Electrochemical Engineering Research Articles

Graduate Education in Electrochemistry and Corrosion Science at the University of Virginia

The goals and methodology of graduate education in corrosion science and engineering at the Center for Electrochemical Science and Engineering at The University of Virginia are reviewed. These include establishment of both core competencies and advanced understanding(s) in materials science, electrochemistry applied to corrosive degradation in aqueous solutions, surface science and engineering, solution chemistry and/or fracture mechanics through a plan of study typically involving 13 graduate classes in Engineering, Chemistry and/or Physics. In addition a key aspect of our educational goal, beyond the classroom, is a significant and in-depth Master of Science and Doctor of Philosophy research experience culminating in a written thesis or dissertation and oral defense. This research experience is designed to provide an excellent training ground for development of individuals capable of not only performing multi-disciplinary research in the corrosion field, but also with the capability of surveying the literature, identifying research gaps and opportunities and developing strategies for addressing such needs. Corrosion science and engineering students perform focused research in the areas of aqueous corrosion, high temperature corrosion, environmentally assisted cracking. Interactions with other faculty and students providing education and performing research in other electrochemical technical areas (e.g., electrodeposition, photoelectrochemistry, batteries) provide critical enhancements to the students’ experience. At the end of this experience, students are capable of either performing as competent corrosion engineers or as scientist making both technological and scientific contributions to our field with good written and oral communication skills. The course curricula, research philosophies and the assessments used to achieve these goals are presented.

CO2 Hydrogenation to Methanol and Formic Acid in Competition with Hydrogen Evolution: A Spreadsheet Model for Use in Capstone Design Courses

Electrochemical reactors (ECR), such as fuel cells and electrolyzers, are ideal systems to include in chemical engineering design courses. Electrochemistry and electrochemical reaction engineering are not normally required in the chemical engineering curriculum, so use of an ECR in a capstone design course requires a brief introduction of the topic and a working model to assist the students in ECR design. Here, we focus on CO2 hydrogenation to make methanol and formic acid in competition with the hydrogen evolution reaction. This project was used in the Spring 2019 Process Design II class in Chemical Engineering at the University of Washington. A spreadsheet model was developed that estimates current densities of the three reactions occurring simultaneously. The model was derived from earlier versions that simulated H2/O2 fuel cells, in proton exchange membrane fuel cell (PEM) and solid oxide fuel cell (SOFC) configurations; and CH4-fed SOFCs with water gas shift and coking. The cathode reactions included in the model were: CO2+ 6 H++ 6 e − → CH3OH + H2O CO2+ 2 H++ 2 e − → HCOOH 2 H++ 2 e − → H2 and were coupled with the oxygen evolution anode reaction: H2O → 2 H++ 2 e − + 1/2 O2 Reactions are represented by a matrix of stoichiometric coefficients and physical properties of all species and reactions including molecular weight, gas and liquid phase viscosities, gas and liquid phase heat capacities, and heats and entropies of reaction. Activities are given by partial pressure for gaseous species and mole fraction for liquid species, under the assumptions of ideal gas and ideal solution. Reversible electrode potentials for non-unity species activities are calculated by the Nernst equation. The spreadsheet is a one-dimensional, along-the-channel model solved step-wise by the Eulerian method. The channel, in parallel or serpentine pattern, is divided into 100 segments and each segment solved by a double (outer and inner) iteration loop. Each segment is assumed to be gradientless, which makes the model a series of CSTRs. Iteration is by the Newton-Raphson method, and both iterations are open-loop. Five iterations are sufficient to achieve convergence in most cases. The outer iteration begins with a guessed initial current density, from which the model solves for the overpotentials of electrolyte resistance, mass transfer limitation, and anode kinetics. The single term (Tafel) form of the Butler-Volmer equation is sufficient for CO2 hydrogenation due to the high overpotentials involved. Individual reaction current densities are determined by the inner iteration, consisting of a guessed current density for methanol synthesis, from which the overpotential of that reaction is determined. Together with the reversible potentials of all three reactions, the cathode potential vs. RHE and the other cathode overpotentials can be determined. The inner iteration continues until the sum of all three reaction current densities equals the originally guessed current density. The outer iteration then proceeds until the outer-iterated cell potential agrees with the input cell potential. At this point, the total current density and individual reaction current densities are known, and the Faradaic efficiency can be determined. The mass balance is updated according to the extents of each reaction, and the solution procedure is repeated for the next segment. Modeling inputs are cell potential; temperature; and inlet pressures, flow rates, compositions, exchange current densities, and limiting current densities for cathode and anode. Physical parameters include cell dimensions (length x width), channel dimensions (width, height, rib), and choice of serpentine (single or multiple pass) or parallel flow fields. The screen shot in Fig. 1 shows a small portion of the control panel at left along with plots of CO2 and H2O conversion, current density, pressure, and species fluxes for the cell operating at −1.9 V cell potential and 70 °C. Serpentine flow fields are used for both cathode and anode with 1 and 2 passes, respectively. The average current density is 0.5 A/cm2, which is almost entirely due to methanol production, with a Faradaic efficiency of essentially 1. Current densities for formic acid and hydrogen evolution are less than 1 μA/cm2 in this case. The model enables solution of a complex, real-world problem with tools readily available and understandable by senior chemical engineering students. It can be adapted for a variety of electrochemical reactions making it a powerful tool in electrochemistry education. Figure 1

