Electrode Engineering Research Articles

Improving the performance stability of direct seawater electrolysis: from catalyst design to electrode engineering.

Direct seawater electrolysis opens a new opportunity to lower the cost of hydrogen production from current water electrolysis technologies. To facilitate its commercialization, the challenges of long-term performance stability of electrochemical devices need to be first addressed and realized. This minireview summarised the common causes of performance decline during seawater electrolysis, from chemical reactions at the electrode surface to physical damage to the cell. The problems triggered by the impurities in seawater are specifically discussed. Following these issues, we further outlined the ongoing effort of counter-measurements: from electrocatalyst optimization to electrode engineering and cell design. The recent progress in selectivity tuning, surface protection, gas diffusion, and cell configuration is highlighted. In the final remark, we emphasized the need for a consensus on evaluating the stability of seawater electrolysis in the current literature.

Enabling directional ion transport over graphene electrode surfaces for kilohertz electrochemical capacitors

The filtering capacitor is an electrochemical energy storage device, which can realize signal stabilization from alternating current to direct current in the modern electronic circuits. Traditional filtering capacitor, an aluminum electrolytic capacitor is usually limited by the bulky and rigid configuration. The graphene-based electrochemical capacitor with a fast frequency response has the potential to be the next-generation filtering capacitor. Kilohertz electrochemical capacitor with alternating current line-filtering performance requires the microstructural engineering of graphene electrodes to facilitate effective electrolyte ion permeation. Vertically-oriented graphene electrode-based electrochemical capacitor by microstructural engineering provides a significant solution for improving the filtering performance, but the underlying mechanism by which the vertical orientation endows graphene electrodes with the fast frequency response is still not clear. Therefore, a fundamental understanding of this mechanism must be developed and improved to ensure the design of superior kilohertz electrochemical capacitors for effective filtering. Here, a vertically-oriented graphene macroporous membrane is prepared to enable directional ion transport over the electrode surface at high frequencies, which is demonstrated by all of the electrochemical analysis, line scanning, schematic illustration and finite element analysis simulation results. Compared with those based on conventional horizontally-oriented and unordered graphene macroporous membrane electrodes, the vertically-oriented electrode-based electrochemical capacitor exhibits excellent filtering performance. Furthermore, it can convert arbitrary alternating current waveforms to straight signals. This work advances the understanding of the mechanism underlying the kilohertz frequency response and enables directional ion transport over the surface of vertically-oriented graphene electrodes, providing new insight into the search for future kilohertz filtering capacitors.

A perspective on electrode engineering in ultrathin ferroelectric heterostructures for enhanced tunneling electroresistance

The combination of ferroelectricity and quantum tunneling enables the tantalizing possibility of next-generation nonvolatile memories based on ferroelectric tunnel junctions (FTJs). In the last two decades, significant progress has been achieved in the understanding of FTJs in terms of the role of the critical thickness for ferroelectricity, interface-related factors that yield an enhanced tunneling electroresistance effect, as well exploiting the combination of magnetism and ferroelectricity to realize multiferroic or magnetoelectric tunnel junctions. One key ingredient in the successful design of FTJs is the type and nature of the electrode used—indeed device performance strongly hinges on the ability to precisely tune and modulate the electrostatic boundary conditions. This perspective presents an overview of the experimental state of the art in electrode engineering for FTJs. We discuss related governing factors and methods for various electrode-FTJ combinations, highlighting and comparing the advantages and weaknesses for each system. Finally, we also reveal the challenges and identify the opportunities for the future development of FTJs. In summary, we aim to provide significant insights into electrode engineering of high-quality FTJs with excellent tunneling electroresistance performance.

