La0.8Sr0.2CoO3 Electrocatalyst for Oxygen Evolution Reaction in Alkaline Electrolysis: From Powder to the Fuel Cell Application

In recent years, there has been a growing need for new renewable energy sources due to the rapid depletion of conventional energy sources and an escalating energy demand. Since environmental protection concerns are increasing, electrochemical processes are becoming increasingly essential [1]. Specifically, the focus has shifted towards storing energy in hydrogen and its subsequent conversion into on-demand electricity [2]. Here, hydrogen, generated via water electrolysis, serves as either an intermediary for generating energy carriers like liquid fuels or plays a key role as an energy carrier [3]. Despite significant efforts focused on enhancing electrolyzers for energy conversion, the progression towards practical application has encountered challenges stemming from differing catalyst development requisites in academic and industrial research. This study proposes a systematic approach for efficiently transitioning electrocatalysts from fundamental research to application readiness for alkaline oxygen evolution reactions.Herein, La0.8Sr0.2CoO3 was chosen as a catalyst and compared with the benchmark material NiFe2O4. Initially, the La0.8Sr0.2CoO3 catalyst was successfully synthesized by scalable spray-flame synthesis. Following this, various inks were formulated utilizing different binders (Nafion®, Naf; Sustainion®, Sus). The dispersion stability of La0.8Sr0.2CoO3 and commercial NiFe2O4 inks was investigated in the presence of Nafion and Sustainion using analytical centrifugation and transmittograms. Subsequently, these selected dispersions were applied onto nickel substrates via spray coating techniques, ensuring a homogeneous catalyst distribution. Finally, the La0.8Sr0.2CoO3 and NiFe2O4 catalysts were subjected to extensive electrochemical evaluations, including glassy carbon rotating disk electrode, scanning droplet cell (SDC), compression cell, flow cell, and zero-gap cell, to evaluate the material performance. SDC findings highlight the excellent uniformity in La0.8Sr0.2CoO3 electrodes and NiFe2O4-Sustainion (standard deviation < 11%). However, the NiFe2O4-Sustainion film experienced delamination, exhibiting a standard deviation of 28%. SDC experiments offer advantages over various half-cell techniques by enabling the detection of any inhomogeneities or coating defects within the catalytic film. Additionally, complementary compression and flow cell experiments provide detailed information on the chemical and mechanical stress parameters resembling those in a full cell configuration. In assessing industrial applicability, the catalytic materials were undergone examination within a scalable full cell under industrial conditions (500 mA/cm² and 60 °C) utilizing a zero-gap cell setup. The observed trend in the full cell for the coated electrodes is as follows: La0.8Sr0.2CoO3-Naf > La0.8Sr0.2CoO3-Sus > NiFe2O4-Sus > NiFe2O4-Naf.These findings achieved through a well-structured coherent workflow, enhance our knowledge of the electrocatalytic system and offer essential insights for implementing novel materials in large-scale industrial applications. REFERENCES: [1] M.-S. Park, J. Kim, K.J. Kim, J.-W. Lee, J.H. Kim, Y. Yamauchi, Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems, Phys. Chem. Chem. Phys. 17 (2015) 30963–30977. https://doi.org/10.1039/C5CP05936D.[2] J.R. Varcoe, P. Atanassov, D.R. Dekel, A.M. Herring, M.A. Hickner, P.A. Kohl, A.R. Kucernak, W.E. Mustain, K. Nijmeijer, K. Scott, T. Xu, L. Zhuang, Anion-exchange membranes in electrochemical energy systems, Energy Environ. Sci. 7 (2014) 3135–3191. https://doi.org/10.1039/C4EE01303D.[3] C. Van Pham, D. Escalera-López, K. Mayrhofer, S. Cherevko, S. Thiele, Essentials of High Performance Water Electrolyzers – From Catalyst Layer Materials to Electrode Engineering, Adv. Energy Mater. 11 (2021) 2101998. https://doi.org/https://doi.org/10.1002/aenm.202101998.