(Invited) Room Temperature All Solid State Sodium Batteries Based on Glassy Electrolytes

All solid-state batteries (ASSB) are regarded as a promising alternative to replace state-of-the-art liquid electrolyte-based batteries. Lithium-ion containing electrolytes are undoubtedly the most successful chemistries to date. However, taking material abundance into consideration, lithium sources are relatively limited and thus the Li compounds are costly to produce. In contrast, sodium sources are considered readily accessible. This makes sodium battery chemistries attractive and justifies their ongoing development targeting the large-scale energy storage. Until recently, the most widely adopted sodium solid electrolytes are NASICON and β-Alumina, with commercial applications of the latter in niche markets. However, demands for high power and cheaper processing have made the class of electrolytes based on Na3PS4 a more promising solid-state electrolyte (SSE) candidate for energy storage and conversion applications. I will discuss the synthesis, modification, interfacial engineering and electrochemical engineering of the ASSB based on this type of electrolytes. New characterization toolkit such as cryo-FIB/SEM and cryo-TEM are indispensable tools for studying the electrode / electrolyte interphases in the room temperature ASSB sodium batteries.

Model Identification for Adsorption Dynamics and Suppression Effect of Polyethylene Glycol Using Inverse Analysis Approach

Cu electroplating is important in LSI manufacturing. In the manufacturing process, some additives are added to a copper sulfate solution. The additive that reduces a deposition rate is called suppressor. Polyethylene Glycol (PEG) has been actively studied as a typical suppressor. PEG adsorbs to the electrode in the presence of a chloride ion and suppresses the deposition rate. The dynamics of adsorption and the mechanism of the suppression effect have been studied, and various mathematical models have been proposed from these results. However, the phenomena have not been perfectly understood and the conventional mathematical models cannot fully reproduce these phenomena.[1] Voltammetry is often performed to observe the behavior of the additives. The rotating disc electrode(RDE) is used in order to control the concentration on the electrode surface. The RDE can control and evaluate the concentration on the electrode surface under the assumption for uniform distribution of concentration and current density on the electrode surface. However, it is observed that the adsorption of PEG occurs non-uniformly on the electrode surface.[2] The voltammogram show dynamics of the current density averaged on the working electrode. It is important to know the local current density and its distribution on the working electrode in order to understand the adsorption dynamics of PEG and the suppression of copper deposition. On the other hand, “Inverse Problems” have attracted attention due to the development of numerical simulation. Inverse Problems is a research area dealing with finding out unknown information from external or indirect observation through a system model. In the fields of electrochemical engineering, there are many problems which can have a benefit from the inverse analysis approach. Using an approach of the Inverse Problems, we identify the current density distribution on the electrode surface. Currents are measured by changing potential and PEG concentration with an electrochemical flow cell. Observation data such as potential, bulk concentration, average flow velocity, and current are used for the inverse analysis. From these observation data, we identify the current density distribution with estimating the models that represent the adsorptiondynamics of PEG and the suppression effect of the copper deposition. The figure shows a procedure of the inverse analysis method. The method consists of an experiment and a numerical simulation as shown. In the experiment, observation data are obtained with the electrochemical flow cell. The experimental system consists of two solution supply devices and the electrochemical flow cell.The solution supply device can arbitrarily control a flow rate of the solution supplied to the flow cell. Copper sulfate solutions with different concentrations of PEG are prepared for the solution supply devices. The experimental system can continuously change PEG concentration supplied to the flow cell by changing a mixing ratio of the two solutions. Currents are measured with a linear sweep of potential under constant PEG concentration and a linear sweep of PEG concentration under constant potential. Potential, concentration, average flow velocity, and current are obtained as observation data. In the numerical simulation, the adsorption dynamics of PEG and the suppression of copper deposition are treated in order to express the phenomena related to PEG. Surface coverage of PEG is introduced to express the adsorption dynamics. In this study, the dynamics of the surface coverage is represented by a piecewise linear function with current density, PEG concentration, and surface coverage. The suppression of copper deposition is expressed by the piecewise linear function with surface coverage, copper ion concentration, potential. A velocity field is modeled by the Navier-Stokes equation, and concentration fields of copper ion and PEG are modeled by the advection-diffusion equation. Boundary conditions of the advection-diffusion equation at the electrode are given by the models representing the adsorption dynamics of PEG and the suppression effect of copper deposition. The current density distribution on the electrode surface is evaluated with solving the advection-diffusion equation. The numerical simulation described above can be performed by assuming the parameters of these models. Currents are calculated with solving the advection-diffusion equation under the same potential, concentration, and average flow velocity as the experiment. The parameters of the models can be obtained by minimizing the residual between measured and calculated currents with a nonlinear least squares method. After the model is identified, the currentdensity distribution on the electrodes is easily calculated by the direct analysis. [1]Liu Yang, Aleksandar Radisic, Johan Deconinck, and Philippe M. Vereeckena; J. Electrochem. Soc., 161(5) D269-D276(2014)[2]D. Josell and T. P. Moffat; J. Electrochem. Soc., 163(7) D322-D331(2016) Figure 1

