Electrochemical Energy Systems Research Articles

Black titanium oxide: synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability.

Since its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives.

Transition metal embedded MoS2 as efficient trifunctional electrocatalyst: A computational study

In the advancement of electrochemical energy systems, multifunctional catalysts for the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) are indispensable. Moreover, catalysts produced by incorporating transition metals into two-dimensional materials via substitutional modification have demonstrated remarkable efficacy. The present study examines the prospective uses of transition metal (TM= Nb, Co, In, and Re) dopants comprising 10% Niobium, Rhenium, Cobalt, and Indium in 2D MoS2. The density functional theory has been utilized to study the atomic level interaction. Based on the result, it can be observed that Nb-doped MoS2 has a ΔGH value of 0.06 eV, which signifies its remarkable HER capability when compared to pristine MoS2 and other doped versions. Our analysis for OER and ORR activities reveals that Co doped MoS2 exhibit superior performance compared to both the pristine and other doped versions of TM-MoS2, with an overpotential value ɳOER = 1.00 V and ɳORR = 0.77 V. A modification in electronic properties is examined by analysing the partial density of states during the HER and OER processes. The number of potential candidates suggested by the present findings will aid in the development of TM-doped MoS2-based electrocatalysts.

Beyond Catalysts: Pioneering a New Era in Aluminum‐Based Electrochemical Energy Systems

AbstractAqueous Aluminum‐air batteries (AABs) hold promise for advancing high‐energy density storage systems in future technologies. However, their widespread practical deployment is limited by the inherent hydrogen side reactions in Aluminum (Al) and incomplete cathodic reactions. To address these challenges, the Al‐sodium persulfate (Na2S2O8) system is introduced as an alternative to traditional AABs. Utilizing Na2S2O8 allows to simultaneously achieve three critical objectives, namely, eliminating the need for a cathode catalyst, increasing the system voltage from 1.4 to 2 V, and reducing the hydrogen evolution reaction (HER). Three distinct configurations of the Aluminum electrochemical energy system (Al‐EES) using Na2S2O8: static, flow, and gel are developed. The static configuration demonstrates a performance 1.7 times superior to that of traditional AABs. The flow configuration of Al‐EES achieves a discharge duration of 77 h, which is three to four times longer than that of AABs and exhibits an energy density of 2,650 Wh kgAl−1. This emerging technology has the potential to significantly enhance electric vehicles by providing powerful, efficient, cost‐effective, and durable power‐generation devices.

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

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

Investigation of the Chemical Changes from N-Doped Graphene and MOF to N-G/MOF Composites for the Enhancement of Electrocatalytic Properties

N-doped graphene (N-G) materials showed high potential as electrocatalysts for oxygen reduction reaction (ORR) in electrochemical energy systems and increasingly gaining ground as alternatives to the expensive and degradation-prone Platinum Group Metal (PGM)-based electrocatalysts. Numerous studies demonstrated that as N-G materials are integrated with Metal-Organic Frameworks (MOFs), the N-G/MOF composites exhibited higher electrocatalytic activities than the individual precursors; on several occasions, even higher than the PGM-based ones. In this essence, it is crucial to analyze and understand the chemical changes that occur through the integration of N-G and MOF, as these changes play key roles in enhancing electrocatalytic properties of the materials by introducing different electrochemically active sites. To investigate such chemical changes, we have synthesized an N-G/MOF composite by integrating an N-G with ZIF-8 (which is the most studied member of the MOF family) following a facile mechanochemical wet ball milling process. In the electrochemical characterization, the N-G/MOF composite performed better than N-G and ZIF-8 for ORR catalysis by generating a higher cathodic current density.Multiple samples of N-G, ZIF-8, and N-G/MOF composite were analyzed by X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy to detect the changes in elemental ratios, chemical bonds, and chemical functional groups from the precursors (N-G and ZIF-8) to the N-G/MOF composite. An increase in the elemental Nitrogen (N) ratio was observed in N-G/MOF compared to its precursors; which signifies an increased N-doping ratio in the material which is advantageous for ORR catalysis. The XPS C 1s spectra of N-G/MOF shifted to a higher binding energy (~1eV) compared to the precursors indicating an overall increase in the oxidation states of Carbon (C) atoms in the material which could facilitate oxygen molecules’ adsorption better on these sites at the beginning of ORR process. Comparing the analyzed XPS N 1s spectra revealed an increased relative ratio of the Pyridinic-N functional group in N-G/MOF, which also partly justifies the composite’s enhanced ORR electrocatalytic performance. FTIR analysis revealed interactions between methyl groups (-CH3) of ZIF-8 with oxygen functional groups (i.e. -OH) of N-G while forming the N-G/MOF composite. Besides, a transition from methyl groups (-CH3) to methylene group ( >CH2) was evident during the synthesis, increasing charge density near those C atoms of the N-G/MOF which can as well be advantageous for ORR electrocatalysis. The combined impact of these chemical alterations from N-G and ZIF-8 to N-G/MOF yielded a synergistic effect, elucidating its superior electrocatalytic properties. The findings of this experimental investigation provide insights into the chemical reasons for the enhancement of electrocatalytic properties of N-G/MOF composites; and hereby offer guidance to the design and optimization endeavors of novel catalysts with N-G and MOF materials for diverse electrochemical applications.