(Invited) Electrochemical Treatment of Aquaculture Wastewater and Water for Irrigation in Off-Grid Locations

The use of electrochemical processes and technology has been a focus for the energy conversion and storage fields, as technologies ranging from batteries to fuel cells and electrolyzers have received significant attention as cutting-edge and advanced next-generation technologies. To date, the application and development of electrochemical technologies for water and wastewater treatment needs have been limited to specific niches; for example, electrochemical technology has been a focus for non-membrane-based desalination (e.g., electrodialysis or capacitive deionization) and for electrocoagulation of metals and organics, as a replacement for chemically-driven coagulation. However, electrochemical processes and technologies offer a much greater range of possibilities for wastewater treatment needs and goals. From chemical-free disinfection to electrocatalytic conversion of contaminants to recovery of critical nutrients, electrode engineering, control of operational voltage and current windows, and optimization of device design can all be used to address key problems in wastewater treatment. In our research group, we focus the use of electrochemical approaches to address the removal of key contaminants and enable a chemical-free disinfection step for remote and rural wastewater treatment needs in the agriculture and aquaculture sectors. In this talk, I will discuss our ongoing work and recent results on electrochemical approach, electrode engineering, electrochemistry experiments, and device development for the off-grid treatment of aquaculture wastewater for the goals of ammonia removal and disinfection, as well as the off-grid treatment of surface water for irrigation uses, where the goal is on-demand disinfection. Electrochemistry studies for aquaculture wastewater treatment using graphite and graphite-supported PtRu films as the anode demonstrate that the presence of PtRu reduces the voltage required for ammonia oxidation. When graphite is used as the cathode, the disinfectant molecule hydrogen peroxide is produced, suggesting electrochemical disinfection is possible in parallel with ammonia oxidation. In addition, the electrode configuration can be used to generate chlorine on demand, providing an alternate route for disinfection. For both water scenarios, we investigate the roles of electrode type, electrochemical operating parameters, and water chemistry parameters. In addition, our research has included several field site studies to demonstrate performance of our flow electrochemical cells for natural water samples.

Current Status of Solid Oxide Fuel Cell Technology Research and Development at National Energy Technology Laboratory

The DOE Office of Fossil Energy Solid Oxide Fuel Cell (SOFC) Program is interested in the near-term commercialization of high-temperature SOFC and solid oxide electrolyzer cell (SOEC) technologies that are robust, reliable, and resilient. A recent report delivered to the United States Congress highlighted several development recommendations including the design of pilot-scale units, continued early stage research and development, increased industrial engagement, and the exploration of reversible operation of SOFC technology.The National Energy Technology Laboratory (NETL) SOFC research group currently addresses most of these recommendations. NETL’s in-house research efforts focus on the characterization, simulation, and mitigation of high temperature degradation of fuel cell components. The capstone of these efforts is NETL’s SOFC degradation modeling framework, which uses NETL supercomputing facilities to simulate SOFC performance degradation of thousands of possible electrode configurations experiencing multiple simultaneous degradation modes under a broad array of relevant operating conditions. The models for the different degradation modes are based upon experimental data (1) generated in-house, (2) referenced from available scientific publications, and (3) shared from collaborations with other industrial, academic, and national laboratory partners within the SOFC Program. The team then employs techniques in data analytics to select optimal electrodes to maximize the SOFC performance for given operating conditions. These modeling efforts guide electrode engineering efforts in-house and through external collaborations by identifying (1) which degradation modes contribute the most to overall performance degradation for given operating conditions and (2) which electrode features will have the greatest impact on lowering cell degradation and system costs. Additionally, the development on non-invasive in situ high temperature fiber optic sensors for temperature and gas composition measurement provides valuable data for inclusion in degradation models as well as informing technology development at the commercial scale. Finally, the wealth of experience gained in development degradation models and materials for reducing the cost of SOFC technology is being readily applied to reducing the cost of SOEC technology.NETL will report on its most recent progress in the field of SOFC and SOEC development, including degradation modeling, in situ fiber optic sensor development, electrode engineering, and relevant systems-level analyses.