Highly Active Nano-Porous Thin-Films for Water Electrolysis Using an Automated Print Technology Based on Spark Ablation

Accelerating hydrogen (H2) deployment via renewable electricity is a key G7 strategy for sustainable transitions in hard-to-decarbonize sectors (e.g., circular-plastics, -steel, -fertilizers,shipping, and aviation) therefore, Alkaline (AWE) and Polymer Electrolyte Membrane water electrolysis (PEMWE) play a crucial role amongst low-temperature power-to-X technologies for establishing a hydrogen network. Assuming all hydrogen will be green by 2030 (with ca. 150 million metric tons), a significant increase in electrolyser capacity to 3,000 gigawatts is necessary, given the current capacity of 0.3 gigawatts. However, the adoption of electrolysers faces a bottleneck due to scarce platinum group materials (PGMs) used as catalyst, specifically Iridium and Platinum. The commercial PGM loading per membrane electrode assembly (MEA) is at 3 mg/cm2, requiring substantial efforts to redesign electrocatalyst materials through a nano-architecture, necessitating a thousandfold increase in surface area (µm to nm scale) and a tenfold reduction in mass loading (mg to µg). The realization of this objective is conceivable through innovative surface engineering and manufacturing techniques, exemplified by. VSPARTICLE is actively advancing its manufacturing technology for green H2, bridging academia and industry . We developed a unique nano-printing technology which utilizes spark ablation for generating nano-porous electrocatalyst thin films across diverse elements and alloys. Unlike traditional methods, it eliminates the need for chemical precursors or binders, reducing waste and extra pre- / post-process steps. The VSP-P1 nano-printer serves as a crucial R&D tool for dry-synthesis, enabling both the production of complex electrocatalyst layers and also sample arrays high-throughput screening. This accelerates the discovery of new catalysts, fostering the creation and application of novel nanomaterials in specialized setups. Our oral presentation will unveil the latest findings concerning oxygen evolution electrodes, employing Ir-based and Ni-based catalysts produced through the innovative VSP-P1 nano-printing technology, which exhibit notable activity in acidic and alkaline water electrolysis, respectively, even at low loadings, such as 0.4 mg/cm2. Therefore, our oral presentation aims to show the latest findings on accelerated electrocatalysts discovery concerning oxygen evolution reaction (OER) produced through the innovative VSP-P1 nano-printing technology. In parallel to comprehensive flow-cell experiments, meticulous control tests and characterization techniques (XRD, XRF, HR-SEM) on proxy samples were conducted, leveraging the versatility of VSP-P1 to create identical nano-porous films on various substrates such as Si-wafer, conductive glass, and glassy carbon disks. The scalability of this dry manufacturing process, coupled with the rapid iteration capability for tuning material parameters and test-beds, promises a tenfold acceleration in electrocatalyst utilization. In summary, this presentation intends to reveal a methodology that not only shows an efficient strategy for catalyst utilization through nano-printed layers, but also shortens the time required to bring novel materials to market. Figure 1

An integrated evaluation of bioenhanced in situ LNAPL dissolution

Performance evaluation of in situ bioremediation processes in the field is difficult due to uncertainty created by matrix and contaminant heterogeneity, inaccessibility to direct observation, expense of sampling, and limitations of some measurements. The goal of this research was to develop a strategy for evaluating in situ bioremediation of light nonaqueous-phase liquid (LNAPL) contamination and demonstrating the occurrence of bioenhanced LNAPL dissolution by: (1) integrating a suite of analyses into a rational evaluation strategy; and (2) demonstrating the strategy's application in intermediate-scale flow-cell (ISFC) experiments simulating an aquifer contaminated with a pool of LNAPL (naphthalene dissolved in dodecane). Two ISFCs were operated to evaluate how the monitored parameters changed between a “no bioremediation” scenario and an “intrinsic in situ bioremediation” scenario. Key was incorporating different measures of microbial activity and contaminant degradation relevant to bioremediation: contaminant loss; consumption of electron acceptors; and changes in total alkalinity, pH, dissolved total inorganic carbon, carbon-stable isotopes, microorganisms, and intermediate metabolites. These measurements were integrated via mass-flux modeling and mass-balance analyses to document that in situ biodegradation of naphthalene was strongly accelerated in the “intrinsic in situ bioremediation” scenario versus “no bioremediation.” Furthermore, the integrated strategy provided consistent evidence of bioenhancement of LNAPL dissolution through intrinsic bioremediation by a factor of approximately 2 due to the biodegradation of the naphthalene near the pool/water interface.

Icarust, a real-time simulator for Oxford Nanopore adaptive sampling.

Oxford Nanopore Technologies (ONT) sequencers enable real-time generation of sequence data, which allows for concurrent analysis during a run. Adaptive sampling leverages this real-time capability in extremis, rejecting or accepting reads for sequencing based on assessment of the sequence from the start of each read. This functionality is provided by ONT's software, MinKNOW (Oxford Nanopore Technologies). Designing and developing software to take advantage of adaptive sampling can be costly in terms of sequencing consumables, using precious samples and preparing sequencing libraries. MinKNOW addresses this in part by allowing the replay of previously sequenced runs for testing. However, as we show, the sequencing output only partially changes in response to adaptive sampling instructions. Here we present Icarust, a tool enabling more accurate approximations of sequencing runs. Icarust recreates all the required endpoints of MinKNOW to perform adaptive sampling and writes output compatible with current base-callers and analysis pipelines. Icarust serves nanopore signal simulating a MinION or PromethION flow cell experiment from any reference genome using either R9 or R10 pore models. We show that simulating sequencing runs with Icarust provides a realistic testing and development environment for software exploiting the real-time nature of Nanopore sequencing. All code is open source and freely available here-https://github.com/LooseLab/Icarust. Icarust is implemented in Rust, with a docker container also available. The data underlying this article will be shared on reasonable request to the corresponding author.