Editorial Overview Electrochemical Materials and Engineering: Directions in electrochemical engineering

Editorial Overview Electrochemical Materials and Engineering: Directions in electrochemical engineering

Characteristics of high-performance anti-corrosion/anti-wear ceramic coatings on magnesium‑lithium alloy by plasma electrolytic oxidation surface engineering

High-performance anti-corrosion/anti-wear coatings on superlight magnesium‑lithium (MgLi) alloy with exceptional durability are of great interest for fundamental research and practical applications. In the present study, oxide coatings are produced on MgLi alloy by electrochemical surface engineering––plasma electrolytic oxidation in an alkaline silicate electrolyte with addition of cerium salt. To understand the nature of coatings, we investigate their surface and cross-sectional morphologies, wettability (35 ± 3° vs 78 ± 2°), phase and chemical compositions, corrosion and tribological behaviors. Our findings show that the oxide coating prepared with cerium salt has a more compact structure with fewer defects (18 μm in thickness). Importantly, it substantially enhances the corrosion resistance of MgLi alloy by three orders of magnitude and significantly retards the occurrence of localized corrosion (150 h), along with notably improved anti-wear performance (friction coefficient of 0.19).

Robust Super-Hydrophobic Coating Prepared by Electrochemical Surface Engineering for Corrosion Protection

Corrosion—reactions occuring between engineering materials and their environment—can cause material failure and catastrophic accidents, which have a serious impact on economic development and social stability. Recently, super-hydrophobic coatings have received much attention due to their effectiveness in preventing engineering materials from further corrosion. In this paper, basic principles of wetting properties and corrosion protection mechanism of super-hydrophobic coatings are introduced firstly. Secondly, the fabrication methods by electrochemical surface engineering—including electrochemical anodization, micro-arc oxidation, electrochemical etching, and deposition—are presented. Finally, the stabilities and future directions of super-hydrophobic coatings are discussed in order to promote the movement of such coatings into real-world applications. The objective of this review is to bring a brief overview of the recent progress in the fabrication of super-hydrophobic coatings by electrochemical surface methods for corrosion protection of engineering materials.

Developments in X-ray tomography characterization for electrochemical devices

Over the last century, X-ray imaging instruments and their accompanying tomographic reconstruction algorithms have developed considerably. With improved tomogram quality and resolution, voxel sizes down to tens of nanometers can now be achieved. Moreover, recent advancements in readily accessible lab-based X-ray computed tomography (X-ray CT) instruments have produced spatial resolutions comparable to specialist synchrotron facilities. Electrochemical energy conversion devices, such as fuel cells and batteries, have inherently complex electrode microstructures to achieve competitive power delivery for consideration as replacements for conventional sources. With resolution capabilities spanning tens of microns to tens of nanometers, X-ray CT has become widely employed in the three-dimensional (3D) characterization of electrochemical materials. The ability to perform multiscale imaging has enabled characterization from system-down to particle-level, with the ability to resolve critical features within device microstructures. X-ray characterization presents a favorable alternative to other 3D methods, such as focused ion beam scanning electron microscopy, due to its non-destructive nature, which allows four-dimensional (4D) studies, three spatial dimensions plus time, linking structural dynamics to device performance and lifetime. X-ray CT has accelerated research from fundamental understanding of the links between cell structure and performance, to the improvement in manufacturing and scale-up of full electrochemical cells. Furthermore, this has aided in the mitigation of degradation and cell-level failures, such as thermal runaway. This review presents recent developments in the use of X-ray CT as a characterization method and its role in the advancement of electrochemical materials engineering.

(Invited) Transition from Coupon Observation to Part Processing and the Challenges in Between

Faraday Technology Inc. is a research, development and engineering firm developing electrochemical innovations based has pulse/pulse reverse electrolytic principles [1]. With that founding basis Faraday has been able to bridge the gap between academic understanding and small scale demonstration to commercialization of practical components over 27 years of operation. This presentation will discuss some of the observations and challenges that have come up as a result of moving from exemplar “coupon scale” materials toward practical part shapes and geometries. Furthermore, we will discuss a range of applications and materials including but not limited to Cu/Cr single metal plating, CoMn/NiCr alloy plating, included deposit formations with CrAlY or WC particles, electropolishing of additively manufactured components, and Nb cavity polishing. Within each of these very distinct processes and applications we will try to identify similarities and differences in the observed challenges and ways that many could be overcome either by electrochemical engineering, process developments, or program planning.

