Electrochemical Energy Devices Research Articles

Molybdenum-doped tungsten nitride coated with carbon shell and cobalt hydroxide nanosheets for efficient alkaline hydrogen evolution reaction

Water electrolysis is currently the most important way to achieve large-scale hydrogen (H2) production. Although many nonprecious electrocatalysts possess promising catalytic performance at low current density below 50 mA cm−2, it remains a substantial challenge to realize H2 production at industry-compatible current density over 500 mA cm−2. Here we have designed a hierarchical heterostructure of molybdenum-doped tungsten nitride coated with carbon shell and cobalt hydroxide nanosheets (Mo-WN@NC@Co(OH)2) for alkaline hydrogen evolution reaction (HER) with industrial current density and stability. The hybrid exhibits efficient alkaline HER activity, reaching the current density of 500 mA cm−2 at an overpotential of 196 mV. The Co(OH)2 nanosheets and Mo doping endow the composite with more active sites and enhanced intrinsic activity of the catalyst, as well as an appropriate water dissociation energy. In addition, the free energy of activation for each step during the HER process suggests a synergistic effect of Mo doping and Co(OH)2 in Mo-WN@NC@Co(OH)2 promoting surface Volmer and Heyrovsky steps during the HER process. This doping and interfacial engineering methods hold great promise for fabricating efficient nitride-based electrocatalysts for electrochemical energy devices.

Star poly(ionic liquid)s: Chain architecture‐property relationships

AbstractIn this study, we report the synthesis of 3‐, 4‐, and 6‐arm star poly(ionic liquid)s (PILs) (specifically, star poly(vinylbenzyl methylimidazolium bis(trifluoromethane)sulfonimide) (poly(VBMIm‐TFSI))) via reversible addition‐fragmentation chain transfer (RAFT) polymerization with a core‐first approach, followed by quaternization and anion exchange. The impact of star polymer architecture on properties was explored by measuring the thermal, mechanical, and ion transport properties of each star PIL compared to those of an analogous linear PIL. The star PILs exhibited up to 2‐fold higher ionic conductivity, 150% higher elastic modulus, and 465% higher ultimate tensile strength compared to the analogous linear PIL. The Williams‐Landel‐Ferry (WLF) equation was employed to explore the effect of increased free volume on the improved ion transport properties of the star PILs. These results highlight the impact of star polymer architecture on PILs and star PILs as promising materials for electrochemical energy devices.

Robust pseudocapacitive Na+ intercalation induced by MoS2 on active Mo2C current collector interface for high areal capacity sodium-ion batteries

Sodium-ion batteries (SIBs) have emerged as compelling alternatives in the realm of electrochemical energy devices, poised to substitute lithium-ion batteries (LIBs). The primary challenge encompasses not only the scarcity of anode materials exhibiting exceptional Na+ storage capacity but also the endeavor to achieve high areal capacity. To address this challenge, a comprehensive strategy is proposed that entails utilizing a highly conductive molybdenum dicarbide (Mo2C) current collector (denoted as CCM) as a supporting scaffold for the bottom-up growth of molybdenum disulfide nanosheets (MoS2, serving as the main active component) (denoted as CCM@MoS2). The CCM improves interfacial bonding with MoS2 nanosheets and offers additional capacity to accommodate the increased Na+ insertion activity. Both theoretical and kinetic analyses reveal that the enhanced Na+ storage properties primarily stem from favorable adsorption energy, reduced diffusion barrier, and intercalation pseudocapacitance due to the strong electronic interfacial interaction between active CCM and MoS2. Hence, the as-prepared optimized CCM@MoS2 electrode exhibits a superior areal capacity of 6.36 mAh cm−2 at 0.4 mA cm−2, excellent rate capability of 1.02 mAh cm−2 at 24 mA cm−2 and long cycle life up to 500 cycles at 4 mA cm−2. Interesting, our as-prepared CCM@MoS2 electrode shows better performance for Na+ storage than Li+ storage at higher current density, affirming the enhanced kinetics in our architecture. This work proposes a rational strategy to enhance the areal capacity and stability of MoS2-based anode for SIBs and beyond.

