Carbon Foam Electrode Research Articles

A Novel Kind of Activated Carbon Foam Electrode for Electric Double Layer Capacitors

A Novel Kind of Activated Carbon Foam Electrode for Electric Double Layer Capacitors

Deposition of Tungsten Metal by an Immersion Process

A new multi-step, solution-phase method for the spontaneous deposition of tungsten from a room temperature ethereal solution is reported. This immersion process relies on the deposition of a sacrificial zinc coating which is galvanically displaced by the ether-mediated reduction of oxophilic WCl6. Subsequent thermal treatment renders a crystalline, metallic tungsten film. The chemical evolution of the surface and formation of a complex intermediate tungsten species is characterized by X-ray diffraction, infrared spectroscopy, and X-ray photoelectron spectroscopy. Efficient metallic tungsten deposition is first characterized on a graphite substrate and then demonstrated on a functional carbon foam electrode. The resulting electrochemical performance of the modified electrode is interrogated with the canonical aqueous ferricyanide system. A tungsten-coated carbon foam electrode showed that both electrode resistance and overall electrochemical cell resistance were reduced by 50%, resulting in a concomitant decrease in redox peak separation from 1.902 V to 0.783 V. This process promises voltage efficiency gains in electrodes for energy storage technologies and demonstrates the viability of a new route to tungsten coating for technologies and industries where high conductivity and chemical stability are paramount.

Exploiting Zinc Dendrite Formation and Bromine Transport Properties to Build a Safer, More Reliable Zn-Br2 Battery

In order to address inefficiencies that exist in our electrical grid, low cost grid scale electrochemical energy storage (EES) systems, such as zinc bromine batteries, are being researched extensively. Zinc bromine batteries, however, have issues at both the anode and the cathode that affect the reliability of the cell as well as present hazardous conditions of operation. At the anode, current density localization from the inhomogeneity of the zinc surface leads to the formation of dendritic structures. These dendritic structures can grow to the point of touching the other electrode, causing shorting of the cell. At the cathode, bromine contamination into the electrolyte can lead to issues of bromine corrosion at the anode as well as safety concerns of corrosive, vapor phase bromine escaping from the system.Standard Zn-Br2 flow-cell designs alleviate these limitations with bromine-complexing agents to improve Br2(l) solubility, separation membranes to prevent crossover and shorting, and flowing electrolyte to remove bromine and to minimize dendrite formation. These approaches are implemented at the expense of cell resistance, performance efficiency, system size, and especially capital costs. However, if constructed properly, the cell design could be used to address the issues at the anode and cathode without the added cost and complexity of complexing agents, membranes, or flow systems. Here, we show a simple and scalable, low-cost, membrane-free, non-flowing single-chamber zinc-bromine (SC-Zn-Br2) secondary battery design that utilizes the physical properties of liquid bromine and a highly-porous carbon foam electrode, and also allows zinc dendrites to form freely. We demonstrate the local containment of Br2 in the carbon foam electrode, and discuss a color tracking and feedback monitoring scheme to actively control the reactive species transport and improve reliability.To take advantage of the density and low miscibility of Br2, an anodic carbon current collector is placed on top of the cell. During charging, metallic Zn gets plated onto the carbon cloth electrode, while Br2(l) is generated at a carbon foam cathode. If dendrites form and creep towards this carbon foam electrode (CFE), Zn(s) will react with Br2(l) on the surface of the foam and dissolve back into the electrolyte as Zn2+ and Br- ions. This spontaneous process can prevent short circuiting, as the Zn(s) + Br2(l) reaction occurs faster than zinc deposition at low charging currents. Thus, the Br2(l) loosely held on the CFE surface acts as a natural protection from shorting, and can be exploited for ‘self-maintenance’, removing the need for separation membranes or protective coatings.We also take advantage of the distinct colors of the ZnBr2(aq) electrolyte, Br2(l), and dissolved Br2(aq): clear, red, and yellow, respectively. By calibrating the solution color with Br2(l,aq) concentration, we can track the generation, consumption, and transport of bromine in real time to improve battery performance and prevent unwanted processes (i.e., crossover). In addition, we can use this color tracking technique to prevent bromine escape from the system and thus alleivate safety concerns of operating with voliltite bromine. To optimize performance, a feedback loop is written into the cycling control algorithm to stop the charge step at this point. This optical visualization, tracking, and in operando feedback technique has never been used for any bromine-based electrochemical cells, to the best of our knowledge.