(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award Address) Fundamental Understanding on Cell Performance Enhancement of Flow Batteries with Serpentine Flow Field Structures

Redox flow batteries are being considered for medium and large-scale stationary energy storage applications. In addition to storing energy by the intermittent resources, such as tide, wind and solar energy, the electrochemical flow battery systems could impact electricity generation and grid effectiveness by supporting energy storage for peaking shaving, load leveling and emergency back up [1,2]. In recent years, flow field designs, such as a serpentine flow field, evolved from proton exchange membrane (PEM) fuel cell have been experimentally demonstrated to deliver improved cell performance and boost cell capacity [3] as compared to flow batteries without flow field designs. However, the mechanisms causing enhanced higher limiting current density with serpentine flow field designs have not been fully understood. In this presentation, I will introduce a concept of maximum current density associated with the stoichiometric availability of the pressure-driven electrolyte flow penetrating into the porous carbon electrode from the from the serpentine flow channel [4-6]. Our three-dimensional model demonstrates that this maximum current density concept can explain the observed limiting current density achieved in a flow battery with a serpentine flow field structure [7]. We hope this fundamental understanding can contribute to a better elucidation of the mechanism on limiting the electrochemical performance and further optimization of flow batteries. Acknowledgement This work was partially supported by the “all-iron flow battery” project with a grant number of DE-AR0000352 funded by the program of the Advanced Research Projects Agency-Energy (ARPA-E) of the Department of Energy (DOE) of the United States. I (XK) would like to acknowledge the late Professor Joseph M. Prahl, who was my advisor and inspirational mentor.

A Tanks-in-Series Electrochemical Engineering Model for Lithium Sulfur Batteries

Lithium sulfur (LiS) batteries are promising for next-generation energy storage. Due to their high energy density, lithium sulfur batteries are attractive for applications like electric vehicles and electric flights where weight is an important constraint. However, LiS batteries suffer from low coulombic efficiency, poor cycle life, and self-discharge. ­­ 1 Physics-based models can give insight into the internal states of the battery, which can be correlated to the mechanisms that contribute to performance degradation under various operating conditions. The first one-dimensional electrochemical discharge model for LiS batteries was developed by Kumaresan et al. using porous electrode theory, and considers transport, kinetics, thermodynamics, and morphological changes.2 The LiS chemistry includes multiple charge carriers and morphology changes as discharge proceeds, which contributes to the complexity and challenges of accurate modeling. The corresponding physics-based model results in a complex and numerically stiff equation system with variables that change across orders of magnitude and require proper initialization. The mathematical complexity of such electrochemical models motivates the use of reformulation and simplification techniques in order to justify their use in estimation, control, and optimization. Even for fast reformulated models, the large number of kinetic and transport parameters resulting from the complex chemistry makes their parameterization a non-trivial task. Several groups have used lumped and one-dimensional models to simplify modeling and study specific characteristics, such as self-discharge, rate-dependence of precipitation, or charging.3–9 This work demonstrates a mass-conserving tank-in-series model based on the original model developed by Kumaresan et al.2 The tank-in-series model is developed through volume-averaging of the model equations. The volume averaging results in overall balance equations governing the evolution of average variables in each region of the cell. The elimination of the spatial dependence from model equations substantially increases computational efficiency and reduces the number of parameters to be estimated. Comparisons of the tank-model simulations with the full model indicate the ability of the averaged model to capture discharge behavior at low to intermediate discharge rates, with deviations mainly observed towards the end of discharge. Other advantages and limitations of this model as compared to the full model are characterized in terms of electrochemical variable predictions, with applications in control and estimation for hybrid electric flights. The model predictions are compared against experimental data from 19.5 Ah pouch cells and have been improved through estimation of parameters. Acknowledgments The authors are thankful for financial support from BAE Systems and the Joint Center for Aerospace Technology Innovation. References X. Zhang, H. Xie, C.-S. Kim, K. Zaghib, A. Mauger, and C. M. Julien, Mater. Sci. Eng. R Reports, 121, 1 (2017).K. Kumaresan, Y. Mikhaylik, and R. E. White, J. Electrochem. Soc., 155, A576 (2008).Y. V. Mikhaylik and J. R. Akridge, J. Electrochem. Soc., 151, A1969 (2004).K. Yoo, M.-K. Song, E. J. Cairns, and P. Dutta, Electrochim. Acta, 213, 174 (2016).Y. X. Ren, T. S. Zhao, M. Liu, P. Tan, and Y. K. Zeng, J. Power Sources, 336, 115 (2016).T. Zhang, M. Marinescu, L. O’Neill, M. Wild, and G. Offer, Phys. Chem. Chem. Phys., 17, 22581 (2015).M. Marinescu, T. Zhang, and G. J. Offer, Phys. Chem. Chem. Phys., 18, 584 (2016).D. N. Fronczek and W. G. Bessler, J. Power Sources, 244, 183 (2013).A. F. Hofmann, D. N. Fronczek, and W. G. Bessler, J. Power Sources, 259, 300 (2014).