Recent Advancement in Porous Graphene from Synthesis to Properties: Critical Review on Functionalization Chemistry and Applications

AbstractGraphene is the main allotropy of carbon which exhibits properties like super conductivity, high electron transfer, and large surface area. Porous graphene (PG) has unique porous structure and many exposed edges. In 2D graphene pore ranges from several angstroms to nanometers. Similar to 3D graphene, which also has a porous structure, there are four different types: foam, sponge, and graphene hydrogel (GH). Graphene oxide (GO) and reduced graphene oxide (rGO) are used to create PG. This review focuses on various methods of synthesis of PG along with its inherent properties and methods to modify its properties by surface functionalization. Emphasis is also given on the discussion of various techniques that are involved in the PG characterization. This article discusses the formation of hybrids, and composites using PG. Applications and limitations of PG have also been indicated. This review shows an extensive overview of the main principles and the recent synthetic technologies about fabricating various innovative 3D graphene‐based materials. Subsequently, recent progresses in electrochemical energy devices and hydrogen energy generation/storage are explicitly covered. The applications of PG and its composites in the fields such as energy storage, solar units, sensors, supercapacitors, etc. have been discussed The up to date progress for pollutants detection and environmental remediation are also reviewed. Finally, challenges and outlooks in materials development for different applications are suggested.

Regulating atomic Fe/Cu dual sites with unsymmetrical Fe-N6 and Cu-N1S2 coordination for promoting bifunctional oxygen electrocatalysis in advanced zinc-air batteries

Dual-metal single-atom catalysts with heteronuclear active sites exhibit superior oxygen catalysis performance than their single-atom counterparts, facilitating the practical applications in advanced electrochemical energy devices. Herein, a Fe-Cu dual-metal single-atom catalyst with Fe-N6 and Cu-N1S2 coordination environment (FeCu-DSAs/NSC) is reported. Due to the synergism of bimetallic active sites and asymmetric heteroatom coordination, the resultant FeCu-DSAs/NSC displays better bifunctional catalytic performance (a small potential gap between the Eη10 and E1/2, ΔE=0.647 V) when compared with the counterparts (Pt/C+IrO2 and Cu-ISAs/NSC), as well as surpassing most of bifunctional metal atom-based catalysts reported to date. As expected, FeCu-DSAs/NSC based rechargeable zinc-air battery shows remarkable superiority than commercial Pt/C+IrO2 benchmark, resulting in a high peak power density (230.66 mW cm−2), open-circuit voltage (1.464 V) and long-term cycling stability (up to 350 h at 10 mA cm−2).

Ordered mesoporous nanofibers mimicking vascular bundles for lithium metal batteries.

Hierarchical self-assembly with long-range order above centimeters widely exists in nature. Mimicking similar structures to promote reaction kinetics of electrochemical energy devices is of immense interest, yet remains challenging. Here, we report a bottom-up self-assembly approach to constructing ordered mesoporous nanofibers with a structure resembling vascular bundles via electrospinning. The synthesis involves self-assembling polystyrene (PS) homopolymer, amphiphilic diblock copolymer, and precursors into supramolecular micelles. Elongational dynamics of viscoelastic micelle solution together with fast solvent evaporation during electrospinning cause simultaneous close packing and uniaxial stretching of micelles, consequently producing polymer nanofibers consisting of oriented micelles. The method is versatile for the fabrication of large-scale ordered mesoporous nanofibers with adjustable pore diameter and various compositions such as carbon, SiO2, TiO2 and WO3. The aligned longitudinal mesopores connected side-by-side by tiny pores offer highly exposed active sites and expedite electron/ion transport. The assembled electrodes deliver outstanding performance for lithium metal batteries.

Carbon Fiber Film with Multi-Hollow Channels to Expedite Oxygen Electrocatalytic Reaction Kinetics for Flexible Zn-Air Battery.

The high oxygen electrocatalytic overpotential of flexible cathodes due to sluggish reaction kinetics result in low energy conversion efficiency of wearable zinc-air batteries (ZABs). Herein, lignin, as a 3D flexible carbon-rich macromolecule, is employed for partial replacement of polyacrylonitrile and constructing flexible freestanding air electrodes (FFAEs) with large amount of mesopores and multi-hollow channels via electrospinning combined with annealing strategy. The presence of lignin with disordered structure decreases the graphitization of carbon fibers, increases the structural defects, and optimizes the pore structure, facilitating the enhancement of electron-transfer kinetics. This unique structure effectively improves the accessibility of graphitic-N/pyridinic-N with oxygen reduction reaction (ORR) activity and pyridinic-N with oxygen evolution reaction (OER) activity for FFAEs, accelerating the mass transfer process of oxygen-active species. The resulting N-doped hollow carbon fiber films (NHCFs) exhibit superior bifunctional ORR/OER performance with a low potential difference of only 0.60V. The rechargeable ZABs with NHCFs as metal-free cathodes possess a long-term cycling stability. Furthermore, the NHCFs can be used as FFAEs for flexible ZABs which have a high specific capacity and good cycling stability under different bending states. This work paves the way to design and produce highly active metal-free bifunctional FFAEs for electrochemical energy devices.