Nanoconfined Supercooled Water in Hydrated Two-Dimensional Polyaniline for Sub-Zero Solid-State Zinc-Ion Hybrid Capacitor.

Solid-state electrochemical energy systems have attracted numerous attentions for their excellent performance, high safety, and low cost. Recently, ice of aqueous electrolytes is reported as a new kind solid-state electrolyte for low-temperature solid-state devices. However, the lack of kinetically favorable electrodes hampers the performance of this new class of icy electrolyte-based solid-state devices at sub-zero temperatures. In this work, a hydrated layered polyaniline cathode active material (h-LPANi) with nanoconfined supercooled water by metatungstate clusters is utilized to improve the performance of sub-zero solid-state zinc ion hybrid capacitors (ZIHCs). The interlayer confined hydrated network of h-LPANi improves kinetics, surpassing pristine polyaniline and conventional porous carbon-based active materials. At -15°C, the solid-state iced ZIHCs with h-LPANi cathode demonstrate an areal energy density of 580.0µWhcm-2 at 1.1mWcm-2 and 155.7µWhcm-2 at 43.3mWcm-2, surpassing other low-temperature solid-state ZIHCs with conventional cathodes.

Unravelling the potential of prussian blue analogues in oxygen electrocatalysis: A perspective on surface reconstruction

Prussian blue analogues (PBAs) hold promises as catalysts for electrochemical energy conversion, especially in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Their high surface area and porosity combined with a tunable electronic structure featuring abundant metallic centers, make them attractive alternatives to traditional noble metal-based catalysts. Amongst these fascinating properties, the capacity for surface reconstruction to form active layers is one of the most sought-after characteristics of PBAs for enhanced activity. Recent advancements in operando and in situ techniques have further highlighted PBAs' capability for surface reconstruction during the electrocatalysis, particularly in alkaline solutions. State-of-the-art strategies for enhancing activity and stability of PBA-based catalysts, such as metal doping, tuning metal centers, introducing coordination sphere vacancies (VFeCN), and utilizing carbon supports, are closely linked to their ability towards surface reconstruction. However, key aspects warrant further exploration to achieve high electrocatalytic activity, including identifying initiators and pathways for surface reconstruction, establishing structure-property-activity correlations, and strategically manipulating in-situ catalyst surface reconstruction. This perspective focuses on understanding the transformation of PBA-based pre-catalysts to surface active layers on catalysts via surface reconstruction. A recent progress in PBA-catalysts towards advancing the electrochemical energy systems is highlighted. This perspective will guide the new entrants in the field to understand the process of surface transformation for establishing structure-property-activity relationships and thus to develop highly efficient PBA-based electrocatalysts.

Density functional theory study on the mechanism of oxygen reduction reaction on nitrogen-doped graphene with adjacent Mn and Ni sites

The catalysts for oxygen reduction reaction (ORR) are of great significance to the development of electrochemical energy systems. In this paper, the ORR catalytic performance of Mn–Ni dual-metal doped N-coordinated graphene is studied by density functional theory (DFT). The results show that the catalysts with dual-metal active sites are more stable than that with single metal site, and all catalysts show certain catalytic activity. The reaction pathway analyses of catalysts with two different adsorption configurations of O2 show that when O2 is adsorbed on two metal sites, OOH will automatically split into OH and O. When O2 is adsorbed on Mn site alone, the other site does not participate in the adsorption of oxygen-containing intermediates. The thermodynamic calculation results show that the catalytic performance is mainly influenced by the adsorption strength of O, which is controlled by the number of active sites involved in the adsorption, bond length and the number of transferred electrons at the active sites. The G-MnNiN6-3 shows the best catalytic performance with an overpotential of 0.453 V and a reaction energy barrier of 0.19 eV. The results of this study highlight the potential application of Mn–Ni dual-metal doped N-coordinated graphene as a highly efficient non-precious catalyst.