Control mechanism of trichloroethylene back diffusion by microstructure in a low permeability zone

The trailing effect caused by the back diffusion (BD) of contaminants in low-permeability zones (LPZs), which prolongs remediation time and increases remediation costs, has caused widespread concern. In this study, the BD of trichloroethylene (TCE) from the LPZ to the high-permeability zone (HPZ) was determined using flow cell experiments. The anomalous variance in the BD flux of the TCE—spanning 2–4 times the deviation under identical experimental conditions, attracted our attention. To determine the cause of this aberrant behavior, a micro computed tomography (micro-CT) characterization of the flow cell was conducted, which revealed significant microstructural disparities in the LPZ. The study found that the pore connectivity of LPZs determines the efficiency of BD and that LPZs with different porosities have different sensitivities to connectivity. The pore shape complexity indicates the possibility of BD retardation, and remediation is more difficult for these types of LPZs. Changing the structure of LPZs to improve their remediation efficiency may be a new research topic. Notably, correcting the model parameters through microstructural characterization significantly refined the prediction accuracy.

Kinetics of the Reaction MSI− + O3 in Deliquesced Aerosol Particles: Implications for Sulfur Chemistry in the Marine Boundary Layer

AbstractMultiphase oxidation of methane sulfinic acid (MSIA) by ozone (O3) in deliquesced aerosol particles is an important but poorly constrained reaction in the marine boundary layer, hindering the accurate prediction of radiative forcing of natural aerosols. Large uncertainties arise from the unmeasured reaction rate constant for the aerosol multiphase reaction between O3 and methanesulfinate (MSI−), the dominant MSIA species in sea salt aerosols. Here, we directly measured by performing flow cell experiments coupled with a Raman spectroscopy to investigate the kinetics of multiphase oxidation of MSI− by O3 in pH‐buffered deliquesced aerosol particles relevant to marine atmospheric conditions. for aerosol particles was determined to be (2.2 ± 0.5) × 107 M−1 s−1, 10 times the value in dilute solutions. This higher rate constant would increase the yield of methane sulfonic acid from multiphase oxidation of MSIA and has important implications for accurate modeling of sulfur species.

The influence of NAPL distribution on the transport of PFOS in Co-contaminated media

The objective of this research was to examine the influence of nonuniform NAPL distribution and hydraulic-conductivity heterogeneity on the retention and transport of PFAS. Two-dimensional flow cell experiments were conducted to investigate the impact of NAPL configuration on PFOS retention. Two simplified NAPL configurations were used, one with decane present as residual and the other with greater-than-residual (pool) NAPL saturation. The measured and predicted retardation factors were 1.7 and 1.6 for the residual-NAPL flow cell. The fractions of retention associated with solid-phase sorption, NAPL-water interfacial adsorption, and NAPL absorption were 0.56, 0.43, and 0.1, respectively. The measured retardation factor was 1.4 for the pool-NAPL flow cell. Notably, the predicted retardation factor assuming no contribution from NAPL-water interfacial adsorption was 1.5. Comparison of the two values indicates a minimal contribution of NAPL-water interfacial adsorption to transport, which is attributed to the impact of by-pass flow effects that limited contact of PFOS with the NAPL present within the pool. Mathematical-model simulations were conducted to examine the impact of heterogeneity on PFOS transport in model NAPL-contaminated heterogeneous source zones. The results demonstrated that the impact of NAPL-water interface adsorption on PFAS transport in NAPL-contaminated source zones can be influenced by the magnitude of hydraulic-conductivity heterogeneity.