Design and Optimization of Carbon Foam Electrode for Local Confinement of Bromine in Non-Flowing Single-Chamber Zinc Bromine Batteries

Zinc Bromine redox flow batteries are well studied, quite inexpensive, and have reasonably high power and energy densities. However, there has been limited commercial implementation of bromine bearing systems in general, and the Zn-Br2 systems in particular, due to the following premises: i) Br2(l), generated at the cathode during charging, can diffuse through the electrolyte and react with Zn deposited at the anode (crossover), leading to self-discharge; ii) Repeated electroplating and dissolution of zinc leads to dendrite formation, which can form a conductive bridge between the electrodes (shorting), and iii) Br2(l) has low miscibility in aqueous solutions (~2.8 vol%) and tends to stratify, resulting in non-uniform concentration distributions. Standard Zn-Br2 flow-cell designs alleviate these limitations with bromine-complexing agents to improve Br2(l) solubility, separation membranes to prevent crossover and shorting, and flowing electrolyte to remove bromine and to minimize dendrite formation. In the membrane-free, non-flowing single-chamber zinc-bromine (SC-Zn-Br2) battery design zinc dendrites are allowed to form freely and Br2(l) is allowed to stratify; expensive membranes, complexing agents, and pumps are eliminated; and yet overall energy efficiency is improved and cost is lowered. This is achieved by using a highly-porous carbon foam electrode (CFE) for local containment of Br2 generated during cycling, thus preventing crossover. Zinc dendrites are allowed to grow, but react with the highly corrosive Br2(l) on the surface of the CFE and dissolve back into the electrolyte as Zn2+ and Br-ions. This prevents shorting. Here, we discuss the design, composition, and fabrication of the CFE, and its effects on the performance of SC-Zn-Br2 battery. In particular, we demonstrate the optimization of CFE porosity through processing parameters to maximize the coulombic and energy efficiencies of the cell. We also introduce a color tracking and feedback monitoring scheme to actively control the active species (deep red Br2(l), yellow Br2(aq), and colorless ZnBr2 electrolyte) transport and prevent self-discharge. Finally, we demonstrate the effect of prolonged exposure to Br2(l) after multiple cycles on various CFE compositions using XPS analysis, and the potential degradation mechanisms. We show coulombic and energy efficiencies of 95% and 75%, respectively, for over 1000 cycles for SC-Zn-Br2 cells, with improvements possible with further optimization of the CFE.

Low Cost Membrane-Free Single Chamber Zinc Bromine Battery for Grid-Scale Electrochemical Energy Storage Applications

Climate change is a major global concern which can potentially be addressed by integrating renewable energy sources and low cost grid scale electrochemical energy storage (EES) systems. Most research efforts to improve energy storage have been directed to redox flow, lithium-ion and next generation sodium and multivalent batteries. The focus has been on incremental improvements in cost, and efficiency of electrode active materials and electrolytes. Most of these batteries still employ traditional cell designs with expensive passive components. Unfortunately, this approach results in the balance-of-plant costs far outweighing the cost of electrochemically active materials. Techno-economic analyses indicate that the cost of energy storage must be <$100/kWh and power cost <$600/kW. Commercially available EES systems today do not meet these targets. In addition, battery life and energy efficiencies must be over 10,000 cycles and 70%, respectively, to be a sustainable option. Based on these targets, a more holistic approach is needed when considering new energy storage system materials and designs. Here, we discuss the design and working principle of a membrane free, non-flowing single-chamber zinc-bromine (SC-Zn-Br2) battery that utilizes the physical properties of liquid bromine, a porous carbon foam electrode, and also allows zinc dendrites to form freely. With this design, we eliminate the need to use failure prone and expensive passive components such as membrane separators, bromine complexing agents, flow-rated hardware, and control software as employed in traditional Zn-Br2 redox flow batteries (RFB). The ultimate figure of merit for feasibility in grid-scale EES system is $/kWh over its lifetime (cycles) at a given energy efficiency, or levelized cost of energy stored (LCOES). We demonstrate an SC-Zn-Br2 system with a maximum specific capacity of 89 mAh/g and energy density >150 Wh/kg (normalized to the mass of ZnBr2 salt in the electrolyte) and cell cost of $94/kWh including passive components. We achieve coulombic and energy efficiencies of up to 95% and 75%, respectively, for over 1000 cycles. The LCOES of SC-Zn-Br2 is shown to be an order of magnitude better than Zn-Br2 and vanadium RFB, as well as grid-scale lead-acid batteries and Li-ion batteries.