A new frontier of flexible energy devices: Aqueous proton supercapacitors

Aqueous proton supercapacitors are considered as promising energy storage devices for next-generation wearable electronics due to their high energy density, rapid kinetics, long cycles, and reliable safety. As of now, the research for electrochemical proton energy storage entails more holistic considerations. In this review, we provide a timely and comprehensive review of recent advances in electrochemical proton storage. First, we discuss the main explored proton storage electrode materials, including carbon materials, metal oxides, Prussian blue, COFs, and MXenes, from the aspects of structure, preparation strategy, and proton storage mechanism. Furthermore, we systematically focus on their multifunctional applications of proton supercapacitors including flexible and wearable electronics, anti-freezing energy storage system, etc. Finally, the challenges and prospects of flexible proton supercapacitors are outlined. We believe that this review will greatly improve the knowledge of proton energy storage and facilitate the development of advanced electrochemical energy systems.

Polyimide-Based Aqueous Potassium Energy Storage Systems Using Concentrated WiSE Electrolyte.

Aqueous batteries are considered as promising alternative power sources due to their eco-friendly, cost-effective, and nonflammable attributes. Employing organic-based electrode materials offers further advantages toward building greener and sustainable systems, owing to their tunability and environmental friendliness. In order to enhance the energy and power densities, superconcentrated aqueous electrolytes, such as water-in-salt electrolytes (WiSE), have renewed the interest in aqueous batteries due to their enhanced stability and much wider electrochemical stability window (>1.23 V) compared with the traditional aqueous electrolytes. Here, we present a perylene diimide-based electrode material (PDI-Urea) as an appealing anode for aqueous potassium energy storage systems and investigate their electrochemical performance in three WiSE electrolytes, namely, 30 M potassium acetate, 40 M potassium formate and 30 M potassium bis(fluorosulfonyl)imide (KFSI). To explore the potential of PDI-Urea for potassium-based electrochemical energy systems, we fabricated full cell devices such as aqueous potassium dual-ion battery (APDIB) and aqueous K-ion battery (AKIB) and studied their electrochemical properties with 30 M KFSI electrolyte. The full cell K-ion battery, using a PBA cathode, exhibited excellent electrochemical performance with good rate capability and impressive capacity retention of 91% upon 1000 cycles. Further, the reaction mechanism of the electrodes is systematically analyzed using ex-situ studies.

Deciphering interfacial charge transfer mechanisms in electrochemical energy systems through impedance spectroscopy

Employing electrochemical impedance spectroscopy as a non-destructive analytical tool for elucidating the interfacial charge transfer in electrochemical energy conversion/storage systems.

Poly(arylene alkylene)s Carrying Quaternary Ammoniums via Flexible Phenylpropyl Spacers as Hydroxide Conducting Membranes

