bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Looping Using Tungsten Oxide for Electrolytic Hydrogenations
Authors: Sharifi Abdar Payman , Miu Evan V , Hughes Isabella , McKone James
Published: December 2024

Global R&D associated with the production and utilization of hydrogen has been increasing dramatically to support the global effort to reduce CO2 emissions. Hydrogen can be used as a source of fuel and electricity, and it is also used as a chemical reductant for a host of industrial processes. One of the widely used applications of hydrogen in chemical industries is for hydrogenation reactions like ammonia synthesis and biomass hydrogenation. However, providing hydrogen for these reactions is practically challenging due to the several issues related to the high cost of infrastructure for hydrogen storage and transportation as well as safety concerns. These challenges could be mitigated if the hydrogen equivalents (i.e, protons and electrons) needed for these reactions can be supplied from water without producing H2 gas.

In this study, we introduce the concept of electrochemical looping hydrogenation, in which, instead of producing H2, a solid hydrogen-transfer mediator is used to activate hydrogen through water electrolysis and subsequently deliver it catalytically to a target molecule. Here, tungsten oxide (WO3) plays the role of the mediator due to its ability to reversibly uptake and donate hydrogen atoms. In this process, hydrogen is electrochemically inserted into WO3 to form tungsten oxide hydrogen bronze (HxWO3). The stored hydrogen is then used to drive a chemical hydrogenation reaction via hydrogen de-insertion from HxWO3 and reformation of WO3. For this study, hydrogenation of 4-hydroxy TEMPO (2,2,6,6-tetramethylpiperidine N-oxyl) to 4-hydroxy TEMPO-H was chosen as a model hydrogen acceptor. The results validate proof-of concept for our electrochemical looping system and permit systematic measurements exploring the interplay between interfacial transfer and intra-phase transport of electrons and protons.
Physics-Based Modeling to Elucidate Design Principles for Redox-Mediated Electrochemical Systems
Authors: Matteucci Nicholas J. , Mallia Christopher T. , Brushett Fikile R.
Published: December 2024

Electrochemical systems are increasingly being developed and deployed as sustainable technologies that support reductions in greenhouse gas emissions across the electric power, transportation, and industrial sectors. However, the need to overcome challenges related to cost, performance, and scalability continues to motivate exploration into alternative material sets and reactor designs that offer new pathways to widespread adoption. Redox-mediated processes, which decouple electrode reactions that activate a soluble mediator from “off-electrode” reactions where the activated mediator exchanges electrons with a solid material, are of growing interest.1,2 Recent literature has illustrated the potential of this approach for increasing the charge-storage capacity of redox flow batteries,2 performing impractical electrochemical processes,3 enhancing selectivity and efficiency of electrochemical separations and recycling,1,4,5 and unlocking spatial and temporal flexibility in electrochemical operations.6 Previously, we have developed and qualitatively validated a model capable of capturing key dynamics observed in redox-mediated flow batteries.7 Grounded in first principles and contextualized by experiments, this model has the potential to rapidly assess tradeoffs and opportunities for redox-mediated systems for applications in energy storage and conversion as well as materials recovery and recycling.

Here, we describe how our model can be used to gain generalizable insights into the design-space for redox-mediated electrochemical processes. By incorporating models for pressure drop in porous media with simulated electrochemical performance, we assess the trade-offs associated with capacity utilization, power output, and parasitic pumping losses. Furthermore, we demonstrate how the model can support constrained optimization to guide the design of a system of known physical parameters. Ultimately, we seek to translate these findings into universal design principles for how electrochemical protocol and solid incorporation can be tuned to develop high-performing redox-mediated systems.

Acknowledgements

N.J.M gratefully acknowledges the NSF Graduate Research Fellowship Program under Grant Number 2141064. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.

References

Xue et al., Green Chem. 2020, 22 (19): 6288-6309.

Yan and Wang, Mat. 2018, 30 (47).

Vardner et al., ChemElectroChem 2022, 9 (24).

Cotty et al., ACS Sustain Chem Eng. 2023, 11(9):3975-3986.

Park et al., ACS Sustain Chem Eng. 2021, 9 (24): 8214-8221.

Wang et al, Joule 2021, 5 (1): 149-165.

Matteucci et al., ECS Meeting Abstracts 2023, MA2023-01 (3), 765.
Investigation of Phosphorus Refining in Hot Metal through Electrochemical Methods
Authors: Lee Sanghoon
Published: December 2024

This study investigates the enhancement of phosphorus removal from hot metal through electrochemical methods to promote sustainable steel production. It introduces electrolytic refining techniques using molten slag as an electrolyte, aiming to overcome the limitations of chemical refining based on conventional CaO-bearing slag.

The research focused on the application of electric potentials to a CaO-SiO2-Al2O3-MgOsat slag system at a temperature of 1550℃ in a CO gas atmosphere, with voltages ranging from -0.5V to -2.0V. Following the attainment of electrochemical equilibrium, the efficiency of phosphorus removal was determined by quantitatively analyzing phosphorus content in the hot metal.