(Invited) The Impact of Work By Dr. Gottesfeld and Coworkers on the Commercial Introduction of the Fuel Cell Vehicle -- Calling the Shots in Polymer Electrolyte Fuel Cells

Dr. Gottesfeld’s entire career has been characterized by developing early stage fuel cell technology using fundamental science and practical engineering intuition and analysis. It is unusual to see fundamental electrochemistry expertise coupled with electrochemical engineering intuition and skills in the same person. This combination has enabled him and his coworkers to identify controlling phenomena that have proven to be focal points for development and the critical points that determine the ultimate capability of the technology and its application outcome. Furthermore, his dedication and passion in these areas guide and inspire the next generation of contributors across four distinct fuel cell families. In this talk, I will describe how this pairing of fundamental and device level intuition from the group that he led at Los Alamos National Lab (LANL) from 1987-2000 impacted the development of proton exchange membrane fuel cells from initial development stages to readiness for automotive market introduction. For example, the pathway for the reduction of precious metal loadings to commercially viable levels was initially defined by experiments and fundamental models from the LANL group. The LANL work on membrane water transport was critical to understanding why thinner membranes offered performance benefits beyond their ionic resistance impact. Even the contemporary R&D work to push to high current density (>2 A/cm2) for the sake of reduction of fuel cell area is informed by initial LANL developments as well as Dr. Gottesfeld’s work (published in 2008) on the impact of the Pt-oxides on oxygen reduction kinetics. More broadly, this body of work reminds us that the pathway to push any fuel cell technology to its best possible outcome is to systematically apply coupled experiments and models in order to identify and focus R&D attention on the rate processes that are “calling the shots”.

(Invited) My First 35 Years in R&D of Polymer Electrolyte Fuel Cells

I deeply appreciate the significant efforts of all colleagues and friends involved in organizing this Symposium and the very impressive list of speakers who agreed to come and actively participate. I am expected to offer here the perspective of an old timer looking at the developments in the field of polymer electrolyte R@D over the last 35 years. So, let me share with you some observations from that perspective, pointing to highlights in the history of this technology and adding some personal insights. 1. The Vision and the Relentless Pursuit: The use of PEFCs as green and efficient power source for terrestrial transport applications, was proposed early in the 1980's by leaders of the Electronics Engineering (EE) Division at LANL. The idea faced strong opposition from the main US centers of R@D in electrochemistry and electrochemical engineering of the 1980's , including Berkeley, Case Western Reserve and Texas A&M. Their strong opposition was based on the very wide gap between the status of PEFC technology in the 1980's and a mature PEFC technology for transportation applications , as demonstrated 35 years later in the form of 100kW PEFC stacks powering commercial FCEVs. The visionaries from LANL did recognize the width of this gap and went on to hire into group EE-11 a team of electrochemists and materials scientists who would prime the technical and scientific work in this new area. Some PEFC technology advancements to be described, made by the LANL fuel cell team back in the 1980's and 1990's , helped to establish recognition of the value and viability of PEFC technology for transport application. The leaders as well as the technical staff at LANL remained strongly committed in spite of the tall technical and budgetary challenges expected and in spite of the very significant opposition -- to large degree because of a strong belief in the high value of this technology for green and efficient transportation. This high value justified , in their view, a long-term , costly development. The outcome , as seen 35 years and >10B$ later, has been the successful development of a new type of electrochemical power source for transport applications, culminating with the market entry of FCEVs in 2015. This outcome has been the result of technical work of the highest level carried out in several R@D@E centers in US, Japan and Europe, however, at the outset, in the early 1980's, the key prerequisite for such outcome was recognition of the high value of the technology and the willingness to pursue it in spite of all sort of barriers. Are there any general conclusions that can be drawn from the history of PEFC technology, that would apply to other fuel cell or electrochemical technology developments being considered, or having just been proposed. ? 2. A Perspective of a Dramatic Drop in Cost : With first market entry of FCEVs in 2015, the relative merits of FCEVs and BEVs is an ongoing discussion/debate and the lower projected cost of the FCEV vs. the BEV, is an important factor in this comparison. From my personal perspective , it is interesting to examine how the production cost of FCEVs, as projected by automotive OEMs for year 2025, has fallen under the projected production cost of not just BEVs , but also under the cost of an equivalent ICE-powered vehicle. In this discussion of the cost of PEFC technology, the potential of further cost lowering by using HEMFCs instead of PEMFCs, will be highlighted. 3. On "fundamental" and "Applied" aspects of PEFC technology : The newest fuel cell technology challenge I have been involved with, is the direct ammonia fuel cell (DAFC). This last chapter of work called for detailed consideration of the kinetics of the ammonia oxidation reaction (AOR) , in order to resolve the very practical question of the probability of reaching , in a DAFC operating around 100 degC, the power density level required for transport applications. The kinetic analysis offered for the AOR , revealed a quadratic dependence of the fuel cell current on [NH3] , supporting achievability of the DAFC power densities targeted when operating on anode feeds of high concentrations/vapor pressures of NH3. Insights into distinguishable effects of the M-N bond strength in the catalysis of the AOR, on: (i) the onset potential and, (ii) the activation energy in the RDS, will be described, followed by description of a common pattern identified in mechanisms of electrocatalytic processes [1]. [1] Shimshon Gottesfeld, J Electrochem.Soc.,165 J3405-J3412 ( 2018)