Anion exchange membranes (AEM)s are attracting growing research interests as central components in various alkaline energy conversion and storage devices such as AEM fuel cells and water electrolyzers.1,2 Compared to the devices operated under acidic conditions, the alkaline conditions open up for possibilities to use, e.g., nickel and iron catalysts instead of platinum. However, the insufficient hydroxide conductivity and long-term stability of AEMs at elevated temperatures are still hindering a widespread application of these devices.3 An effective strategy to improve AEM properties by structure design is to functionalize hetero-atom free polymer backbones with quaternary ammonium cations via flexible spacers.4-6 In the present work, we have synthesized a series of AEM materials by tethering three different quaternary ammonium cations to poly(arylene alkylene)s via a phenylpropyl spacer (Figure 1a). The Friedel-Crafts acylation and polyhydroxyalkylation employed in the monomer and polymer syntheses are both free of noble metals and have excellent yields. All the polymers prepared in this way formed robust membranes reaching high hydroxide conductivities – up to 175 mS/cm at 80 °C (Figure 1b). PpT-DMP, carrying dimethyl piperidinium cations, was found to have the highest alkaline stability with less than 7% ionic loss after treatment in 7 M aq. NaOH at 90 oC during 240 h. The hydroxide conductivity of PpT-DMP reached 104 mS/cm at an ion exchange capacity (IEC) of 1.79 mequiv./g., which is still quite high. Atom force microscope (AFM) phase imaging revealed a phase separated morphology of PpT-DMP, most probably involving ion-clustering (Figure 1c). In this presentation we will further discuss the synthesis of these polymers, and influence of the phenylpropyl spacer on AEM properties.[1] Xue, J.; Zhang, J.; Liu, X.; Huang, T.; Jiang, H.; Yin, Y.; Qin, Y.; Guiver, M. D. Toward alkaline-stable anion exchange membranes in fuel cells: cycloaliphatic quaternary ammonium-based anion conductors. Electrochem. Energy Rev. 2022, 5, 348-400.[2] Chatenet, M.; Pollet, B. G.; Dekel, D. R.; Dionigi, F.; Deseure, J.; Millet, P.; Braatz, R. D.; Bazant, M. Z.; Eikerling, M.; Staffell, I.; Balcombe, P.; Horn, Y. S.; Schafer, H. Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments. Chem. Soc. Rev. 2022, 51, 4583-4762.[3] Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K. N.; Scott, K.; Xu, T.; Zhuang, L. Anion-exchange membranes in electrochemical energy systems. Energy Environ. Sci. 2014, 7, 3135-3197.[4] Dang, H. S.; Jannasch, P. Exploring different cationic alkyl side chain designs for enhanced alkaline stability and hydroxide ion conductivity of anion-exchange membranes. Macromolecules 2015, 48, 5742-5751.[5] Allushi, A.; Pham, T. P.; Olsson, J. S.; Jannasch, P. Ether-free polyfluorenes tethered with quinuclidinium cations as hydroxide exchange membranes. J. Mater. Chem. A 2019, 7, 27164-27174.[6] Lee, W. H.; Kim, Y. S.; Bae, C. Robust Hydroxide Ion Conducting Poly(biphenyl alkylene)s for Alkaline Fuel Cell Membranes. ACS Macro Lett. 2015, 4, 814-818. Figure 1. a) Poly(arylene alkylene)s tethered with different quaternary ammonium cations via phenylpropyl spacers, b) hydroxide conductivity of the AEMs in the fully hydrated state, and c) an AFM phase image of PpT-DMP. Figure 1

(Invited) Challenges and Opportunities for the Computational Analysis of Electrochemical Energy Systems

Electrochemical systems are challenging to analyze and design due to their multi-dimensional, time-dependent, and multi-physics nature. For this reason, many computational electrochemical system models have been developed in the past three decades, some of which can now be found in commercial software packages, e.g., COMSOL or ANSYS Fluent. These models however: i) are based on simplifying assumptions, e.g., reduced dimensionality, infinite dilution, Tafel kinetics; ii) contain uncertain input parameters, e.g., effective transport properties and kinetic parameters; and, iii) are only validated with a limited number of experiments, e.g., polarization curves. These limitations, understandable at the time due to limited computational resources, characterization techniques, and material understanding and stability, are difficult to justify today that parallel programming and computer clusters enable scientists to perform large multi-dimensional simulations; electrochemical testing has expanded to include segmented cell testing, impedance spectroscopy, water flux estimation, and in-operando visualization; and, characterization tools and techniques have been developed to, for example, easily measure adsorption isotherms, effective proton conductivity and, within a given resolution, visualize the three-dimensional microstructure of the electrodes.Scientists working on computational analysis of electrochemical systems must acknowledge that further model development is still needed and must take advantage of new resources to improve the robustness and accuracy of cell-level models. The path is long and crooked, but it is very likely that the opportunity for a truly useful computational model, one that can be used for design, is beyond simplistic implementations and polarization curves. The effort is great, but it can be minimized by concurrent software development, as well as, by careful experimental work dedicated to parameter estimation and model validation.This presentation aims at outlining the limitations of state-of-the-art models, the challenges and opportunities of concurrent development and maintenance of a multi-scale, transient electrochemical energy system software, such as the open-source fuel cell simulation toolbox (OpenFCST) [1], and the new opportunities provided by combining advanced characterization tools with computational analysis. As an example, the development and validation of the transient, two-phase fuel cell and electrolyzer cell-level models in OpenFCST will be discussed [2]. The use of a hydrogen-pump model to study the effect of an active catalyst in CL effective proton conductivity measurements will also be discussed as an example of concurrent experimental/model design [3].