Electrochemical Devices to Power a Sustainable Energy Transition—An Overview of Green Hydrogen Contribution

This work discusses the current scenario and future growth of electrochemical energy devices, such as water electrolyzers and fuel cells. It is based on the pivotal role that hydrogen can play as an energy carrier to replace fossil fuels. Moreover, it is envisaged that the scaled-up and broader deployment of the technologies can hold the potential to address the challenges associated with intermittent renewable energy generation. From a sustainability perspective, this synergy between hydrogen and electricity from renewable sources is particularly attractive: electrolyzers convert the excess energy from renewables into green hydrogen, and fuel cells use this hydrogen to convert it back into electricity when it is needed. Although this transition endorses the ambitious goal to supply greener energy for all, it also entails increased demand for the materials that are essential for developing such cleaner energy technologies. Herein, several economic and environmental issues are highlighted, besides a critical overview regarding each technology. The aim is to raise awareness and provide the reader (a non-specialist in the field) with useful resources regarding the challenges that need to be overcome so that a green hydrogen energy transition and a better life can be fully achieved.

Sulfurization of cobalt oxide to cobalt sulfide: A positrode for the high-performance supercapacitor

The conversion of transition metal oxide to sulfide has attracted researchers in the use of electrochemical energy devices due to their unique features, like highly oriented crystalline nanostructure, high electrochemical active sites, and tailored morphology. Herein, we demonstrate the preparation of binder-free cobalt sulfide (Co3S4) nanostructure by converting hydrothermally synthesized cobalt oxide (Co3O4) on nickel foam using the hydrothermal method. X-ray photoelectron and diffraction analysis confirms the chemical state and phase of Co3S4 after sulfurization process. The FE-SEM analysis reveals the synthesized nanostructures are rod-like morphology for both Co3O4 and Co3S4 grown on Ni foam. The electrochemical performance of the synthesized binder-free electrode was investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy analysis, which reveals the charge storage mechanism is like faradaic type intercalation and Co3S4/NF electrode reaches areal capacity of 543.7 μAh cm−2 at scan rate of 1 mV s−1 which is approximately 24-folds higher than the Co3O4/NF electrode (22.7 μAh cm−2). The self-discharge study was carried out to identify the factors behind the energy dissipation in the Co3S4/NF electrode. The experimental outcomes disclose insightful information on electrode material prepared via hydrothermal process, and it could accelerate the development of new high-energy density supercapacitor applications.

Molecular weight impacts the alkaline stability of poly(terphenylene alkylene) anion exchange membranes

Improving the alkaline durability is crucial for developing anion exchange membranes used for electrochemical energy devices. In contrast to the exploitation of new cationic moieties or robust polymer backbone, the influence of polyelectrolyte molecular weight on the membrane's alkaline stability has received little attention. In this contribution, quaternized poly(terphenylene alkylene)s with Mw ranging from 30 to 118 kDa were synthesized to quantify the variations in alkaline stability and other physicochemical properties. Measurements of ex-situ alkaline soaking, either in high or low hydration levels, and in-situ cell operating demonstrate that Mw is positively correlated to the alkaline stability of the membrane. In addition, the water absorption and ion conductivity of AEM are negatively correlated to its Mws, and incline to reach a plateau as the Mw over 100 kDa. These results have important implications to elucidate the alkaline stability limitation and may open the way toward highly stable AEMs.

Graphene quantum dots: Synthesis and applications

Graphene quantum dots (GQDs) are the latest superstars added from the carbon family. These are 0D materials with non-zero bandgap and are the most prominent category of nano materials, having a variety of applications in bio-imaging, optical, electrochemical energy devices, and so on and have been studied to great extent in recent years. In this review we have discussed various methods of preparation like hydrothermal, electrochemical, ultrasonic, pyrolysis, etc. and applications of GQDs. Besides, the article highlights challenges and interesting future directions of GQDs.

A two-dimensional semiconducting Cu(i)-MOF for binder and conductive additive-free supercapattery

A two dimensional CuCN-based semiconducting MOF with nitrogen rich ligand has been synthesized which shows supercapattery behaviour. The energy storage device formed by CuCN-MOF exhibits excellent energy density, power density and cyclic stability.