(Industrial Electrochemistry and Electrochemical Engineering Division New Electrochemical Technology (NET) Award Address) Development and Commercialization of Large Scale PEM Water Electrolysis

Keywords: PEM Electrolyzer, Power to Gas, Mega Watt (MW) In future energy systems with high percentages of fluctuating renewable energy generation, electricity storage will become increasingly important for the utilization of surplus energy. Among several electricity storage options, the Power to Gas technology is one promising option for solving the challenge of long-term electricity storage [1]. In this approach, excess renewable energy is converted via water electrolysis to hydrogen and used directly as an energy storage medium or it can go thru further conversion to methane [2]. To fully utilize the potential of Power to Gas, large-scale technology implementation should be accelerated so the costs are driven down. PEM electrolyzers need to become quickly available on multi-mega watt (MW) scale [3]. Hydrogenics has been developing water electrolysis technology based on proton exchange membrane (PEM) since the late 1990s. Driven by Power to Gas applications and corresponding cost modeling, Hydrogenics increased the scale of its PEM water electrolysis stack and launched its new MW scale electrolysis platform in 2014. This MW scale platform is still the most compact, highest capacity PEM electrolyzer cell stack in the world and capable of absorbing 3 MW of electricity with a single stack. To date, Hydrogenics has delivered numerous MW systems globally, with the majority of them in Power to Gas, renewable energy storage and grid balancing applications. Hydrogenics is developing the next-generation systems with continuing focus on cost reduction through technology innovation and scale up. With the market introduction of a single 3 MW stack, Hydrogenics continues to demonstrate that its hydrogen-based energy storage technology will transform the energy sector by providing ancillary and grid balancing services to grid operators while converting large scale renewable energy at a utility scale.

(Invited) Electrocatalytic Reduction of CO2in Gas-Phase Electrolyzers: Moving Towards a Relevant Use of CO2

Controlling product selectivity in electrocatalytic CO2 reduction is critical for achieving an economically viable process due to costly downstream separations of valuable products. Thermodynamically, several possible products of CO2 reduction, as well as the undesired (in this case) H+ reduction reaction, reside within a few tenths of a Volt. Thus, product selection cannot be manipulated by controlling the potential but rather must occur via engineering catalyst-intermediate kinetics. Because most CO2 reduction reactions utilize H+ as a reactant, the products are also a strong function of pH. As the local pH varies due to the consumption of protons, the local product changes at a fixed potential. The majority of CO2 electrocatalyst development occurs in a buffered, liquid electrolyte half-cell with a configuration that portrays a misleading parameter set. Aqueous-based cathode systems are limited by minimal water solubility limits of CO2, which at ~30 mM can only support current densities1 around 30 mA/cm2. Such current densities are at least an order of magnitude too low to be considered for an industrially-relevant device. The product selectivity and efficiency of any catalyst measured in aqueous half-cells will undoubtedly be different in high rate (current) devices. A new analytical solution is required for screening materials designed to utilize CO2 at a scale commensurate with which it is currently being produced. In this talk, we will present an overview of our approach for transforming the CO2 reduction reaction from an aqueous environment to an industry-relevant gas-phase environment, where high rates of conversion are possible. Through a robust fuel cell and electrochemical engineering research program, the National Renewable Energy Laboratory has developed considerable expertise in transforming gas-phase reactions from utilizing material properties to a functioning device level. This expertise is leveraged to develop a CO2 electrolyzer utilizing a gas phase cathode, and alkaline oxidation anode assembly. The electrodes are separated by a bipolar membrane with an engineered 3-D interfacial layer. Accelerating the water dissociation reaction at the interface of the cation and anion exchange layers in the bipolar membrane is necessary for achieving and maintaining high current densities in our advanced CO2 electrolyzer assembly. Initial results of this endeavor will be presented. We will also describe our progress in designing and fabricating new automated test stands, with real-time online reduction product analysis, capable of performing in-situ electrochemical diagnostics on dynamic processes in these complex systems. The ultimate goal of this project is to establish a platform to evaluate and benchmark promising CO2 electrocatalysts subject to conditions relevant for incorporation into a viable solution for efficient industrial reduction of CO2. Acc. Chem. Res. 2018, 51, 910−918