The results demonstrated that applying external electric potentials significantly enhanced phosphorus removal rates compared to the chemical equilibrium between the molten slag and hot metal. Moreover, the influence of slag basicity on the efficiency of phosphorus removal during the electrolytic refining process was confirmed. Consequently, the correlation between slag basicity and phosphorus electrolytic refining efficiency was discussed in detail, based on the physicochemical and electrical properties of the slag.
Molecular Design of Redox-Copolymers for Selective Electrochemical PGM Recovery
Authors: Kim Hee-Eun , Chung Ching-Hsiu , Elbert Johannes , Su Xiao
Published: December 2024

Platinum group metals (PGMs) are of vital importance to various industries such as manufacturing, transportation, and energy economy. To secure the supply chain of PGMs, it is important to selectively extract target species from the mining ores and recycle spent automobile catalytic converters or e-waste. However, PGMs are challenging species to separate due to very similar physical and chemical properties and low concentration and complex speciation depending on pH or type of electrolyte used.1 Electrochemical separation is environmentally benign with good modularity and scalability. The development of next-generation electrodes with selective interactions for metal-binding and recovery is critical for innovating sustainable mining processes.

Redox electrodes were also shown to be efficient in controlling the operational voltage windows in aqueous-phase electrochemical systems, by increasing the Faradaic efficiency towards ion-binding and suppressing side reactions that would otherwise increase energetic costs. At the same time, polymer-functionalized electrodes have been shown to facilitate selective electrodeposition and regeneration of metals, thus providing an alternative approach for energy-efficient metal recovery. Redox-active polymers containing ferrocene have shown high selectivity towards anionic species such as metal oxyanions of arsenic and chromium.2 By modulating functional groups of redox polymers, charge-transfer behavior can be changed, and it can also provide new binding sites for target ions. We investigated a series of ferrocene-containing redox polymers to understand the kinetic and equilibrium uptake of PGM chloroanions. Different functional groups such as amide, alkyl, amine, and ester, respectively can modulate different redox potential within metallopolymers due to electron donating or electron withdrawing effects. The effect of these homopolymers was evaluated, with high uptake and regeneration being achieved for a range of PGMs. Going further than individual monomers, PGM-specific ligands were designed and incorporated into redox polymer by copolymerization. By leveraging heteroatom ligands as metal-specific functionality, the selectivity of the redox-copolymers in different pairs of PGM binary mixtures was tuned beyond the original homopolymers. The effect of ligand binding strength, ratio between redox group to ligand, and releasing solution on selectivity and uptake was investigated in detail.

(1) Kim, K.; Candeago, R.; Rim, G.; Raymond, D.; Park, A. H. A.; Su, X. Electrochemical approaches for selective recovery of critical elements in hydrometallurgical processes of complex feedstocks. iScience
2021, 24 (5), 31, Review. DOI: 10.1016/j.isci.2021.102374.

(2) Su, X.; Kushima, A.; Halliday, C.; Zhou, J.; Li, J.; Hatton, T. A. Electrochemically-mediated selective capture of heavy metal chromium and arsenic oxyanions from water. Nat. Commun.
2018, 9 (1), 4701. DOI: 10.1038/s41467-018-07159-0.
Towards Oxygen-Tolerant Proton-Coupled Redox Organics for Aqueous Electrochemical CO2 Capture
Authors: Alfaraidi Abdulrahman , Ni Nina , Lee Kyumin , Faialaga Nathan , Liu Richard , Aziz Michael J.
Published: December 2024

Capture of CO2 from point sources or directly from the atmosphere can provide an important contribution to climate-change mitigation efforts in the coming decades. Electrochemically driven CO2 capture utilizing proton-coupled redox organics (PCROs) in aqueous solution has great potential because of the process's low energy use, the nonflammability and high ionic conductivity of the medium, and the ability to be powered by cheap, clean electricity at high current density. However, all PCROs reported previously for this application are, in their reduced form, reversibly chemically oxidized by oxygen, resulting in impractically low efficiency. In this work, we attempt to better understand this sensitivity by studying the oxidation mechanism using electrochemical techniques and by measuring the oxidation rate of various reported and newly developed PCROs. This guides us in the development of new PCROs for electrochemical CO2 capture with decreased reactivity with oxygen, and we experimentally demonstrate their performance in electrochemical flow CO2 capture system.
Fabrication of Superomniphobic TiAl6V4 Surface for Self-Cleaning and Anti-Biofouling Effect of Medical Devices
Authors: Lee Jeong-Won
Published: December 2024

Ever since Wenzel and Cassie-Baxter announced their theories with respect to wettability transition with surface roughness, numerous studies on fabricating superhydrophobic surface have been carried out to provide industries with the advantages of the superhydrophobic surfaces such as anti-frosting, water proof, and self-cleaning. In metal industries, several methods have been developed to achieve superhydrophobic surfaces on various metals, including aluminum, copper, and steel. However, the fabricated surfaces only show over 150 of contact angles (CAs) for water (surface tension = 72.0 mN/m at 25 ℃) and do not show excellent repellency to low surface tension oils.

In the past few years, advantages of superomniphobic surfaces have been identified and many efforts are directed toward their practical industrial applications. Superomniphobic surfaces, unlike the superhydrophobic surfaces, show high repellency to low surface tension oils as well as anti-fouling, oil transfer, and oil-water separation properties. A superomniphobic surface is required to have not only a low surface energy but also a specific surface structure, because of which, it is much more difficult to fabricate than a typical superhydrophobic surface. Although a few fabrications of superomniphobic surface on titanium alloy (TiAl6V4) substrates have been reported, they are not superomniphobic to low surface tension oils like hexadecane, or are too far from industrialization because their fabrication relies on difficult methods such as laser micromachining. Further, there has been no report on achieving superomniphobic TiAl6V4 surfaces for hexadecane (surface tension = 27.1 mN/m at 25℃) using a simple method.