Understanding the Effects of Transition Metal Impurities on Nickel (oxy) Hydroxide Electrocatalysts in Alkaline Media

Nickel-based materials are widely used as critical components of electrochemical energy devices, including alkaline electrolyzers, capacitors, and alkaline batteries. These materials are often preferred because of their availability and low cost compared to precious metals, which makes them excellent candidates for accomplishing the decarbonization goals and electrifying our society. However, several studies have demonstrated that the incorporation of trace impurities from commercial alkaline electrolytes induces significant changes in the intrinsic activity, pseudocapacitance, and stability of Ni-based materials, resulting in erroneous descriptions of their performance. Thus, having a better understanding of the effects of these impurities will lead to practical ways to prevent or control their impact on electrochemical energy devices.In this work, we study the incorporation of transition metals (i.e., Fe, Co, Cu) that form insoluble hydroxides in alkaline media over nickel (oxy) hydroxide electrocatalysts. We systematically examine how these trace impurities modify the OER activity, stability, and the pseudocapacitive properties of NiOOH. As depicted in Figure 1, KOH electrolytes containing trace impurities of Fe and Co induce significant changes in the OER onset potential of Ni(OH)2/NiOOH electrocatalysts, according to the irreversible charge increase measured through coulovoltammetry (QV) curves. Moreover, distinct redox peaks can be seen for each scenario. After aging in purified KOH electrolyte (Fig. 1a), the cyclic voltammogram (CV) of Ni(OH)2/NiOOH exhibits four oxidation peaks that can be ascribed to a mixture of both α and β structural phases (Fig. 1b) while aging in Fe-unpurified KOH promotes the α phase and shifts the redox peak anodically (Fig. 1c). Aging in Co-unpurified KOH promotes a more ordered β structural phase without changing the OER activity significantly (Fig. 1d), which is desirable for pseudocapacitive materials. Additional experiments examining the OER activity, stability, and capacitance provide valuable insights into these impurities, and specific strategies to prevent and minimize their effects will be discussed. Overall, this work illustrates the importance of tracking trace metal impurities in alkaline electrolytes to minimize undesirable effects in electrochemical energy devices. Figure 1

(Invited) Electrochemical Characterization of Catalyst/Ionomer Interfaces

Electrochemical energy conversion devices such as polymer-electrolyte fuel cells, water-splitting or carbon dioxide reduction electrolyzers, utilize ionically-conductive polymers (ionomers) in their electrode structure where an ionomer forms interfaces with the catalysts. The ionomers exist as nanometer-thick film to cover the catalyst particles and act as a binder while enabling the transport of active species necessary for the reactions. While the nature of species and operational environment differs across these devices, their overall efficiency and performance is influenced by the electrode architecture, where the interfaces and interactions between the ionomers and catalysts play an important role. In hydrogen technologies, for example, ionomer thin films bind the catalyst sites and carbon supports to facilitate transport of ionic (e.g. protons), liquid (water) and gaseous (e.g., oxygen) species under a nano-confined environment. Such confinement effects not only change the ionomer structure and properties, usually with a tendency to increase transport resistances, but also amplify the impact of the electrocatalyst-ionomer interactions in the electrodes, thereby reducing the catalyst activity. Thus, understanding the behavior of nano-confined ionomers and their interactions with the catalyst surfaces is key for mitigating the transport resistances in catalyst ionomers and improving the electrode performance and cell efficiency.This talk will provide insights into electrochemical characterization of catalyst ionomers by focusing on varying chemistries of perfluorosulfonated cation-exchange ionomers with additional examples of anion-exchange ionomers for emerging technologies. The hydration and transport properties of proton-exchange catalyst-ionomers will be examined with the effects of chemistry, processing and thickness (degree of confinement), along with their impact on the morphological changes governing the film function. Through a systematic variation of material chemistries and environmental parameters, primary factors impacting the structure-property relationship of catalyst ionomers are described along with a discussion of secondary factors altering the cation-anion interactions. Then, the interplay between the effects of chemistry and ion exchange (capacity) on modifying the transport function and the strength of ionomer-catalyst interactions will be presented. The results will be collated to elucidate the underlying origins of the transport resistances occurring in electrodes, and to develop materials and processing strategies for their mitigation for improved performance and efficiency in electrochemical energy devices.

Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions

Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can switch reversibly between power generation as a solid oxide fuel cell (SOFC) and hydrogen production as a solid oxide electrolysis cell (SOEC). It is important to systematically understand the electrode reaction processes and degradation factors in these two modes to tailor high-performance and durable r-SOC electrodes. The dependence of polarization resistance on cell fabrication conditions and operating conditions has been individually investigated for SOFC and SOEC by impedance measurement and distribution of relaxation times (DRT) analysis [1-4], but it is necessary to evaluate r-SOC as a whole [5]. Here in this study, we aim to systematically clarify the similarities and differences in the electrode reaction processes at the fuel electrodes of both SOFC and SOEC modes of r-SOCs, with respect to fuel electrode fabrication conditions. Experimental Several types of cells were fabricated with different fuel electrode constituent materials, thicknesses, and sintering temperatures. Three types of fuel electrode materials were used: Ni-GDC cermet, a composite of Ni and mixed ionic-electronic conductor Gd0.9Ce0.1O3 (GDC); Ni-YSZ cermet, a composite of Ni and pure ionic conductor YSZ (8 mol% Y2O3 - stabilized ZrO2); and Ni-GDC co-impregnated electrode with LST-GDC as a backbone support (LST: La0.1Sr0.9TiO3). Scandia-stabilized zirconia (ScSZ) was used as the electrolyte plate, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode. GDC buffer layer was prepared between the electrolyte and the air electrode to suppress the formation of interfacial insulting layers.Electrochemical impedance measurements were performed for the fuel electrode of the fabricated cell under SOFC and SOEC modes by supplying H2-H2O mixture and varying operating temperature, fuel humidification, and current density. The DRT analysis was conducted to separate various polarization resistance components of the fuel electrode with different relaxation times. The area of each DRT peak corresponds to the resistance of each electrode reaction process. In this study, activation energy was derived based on the assumption that the electrical conductance is of an Arrhenius-type thermally activated character. Its dependence on the fuel electrode fabrication conditions was investigated. Furthermore, electrode microstructure was observed by using focused-ion beam scanning electron microscopy (FIB-SEM). Results and Discussion Figure 1 shows typical DRT peaks of the Ni-GDC cermet fuel electrode in (a) SOFC and (b) SOEC modes, measured at different temperatures. In the range of 10-1 to 106 Hz where the frequency response was measured, three DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all with a DRT peak area decreasing with increasing operating temperature. This indicates that there are at least three electrode reaction processes with different relaxation times, which are thermally active processes. Activation energies of 0.1-0.3 eV (SOFC mode) and 0.2-0.5 eV (SOEC mode) were obtained for P1, and 0.9-1.0 eV (SOFC mode) and 1.1-1.3 eV (SOEC mode) for P2. The activation energies in SOEC mode were higher than those in SOFC mode for both P1 and P2. In the presentation, the dependence of activation energies on the fuel electrode constituent materials and related electrode reaction processes will be discussed.

