Anodic Layer Research Articles

Reactivity and Stability of Reduced Ir-Weight TiO2-Supported Oxygen Evolution Catalysts for Proton Exchange Membrane (PEM) Water Electrolyzer Anodes.

Reducing the iridium demand in Proton Exchange Membrane Water Electrolyzers (PEM WE) is a critical priority for the green hydrogen industry. This study reports the discovery of a TiO2-supported Ir@IrO(OH)x core-shell nanoparticle catalyst with reduced Ir content, which exhibits superior catalytic performance for the electrochemical oxygen evolution reaction (OER) compared to a commercial reference. The TiO2-supported Ir@IrO(OH)x core-shell nanoparticle configuration significantly enhances the OER Ir mass activity from 8 to approximately 150 A gIr-1 at 1.53 VRHE while reducing the iridium packing density from 1.6 to below 0.77 gIr cm-3. These advancements allow for viable anode layer thicknesses with lower Ir loading, reducing iridium utilization at 70% LHV from 0.42 to 0.075 gIr kW-1 compared to commercial IrO2/TiO2. The identification of the Ir@IrO(OH)x/TiO2 OER catalyst resulted from extensive HAADF-EDX microscopic analysis, operando XAS, and online ICP-MS analysis of 30-80 wt % Ir/TiO2 materials. These analyses established correlations among Ir weight loading, electrode electrical conductivity, electrochemical stability, and Ir mass-based OER activity. The activated Ir@IrO(OH)x/TiO2 catalyst-support system demonstrated an exceptionally stable morphology of supported core-shell particles, suggesting strong catalyst-support interactions (CSIs) between nanoparticles and crystalline oxide facets. Operando XAS analysis revealed the reversible evolution of significantly contracted Ir-O bond motifs with enhanced covalent character, conducive to the formation of catalytically active electrophilic OI- ligand species. These findings indicate that atomic Ir surface dissolution generates Ir lattice vacancies, facilitating the emergence of electrophilic OI- species under OER conditions, while CSIs promote the reversible contraction of Ir-O distances, reforming electrophilic OI- and enhancing both catalytic activity and stability.

Three-dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High-Performance Lithium Metal Battery.

Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three-dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32wt%) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6-connected cyclotriphosphazene derivative aldehyde and 4-connected porphyrin-based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron-rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por-PN-COF-Cu cells achieved a record average CE of 99.1% for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π-electron system.

Three‐dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High‐Performance Lithium Metal Battery

Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three‐dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32wt%) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6‐connected cyclotriphosphazene derivative aldehyde and 4‐connected porphyrin‐based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron‐rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por‐PN‐COF‐Cu cells achieved a record average CE of 99.1% for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π‐electron system.

Honeycomb‐Structured IrOx Foam Platelets as the Building Block of Anode Catalyst Layer in PEM Water Electrolyzer

AbstractAchieving robust long‐term durability with high catalytic activity at low iridium loading remains one of great challenges for proton exchange membrane water electrolyzer (PEMWE). Herein, we report the low‐temperature synthesis of iridium oxide foam platelets comprising edge‐sharing IrO6 octahedral honeycomb framework, and demonstrate the structural advantages of this material for multilevel tuning of anodic catalyst layer across atomic‐to‐microscopic scales for PEMWE. The integration of IrO6 octahedral honeycomb framework, foam‐like texture and platelet morphology into a single material system assures the generation and exposure of highly active and stable iridium catalytic sites for the oxygen evolution reaction (OER), while facilitating the reduction of both mass transport loss and electronic resistance of catalyst layer. As a proof of concept, the membrane electrode assembly in single‐cell PEMWE based on honeycomb‐structured IrOx foam platelets, with a low iridium loading (~0.3 mgIr/cm2), is demonstrated to exhibit high catalytic activity at ampere‐level current densities and to remain stable for more than 2000 hours.

Honeycomb-Structured IrOx Foam Platelets as the Building Block of Anode Catalyst Layer in PEM Water Electrolyzer.