Asymmetric dinitrogen-coordinated nickel single-atomic sites for efficient CO2 electroreduction

Developing highly efficient, selective and low-overpotential electrocatalysts for carbon dioxide (CO2) reduction is crucial. This study reports an efficient Ni single-atom catalyst coordinated with pyrrolic nitrogen and pyridinic nitrogen for CO2 reduction to carbon monoxide (CO). In flow cell experiments, the catalyst achieves a CO partial current density of 20.1 mA cmgeo−2 at −0.15 V vs. reversible hydrogen electrode (VRHE). It exhibits a high turnover frequency of over 274,000 site−1 h−1 at −1.0 VRHE and maintains high Faradaic efficiency of CO (FECO) exceeding 90% within −0.15 to −0.9 VRHE. Operando synchrotron-based infrared and X-ray absorption spectra, and theoretical calculations reveal that mono CO-adsorbed Ni single sites formed during electrochemical processes contribute to the balance between key intermediates formation and CO desorption, providing insights into the catalyst’s origin of catalytic activity. Overall, this work presents a Ni single-atom catalyst with good selectivity and activity for CO2 reduction while shedding light on its underlying mechanism.

Remediation of Pool Dominated Trichloroethene Source Zones in Heterogeneous Porous Media by Cosmetic Surfactant Flooding

&lt;p&gt;A series of flow-cell experiments were performed to investigate the performance of cosmetic rhamnolipid surfactant flooding on the relationship between source zone mass removal and mass flux reduction for pool-dominated DNAPL TCE source zones in heterogeneous porous media. The results were also compared to those of water-flood control experiments to assess the surfactant enhanced flushing efficacy. The flooding experiments were performed for silica sand and natural calcareous soil representing two different degrees of physical heterogeneity. The result from the flow-cell experiments showed that higher than 97% of TCE mass was removed during rhamnolipid flooding for both porous media scenarios. Although, rhamnolipid flooding experiment results showed successful remediation performance, DNAPL TCE dissolution and rhamnolipid-enhanced dissolution in heterogeneous porous media system exhibited multi-step mass-flux reduction/mass-removal behavior due to the presence of less hydraulically-accessible pool-dominated TCE source zone. However, mass removal and mass-flux reduction relationships for rhamnolipid flushing cases exhibited more ideal removal behavior, indicating the more efficient remediation performance compared to water flooding alone. For all cases, the later stage of mass removal was controlled by the more poorly-accessible mass associated with pool-dominated source zones. The results of this study revealed the impact of non-uniformity of the flow-field and effect of enhanced-solubilization agent on mass removal and mass-flux reduction behavior for DNAPL source zones in saturated porous media&lt;/p&gt;&#x0D;

Membrane Transport and Performance in the All-Aqueous Copper Thermally Regenerative Battery

Redox flow batteries are emerging as a promising method to provide grid-scale power and long-duration energy storage safely and economically. The thermally regenerative ammonia battery (TRAB) is a new redox flow battery category that can be recharged using low-grade waste heat rather than electric energy, adding further flexibility to the applicability of flow battery systems. Recently, a new TRAB with all-aqueous electroactive species (referred to as the Cuaq-TRAB), as opposed to deposition-dissolution reactions, was found to have superior energy and power densities relative to competing TRABs. The use of bromide and ammonia stabilizes for both Cu(I) and Cu(II) oxidation states, while also creating a cell potential of up to 1.0 V. The potential can be recovered by thermally separating ammonia from the electrolyte and adding it back to alternate electrolyte chambers in successive cycles. Potential improvements in overall cell performance are possible by reducing ohmic losses associated with membrane selection. However, the ideal membrane for the Cuaq-TRAB is not obvious and raises interesting transport questions relative to the dominant redox-active copper species being negatively charged in the catholyte but positively charged in the anolyte. Furthermore, membrane crossover of ammonia, a small, uncharged molecule, was previously shown to be a primary source of parasitic losses for TRABs. Therefore, we investigated how different membrane types (cation, anion, and non-selective) affected ion transport and TRAB performance. A batch symmetry cell was used to determine membrane conductivity in the Cuaq-TRAB environment and membrane diffusion coefficients of each species in the electrolytes. Flow cell experiments were also conducted to find peak power, energy density, average power during discharge, and capacity fade over successive electric charge/discharge cycles. Tradeoffs between membrane conductivity and permeability observed in the symmetry cell are manifested in flow cell results as either high peak and average power or high energy density and low capacity fade. These results expand on potential methods for controlling transport in redox flow batteries and demonstrate the potential for non-selective membranes for electrochemical energy technologies.