The Effect of Junction Composition of Polarization Behaviour of Bipolar Membranes

Bipolar membranes (BPMs), i.e, laminates cationic and anionic polymer membranes, have a wide range of applications. Starting from an early application in electrodialysis systems, the application scope has more recently broaden to electrochemical energy conversion systems such as water electrolyzer and CO2 reduction reaction, fuel cells and flow batteries.1 In connection to CO2 reduction reaction, the implementation of BPM effectively mitigates CO2 crossover driven by (bi)carbonate migrations, but the rate capability is limited by the large overpotential across current state-of-the-art BPMs.2 The large overpotential primarily originates from the slow water dissociation (WD) kinetics at the interface between the cation exchange layer (CEL) and anion exchange layer (AEL), and largely depends on junction morphology. The detailed structure-properties relationships remain poorly understood, but physical properties of individual polymeric membranes and the composition and morphology of the WD catalyst are important parameters and the optimal combination of materials may be different for different systems. Furthermore, the WD performance of BPM in MEA water electrolyzer not only depends on BPM’s junction contact, but also the interface contact between electrodes and CEL/AEL.In this work, a series of BPM system featuring different compositions of membrane layers and WD catalysts are explored and characterized by polarization behaviour (J-V curve) via H-cell and MEA water electrolyzer. We attempt to link the junction composition created by different BPM systems to its WD performance and provide a systematic choice of CEL/AEL and WD catalyst in the BPM system.(1) Blommaert, M. A.; Aili, D.; Tufa, R. A.; Li, Q.; Smith, W. A.; Vermaas, D. A. Insights and Challenges for Applying Bipolar Membranes in Advanced Electrochemical Energy Systems. ACS Energy Lett. 2021, 2539–2548. https://doi.org/10.1021/acsenergylett.1c00618.(2) Garg, S.; Giron Rodriguez, C. A.; Rufford, T. E.; Varcoe, J. R.; Seger, B. How Membrane Characteristics Influence the Performance of CO 2 and CO Electrolysis. Energy Environ. Sci. 2022. https://doi.org/10.1039/D2EE01818G.

Dynamic Response of Ion Transport in Nanoconfined Electrolytes.

Ion transport in nanoconfined electrolytes exhibits nonlinear effects caused by large driving forces and pronounced boundary effects. An improved understanding of these impacts is urgently needed to guide the design of key components of the electrochemical energy systems. Herein, we employ a nonlinear Poisson-Nernst-Planck theory to describe ion transport in nanoconfined electrolytes coupled with two sets of boundary conditions to mimic different cell configurations in experiments. A peculiar nonmonotonic charging behavior is discovered when the electrolyte is placed between a blocking electrode and an electrolyte reservoir, while normal monotonic behaviors are seen when the electrolyte is placed between two blocking electrodes. We reveal that impedance shapes depend on the definition of surface charge and the electrode potential. Particularly, an additional arc can emerge in the intermediate-frequency range at potentials away from the potential of zero charge. The obtained insights are instrumental to experimental characterization of ion transport in nanoconfined electrolytes.

Teaching Electrochemical Science and Engineering Online

In many schools of science and engineering where electrochemistry is beginning to play a major role in research and advanced study, it is still missing from the curriculum, especially at the undergraduate level. One way to address this problem and draw students into electrochemistry is to teach online. This talk will describe the teaching of electrochemistry online at MIT by two different approaches: free course materials for 10.626/10.426 Electrochemical Energy Systems on OpenCourseWare and massive open online courses (MOOCs) for 10.50 Analysis of Transport Phenomena on edX and MITx Online.

(General Student Poster Award Winner - 1st Place) Six Practices to Improve Alkaline Electrolyte Preparation