(Invited) Engineering Polypeptides for Controlled Assembly of Ionomer Thin Films

Increasing evidence suggests that control of ionomer thin film structures on metal surfaces is pivotal for efficient performance in electrochemical devices such as fuel cells and electrolyzers. Unfortunately, the assembly of these thin film structures is difficult to control using conventional methods and ideal arrangements remain unknown. Engineered polypeptides have emerged as powerful biomolecular tools in electrode assembly because binding sites and polypeptide structures can be easily modulated by changing the amino acid sequence. However, no studies have been conducted showing polypeptides can be engineered to interact with ionomers, attach them to metal surfaces, and control their arrangement. Our lab has recently developed this technology, using an elastin-like polypeptide to bind to metals, and bind to acidic and basic ionomer via ionic interactions. We use a quartz crystal microbalance with dissipation to provide detailed information about the loading, thickness, and binding behavior of the polypeptide and ionomer layers. We also use atomic force microscopy and grazing-incidence small-angle X-ray scattering to understand the impact of the biomolecules on ionomer phase separation. Finally, we have begun to analyze the performance (ionic conductivity) of the assembled films using interdigitated electrodes and electrochemical impedance spectroscopy. Through these techniques, we show that 1) our biomolecular system is highly flexible, easily adapting to different materials, 2) the polypeptide sequence can dictate ionomer phase separated structures, and 3) this system can be used to improve the performance of ionomer thin films and gain structure-function understanding. Generally, our results demonstrate that engineered polypeptides are promising tools for ionomer control in electrode engineering.

Mesoscale Electrode Analytics for Fast Charging

Fast charging of lithium-ion batteries is paramount toward widespread adoption of electric vehicles. Fast charging, however, poses safety concerns due to the occurrence of lithium plating and local thermal excursions. Preserving the thermal safety, performance and life of LIBs at such operating extremes necessitates a thorough understating of the thermal and degradation interactions emanating at the electrode level. In this work, the electrode-level implications of thermal and electrochemical characteristics of Li-ion cells during fast charge conditions is examined. Suggestions for improvement in fast charging capabilities via electrode engineering are made.

Rechargeable Sodium‐Based Hybrid Metal‐Ion Batteries toward Advanced Energy Storage

AbstractGrowing demands on energy storage devices have inspired a tremendous amount of research on rechargeable batteries. Future generations of rechargeable batteries are required to have high energy density, long lifespan, low cost, high safety, low environmental impact, and wide commercial affordability. To achieve these goals, significant efforts are underway to focus on electrolyte chemistry, electrode engineering, and new designs for energy storage systems. Herein, a comprehensive overview of an innovative sodium‐based hybrid metal‐ion battery (HMIBs) for advanced next‐generation energy storage is presented. Recent advances on sodium‐based HMIBs from the development of reformulated or novel materials associated with Na+ ions and other metal ions (such as Li+, K+, Mg2+, Zn2+, etc.), are summarized in this work. Daniell cell and “rocking‐chair” type batteries are covered. Finally, the current challenges and future remedies in terms of the design and fabrication of new electrolytes, cathodes, and anodes for advanced HMIBs are discussed in this report.

Fluorine-doped carbon quantum dot interfacial layer on stockade-like etched copper foil for boosting Li-ion storage

The interface engineering of anode electrodes in lithium-ion batteries (LIBs) is a key strategy in improving the Li-ion storage kinetics and interface stability to achieve outstanding ultrafast cycling capacities and cycling stabilities of LIBs. However, despite extensive research on the interfacial engineering of electrode materials, studies on the interface design between the electrode and current collector to improve the ultrafast cycling performance are rare. In this study, we designed a novel interface architecture for a fluorine-doped carbon quantum dot (F-CQD) interfacial layer on a stockade-like etched Cu foil via electrochemical modification and a spray coating process. The anode electrode assembled with the resultant Cu foil showed enhanced adhesion, high reaction kinetics, and excellent interface stability between the electrode and Cu foil due to the F-CQD interfacial layer on the stockade-like etched Cu foil, leading to an improved ultrafast cycling performance. Consequently, the novel architecture of a Cu foil having stockade-like etching patterns with an F-CQD interfacial layer showed an increased ultrafast cycling capacity of 82.9 mAh g−1 and excellent ultrafast cycling stability of 94.1% after 500 cycles under ultrafast cycling conditions. These improved ultrafast cycling performances are due to the high contact area between the electrode and Cu foil, excellent reaction sites, and superb corrosion resistance.