(Invited) Concentrated Hydrogen Bonded Electrolytes with Ferrocene and Viologen for Redox Flow Batteries

We developed concentrated hydrogen bonded electrolytes (CoHBEs) derived from a mixture of choline chloride (ChCl) and ethylene glycol (EG) containing ferrocene and viologen redox species for redox flow batteries. CoHBEs are similar to deep eutectic solvents (DESs) in terms of having distinct physical properties including wide electrochemical window, and low volatility. However, CoHBEs do not necessarily meet the requirement of “deep eutectic temperature” at a specific composition of the parent compounds that form the DES. CoHBEs formed with viologen and ferrocene species in ChCl:EG demonstrate reversible redox reactions. More importantly, 0.5 M of a viologen derivative coupled with 1 M of a ferrocene derivative was achieved owing to the good solvent strength of ChCl:EG at 1:4 and 1:6 compositions. The resulting electrolyte presents about 2M equivalent concentration of the redox couple since the viologen derivative is able to undergo two successive electron transfer. A theoretical cell voltage of 1.35V is possible with this electrolyte. This presentation will discuss the electrochemical and transport properties of this electrolyte system, and their applicability in redox flow batteries as studied by spectro-electrochemical and flow cell experiments.

(Invited) In-Situ Observation of Copper Electroplating with Additives Using Micofluidic Devices

Recent advances in integrated circuit have been driven by packaging technology. 3D packaging using TSV (Through-Silicon Via) is becoming common in commercial products. TSVs are formed by filling deep holes with a conductive material. Copper is widely used as the conductive material, since filling the deep holes with copper is enabled by bottom-up electrodeposition using a combination of several additives. Suppressors, levelers, and accelerators are well known categories of additive to acid copper sulfate plating solutions. Bottom-up deposition is realized by various additive formulas. Using leveler alone as additive, extreme bottom-up filling has been demonstrated, and levelers are considered to be essential for bottom-up deposition. But the mechanism is not yet clear with multiple additives addition.Therefore, understanding of additive behaviors is important. Cyclic voltammetry using a rotational disk electrode has been widely used in additive studies, but interpretation of the results is not easy because adsorption occurs simultaneously with deactivation. The history of additive supply onto the plating surface also influences the hysteretic behavior. Recently, we constructed a microfluidic device in which flow cell experiments and rapid switching of the plating solution are enabled. Using the device, characteristic behavior of leveler, strong suppression and rapid deactivation, was directly observed optical microscopically and electrochemically, and difference with levelers and suppressors was clarified. Further, a TSV-like structure with similar dimensions to real TSVs was constructed in a microchannel, and real-time optical observation of bottom-up deposition was demonstrated.References T. Akita, et al., J. Electrochem. Soc., 166(1), D3058 (2019)M. Tomie, et al., J. Electrochem. Soc., 167, 082513 (2020)T. Akita, Y. Otsuka, M. Hayase, J. Electrochem. Soc., 167, 162515 (2020)

(Invited) Some Aspects of Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries

The redox flow battery (RFB) has seen an explosion in research activity in recent years due to its attractiveness for large-scale energy storage applications (e.g. grid level storage). RFBs1,2 offer many advantages over conventional batteries including their relatively high reliability and long cycle life, as well as the ability to scale their energy and power outputs independently. The vanadium flow battery (VFB)1,3-6 is currently the most promising of these technologies, with a number of large-scale applications and demonstration projects already underway.6 The power density of VFBs is limited primarily by the kinetics of the redox reactions at the carbon electrodes while the energy density is limited primarily by the concentration of vanadium in the electrolyte. In this talk we will review our work on two aspects of VFBs – kinetics on carbon electrodes and thermal stability of electrolytes – which impact these two limitations respectively.We have investigated3,7,8 the kinetics of the VII-VIII, VIII-VIV and VIV-VV redox couples for a range of different carbon materials using a variety of techniques, and it is clear that the kinetic rates depend strongly both on the type of carbon used and on the preparation of the electrode surface. We will discuss our investigations of the effects of anodic and cathodic pretreatments of carbon on electrode kinetics in the VFB. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we showed for four different types of carbon that electrode treatments at negative potentials enhance the kinetics of VIV-VV and inhibit the kinetics of VII-VIII while electrode treatments at positive potentials inhibit the kinetics of VIV-VV and enhance the kinetics of VII-VIII. These observations may explain conflicting reports in the literature. We examined in detail the potentials required for activation and deactivation of electrodes. The results suggest that interchanging the positive and negative electrodes in a vanadium flow battery (VFB) would reduce the overpotential at the negative electrode and so improve the performance. This is supported by flow-cell experiments.3 Thus, periodic catholyte-anolyte interchange, or equivalent alternatives such as battery overdischarge, show promise of improving the voltage efficiency of VFBs.We have developed9-11 a standard methodology for measuring the thermal stability of vanadium catholytes based on their induction time for precipitation of V2O3. Using this, we have investigated the thermal stability of typical vanadium flow battery (VFB) catholytes at temperatures in the range 30–70°C for VV concentrations of 1.4–2.2 mol dm-3 and sulfate concentrations of 3.6–5.4 mol dm-3. In all cases, V2O5 precipitates after an induction time, which decreases with increasing temperature. Plots of the logarithm of induction time versus the inverse of temperature (equivalent to Arrhenius plots) show excellent linearity and all have similar slopes, yielding a value of 1.791±0.020 eV for the activation energy. The logarithm of induction time also increases linearly with sulfate concentration and decreases linearly with VV concentration. The slopes of these plots give values of concentration coefficients β S and β V5 which quantify the effects of concentration on induction times. Combining these with the Arrhenius slope, we have constructed a model11 to predict the stability of sulfate-based vanadium catholytes. The model can also be used as a basis for accelerated testing12 of electrolyte stability.We have investigated a range of additives and shown that many suggested additives are ineffective. However, the Group V elements phosphorus and arsenic in the +5 oxidation state have a significant stabilizing effect.13 We have also used our methodology for measurement of thermal stability to examine the stability of VFB catholytes under actual operating conditions. Results on the effect of state of charge, and deterioration and recovery of stability will be discussed. REFERENCES M. Skyllas-Kazacos et al., J. Electrochem. Soc., 158, R55 (2011). A. Weber et al., J. Appl. Electrochem., 41, 1137 (2011). M. A. Miller et al., J. Electrochem. Soc., 163, A2095 (2016).D. Oboroceanu et al., J. Electrochem. Soc., 163, A2919 (2016).C. Petchsingh et al., J. Electrochem. Soc., 163, A5068 (2016). Á. Cunha et al., Int. J. Energy Res., 39, 889 (2015).A. Bourke et al., J. Electrochem. Soc., 163, A5097 (2016). A. Bourke et al., J. Electrochem. Soc., 162, A1547 (2015).D. Oboroceanu et al., J. Electrochem. Soc., 163, A2919 (2016).D. Oboroceanu et al., J. Electrochem. Soc., 164, A2101 (2017).D. N. Buckley et al., J. Electrochem. Soc., 165, A3263 (2018).D. N. Buckley et al., J. Electrochem. Soc., 168, 030530 (2021).D. Oboroceanu et al., J. Electrochem. Soc., 166, A2270 (2019).