In this study, we render TiAl6V4 substrates superomniphobic by acid etching followed by anodization. Each process is analyzed with respect to processing times for obtaining optimal hierarchical microhorn/nanopore structures. The surface structures were then fluorinated by a self-assembled monolayer (SAM) coating, thereby imparting great repellency to low surface tension oils, including hexadecane. The surface morphology of TiAl6V4 in each process and analyses of the surface chemical change are discussed.

Figure 1
Probing the Reaction Mechanisms for Electroreduction of Furanics on Copper
Authors: May Andrew S. , Talipov Sarvarjon , Chilunda Moses D. , Biddinger Elizabeth J.
Published: December 2024

The increase of renewables on the electricity grid and diversification of chemical feedstocks offers opportunities for electrochemical reactions to be performed. Biomass-derived feedstocks can be upgraded electrochemically at the biorefinery before use or transportation for further valorization. Furanics are commonly found biomass-derived chemicals as a result of biomass upgrading from pyrolysis and other conversion methods and are considered key platform chemicals. Additionally, furfural is produced commercially, making it an existing feedstock stream that can be upgraded directly. 5-Hydroxymethylfuran (HMF) is also a valuable platform chemical, though has yet to be produced commercially at scale. Electrochemical hydrogenation and hydrogenolysis (ECH) of the furanics can result in the formation of valuable fuel and chemical intermediates. Furfural ECH serves as a good model reaction, as it has fewer functional groups to react. Performing ECH on HMF intermediates can also help understand the reaction pathways better. The ECH reactions also compete with hydrogen evolution and acid-derived side products in the reactor. By tuning the reaction conditions, the desired products can be formed and undesired products minimized. Utilizing traditional heterogeneous catalysis techniques, the kinetics of the ECH reactions and competing side reactions can be determined. The source of the catalyst fouling and its potential dependence can also be identified. The kinetics and reactor operation details can be combined into an overall mass balance that enables better understanding of the system and identify opportunities for further improvement.
Magic Angle Moiré Bilayer Graphene for Enhanced Electrochemical Oxygen Reduction Reaction in PGM-Free Catalysts
Authors: Li Sirui , Zelenay Piotr , Holby Edward F. , Kort-Kamp Wilton
Published: December 2024

Tuning active site electronic structures is crucial to the efficient interconversion of electrochemical energy. The recent discovery of flat electronic bands in stacked atomically thin layers of graphene has sparked unprecedented interest in moiré superlattices with small twist angles (0.22º < theta < 5º).1 A recent work in electrocatalysis demonstrated enhancement of hydrogen evolution using Ru embedded in twisted bilayer graphene (TBG) nanosheets.2 In this talk, we explore moiré superlattice effects for applications in PGM-free fuel cell cathode catalysts, where molecular oxygen is electrochemically reduced at the catalyst-electrolyte interfaces (i.e., oxygen reduction reaction, ORR) to power polymer electrolyte fuel cells (PEFCs). The activity, stability, and affordability of catalysts are current bottlenecks at the materials level that prevent widespread adoption of PEFCs in the clean energy sector. Replacing rare and expensive Pt/C catalysts with graphene-based structures would greatly aid in addressing cost, but co-optimization in the activity and stability of such structures is required. We will discuss the theoretical and computational framework needed to unveil the mechanisms and merits of TBG as an effective material platform for realizing highly active and stable ORR precious metal free catalysts. This includes the feasibility of driving 4 electrons ORR pathways on TBG systems as a function of twist angle, which will provide us with an activity descriptor. For structures demonstrating feasible 4 electrons reduction pathway, we will further explore stability against metal dissolution. These efforts enable us to explore the existence of “magic angles” of TBG in ORR applications. This work will leverage our prior efforts in developing activity and stability descriptors for electrocatalyst and atomically dispersed systems.3–6 We will also combine uncertainty quantification approaches with multi-objective Bayesian optimization to navigate the TBG structural-chemical material space and suggest new synthesis target structures exhibiting both high activity and stability.

References

Y. Cao et al., Nature, 556, 43–50 (2018).

J. Zhang et al., Angew Chem Int Ed, 61, e202116867 (2022).

S. Li, G. S. Frankel, and C. Taylor, J. Electrochem. Soc. (2022) https://iopscience.iop.org/article/10.1149/1945-7111/ac86f8.

E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).

H. Hafiz, P. Zelenay, and E. F. Holby, Applied Catalysis B: Environmental, 339, 123158 (2023).

W. J. M. Kort-Kamp et al., Journal of Power Sources, 559, 232583 (2023).
Simultaneous Entropic Coefficient Measurement and Multi-Species, Multi-Reaction Modelling
Authors: Wolfe Kody D , Paul Abigail , Magee Regan , Wilczewski Warren , Wichert Nathan , Lowe Jeffrey , Trembly Jason , Staser John A. , Garrick Taylor R.
Published: December 2024

The multi-species, multi-reaction (MSMR) model is developed through the fitting of pseudo-open circuit voltage (POCV) data acquired by cycling a cell at a sufficiently low rate (C/50).1 By comparing MSMR fitted data taken at various temperatures, both temperature dependence of fitting parameters and thermodynamic data including the state-of-charge (SOC) dependent entropic coefficient (dU/dT), entropy (ΔS), and enthalpy (ΔH) can be gleaned.2 In this presentation, POCV behavior of coal-derived graphite will be discussed and compared to thermodynamic measurements of lithium-intercalation under potentiostatic testing conditions.3 Simultaneously measuring POCV data and determining

thermodynamic parameters has the advantages of minimizing testing time and complexity. The MSMR model’s ability to distinguish minute changes in temperature dependent active material behavior will be highlighted through a comparison of coal-derived graphite and commercially available

synthetic graphite.4 Implications of thermodynamic parameters and temperature dependent behavior on cell and pack level engineering will also be presented.