Achieving robust long-term durability with high catalytic activity at low iridium loading remains one of great challenges for proton exchange membrane water electrolyzer (PEMWE). Herein, we report the low-temperature synthesis of iridium oxide foam platelets comprising edge-sharing IrO6 octahedral honeycomb framework, and demonstrate the structural advantages of this material for multilevel tuning of anodic catalyst layer across atomic-to-microscopic scales for PEMWE. The integration of IrO6 octahedral honeycomb framework, foam-like texture and platelet morphology into a single material system assures the generation and exposure of highly active and stable iridium catalytic sites for the oxygen evolution reaction (OER), while facilitating the reduction of both mass transport loss and electronic resistance of catalyst layer. As a proof of concept, the membrane electrode assembly in single-cell PEMWE based on honeycomb-structured IrOx foam platelets, with a low iridium loading (~0.3 mgIr/cm2), is demonstrated to exhibit high catalytic activity at ampere-level current densities and to remain stable for more than 2000 hours.

Nanofluid channels mitigated Zn2+ concentration polarization prolonged over 30 times lifespan for reversible zinc anodes

Despite interfacial engineering protects zinc anode from electrolyte corrosion, the suppressed kinetics process on the anode surface/interface circumscribes their cyclic stability, especially dendritic growth induced by ion concentration gradients. Here, the zinophilic nanofluid channels (ZNC) protective layer on zinc surface are designed for the rapid Zn2+ transport kinetic in the reversible cycling process. The ZNC demonstrates high separation pressure between ions and the channel surface due to the capillary effect, allowing Zn2+ to quickly migrate along the channel wall (Zn2+ transference numbers up to 0.72). Therefore, the unique channel modules alleviate concentration polarization from rapid Zn2+ consumption and maintain uniform deposition of Zn ions. Consequently, The ZNC protective layer anode exhibits significantly improved cycle life by more than 30 times (over 4000 h at 1 mA cm−2) that of bare Zn. The full battery exhibits stable cycling performance with excellent capacity retention (∼100%) after 5000 cycles. Our work provides innovative insights into the role of nanofluids in improving the stability of zinc anodes, offering enlightening perspectives for long-cycle life zinc-based batteries.

The Influence of Surface Segregation on the Anodizing of AlSi11Cu2(Fe) Diecastings

A positive segregation is usually formed on the casting surfaces produced by high-pressure die casting (HPDC). In diecast Al-Si-Cu alloy components, this segregation shows a higher content of Si compared to the nominal composition of the alloy and it drastically affects the anodizing response of the casting surface. In the present work, HPDC components were produced by AlSi11Cu2(Fe) alloy, grit-blasted, and then anodized in a sulfuric acid electrolyte at the temperature of -4.5°C. Before the anodizing process, some regions of the casting were also milled, in order to completely remove the surface segregation. Microstructural investigations were carried out on grit-blasted and milled surfaces to characterize the initial substrates before anodizing, and to study their effect on the growth of the anodic layer. Scratch and wear tests were also performed to investigate the surface mechanical properties after anodizing. The results show that the surface segregation and the rough surface present on grit-blasted substrate leads to the formation of a thin and homogeneous anodic layer. On the contrary, a thicker and scalloped oxide film is formed on the milled surfaces. After anodizing, grit-blasted surfaces show lower wear and scratch resistance than milled substrates. The presence of surface segregation prevents the thickening of the anodic layer, negatively affecting the surface wear resistance due to the reduced oxide thickness.

Zincophilic Sites Enriched Hydrogen‐Bonded Organic Framework as Multifunctional Regulating Interfacial Layers for Stable Zinc Metal Batteries

AbstractTo construct an efficient regulating layer for Zn anodes that can simultaneously address the issues of dendritic growth and side reactions is highly demanded for stable zinc metal batteries (ZMBs). Herein, we fabricate a hydrogen‐bonded organic framework (HOF) enriched with zincophilic sites as a multifunctional layer to regulate Zn anodes with controlled spatial ion flux and stable interfacial chemistry (MA‐BTA@Zn). The framework with abundant H‐bonds helps capture H2O and remove the solvated shells on [Zn(H2O)6]2+, leading to suppressed side reactions. The HOF layer also helps form electrolyte‐philic surfaces and expose Zn (002) crystal planes which benefit for rapid conduction and uniform deposition of Zn2+, and weakened sides reactions. Additionally, the electrochemically active zincophilic sites (C=O, −NH2 and triazine groups) favor the targeted guidance and penetration of Zn2+ and provide advantageous sites for uniform Zn deposition. High Young's modulus of the HOF layer further contributes to a high interfacial flexibility and stability against Zn plating‐associated stress. The MA‐BTA@Zn symmetric cells thereby obtain a substantially extended battery life over 1000 h at 4 mA cm−2. The MA‐BTA@Zn||Cu half‐cell demonstrates a highly reversible Zn stripping/plating process over 1500 cycles with impressive average Coulombic efficiency (CE) of 99.5 % at 10 mA cm−2.