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Transport Study Inside Porous Layers of PEFC Using Direct Numerical Simulation

The purpose of this work is to use direct modeling based Lattice Boltzmann Method (LBM) [1-4] to understand the multi-scalar/multi-physics transports of various porous layers in a polymer electrolyte fuel cells (PEFCs). The studies include the understanding of water evolution, water saturation, breakthrough pressure, heat transfer, species transport, and electrochemical kinetics inside porous layers under different conditions and situations that could occur in fuel cells. Condensed water in the flow field and porous layers reduces oxygen transport to the oxygen reduction reaction region. Current platinum group metal (PGM) catalysts tend to experience transport resistance, which results in kinetic limitations within the hydrogen oxidation reaction (HOR) and the oxidation reduction reaction (ORR). Due to these limitations, the enhancement of mass transport is critical to improving fuel cell performance and durability, and therefore the development of a PGM-free catalyst is vital in understanding multi-scalar transport. This will enrich the development of novel structures that address local oxygen transport resistance in the PGM-free catalyst layer, and will outline the urgent need to further investigate multi-physical phenomena and the electrochemical nature of a fuel cell. The model geometries of porous layers [gas diffusion layer (GDL), micro porous layer (MPL), and catalyst layer (CL)] provided in this study were obtained by a 3D, reconstructed microstructure from both micro and nano X-ray computed tomography (CT) as shown in Figure 1. Current research outcomes reveal that the liquid water saturation profiles inside the GDL, breakthrough pressures, heat, and mass transport are dependent on GDL type, operating conditions, cell assembly specifications, and flow field geometry [3]. This work also shows the enhancement of my approach that include the kinetics model in the catalyst layer, which will involve coupling electrochemical kinetics with LBM computational fluid dynamics (CFD) as shown in Figure 2. This kinetic model simulates the chemical reaction in the cathode side in order to investigate the electrical potentials, electrical current, electron transfer, and exchange current in the catalyst layers. It shows the potential capability of a CFD-based investigation of multi-physical transport to find solutions of design and operational conditions in the PEFC. The output of this work will be used for the optimization of catalyst layer thickness, with durability and water management improvement, for novel porous materials, particularly in the catalyst layer. Moreover, the predictions from CFD simulations can help to optimize the design of porous layer structures and other components, such as flow fields, thereby improving the PEFC’s overall performance, cost of production, and development time.

A Novel Flow Electrochemical Reactor for Intensifying Diffusion-Limited Electrochemical Processes

Electrochemical processing is attracting renewed interest in industry for synthesis of chemicals or for the removal of a range of contaminants because it is cleaner than most alternatives. Redox reactions that are controlled by applying a potential between two electrodes avoid the use of potentially harmful auxiliary chemicals, an increasingly important advantage that offsets the electrical energy that is required. However, electrochemical processing is still limited in many applications by electrochemical engineering issues such as electrode material selection and construction, efficiency losses caused by mass transfer limitations and batch mode of operation. The CSIRO flow electrochemical cell aims to address these issues by using advanced computational fluid dynamics (CFD) to design, manufacture and optimize an electrode that can maximize mixing within an axial flow cell. The static mixer working electrode is made using additive manufacturing techniques that allows complex designs to be realised using a range of different metals with different surface roughnesses. The current design of the CSIRO electrochemical flow cell employs an additively manufactured, high surface area static mixer as a central working electrode that fits snugly within a tubular porous polymeric separator which defines a working compartment. Two ports at either end of the electrode, manufactured as an integral part of the design provide connections for fluid flow. As with all static mixers, the momentum of the solution induces mixing as it flows past the electrode surface. In the current version of the cell, an inert tubular counter electrode surrounds the working compartment at a small distance from the separator, creating a low volume counter compartment and formed the outside casing of the cell. Separate ports provide fluid flow into this latter compartment. Figure 1 shows a schematic drawing of one configuration of the electrochemical cell with the arrangement of the electrodes, the fluidic setup including the peristaltic pump(s) used to control the solution flow into and out of the cell and the power supply connection to the cell. The efficiency with which the cell works may be evaluated by comparing the limiting current measured at various flow rates with results from a Rotating disk electrode (RDE) in the same solution. These comparisons are useful indicators of performance only, and are not used to draw any conclusions about the hydrodynamic conditions at the static mixer surface. The CSIRO flow electrochemical cell has been characterized using the reduction of Ferricyanide, [Fe(CN)6]3+) at three different reactant concentrations and seven different flow rates. Results show that the cell can accelerate the rate of the reduction reaction by nearly forty-five times. As expected, the rate of this acceleration is highest when the reaction is diffusion limited, so the impact is seen most clearly in dilute solutions. By comparison, results obtained with an RDE were not as promising confirming the effectiveness of the CSIRO designed flow electrochemical cell. Exhaustive electrolysis experiments were also undertaken to show how effectively the cell can remove contaminants from a fixed volume of a contaminated aqueous solution. A two Litre solution of copper contaminated water (i.e. 100 pm CuSO4.4H2O in 0.01M H2SO4) was processed using the flow cell at a constant flow rate of 100 mL/min for 5 hours. SEM/EDS results confirmed the deposition of copper ions onto the static mixer working electrode. ICP results showed that a 50% reduction in the copper concentration from 100 ppm to 51 ppm was achieved in 5 hours which is encouraging. Figure 1