References:

1. D. R. Baker and M. W. Verbrugge, Journal of The Electrochemical Society, 165, A3952 (2018).

2. T. R. Garrick et al., Journal of The Electrochemical Society, 171, 023502 (2024).

3. J. Sturm et al., Journal of Power Sources, 412, 204–223 (2019).

4. A. Paul et al., Journal of The Electrochemical Society, 171, 039001 (2024)
A Reduced Order Modeling Approach to Capture Transport within a Three-Electrode System Towards Fast Charge Applications
Authors: Mollah Rafid , Garrick Taylor R. , Gao Jing , Zeng Yangbing , Koch Brian
Published: December 2024

In support of GM's traction battery efforts, we derive and implement a reduced order modeling method to describe the electrochemical performance of a battery cell through the combination of a modified Newman Pseudo-2-Dimensional model and a three-electrode experimental apparatus. To assess the capability of the method, we compare the modeling results with experimental data for a lithiated graphite electrode and a lithiated nickel rich electrode system. The model is applied to simulate the electrochemical and transport processes within the battery cell to predict the negative electrode potential and positive electrode potential with respect to a lithium iron phosphate reference electrode, as well as the terminal voltage.

The manufacture and set up of the three-electrode system, model development and reduction approaches, as well as a discussion of applicability to fast charge considerations to avoid lithium plating at the anode during a charging event will be presented.

References:

T. R. Garrick, J. Gao, X. Yang, and B. J. Koch. 2021. J. Electrochem. Soc. 168 010530

T. R. Garrick, J. Gao, X. Yang, and B. Koch. 2021, Meet. Abstr. MA2021-02 485

T. R. Garrick, J. Gao, and B. J. Koch. 2022. Meet. Abstr. MA2022-02 1077

T. R. Garrick, Y. Zeng, J. B. Siegel, and V. R. Subramanian, J. Electrochem. Soc., 170, 113502 (2023)
Three-Dimensional Microstructure Modeling of Lithium Deposition and Dendrite Formation during Automotive Relevant Cycling
Authors: Teel Hunter , Garrick Taylor R. , Lopata Joseph Steven , Shimpalee Sirivatch
Published: December 2024

Dendrites generally form during rapid charging of lithium-ion batteries when lithium plating is favored over intercalation. If not removed during discharging cycles, the potential exists for dendrites to grow through the separator and short between the anode and cathode. One metric for diagnosing lithium plating conditions in a computational model is the minimum local potential at the anode, where lithium plating is seen to be thermodynamically favorable below 0.0 V with respect to Li metal. [1-2] Three-dimensional (3D) microstructure model can provide insight to predict the possibility of local lithium plating as well as the possible formation of dendrites. This model can also be used as a tool to detect possible global lithium plating onset. The moving boundary technique with mesh movement can be employed to separate the electrolyte region into a liquid phase and a solid phase.[3]

This approach is applied in our 3D microstructure model of a lithium-ion battery[4] to observe the growth of lithium plating as well as dendrites at the anode during rapid charging cycles. Under beginning conditions at the solid/electrolyte interface (SEI), the solid metal phase is deposited at the SEI. Upon growth, the overall electrolyte resistance at the tip of the metal phase is reduced, leading to dendrite growth. The 3D microstructure model provides valuable insight into various conditions that may cause plating, if dendrites are formed due to plating, and whether the dendrites formed may proceed through the separator.

References

T. R. Garrick, J. Gao, X. Yang and B. J. Koch, J Electrochem Soc, 168, 010530 (2021).

U. Janakiraman, T. R. Garrick and M. E. Fortier, J Electrochem Soc, 167, 160552 (2020).

T. Jang, L. Mishra, S. A. Roberts, B. Planden, A. Subramaniam, M. Uppaluri, D. Linder, M. P. Gururajan, J.-G. Zhang and V. R. Subramanian, J Electrochem Soc, 169, 080516 (2022).