A comparative study on the Lattice Boltzmann Method and the VoF-Continuum method for oxygen transport in the anodic porous transport layer of an electrolyzer

The optimization of Polymer Electrolyte Membrane (PEM) electrolyzers necessitates an intimate knowledge of the oxygen flows within the anodic porous transport layers (PTLs) to determine any possible reduction in performance. In this field, as experimental studies are cumbersome and expensive, numerical modeling has arisen as a viable alternative for studying the oxygen transport within the Anodic PTLs of a PEM electrolyzer. Amongst the various numerical modeling techniques, the Lattice Boltzmann Method (LBM) is gaining prominence for its effectiveness in analyzing fluid transport within porous media due to its mesoscopic nature and ease of implementation. This study utilizes the Shan-Chen LBM methodology to model the flow of oxygen within the Anodic PTL of a PEM electrolyzer and compares it against the Volume-of-Fluid-based Continuum Model. The results show that LBM can not only replicate the experimental studies accurately, but can also maintain its high accuracy at progressively shrinking length scales of PTLs, even at length scales where the VoF-based Continuum Model would run into accuracy issues. The high accuracy of the LBM model, combined with the simplicity of the LB algorithm makes LBM a powerful technique for simulating the microfluidic flows such as the flow of oxygen within the Anodic PTL of a PEM electrolyzer.

Machine learning descriptors for crystal materials: applications in Ni-rich layered cathode and lithium anode materials for high-energy-density lithium batteries

Lithium batteries have revolutionized energy storage with their high energy density and long lifespan, but challenges such as energy density limitations, safety, and cost still need to be addressed. Crystalline materials, including Ni-rich cathodes and lithium anodes, play pivotal roles in the performance of high-energy-density lithium batteries. Understanding the micro-scale behavior and degradation mechanisms of these materials is crucial for improving macro-scale battery performance. Simulation methods, particularly machine learning (ML) techniques, have become indispensable tools in elucidating these intricate processes because of great efficiency and acceptable accuracy. ML methods depend on descriptors, which bridge the gap between crystal structures and input matrices of models. These descriptors encode essential atomic-level details in crystal structures, enabling predictions of material properties and behaviors relevant to lithium batteries. This paper reviews and discusses the diverse array of descriptors employed in the simulation of crystalline materials for lithium batteries with high energy density. Case studies highlight the effectiveness of different descriptors in simulating cathode behaviors such as Li/Ni disordering, screening of stable LiNi0.8Co0.1Mn0.1O2 (NMC811) configurations, and lithium deposition behaviors at the anode interface. The discussed descriptors can also be applied to other crystalline cathode, anode, and electrolyte materials in lithium batteries and advance the development of lithium batteries with superior energy density.

Design Double Layered Anode for Stably Introducing Lithium Source to Achieve Sulfur‐Carbon Full Batteries

AbstractLithium‐sulfur batteries offer high energy density but face great safety and cycle life challenges due to the use of Li metal anode. Replacing the Li metal anode with pre‐lithiated carbon anodes can thoroughly address cycling stability and safety issues. Directly contacting Li foil with graphite electrode is one of the most efficient and simple strategy to introduce a high content of lithium source into the sulfur‐carbon full batteries. However, the 100% lithiation of the graphite anode through the direct contact method generates excessive heat and stress heterogeneity, which leads to electrode structure cracking and electrochemical properties fading. This study implements a double‐layer anode to mitigate these issues. A thin layer of hard carbon placed between graphite and Cu foil limits heat generation and stress heterogeneity due to its structural and electrochemical stability. Additionally, differing from traditional electrochemical lithiation, this method gains better solid electrolyte interphase (SEI) for the graphite anode after several cycles. This research highlights the mass production potential of coupling high energy density lithium source‐free cathode materials with various lithium source‐free anodes for constructing long‐cycle and high‐safety rechargeable batteries.

Lateral Diffusion of Holes in Anodic Buffer Layers and Its Application in Organic Light-Emitting Diodes

Lateral Diffusion of Holes in Anodic Buffer Layers and Its Application in Organic Light-Emitting Diodes

ZnO Nanoparticle Assisted Liquid Metal for Dendrite-Free Zn Metal Anodes.