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells

Introduction Reversible solid oxide cells (r-SOCs) enable both power generation and steam electrolysis, and have attracted attention as a solid state electrochemical energy device for a decarbonized society (1). R-SOCs have the advantage of high efficiency due to high temperature operation, but there exist various technical issues remained in materials selection, start-up and shutdown, and long-term durability. Therefore, reducing operating temperature is desirable for practical applications (2,3). Electrode-supported cells, in which the electrode acts as a structural support, enable lower temperature operation by reducing the thickness of the electrolyte, which has certain electrical resistivity. Here in this study, the current-voltage characteristics and reversible cycle durability under r-SOC operating conditions are evaluated using fuel-electrode-supported cells, with the aim of developing r-SOCs capable of highly efficient fuel cell power generation and steam electrolysis. Experimental For the experiments, fuel-electrode-supported cells were fabricated using fuel electrode-supported half-cells (Japan Fine Ceramics, Japan), schematically shown in Fig. 1. The half-cell consists of scandia-stabilized zirconia (ScSZ: 10 mol%Sc2O3-1mol%CeO2-89 mol%ZrO2) or yttria-stabilized zirconia (YSZ: 8 mol%Y2O3-92 mol%ZrO2) electrolyte and a Ni-cermet fuel electrode, such as Ni-ScSZ or Ni-YSZ. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was applied for the air electrode, and Gd0.1Ce0.9O2 (GDC) was inserted between the electrolyte and the air electrode to suppress interdiffusion and chemical reactions. Four types of cells were used with different combinations of the electrolyte component (YSZ or ScSZ) in the electrolyte layer or the supporting fuel electrode.In electrochemical tests, 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. R-SOC initial performance tests were conducted using an electrochemical analyzer (1255B, Solartron). Cell voltage and impedance were measured at 700-800°C at current densities ranging from -0.5 A cm-2 to +0.5 A cm-2. Positive current density means the value in SOFC mode, while negative current density means the value in SOEC mode. In r-SOC 1,000 cycle durability tests, cycles of switching between SOFC and SOEC operation were repeated 1,000 times by varying current density. The range of current density in the cycle tests was between -0.2 A cm-2 and +0.2 A cm-2. The cell impedance was measured before the cycling test and every 100 cycles. After each test, the cells were analyzed by using a focused-ion beam scanning electron microscopy (FIB-SEM) to observe and evaluate the electrode microstructure. Results and discussion Figure 2 (a) shows the r-SOC initial performance of each fuel-electrode-supported cell. The cell with the Ni-YSZ fuel electrode and the YSZ electrolyte showed better current voltage characteristics than other cells. Figure 2 (b) shows the r-SOC 1000-cycle durability of the cell with the Ni-YSZ fuel electrode and the YSZ electrolyte. The results showed a decrease in power generation and electrolysis performance with increasing the number of cycles in both SOFC and SOEC modes. Possible degradation mechanisms will be discussed. Acknowledgments This paper is based on results obtained from a project (Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration), JPNP20005, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) is gratefully acknowledged. References (1) Venkataraman, M. Pérez-Fortes, L. Wang, Y. S. Hajimolana, C. Boigues-Muñoz, A. Agostini, S. J. Mcphail, F. Mar échal, J. V. Herle, and P. V. Aravind, J. Energy Storage, 24, 100782 (2019).(2) Subotić, S. Pofahl, V. Lawlor, N. H. Menzler, T. Thaller, and C. Hochenauer, Energy Proc., 158, 2329 (2019).(3) B. Mogensen, Current Opinion Electrochem., 21, 265 (2020). Figure 1

Traditional and Iterative Group-IV Material Batteries through Ion Migration

In this review, we emphasize the significant potential of carbon group element-based (Group-IV) electrochemical energy devices prepared on the basis of ion migration in the realm of high-efficiency batteries. Based primarily on our group research findings, we elucidate the key advantages of traditional Group-IV materials as electrodes in ion batteries powered by metal ion migration. Subsequently, we delve into the operational principles and research progress of iterative Group-IV material moisture ion batteries, driven by ion migration through external moisture. Finally, considering the practical challenges and issues in real-world applications, we offer prospects for the development and commercialization of Group-IV materials utilizing ion migration in both conventional and next-generation battery technologies.

Simultaneous multimaterial operando tomography of electrochemical devices.

The performance of electrochemical energy devices, such as fuel cells and batteries, is dictated by intricate physiochemical processes within. To better understand and rationally engineer these processes, we need robust operando characterization tools that detect and distinguish multiple interacting components/interfaces in high contrast. Here, we uniquely combine dual-modality tomography (simultaneous neutron and x-ray tomography) and advanced image processing (iterative reconstruction and metal artifact reduction) for high-contrast multimaterial imaging, with signal and contrast enhancements of up to 10 and 48 times, respectively, compared to conventional single-modality imaging. Targeted development and application of these methods to electrochemical devices allow us to resolve operando distributions of six interacting fuel cell components (including void space) with the highest reported pairwise contrast for simultaneous yet decoupled spatiotemporal characterization of component morphology and hydration. Such high-contrast tomography ushers in key gold standards for operando electrochemical characterization, with broader applicability to numerous multimaterial systems.

Biofluid-Activated Biofuel Cells, Batteries, and Supercapacitors: A Comprehensive Review.

Recent developments in wearable and implanted devices have resulted in numerous, unprecedented capabilities that generate increasingly detailed information about a user's health or provide targeted therapy. However, options for powering such systems remain limited to conventional batteries which are large and have toxic components and as such are not suitable for close integration with the human body. This work provides an in-depth overview of biofluid-activated electrochemical energy devices, an emerging class of energy sources judiciously designed for biomedical applications. These unconventional energy devices are composed of biocompatible materials that harness the inherent chemistries of various biofluids to produce useable electrical energy. This work covers examples of such biofluid-activated energy devices in the form of biofuel cells, batteries, and supercapacitors. Advances in materials, design engineering, and biotechnology that form the basis for high-performance, biofluid-activated energy devices are discussed. Innovations in hybrid manufacturing and heterogeneous integration of device components to maximize power output are also included. Finally, key challenges and future scopes of this nascent field are provided.