Electrolyte Engineering Toward High‐Voltage Aqueous Energy Storage Devices

Aqueous electrochemical energy storage (EES) devices are highly safe, environmentally benign, and inexpensive, but their operating voltage and energy density must be increased if they are to efficiently power multifunctional electronics, new‐energy cars as well as to be used in smart grids. This Minireview summarizes the key breakthroughs and progress in expanding the electrochemical stability window (ESW) of aqueous EES devices over the past five years. After briefly introducing the electrode engineering ways to widen ESW, we focus on four ground‐breaking electrolyte engineering strategies and classify them into two kinds from the perspective of salts and exotic solutes/solvents. The widening degree toward ESW of these emerging electrolytes is compared and the universal fundamental mechanism relating to the interactions between limited water molecules and high‐concentration salts (or large amounts of exotic solutes/solvents) is elucidated. Key challenges and perspectives for high‐ESW electrolytes as well as recent advances in low‐cost and other metal ion (sodium, potassium, zinc, etc.)‐based electrolytes for expanding ESW are also outlined.

A critical review on semitransparent organic solar cells

Semitransparent solar cells not only can generate electricity but also exhibit promising application in facades and roofs of building, as well as the coatings of vehicle. Ideal semitransparent solar cells should have a high utilization efficiency of ultraviolet and near infrared photons, and maintain an appropriate balance between absorption and transparency in visible light range. Organic semiconducting materials with adjustable optical band gap own great potential in preparing highly efficient semitransparent organic solar cells (OSCs). There are great challenges in achieving semitransparent electrodes with good conductivity and high transmittance in visible light range, as well as high reflectance in ultraviolet and near infrared range. In this critical review, we summarize the recent progress of semitransparent OSCs, concentrating on organic semiconducting materials, semitransparent top electrode and device engineering. Semitransparent OSCs have attracted more and more attention due to its great potential in energy source in door, electricity-generating windows, building-integrated photovoltaics and agricultural greenhouse. Semitransparent OSCs have attracted more and more attention due to its great potential in electricity-generating windows, building-integrated photovoltaics and agricultural greenhouse. This review comprehensively summarizes recent progresses of organic material, semitransparent top electrode and device engineering, the challenges on achieving semitransparent OSCs are highlighted to promote the development of this field. • Recent development of organic materials with strong ultraviolet or near infrared absorption were summarized. • The key parameters for evaluating the performance of semitransparent OSCs were discussed. • This review comprehensively summarized recent progress of transparent top electrodes. • The light management methods and device designs are firstly comprehensively reported.

Modulation of Electrical Properties with Controllable Local Doping in Multilayer MoTe2 Transistors

AbstractIt has been found that substitutional atoms, surface modification, electrostatic gating, and contact electrode engineering can induce doping effects in 2D materials. However, the doping level, area, position, and pattern shape are not well controlled; thus, it is hard to generate high‐performance, multifunctional devices and logic circuits with these doping approaches. Here, it is found that a damage‐free, highly controllable, local doping in multilayer molybdenum ditelluride (MoTe2) flakes can be realized with highly controllable laser beam scanning irradiation. The doping level, area, position, and pattern shape are well controlled by adjusting parameters of the scanning laser beam. With the controllable doping, the subthreshold swing of MoTe2‐based transistors can be decreased by one order of magnitude, well‐matched p‐type and n‐type transports can be formed, and threshold voltages can be modulated, then a complementary inverter with ultra‐high gain ≈242 is realized, which is the highest in all reported inverters based on 2D materials. It is also found that a stable negative transconductance behavior can be created for the MoTe2 transistor by controlling doping position, then a frequency doubler is successfully demonstrated. Therefore, it is proposed that the position‐controlled local doping in multilayer MoTe2 may offer exciting application potentials in future nanoelectronics.