Dendrite growth and interfacial side reactions on Zn anode seriously affect the safety and service life of Zn ions batteries. Interface engineering is an effective way to solve these problems. Here, a liquid metal-ZnO composite coating with high ionic conductivity is creatively designed, which not only reduces the Zn2+ diffusion barrier but also increases the hydrogen evolution overpotential, thereby eliminating dendrite growth behavior and corrosion on the modified Zn anode. Moreover, its unique structure induces Zn deposition into the inner of coating, which can effectively avoid the volume expansion in the deposit layer of Zn anode. Therefore, it can cycle for 3000 h at an ultra-small polarization of 28 mV at 1 mA cm-2, and the microbattery assembled in combination with the MnO2 cathode also maintains 2000 cycles with high Coulomb efficiency, providing a general idea for the development of the next generation of rechargeable metal batteries.

Cathode-supported SOFCs enabling redox cycling and coking recovery in hydrocarbon fuel utilization

Although cathode-supported solid oxide fuel cells (SOFCs), characterized by significantly thinner anode layers than anode-supported SOFCs, are known to have unique advantages in ensuring stability and reliability against redox operating conditions and carbon deposition, they have received relatively less attention due to their lower performance. Furthermore, there is a lack of in-depth theoretical and experimental studies on their outstanding redox cycle characteristics than the anode-supported cells. Here, applying a sintering aid to the electrolyte considerably reduces the sintering temperature of the electrolyte, with the shrinkage and microstructure of the cathode effectively controlled to lower the diffusion resistance. Consequently, the operating temperature was lowered by more than 100 °C compared to previously reported cathode-supported SOFCs; moreover, at 650 °C, a maximum power density more than twice that reported in previous reports. The redox stability of the cathode-supported cells was demonstrated experimentally and theoretically through a redox cycling test and a 3-D finite element method-based SOFC structure model. Moreover, the outstanding redox cycle property of cathode-supported cells has been experimentally demonstrated for the first time to have the potential to mitigate carbon deposition that occurs when utilizing methane fuel. Hence, this study presents new insights for achieving stable and reliable SOFC operation.

Fluorine containing diamond-like carbon coatings

Fluorine containing diamond-like carbon (DLC) coatings were obtained by CVD deposition using the destruction of gaseous hydrocarbons by a high-energy ion source with an anode layer. The chemical composition, structure, surface energy, mechano-tribological characteristics of the synthesized thin-film material were studied. It has been shown that the fluorine content in the deposited coatings reaches 31 at.%. It has been established that the presence of fluorine in the DLC coating promotes the formation of nanodispersed graphite-like structures. Fluorine containing coatings with a high content of sp2 hybridized carbon atoms and graphite fragments show a decrease in hardness. Such coatings have a very low coefficient of friction at the level of 0.03–0.07 due to the low surface energy, which can be reduced by 1.5 times compared to pure DLC. It has been established that different fluorine contents in thin-film diamond-like carbon material have different effects on the interaction of the DLC coating with polar/non-polar dielectrics. The research results can be used for the technology of producing solid lubricants in friction units of machines and mechanisms, and are also of interest for medicine, the food industry, the production of plastics, and chemical fibers as chemically inert and corrosion-resistant coatings.

Investigation of the Effect of Initial Anode Structures on the Durability of Water Electrolysis Cells

Water electrolysis systems directly using renewable energy have been focused on this study. From our previous finding in the long-term accelerated voltage fluctuation test using actual wind power voltage fluctuations, increasing hydrophobicity and reducing gas stagnation within the anode catalyst layer were suggested. Then, controlling hydrophobic characters was considered in this study. Hydrophobic materials, such as polytetrafluoroethylene and polypyrrole, were chosen and added to the anode layers. As expected, the addition of 30% polytetrafluoroethylene improved hydrophobicity but also increased ohmic resistance, lowering IV performance. On the other hand, the use of polypyrrole was found to improve hydrophobicity while maintaining IV performance. However, the slight increase in activation and diffusion overvoltages was also observed, which was most likely owing to poor distribution of polypyrrole in the anode layer and possibly improved by adding a milling process.