A Low Voltage, High Current All-Tungsten Redox Flow Battery

With the exponential growth of electricity generation using intermittent renewable power sources, there is a need for affordable energy storage. For grid level storage in past years, redox flow batteries (RFB) have drawn considerable attention. Most successful RFBs till now are all-vanadium RFB and all-iron RFB. But these RFBs have a few drawbacks associated with them like; First RFB developed by NASA[1], Iron-chromium RFB, had problems of ions crossing over; all-iron RFB [2] have a problem of hydrogen evolution reaction (HER) at the negative electrode which causes capacity decay; and the commercialized all-vanadium RFB's [3] is expensive and has limited vanadium reserves.In an effort to address these problems, we present here the initial development of an all-tungsten RFB. Its key advantage is no capacity fading with cycles due to ions crossing over. The tungsten salt used was phosphotungstic acid (PTA). As shown in cyclic voltammograms (CV) of PTA in Figure 1(a), it is clear that PTA ions exist in four different oxidation states (PTA3-, PTA4-, PTA5- and PTA6-). For all-PTA redox flow battery experiments, we used the same PTA5- active species for both negative as well as positive electrolyte. Prior to the all-PTA RFB tests, PTA3- was reduced to PTA5-. Since PTA3- is the only salt available, it was reduced to PTA5- by using it as a negative electrolyte for the iron-tungsten RFB using a procedure developed earlier [4].As shown in reaction 1, during charging on the negative side, PTA5- gains 2 electrons and reduces to PTA6- oxidation state. Simultaneously, on the positive side PTA5- loses 2 electrons and gets oxidized to PTA3-. Moreover, the maximum potential difference that can be achieved by using the highest reduced form of phosphotungstic acid as a single cell is +0.611 V vs. RHE (Eq. 4). Although we are getting half the potential when compared to an all-vanadium or an all-iron battery. But due to its extremely fast kinetics and large discharge currents makes all-PTA RFB a promising alternative. For the large capacity of the battery, one of the deciding factors is the solubility of its active species salts and the maximum solubility of PTA3- is 0.7 M.Flow cell experiments were conducted using an in-house constructed standard fuel cell setup [4]. Meanwhile, CV experiments were conducted in 3 electrode setup using glassy carbon as working electrode, platinum mesh as counter electrode and mercury/mercurous sulphate (Hg/Hg2SO4) as reference electrode. Hg/Hg2SO4 was calibrated in 0.5 M H2SO4 using an in house RHE. Also, all the potentials mentioned here are with respect to RHE. A CV (see Figure 1(a)) for phosphotungstic acid was obtained which showed 3 distinct peaks corresponding to the 3 reactions. Reactions 2 and 3 involve transfer of 1 electron each, while reaction 1 requires 2 electrons as proven from the current peaks of the CVs as well as limiting currents obtained from their RDEs [5]. The involvement of parasitic HER is clear from the 3rd reduction peak. Kinetic parameters such as rate constant (k0), Tafel slope, diffusion coefficients (Do) and transfer coefficient (α) were determined using RDE studies. From RDE analysis at different RPM, rate constant for PTA3- was found to be 4.49 x 10-3 cm s-1.Meanwhile, for the flow cell experiments we have taken electrolyte solution concentrations similar to that for the CVs. The flow rate (120 mL min-1) and volume (40 mL) for both the electrolyte were kept same. As shown in Figure 1(b), the all-PTA battery was charged and discharged using chronopotentiometry at a current density of 50 mA cm-2. Furthermore, to obtain the i-V performance curve the cell was discharged from 2 mA to 1000 mA for 10s. The potential at the end of 10th second was reported to eliminate the pseudo steady state [6]. i-V and power density performance curve was plotted from these current and potential values (see Figure 1(c)).From just 40mM concentration of PTA5- the maximum volumetric capacity we got is around 200 mAh L-1, the maximum power density obtained was 10 mW cm-2 and the maximum current that can be drawn was 85 mA cm-2. The above results strongly suggest that the all-PTA RFB could indeed be a promising alternative. Figure 1