J. Lopata, T. R. Garrick, F. Wang, H. Zhang, Y. Zeng, S. Shimpalee, Journal of The Electrochemical Society, 170, 020530 (2023).
(Keynote) Atomic Scale Modeling of "Anode Free" Li-Metal Batteries
Authors: Siegel Donald J.
Published: December 2024

A rechargeable battery that employs a Li metal anode requires that Li be plated and stripped in a uniform fashion during cycling. In “anode-free” configurations, plating will occur on the surface of the Cu current collector (CC) during the initial cycle and in any subsequent cycle where the capacity of the cell is fully accessed. Under these circumstances phenomena at the Li/CC interface play an important role. On the other hand, at intermediate states of charge, maintaining interfacial contact between the anode and the solid electrolyte is a key factor in the operation of solid state batteries. This contact is controlled by chemical interactions at the interface (DOI: 10.1021/acs.chemmater.7b03002), but is also influenced by phenomena in the bulk regions of the anode, such as mass transport and plastic deformation. This presentation will provide an overview of atomic scale simulations that characterize several of these phenomena: interfacial interactions with the CC and with the solid electrolyte, mass transport within the anode, and deformation mechanisms of bulk Li. As one example, a multi-scale model is developed for predicting transport properties within the anode. The model predicts that a Li microstructure consisting of columnar, micron-scale grains can improve cycling performance due to fast grain boundary diffusion that can minimize void formation at the solid electrolyte interface (DOI: 10.1039/D3TA03814A). As another example, a combination of first-principles calculations and sessile drop experiments were used characterize the thermodynamics and adhesive (i.e., wetting) properties of interfaces involving Li and other phases present on or near the CC. It is demonstrated that Cu CCs can exhibit both lithiophillic and lithiophobic interactions with Li. These heterogeneities impact the performance of anode-free Li metal batteries (DOI: 10.1021/acsami.3c19034).
(Invited) (Digital Presentation) Development of Temperature-Dependent Degradation Models for Large-Format Lithium-Ion Batteries
Authors: Mishra Lubhani , Subramaniam Akshay , Garrick Taylor R. , Subramanian Venkat R.
Published: December 2024

Advancing electric transportation technologies is critically dependent on maximizing the performance and lifetime of Electric Vehicle (EV) batteries, which is directly related to the economic case for EVs. Large-format cells are achieving increasing popularity for EVs to maximize volumetric and gravimetric energy densities. However, due to the large format size cells that are currently used for applications within the electrification portfolio, challenges have arisen that are tied to thermal management. Spatial variations in current density and temperature negatively affect overall cell utilization and lifetime. Identifying these temperature-dependent degradation mechanisms often relies on post-mortem analysis of cells, while model systems may be required to characterize spatial non-uniformities in degradation adequately. These challenges, along with the need for a comprehensive understanding of the degradation mechanisms, have led to the development of rigorous electrochemical models for battery degradation. These physics-based models serve as a powerful complementary tool in obtaining a better understanding of such phenomena. Simulating performance scenarios can lead to significant improvements in cell design and experimentation while also reducing time and cost commitments for the same.

The primary goal of this work is the development and validation of a physicochemical degradation model for automotive lithium-ion batteries to predict the degradation in the large-format cell in the presence of temperature gradients using the given set of cell parameters with temperature dependence. It was realized that the degradation trajectories are a result of a combination of both LLI (loss of lithium inventory) and LAM (loss of active material) fade mechanisms at both anode and cathode. The state-of-the-art electrochemical models for lithium-ion cells (p2D models) were implemented in both in-house codes and equation-based formulation in COMSOL Multiphysics with weak form implementation. The codes were validated against experimental cycling data at different operating temperatures at each stage of the model development. The validated codes possess the ability to estimate local degradation rates and consequent impact on cycling performance for EV batteries at a range of operating conditions. Thus, the model is a means of identifying dominant degradation mechanisms in practically relevant operating conditions, helping improve overall lifetime, and enhancing value by helping identify improvements in battery operations. The errors between the model and data can provide information on the suitability of a given model and the relative prevalence of a given degradation mechanism, with useful, practical benefits.
On the Proper Use of a Warburg Impedance
Authors: Orazem Mark E. , Ülgüt Burak
Published: December 2024

Recent battery papers commonly employ interpretation models for which diffusion impedances are in series with interfacial impedance. The models are fundamentally flawed because the diffusion impedance is inherently part of the interfacial impedance.

This presentation is based on a recent publication [1]. A derivation for faradaic impedance is presented which shows how the charge-transfer resistance and diffusion resistance are functions of the concentration of reacting species at the electrode surface, and the resulting impedance model incorporates diffusion impedances as part of the interfacial impedance. Conditions are identified under which the two model formulations yield the same results. These conditions do not apply for batteries.

Mark E. Orazem and Burak Ulgut, J. Electrochem. Soc., 171 (2024), 040526
(Invited) Fourier Transformed AC Voltammetry and Relationship to Electrochemical Impedance Spectroscopy
Authors: Bond Alan Maxwell
Published: December 2024