Status and challenges for the application of platinum group metal-free catalysts in proton-exchange membrane fuel cells

Platinum group metal-free electrocatalysts are an important class of materials for the sustainable energy economy and significant effort has been made toward developing platinum group metal-free catalysts to replace their costly Pt counterparts in fuel cell electric vehicles. The progress made in activity over the last decade is reviewed, along with synthesis strategies for more controlled active site formation and performance gains achieved through electrode engineering. The increased focus on durability, the growing understanding of degradation mechanisms, and the need for standard performance and accelerated stress test protocols are discussed.

Achieving High‐Performance and 2000 h Stability in Anion Exchange Membrane Fuel Cells by Manipulating Ionomer Properties and Electrode Optimization

AbstractThe primary function of the ionomers that are incorporated into fuel cell electrode catalyst layers is to provide pathways for ion transport between the catalyst active sites and the electrolyte. This is influenced by many variables, including the ion‐exchange capacity, water uptake, and molecular weight. In anion exchange membrane fuel cells (AEMFCs), controlling ionomer water uptake is particularly important and tailoring this property in each electrode is an important consideration when looking to maximize cell performance. In this study, three poly(norbornene) tetrablock copolymer ionomers with a range of physical properties are synthesized and incorporated into AEMFC anode and cathode electrodes. Systematic electrode engineering with these ionomers allows the peak power density to be increased by 100% (1.6 W cm‐2 → 3.2 W cm‐2) and the current density at 0.2 V to be increased by 59% (5.9 A cm‐2 → 9.4 A cm‐2). Moreover, the top‐performing electrode configuration is tested in an operating AEMFC at the US Department of Energy defined current density of 600 mA cm‐2 for 2000 h, showing a record‐low voltage decay rate of 15.36 µV h‐1 – only 3.65% –a over 2000 h. This work sets a new bar for AEMFCs, reporting the best combination of performance and durability of any AEMFC to date.

Ferroelectric HfZrO2 With Electrode Engineering and Stimulation Schemes as Symmetric Analog Synaptic Weight Element for Deep Neural Network Training

Atomic layer deposition (ALD)-based TiN electrode on ferroelectric HfZrO2 metal/ferroelectric/metal (MFM) capacitor and ferroelectric field-effect transistor (FeFET) is demonstrated experimentally with weight transfer, that is, $\Delta {P}$ , per pulse analysis through consecutive alternating potentiation/depression (Pot./Dep.) training pulses. The weight training pulse schemes are studied to have symmetric and linear synapse weight transfer to increase the accuracy and accelerate the deep neural network (DNN) training. With ALD TiN inserted, $\alpha _{p} / \alpha _{d} = -0.63$ / −0.84, asymmetry $\vert \alpha _{p} - \alpha _{d}\vert =0.21$ , and polarization modulation ratio (Pot./Dep.) = 97%/98% are achieved for MFM capacitor, and $\alpha _{p} / \alpha _{d} = -1.32$ / −1.88, asymmetry $\vert \alpha _{p} - \alpha _{d}\vert =0.56$ , and $G_{\text {max}} / G_{\text {min}} > 10\times $ are delivered for FeFET.

Ultrathin Conformal oCVD PEDOT Coatings on Carbon Electrodes Enable Improved Performance of Redox Flow Batteries

AbstractSurface engineering of porous carbon electrodes is an effective strategy to enhance the power output of redox flow batteries (RFBs) and may enable new cost reduction pathways for energy storage. Here, a surface modification strategy that enhances the electrochemical performance of RFBs in iron‐based electrolytes is demonstrated. Nanometric films of poly(3,4‐ethylenedioxythiophene) (PEDOT) are grown conformally onto carbon cloth electrodes using oxidative chemical vapor deposition (oCVD) and the impact of film properties on electrode performance in model iron‐based electrolytes is investigated. Depositing oCVD PEDOT films on the electrode surface is found to reduce ohmic, kinetic, and mass transport resistances, with the highest current densities and lowest resistances observed for electrodes coated with a ≈78 nm thick film. As compared to unmodified electrodes, coated electrodes enhance the maximum obtained current density at an applied overpotential of 350 mV by 6.7× and 3.7× in iron sulfate and iron chloride, respectively. The oCVD PEDOT film described here represents an initial step toward electrode surfaces of tailored activity, selectivity, and wettability for specific RFB chemistries and, more generally, electrochemical systems with liquid‐phase reactants.