Electrochemical Reduction of CO2 to Oxalic Acid: Experiments, Process Modeling, and Economics.

We performed H-cell and flow cell experiments to study the electrochemical reduction of CO2 to oxalic acid (OA) on a lead (Pb) cathode in various nonaqueous solvents. The effects of anolyte, catholyte, supporting electrolyte, temperature, water content, and cathode potential on the Faraday efficiency (FE), current density (CD), and product concentration were investigated. We show that a high FE for OA can be achieved (up to 90%) at a cathode potential of −2.5 V vs Ag/AgCl but at relatively low CDs (10–20 mA/cm2). The FE of OA decreases significantly with increasing water content of the catholyte, which causes byproduct formation (e.g., formate, glycolic acid, and glyoxylic acid). A process design and techno-economic evaluation of the electrochemical conversion of CO2 to OA is presented. The results show that the electrochemical route for OA production can compete with the fossil-fuel based route for the base case scenario (CD of 100 mA/cm2, OA FE of 80%, cell voltage of 4 V, electrolyzer CAPEX of $20000/m2, electricity price of $30/MWh, and OA price of $1000/ton). A sensitivity analysis shows that the market price of OA has a huge influence on the economics. A market price of at least $700/ton is required to have a positive net present value and a payback time of less than 10 years. The performance and economics of the process can be further improved by increasing the CD and FE of OA by using gas diffusion electrodes and eliminating water from the cathode, lowering the cell voltage by increasing the conductivity of the electrolyte solutions, and developing better OA separation methods.

PFOS Mass Flux Reduction/Mass Removal: Impacts of a Lower-Permeability Sand Lens within Otherwise Homogeneous Systems.

Perfluorooctane sulfonic acid (PFOS) is one of the most common per- and polyfluoroalkyl substances (PFAS) and is a significant risk driver for these emerging contaminants of concern. A series of two-dimensional flow cell experiments was conducted to investigate the impact of flow field heterogeneity on the transport, attenuation, and mass removal of PFOS. A simplified model heterogeneous system was employed consisting of a lower-permeability fine sand lens placed within a higher-permeability coarse sand matrix. Three nonreactive tracers with different aqueous diffusion coefficients, sodium chloride, pentafluorobenzoic acid, and β-cyclodextrin, were used to characterize the influence of diffusive mass transfer on transport and for comparison to PFOS results. The results confirm that the attenuation and subsequent mass removal of the nonreactive tracers and PFOS were influenced by mass transfer between the hydraulically less accessible zone and the coarser matrix (i.e., back diffusion). A mathematical model was used to simulate flow and transport, with the values for all input parameters determined independently. The model predictions provided good matches to the measured breakthrough curves, as well as to plots of reductions in mass flux as a function of mass removed. These results reveal the importance of molecular diffusion and pore water velocity variability even for systems with relatively minor hydraulic conductivity heterogeneity. The impacts of the diffusive mass transfer limitation were quantified using an empirical function relating reductions in contaminant mass flux (MFR) to mass removal (MR). Multi-step regression was used to quantify the nonlinear, multi-stage MFR/MR behavior observed for the heterogeneous experiments. The MFR/MR function adequately reproduced the measured data, which suggests that the MFR/MR approach can be used to evaluate PFOS removal from heterogeneous media.