Fourier Transformed AC Voltammetry (FTACV) commonly employs a single frequency sinusoidal waveform superimposed onto a DC ramped potential. If the amplitude is large enough, non-linearity in the faradaic electron transfer response leads to detection of the aperiodic DC, fundamental harmonic, second harmonic and a series of higher order harmonics. The features of the faradaic response are governed by the thermodynamics in combination with the kinetics of the electron transfer process and coupled chemistry, with the higher order AC components being particularly sensitive to the electrode kinetics. Importantly, the second harmonic ideally, but third and higher in practice, are devoid of background current arising from double layer capacitance charging or other processes. Many variations of FTACV are also available. For example, a single sinewave with no DC ramp or instead of a single sine wave, two, three or multiple sinewaves can be superimposed onto the DC ramp, or a square wave can be employed. Electrochemical Impedance Spectroscopy (EIS) represents one limit of applying multiple sine waves, traditionally at a fixed DC potential but now more commonly also onto a ramped DC potential. Thus, it can now be recognised there is large family of AC methods are available that are all governed by closely related instrumental and theoretical principles. In the first part of this lecture, data analysis by FTACV for the well-known Fc0/+ process(Fc = Ferrocene) will be extended to the rarely studied Fc+/2+ reaction which is an Fe(III) to Fe(IV) reaction accessible at very positive potentials in ionic liquids at glassy carbon and boron doped diamond electrodes. Novel features relevant to the Fc0/+/2+ reaction sequence, anomalous background current, ionic liquid voltammetry, and carbon electrodes at very positive potentials emerge from analysis of single sine wave FTACV based on comparisons of simulated responses and experimental data, use of multiparameter fitting by data optimisation and Bayesian inference. The lecture will then conclude by considering the implications of using an analogous approach to analyse data obtained by application of multiple sine waves rather than a single sine wave and the relationship to data analysis as in EIS where equivalent circuit analysis has been employed instead of models based on thermodynamics combined with electrode and chemical kinetics.
Innovative Methods for Crafting Hierarchically Structured, High-Performance Self-Supporting Flexible Bifunctional Electrocatalysts in Rechargeable Zinc-Air Batteries
Authors: Chen Yingjie , Meng Xiangyu , Dong Lifeng
Published: December 2024

Efficient bifunctional electrocatalysts are pivotal for enhancing the performance of rechargeable zinc-air batteries, particularly in facilitating the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Recent strides in electrostatic spinning technology have yielded notable progress in polymer-zinc-air battery systems. This study introduces two innovative methodologies for synthesizing self-supporting flexible bifunctional electrocatalysts featuring hierarchical structures and high catalytic activity through meticulous adjustment of electrostatic spinning parameters.

The first approach integrates metal-organic frameworks with electrospinning technology to fabricate FeCoNi nanoparticle-decorated N-doped carbon hierarchical networks. These nanoparticles, originating from Fe3+/Co2+/Ni2+ ions within the electrospun fibers, catalyze the pyrolysis of ZIF-67 on the fiber surface, thereby generating reticulated carbon microfibers.

The second approach capitalizes on the characteristics of organic salts in polymer solutions via electrospinning to produce FeCoNi flexible carbon nanofibers. These catalysts undergo secondary growth of FeCoNi- and N-doped carbon nanotubes on fiber surfaces, yielding numerous metal-nitrogen-carbon (M-N-C) ORR active sites and FeCoNi alloy-based OER active sites.

Both methodologies yield bifunctional electrocatalysts exhibiting outstanding ORR and OER activity, surpassing conventional Pt/C and RuO2 catalysts. Rechargeable zinc-air batteries employing these catalysts demonstrate high peak power density and remarkable cycling stability, positioning them as promising contenders for next-generation energy storage solutions.
Selective CO2 Reduction to Multicarbon Products on Cu-Based Electrocatalysts in Membrane Electrode Assembly
Authors: Dauda Monsuru Olatunji , Bello Mustapha , Hendershot John C , Park Junghyun , Agbadan Ignace , Tasnim Soundarzo , Kizilkaya Orhan , Sprunger Phillip , Yao Koffi , Flake John C.
Published: December 2024

Electrochemical reduction of CO2 in membrane electrode assembly (MEA) cells with gas diffusion electrodes (GDEs) offers a sustainable path to produce chemicals and fuels. Although these systems enable high-current densities and Cu electrocatalysts favor C2+ products like ethylene, the mechanisms controlling selectivity towards specific C2 products (ethylene, ethanol, and acetate) are not well understood. This study explores CO2 reduction selectivity trends and mechanisms on Cu-based electrocatalysts, emphasizing multicarbon product formation using different Cu alloys. In particular, CuSnx, Cu-P, and Cu-Se electrocatalysts were synthesized via a one-pot method and tested in MEA cells with alkaline electrolytes. Several ex situ characterization techniques (XRD, XPS, SEM, EDS, and ICP-OES) were employed to study the structural, compositional, and electronic properties of the electrocatalysts. Sn content in CuSnx alloys critically influenced the main CO2 reduction product, with high Sn (x ≥ 0.10) promoting formate. and low Sn (x ≤ 0.10) favoring CO, ethylene, and ethanol, depending on cell potential and pH. Comparing Cu, Cu-P0.065, Cu-Sn0.03, and Cu2Se electrocatalysts revealed the impact of dopants, alloys, and compounds on selectivity. In 0.1 M KHCO3, P-doped Cu showed higher ethylene FE (52%) than pure Cu (31%), while Cu-Sn and Cu-Se favored ethanol (24% FE) and acetate (32% FE), respectively. In 1 M KOH, Sn alloys promoted ethanol (48% FE), and Cu-Se achieved high acetate selectivity (40% FE) at 350 mA cm-2. The electrocatalysts demonstrated stability over 250 hours. A mechanism involving a common acetyl intermediate is proposed, with selectivity governed by the partial positive charge (δ+) on Cu sites calculated using density functional theory (DFT). Cu-P0.065 (Cuδ+ = 0.13) promotes ethylene, Cu-Sn0.03 (Cuδ+ = 0.27) favors ethanol, and Cu2Se (Cuδ+ = 0.47) enhances acetate selectivity.
Reduced Graphene Oxide Supported MoSxSe2-X Bifunctional Electrocatalysts for Electrochemical Ammonia Production from Nitrate
Authors: Lim Hyojung , Choi Jinuk , Jeong Gyoung Hwa , Surendran Subramani , Janani Gnanaprakasam , Sim Uk
Published: December 2024