Advancement of technology towards high-performance non-aqueous aluminum-ion batteries

Al-ion batteries (AIBs) have been identified as one of the most hopeful energy storage systems after Li-ion batteries on account for the ultrahigh volumetric capacity, high safety and low cost from the rich abundance of Al. Nonetheless, some inevitable shortcomings, such as the formation of passive oxide film, hydrogen side reactions and anode corrosion, finally limit the large-scale application of aqueous AIBs. The nonaqueous AIBs have been considered as one of most hopeful alternatives for high-powered electrochemical energy storage devices. Nonetheless, various technical and scientific obstacles should be resolved because nonaqueous AIBs are still nascent. Some significant efforts have aimed to resolve these issues towards large-scale applications, and some important advancement has been made. In the present review, we mainly intended to offer an overview of non-aqueous AIBs systems, and we comprehensively reviewed the recent research advancement of the cathode materials, anode materials electrolyte and collectors as well as the fundamental understanding of the functional mechanisms. In addition, we have also analyzed several technical challenges and summarized the strategies used for overcoming the challenges in improving the electrochemical properties, including morphology control, surface engineering, doping and construction of composite electrodes as well as the charge storage mechanisms of the materials with different crystal structures. At last, future research orientation and development prospect of the AIBs are proposed.

Electrode Engineering of Redox-Active Conjugated Microporous Polymers for Ultra-High Areal Capacity Organic Batteries

Redox-active organic compounds have become promising electrode materials for the development of more sustainable, economical, and safer batteries. However, their high electrochemical performance is...

Honeycomb-like carbon with tunable pore size from bio-oil for supercapacitor

Abstract As an emerging carbon precursor, bio-oil, consisting of numerous aromatic hydrocarbons and polycyclic carbon compounds, is the liquid derived from waste biomass pyrolysis. In this study, we adopt a facile and effective strategy with cetyltrimethylammonium bromide (CTAB) as pore-adjusting agents, and coupled with chemical activation and Ni2+ catalyzed graphitization to prepare bio-oil derived hierarchical porous carbon. The mesopore size of carbon material can be controlled by the size of macromolecular polymers by hydrogen bonding and electrostatic interactions between CTAB micelles and the oxygen-containing groups contained in bio-oil. Furthermore, increasing the CTAB amount enlarges pore size distribution from microporosity dominated to a wide range of 2–32 nm with increased specific surface area from 775 to 1302 m2 g−1. The resulting honeycomb-like carbon exhibits high specific capacitance as well as superior rate capability and excellent cycling stability. This work is believed to inspire the practical application of bio-oil and open up a new possibility to the pore engineering of biochar electrodes for energy storage and conversion.

Correlating the influence of porosity, tortuosity, and mass loading on the energy density of LiNi0.6Mn0.2Co0.2O2 cathodes under extreme fast charging (XFC) conditions

Extreme fast charging capabilities along with high energy density of Li-ion batteries are the key factors to increase the adoption of electric vehicles while eliminating the problem of range anxiety. The U.S Department of Energy has a goal of <12 min charging time with energy density of >200 Wh kg−1. A combined improvement in the electrode architecture, electrolyte properties, and separator membrane is necessary to achieve this goal. Cells with thin electrodes are capable of extreme fast charging at the expense of low energy density and high cost. Electrode engineering can maximize energy density. Here, the influence of porosity, mass loading and charging protocols on capacity and energy density and electrode kinetics are investigated under extreme fast charging conditions. Increasing the mass loading from 11.5 mg cm−2 to 25 mg cm−2 compromises the rate performance due to the mass transport limitation and underutilization of thick electrodes. Reducing the electrode porosity from 50% to 35% improves the rate performance ascribed to shorter Li ion diffusion length. Symmetric cells are cycled to verify the performance of the half cells, suggesting that Li metal plating is the rate limiting step under high current density.