Investigation of the Durability of a Water Electrolysis Cell with Iridium Fiber Anode Against Voltage Fluctuations Simulating Wind Power

Durability of a water electrolysis cell against the voltage fluctuations is focused on in this study. An accelerated potential fluctuation test was performed for a newly developed MEA with Iridium fiber anode in our lab. In the first 40 sets of the test, no positive effect of the fiber structure was seen, and rather the fast current loss related to gas stagnation was observed. That was assumed to be owing to the coverage on inter-fiber pores by extra Nafion® ionomer. However, in the latter 40 sets, the expansion of the anode layer was confirmed by SEM images, and the rate of gas stagnation was decreased. Furthermore, the recovery of I-V performance after the rest period was sufficiently good, and almost no irreversible degradation was considered. Therefore, the Iridium fiber anode most likely has high durability against the increased internal pressure in the anode layer derived by stagnated gases.

A high-capacity and stable dual-ion battery based on an ultra-large lattice-spacing amorphous carbon anode

Compared with traditional lithium-ion batteries (LIBs), dual-ion batteries (DIBs) offer advantages such as high operating voltage, good safety performance, and low cost. However, DIBs often suffer from challenges such as low specific capacity and poor cycling performance in practical applications. Here, a layered nitrogen-doped carbon anode has been prepared using a one-step pyrolysis method with excellent Li+ storage sites. The large lattice spacing of 0.55 nm provides more space for the storage and migration of active ions. Concurrently, the utilization of concentrated electrolyte facilitated the electrochemical window and the restrained solvation of ions, which helps to boost ion transport and improve the stability of the electrolyte and the operating voltage of DIBs. The assembled DIBs exhibit a high specific discharge capacity of 179.27 mA h g−1, within a 2.5–4.8 V voltage range, and excellent cycling stability of 3500 cycles without degradation. Specifically, the structural evolution of the electrodes during charging and discharging and the working mechanism of the DIBs are also explored. The DIBs system designed in this paper provides a facile and scalable approach to promote the development of DIBs with low-cost and high-performance.

Self‐Powered and 3D Printable Soft Sensor for Human Health Monitoring, Object Recognition, and Contactless Hand Gesture Recognition

AbstractA new galvanic cell design of a self‐powered and 3D‐printable soft sensor showing health monitoring, object recognition, and contactless hand gesture recognition, is reported. The soft sensor consists of a 3D‐printed poly(acrylic acid) (PAA) hydrogel electrolyte layer, a soft anode layer, and a soft cathode layer. The anode layer is a 3D‐printed and Cu2+ cross‐linked poly(N,N‐dimethylacrylamide‐co‐3‐alanine‐2‐hydroxypropylmethacrylate) (PDA) hydrogel dispersed with Cu metal particles (PDA/Cu2+/Cu hydrogel), while the cathode layer is a bottom thin layer of the PAA hydrogel containing MnO2 (PAA/MnO2). Using graphite films as the soft electrodes, the soft sensor is finally assembled. The soft sensor has high force and temperature sensitivities. It gives different electric current responses under stretching, bending, pressing, and impact loading. The soft sensor is demonstrated to be useful in detecting human motion and physiological activities, e.g., breath. Based on the force and contactless temperature sensitivities, the soft sensor is used to recognize human hand gestures and plastic balls with different diameters. This 3D printable soft sensor with self‐powering, contactless motion capturing, and multi‐pimulus sensing capabilities illustrates a new pathway to make soft sensory devices for healthcare and human‐machine interaction applications.

Few-layered graphene from cathodic exfoliation in binary solvents and application as a protective layer for lithium metal anodes

Electrochemical exfoliation is a top-down method recognized for its environmentally friendly and scalable approach for producing solution-processable graphene. Among its variation, cathodic exfoliation stands out for its potential in generating few-layer graphene with minimal defects. In this study, we developed a cathodic exfoliation method for graphite foil using a binary solvent system to produce graphene with a reduced number of layers. By employing a 0.1 M LiClO4 solution in a dimethyl sulfoxide and dimethyl carbonate solvents mixture at a 1:2 vol ratio, we enhanced the intercalation of solvated lithium ions into graphite, successfully exfoliating graphene with 5–6 layers. The exfoliated graphene exhibited a low defect density (ID/IG ∼0.05) and a C/O ratio of 33.2. Furthermore, when used as a coating on a separator, the exfoliated few-layered graphene (FLG) sheets demonstrated notable performance as a protective layer for Li metal anode in Li metal battery technology.