Ammonia (NH₃) holds significant importance across various human activities, finding applications in fertilizers, pharmaceuticals, and carbon-free energy fuel. Traditionally, NH₃ production relies on the energy-intensive Haber-Bosch process, leading to substantial CO₂ emissions. As an alternative, there's growing interest in electrochemical NH₃ production. The electrochemical nitrate reduction reaction (NO₃RR) is particularly promising due to its low energy barrier, high nitrogen source solubility, and high activity. Molybdenum dichalcogenides (Mo-based TMDs) have emerged as catalysts for electrochemical NH₃ production, leveraging their 2D structure, large surface area, and tunable electrical properties. However, Mo-based TMDs having 2H crystal structure face challenges like low electrical conductivity and high hydrogen evolution reaction (HER) activity, which competes with NH₃ production. To address this, we developed various 1T-MoSxSe2-x/rGO electrocatalysts. These catalysts exhibited a yield rate exceeding 3511.9 μg h-1 cm-2 (at -0.6 V vs. RHE) and a 70 % faradaic efficiency (at -0.2 V vs. RHE) in a 1 M KOH and 0.1 M NaNO₃ solution. And their bifunctional properties (Oxygen evolution reaction, OER) show a low overpotential of 338.8 mV at 10 mA. Our research aims to enhance NO3RR under ambient conditions and investigate the potential of bifunctional properties (OER) for the commercialization of electrochemical NH₃ production.
Development of Large-Sized CO2 Electrolyzer Producing CO for Industrial Applications
Authors: Kofuji Yusuke , Fujiwara Naoya , Yonetsu Maki , Kiyota Yasuhiro , Kudo Yuki , Mikoshiba Satoshi , Yanagi Kosuke , Kikuchi Isamu , Kimura Shunsuke , Kitagawa Ryota
Published: December 2024

Utilization of carbon dioxide (CO2) as a feedstock of valuable chemicals is necessary to achieve carbon neutrality. CO2 electrolysis producing valuable organic molecules such as carbon monoxide (CO) is one of the most promising methods. To implement this technology in society, a large-sized electrolyzer that can convert a huge amount of CO2 are required. Toshiba is developing a low-temperature zero-gap type CO2 electrolysis cell/stacks with 400 cm2 electrodes to produce CO [1,2], which can be converted into chemicals and fuels by catalytic reactions with hydrogen. With properly designed gas flow plates and optimal operation conditions, CO faradaic efficiency of the 400cm2 single cell were comparable to that of a smaller cell with 4 cm2 electrode [3]. Another problem to be solved is low durability of the electrolyzer. During continuous operation of the electrolyzer, several failure modes such as cathode flooding, salt precipitation, diaphragm degradation, corrosion of flow plates, and catalyst dissolution often occur. By resolving each of these failure modes, stable performance over 500 h was achieved. Additionally, in this presentation, we report the results of electrolysis tests using CO2 gas containing impurities that are expected to be contaminated in an actual environment, and the results of electrolysis tests to confirm effects of a ripple current generated from AC/DC converter on the efficiency of CO2 electrolyzer.

Part of this work is commissioned by Ministry of the Environment, Government of Japan.

[1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba, and

R. Kitagawa, Chem. Lett., 50, 482-484 (2021).

[2] Y. Kiyota, Y. Kofuji, A. Ono, S. Mikoshiba, and R. Kitagawa, 242nd ECS Meeting, I05, 1942,

(2022).

[3] Naoya Fujiwara, Yusuke Kofuji, Satoshi Mikoshiba, Ryota Kitagawa, Atsushi Matsunaga, Isamu

Kikuchi, Soichiro Shimotori, 244th ECS Meeting, I05, 2328, (2023).
Insights from the Systems Scale to Design Practical CO2 Electrolyzers
Authors: da Cunha Shashwati C , Resasco Joaquin
Published: December 2024

Electrochemical CO2 reduction (CO2R) can convert captured CO2 into chemical feedstocks and fuels using renewable electricity and water, but scaleup has been limited. To guide targets that set the direction of research in the field, we connect a systems-level perspective on CO2R with electrolyzer design. A physics-informed technoeconomic assessment can highlight the sensitivity of overall process cost towards improvements at the electrolyzer scale, identifying the most impactful opportunities to improve performance. The assessment confirms the importance of better materials (membranes, catalysts), which has been the focus of the field, and that electricity prices are currently too high for economical CO2R. However, we find a critical and overlooked need for improved reactor design to make CO2R economically viable. Analyzing the separations needed for state-of-the-art CO2R electrolyzers shows that maximizing single-pass conversion comes at the cost of product composition and process energy. This is because electrolyzers increase conversion by restricting feed flow rate or by using strongly acidic electrolytes. Both these conditions promote the HER side reaction, wasting expensive electricity on making byproducts.