Towards Bottom-up Design of Porous Electrode Microstructures – an Approach Coupling Evolutionary Algorithms and Pore Network Modeling

Porous electrodes are performance- and cost-defining components in modern electrochemical systems such as redox flow batteries, fuel cells, and electrolyzers. They must facilitate mass transport, provide surfaces for electrochemical reactions, and conduct electrons and heat. Thus, understanding and optimizing the porous electrode microstructure offers a promising pathway to cost reduction by increasing power density (1). However, our current arsenal of materials is limited to fibrous carbonaceous electrodes that were developed for low temperature fuel cells and are now repurposed to emerging systems (i.e., redox flow batteries), which fundamentally limits the performance. The empirical design of electrodes is time- and resource-intensive which limits exploration of the wider design space. To accelerate progress, microstructure-informed multiphysics simulations can be leveraged to aid the theoretical understanding and design of advanced electrode architectures but has primarily focused to the investigation of existing, carbon-fiber-based electrodes (2–4). In this work, we explore the following scientific question: Can we deploy three-dimensional simulations in combination with evolutionary algorithms to enable bottom-up artificial generation of porous electrodes? In the first part of this talk, I will discuss the modeling framework and experimental validation. Using a pore network modeling open-access platform (OpenPNM) (4, 5), we built a microstructure-informed, electrolyte-agnostic simulation framework. In this work, we focus on redox flow batteries as an application case. The model utilizes a network-in-series approach to account for species depletion over the entire length of the electrode, thus enabling the simulation of large electrode sizes (17 mm x 1 mm x 210-400 μm). To validate the robustness of the modeling framework, we performed symmetric flow cell experiments for two distinct electrolytes - an aqueous Fe2+/Fe3+ and a non-aqueous TEMPO./TEMPO+ - and two types of porous electrodes – a Freudenberg carbon paper and an ELAT carbon cloth - (Figure 1a). The dry electrode microstructures were obtained with x-ray computed tomography and converted into a network of spherical pores and cylindrical throats using the SNOW algorithm (6). The electrochemical model is solved for the electrolyte fluid transport and couples both half-cells by iteratively solving the species and charge transport with low computational cost (-1 – 0 V, with -0.05 V step intervals takes 60-120 min on an Intel® Core(TM) i7-8750H CPU). The electrochemical performance of the non-aqueous electrolyte was well captured by the model without fitting parameters, allowing rapid benchmarking of porous electrode microstructures. For the aqueous electrolyte, we find that incomplete wetting of the electrode results in overprediction of the electrochemical performance. To account for incomplete wetting, we successfully employ a fitting parameter to account for the near-surface mass transfer coefficient (7).In the second part of the talk, I will describe a genetic algorithm that optimizes porous electrode microstructures from the bottom-up by coupling the pore network modeling framework with an evolutionary algorithm. Our goal is to optimize electrode microstructures by only having the electrolyte chemistry and flow field geometry as inputs. The microstructure evolves driven by a fitness function that minimizes pumping power requirements and maximizes electrochemical power output. The analyzed systems show significant improvement of the networks’ fitness, which increased by 30-400%. For flow-through flow fields, the pumping requirements are dominant and were reduced by 60-70%, resulting in a bimodal pore size distribution with large-pore longitudinal electrolyte flow pathways (Figure 1b). Additionally, the surface area at the membrane-electrode interface is increased for all systems, resulting in an increased electrochemical performance of 3-8%. The presented framework offers great potential for predictive design of electrode microstructures tailored for specific redox chemistries and reactor architectures, which will accelerate and broaden the design and fabrication process of advanced electrode structures. While applied to flow batteries here, this methodology can be leveraged to advance other electrochemical systems by adapting the relevant physics. References A. Forner-Cuenca, F. R. Brushett, Curr. Opin. Electrochem., 10 (2019).G. Qiu et al., Electrochim. Acta. 64, 46–64 (2012).A. G. Lombardo, et al., J. Energy Storage. 24 (2019).M. A. Sadeghi et al., J. Electrochem. Soc. 166, A2121–A2130 (2019).J. Gostick et al., Comput. Sci. Eng. 18, 60–74 (2016).J. T. Gostick, Phys. Rev. E. 96, 1–15 (2017).K. V. Greco, et al., ACS Appl. Mater. Interfaces. 10, 44430–44442 (2018). Figure 1

BiO 2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO 2 Reduction to Formate

BiO _2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO ₂ Reduction to Formate