Solution processed nanostructured cerium oxide electrode: Electrochemical engineering towards solid-state symmetric supercapacitor device

Present work portrays the surface morphology dependent electrochemical behaviors tuned by annealing the chemical bath deposited (CBD) cerium oxide electrodes. The altered nanostructure properties are well-supported by in-depth structural and morphological analysis. Cerium oxide electrode annealed at 200°C exhibits good surface properties enabling maximum electro-active porous cavities to penetrate electrolyte ions towards enhanced electron transfer. Consequently, the electrode exhibits maximum specific capacitance of 750F/g with remarkably stable charge-discharge cycles. Fabricated symmetric solid-state supercapacitor device impressively expands potential window to 1.2V with the aid of PVA-LiClO4 gel electrolyte with a peak specific capacitance of 321.3F/g with top-up of 61.4Wh/kg specific energy. The series combination of two devices confirms the strong energy storage ability by glowing ‘VNIT’ acronym designed through 21 red LEDs from the practical point of view.

Role of polydopamine’s redox-activity on its pro-oxidant, radical-scavenging, and antimicrobial activities

Polydopamine (PDA) is a bioinspired material and coating that offers diverse functional activities (e.g., photothermal, antioxidant, and antimicrobial) for a broad range of applications. Although PDA is reported to be redox active, the association between PDA’s redox state and its functional performance has been difficult to discern because of PDA’s complex structure and limitations in methods to characterize redox-based functions. Here, we use an electrochemical reverse engineering approach to confirm that PDA is redox-active and can repeatedly accept and donate electrons. We observed that the electron-donating ability of PDA offers the detrimental pro-oxidant effect of donating electrons to O2 to generate reactive oxygen species (ROS) or, alternatively, the beneficial antioxidant effect of quenching oxidative free radicals. Importantly, PDA’s electron-donating ability depends on its redox state and is strongly influenced by external factors including metal ion binding as well as near-infrared (NIR) irradiation. Furthermore, we demonstrated that PDA possesses redox state-dependent antimicrobial properties in vitro and in vivo. We envision that clarification of PDA’s redox activity will enable better understanding of PDA’s context-dependent properties (e.g., antioxidant and pro-oxidant) and provide new insights for further applications of PDA. Statement of significanceWe believe this is the first report to characterize the redox activities of polydopamine (PDA) and to relate these redox activities to functional properties important for various proposed applications of PDA.We observed that polydopamine nanoparticles 1) are redox-active; 2) can repeatedly donate and accept electrons; 3) can accept electrons from reducing agents (e.g., ascorbate), donate electrons to O2 to generate ROS, and donate electrons to free radicals to quench them; 4) have redox state-dependent electron-donating abilities that are strongly influenced by metal ion binding as well as NIR irradiation; and 5) have redox state-dependent antimicrobial activities.

Measurement of Cole–Davidson Diffusion Through Padé Approximations for (Bio)Impedance Spectroscopy

Throughout various engineering applications, measurement science faces the problem that parameters of interest are not directly measurable with a specifically designed instrument. As such, one relies on indirect measurement which is mapped through a mathematical model to the parameters of interest. The parameters of interest are consequently estimated statistically through analyzing the measurements. This field is known as system identification and serves applications in control, mechanical, and biomedical engineering among others. Anomalous diffusion pops up in impedance and dielectric spectroscopy such that the application of system identification techniques in electrochemical, microwave, and biomedical engineering may be affected by diffusion. The presence of diffusion may introduce systematic errors or bias when applying system identification techniques of linear time-invariant (LTI) systems. In this paper, we revisit classical LTI identification in the presence of Cole-Davidson (CD) diffusion wherein we accomplish: 1) detecting the CD diffusion component; 2) discriminating the diffusion from the remaining dynamics; and 3) modeling the CD diffusion through a fractional-order model, in particular, a pole of fractional-order multiplicity.