Our work has shown the tradeoff between single-pass conversion and selectivity for CO2 electrolyzers, a limitation that arises directly from current reactor design. Due to selectivity loss, we show that increasing single-pass conversion beyond ~10% increases process cost for current electrolyzer designs and process costs. Since the relationship between selectivity and single-pass conversion comes from the plug-flow channel design, we call on the field to investigate reactor designs that modify this crucial handle on CO2R cost by improving the availability of CO2 to the catalyst surface. On the other hand, we show that mitigating the “carbonate problem” leads to relatively small improvements in cost for relevant electrolytes. Moreover, operation at high current density (>1 A/cm2)has been repeatedly proposed as a target for the field. Such high currents lead to a tradeoff between capex and utility cost at a much lower current density than has been proposed. At current electricity prices, the optimal total current density is <300 mA/cm2. Therefore, high operating currents will worsen process costs, unless accompanied by much lower electricity costs or considerable improvement in the full-cell polarization curve for CO2R in membrane electrode assemblies.
In Preparation of Using Confocal Raman Spectroscopy to Study Mass Transport in Bipolar Membranes
Authors: Beswick Rebecca , Crow Allison M , Deutsch Todd G , Smith Wilson A , Kleimenhagen Beth
Published: December 2024

As the world produces more renewable energy in the need to transition away from fossil fuels, the use of low-temperature electrochemical reactors is an increasingly important topic of research. An enabling component of electrochemical reactors is an ion exchange membrane, which selectively transports either cations, in a cation exchange membrane (CEM), or anions, in an anion exchange membrane (AEM), from one compartment of a reactor to another. When a CEM and AEM are physically combined they can create a bipolar membrane (BPM), which can generate protons and hydroxide ions from water dissociation at the junction of the AEM and CEM when operated in reverse bias, while also reducing unwanted ion crossover in electrodialysis and electrolysis applications. Maintaining the junction interface is critical to the operation of a BPM, however due to the small size of the junction and the similarities of appearance between the AEM and CEM, it is difficult to obtain spectroscopic information about the BPM junctions. Additionally, in the literature the mechanism behind BPM failures are not well reported. These gaps in knowledge make rational design for improved membranes hard to achieve. Here, we use Confocal Raman Spectroscopy (CRS) to spatially observe spectral data throughout the AEM, CEM and AEM/CEM junction of a novel 3D spun bipolar membrane. CRS uses a monochromatic light to initiate and observe Raman scattering from the polymers in each membrane, showing characteristics of the polymer backbone structure, linkers, and ion exchange functional groups, throughout the membrane thickness. The confocal Raman microscope enables spectrum collection from a micron scale voxel, as opposed to the bulk volume, resulting in a nominally non-destructive technique for making spatiotemporal measurements. Using CRS, we identify the BPM junction thickness and homogeneity through 3-dimensional spatial mapping. We also demonstrate the ability of CRS to analyze the method of BPM failure when used in an electrodialysis reactor by obtaining spectral maps of failed membranes, showing junction delamination, ionic buildup in either the CEM or AEM, and ionic polymer breakdowns of the CEM or AEM due to contaminants. In collaboration with experimental collaborators, 3D BPM fabrication techniques were assessed for their impact on overall BPM performance and durability, while demonstrating the non-destructive usage of the CRS technique.
Exploring the Role of Natural Convection in 2-Stage Electrochemical CO2 Separation
Authors: Ripley Katelyn M. , Clarke Lauren E. , Caruso Isabella , Brushett Fikile R.
Published: December 2024

Current state-of-the-art carbon dioxide (CO2) capture systems are often implemented at large scale thermal power plants and industrial facilities due to their capital-intensive designs.1 However, there are many smaller scale applications for CO2 separation, such as from commercial buildings, airplanes, and/or submarines, that could benefit from scalable technologies with lower energy requirements. Consequently, 2-stage electrochemical CO2 separators have been proposed as systems with the potential to achieve high energy efficiencies and to operate at the compact sizes required for space-constrained applications.2 While electrochemical capture systems most similar to thermochemical capture systems employ separation units such as absorption columns and flash tanks in addition to the electrochemical reactor, the envisioned 2-stage process combines the activation step with CO2 absorption and the deactivation step with CO2 desorption, all within a single unit. Unfortunately, experimental studies have thus far shown these devices cannot support high current densities and exhibit considerable losses. Understanding and mitigating these losses is key to improving the performance of these separators.

Here, we develop a two-dimensional cell model to simulate the capture and release of CO2 from a 2-stage electrochemical separator with freely-solubilized, redox-active capture molecules. We first discuss the governing equations within the model and, using representative redox couples, we experimentally validate that the model can adequately predict voltage–current relationships. Through this validation, we observe that electrode reactions generate concentration gradients that induce natural convection within the device, enabling higher than expected current densities. To maximize the benefits of natural convection, we then explore the impacts of capture species and electrolyte properties, cell design, and operating conditions on performance by experimentally and computationally varying redox species concentrations, cell orientation, and electrode dimensions. Finally, we incorporate the CO2 binding/release reactions to predict the effect of natural convection on CO2 capture and release. We find that density gradients within the cell also impact the CO2 back-flux from the higher concentration anode to the lower concentration cathode, affecting the separation flux and minimum work. We anticipate that this model will support electrochemical reactor design campaigns leading to higher-performing devices for a range of CO2 separation applications.

References

M. Wang, A. Lawal, P. Stephenson, J. Sidders, and C. Ramshaw, Chem Eng Res Des, 89, 1609–1624 (2011).

L. E. Clarke, M. E. Leonard, T. A. Hatton, and F. R. Brushett, Ind Eng Chem Res, 61, 10531–10546 (2022).