Alkaline electrolytes represent a critical component of electrochemical energy devices, including alkaline electrolyzers, fuel cells, supercapacitors, and alkaline batteries. In addition, these electrolytes define essential properties of electrocatalytic reactions, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and the oxygen reduction reaction (ORR). However, alkaline electrolyte concentrations and compositions are often considered trivial, resulting in misinterpretation of different phenomena and overestimating critical performance metrics. Thus, in an expanding field full of interdisciplinary research groups, there is an urgent need for standardized protocols designed to improve and evaluate the quality of alkaline electrolytes so that electrochemical energy systems can be objectively examined and compared.In this work, we propose a protocol composed of six steps to prepare, characterize and validate the quality of common alkaline electrolytes. By adapting well-established methods in the literature and validating additional features experimentally, we standardize six general practices: (1) proper alkaline electrolyte handling and preparation, (2) removal of Fe impurities, (3) alkali molarity standardization via pH titrations, (4) electrolyte composition analysis via inductively-coupled plasma mass spectrometry (ICP-MS), (5) statistical quality control assessment and (6) electrolyte validation through electrochemical aging of Ni electrodes in alkaline media. The effects of Fe incorporation for different alkaline electrolytes were examined using Ni and NiFe foam electrodes. Furthermore, ICP-MS measurements were complemented with prolonged cyclic voltammetry tests to confirm the effectiveness of the Fe purification procedure. We believe this work illustrates the importance of standardizing protocols and reporting reliable quality metrics to improve consistency and accuracy in electrochemistry. Furthermore, adopting the practices presented in this work would greatly benefit the evaluation and comparison of electrochemical energy materials and devices operating with alkaline electrolytes. Figure 1

Electrochemical Methods in the Cloud: FreiStat, an IoT-Enabled Embedded Potentiostat.

Embedded potentiostats enable electrochemical measurements in the Internet-of-Things (IoT) or other decentralized applications, such as remote environmental monitoring, electrochemical energy systems, and biomedical point-of-care applications. We report on Freiburg's Potentiostat (FreiStat) based on the AD5941 potentiostat circuit from Analog Devices, together with custom firmware, as the key to precise and advanced electrochemical methods. We demonstrated its analytical performance by various cyclic voltammetry measurements, advanced techniques such as differential pulse voltammetry, and a lactate biosensor measurement with currents in the nA range and a resolution of 54 pA. The FreiStat yielded analytical results comparable to benchtop devices and outperformed current commercial embedded potentiostats at significantly lower cost, smaller size, and lower power consumption. Decentralized corrosion analysis by a Tafel plot using the IBM Cloud showed its applicability in a typical IoT scenario. The developed open-source software framework facilitates the integration of electrochemical instrumentation into applications utilizing machine learning and other artificial intelligence. Together with the affordable and highly capable embedded potentiostat, our approach can leverage analytical chemistry toward increasingly important, more widespread and decentralized applications.

Redox Flow Batteries: Recent Development in Main Components, Emerging Technologies, Diagnostic Techniques, Large-Scale Applications, and Challenges and Barriers

Redox flow batteries represent a captivating class of electrochemical energy systems that are gaining prominence in large-scale storage applications. These batteries offer remarkable scalability, flexible operation, extended cycling life, and moderate maintenance costs. The fundamental operation and structure of these batteries revolve around the flow of an electrolyte, which facilitates energy conversion and storage. Notably, the power and energy capacities can be independently designed, allowing for the conversion of chemical energy from input fuel into electricity at working electrodes, resembling the functioning of fuel cells. This work provides a comprehensive overview of the components, advantages, disadvantages, and challenges of redox flow batteries (RFBs). Moreover, it explores various diagnostic techniques employed in analyzing flow batteries. The discussion encompasses the utilization of RFBs for large-scale energy storage applications and summarizes the engineering design aspects related to these batteries. Additionally, this study delves into emerging technologies, applications, and challenges in the realm of redox flow batteries.

Atomic coordination environment engineering of bimetallic alloy nanostructures for efficient ammonia electrosynthesis from nitrate

Electrochemical nitrate reduction reaction (NO3RR) to ammonia has been regarded as a promising strategy to balance the global nitrogen cycle. However, it still suffers from poor Faradaic efficiency (FE) and limited yield rate for ammonia production on heterogeneous electrocatalysts, especially in neutral solutions. Herein, we report one-pot synthesis of ultrathin nanosheet-assembled RuFe nanoflowers with low-coordinated Ru sites to enhance NO3RR performances in neutral electrolyte. Significantly, RuFe nanoflowers exhibit outstanding ammonia FE of 92.9% and yield rate of 38.68 mg h-1 mgcat-1 (64.47 mg h-1 mgRu-1) at -0.30 and -0.65 V (vs. reversible hydrogen electrode), respectively. Experimental studies and theoretical calculations reveal that RuFe nanoflowers with low-coordinated Ru sites are highly electroactive with an increased d-band center to guarantee efficient electron transfer, leading to low energy barriers of nitrate reduction. The demonstration of rechargeable zinc-nitrate batteries with large-specific capacity using RuFe nanoflowers indicates their great potential in next-generation electrochemical energy systems.