Mixed Valence Niobium Oxides for High Power 3D Microbattery Applications

Research in microbatteries is stimulated by the need for miniature power sources for use in autonomous sensing, wireless communications, medical implants and other microscale devices (1-10 mm3).1, 2 In such applications wherein physical space is at premium, sufficiently small, yet powerful, energy storage devices are desired. Currently, either thin or thick film microbatteries are in common use; however, 2D geometries suffer from severe limitations in that they are unable to deliver both high power and high energy densities simultaneously. The requirement for high energy and power densities can be met using (1) high energy materials that are structurally and electronically suited for fast rate cycling (examples: b-TiO2, Nb2O5, α-MoO3…)3-5 and (2) 3D–structured electrodes which allow for the use of an increased amount of active material without affecting the power delivery.1, 2, 6-8 In the latter context, a variety of electrode architectures have been considered including various types of carbon foams.9-11 By virtue of its bicontinuous architecture and reasonably high electrical conductivity, a carbon foam electrode provides an effective conduit for the transport of electrons and an interconnected porosity for the percolation of the electrolyte throughout the electrode. As a result, an intimate contact can be maintained amongst the current collector (the carbon foam), the active material (deposited onto the carbon foam) and the electrolyte (flooding the voids) over a microscale length. This in turn ensures efficient utilization of the active material at the desired cycling rates. It should be noted, however, that practical applications require optimal porosity and void sizes to ensure an acceptable trade-off between power and energy densities. To this end, part of the research in microbatteries focuses on the development of suitable porous electrodes. This presentation highlights the fabrication of 3D microstructured electrodes using emulsion-templated carbon foams as scaffold for niobium oxide nanoparticles. As compared to commercially available carbon foams, they have higher specific surface areas and void sizes that are two orders of magnitude smaller.10-12The void size distribution, surface areas and electrical conductivity of the carbon foams can be fine-tuned by optimizing the synthesis conditions. A brief discussion will be presented in this regard. Niobium is known to form both stoichiometric and non-stoichiometric oxides. The mixed valency present in the nonstoichiometric oxides is associated with increased electrical conductivity.13 The semiconducting nature of these oxides makes them ideal candidates for high power applications. In this particular case, the carbon foam has been used for dual purposes: (1) to entrap the oxide nanoparticles and (b) to promote the reduction of part of the Nb5+ to Nb4+ at elevated temperatures: Nb2O5 + δC à NbO2.5-δ + δCO Two types of mixed valence oxides have been synthesized and investigated for potential applications in high power 3D microbatteries. Detailed discussions on the structures and electrochemical behaviors of the oxides will be offered in the presentation. Figure 1. (A) SEM of NbOx-coated carbon foam (B) CV of electrode in (A) 1. K. Edström, D. Brandell, T. Gustafsson and L. Nyholm, Electrochem. Soc. Interface, 2011, 20, 41-46. 2. J. W. Long, B. Dunn, D. R. Rolison and H. S. White, Chem. Rev., 2004, 104, 4463-4492. 3. V. Augustyn, J. Come, M. A. Lowe, J. W. Kim, P.-L. Taberna, S. H. Tolbert, H. D. Abruña, P. Simon and B. Dunn, Nat Mater, 2013, 12, 518-522. 4. M. Zukalová, M. Kalbáč, L. Kavan, I. Exnar and M. Graetzel, Chem. Mater., 2005, 17, 1248-1255. 5. T. Brezesinski, J. Wang, S. H. Tolbert and B. Dunn, Nat Mater, 2010, 9, 146-151. 6. M. Valvo, M. Roberts, G. Oltean, B. Sun, D. Rehnlund, D. Brandell, L. Nyholm, T. Gustafsson and k. Edstrom, Journal of Materials Chemistry A, 2013. 7. M. Roberts, P. Johns, J. Owen, D. Brandell, K. Edstrom, G. El Enany, C. Guery, D. Golodnitsky, M. Lacey, C. Lecoeur, H. Mazor, E. Peled, E. Perre, M. M. Shaijumon, P. Simon and P.-L. Taberna, J. Mater. Chem., 2011, 21, 9876-9890. 8. H. P. James, Z. Hui Gang, C. Jiung, V. B. Paul and P. K. William, Nat. Commun., 2013, 4, 1732-1732. 9. P. Johns, M. Roberts and J. Owen, J. Mater. Chem., 2011, 21, 10153-10159. 10. H. D. Asfaw, M. Roberts, R. Younesi and K. Edstrom, Journal of Materials Chemistry A, 2013, 1, 13750-13758. 11. H. D. Asfaw, M. R. Roberts, C.-W. Tai, R. Younesi, M. Valvo, L. Nyholm and K. Edstrom, Nanoscale, 2014, 6, 8804-8813. 12. D. Wang, N. L. Smith and P. M. Budd, Polym. Int., 2005, 54, 297-303. 13. O. G. D’yachenko, S. Y. Istomin, A. M. Abakumov and E. V. Antipov, Inorg. Mater., 36, 247-259. Figure 1

Electrocatalytic Hydrogen Evolution from Molybdenum Sulfide-Polymer Composite Films on Carbon Electrodes.

The design of more efficient catalytic electrodes remains an important objective for the development of water splitting electrolyzers. In this context a structured composite cathode material has been synthesized by electrodeposition of molybdenum sulfide (MoSx) into a poly(pyrrole-alkylammonium) matrix, previously coated onto carbon electrodes by oxidative electropolymerization of a pyrrole-alkylammonium monomer. The composite material showed an efficient electrocatalytic activity toward proton reduction and the hydrogen evolution reaction (HER). Data from Tafel plots have demonstrated that the electron transfer rate in the composite films is fast, in agreement with the high catalytic activity of this cathode material. Bulk electrolysis of acidic water at carbon foam electrodes modified with the composite have shown that the cathodes display a high catalytic activity and a reasonable operational stability, largely exceeding that of regular amorphous MoSx electrodeposited on naked carbon foam. The enhanced catalytic performances of the composite electrode material were attributed to the structuration of the composite, which led to a homogeneous distribution of the catalyst on the carbon foam network, as shown by SEM characterizations.

IRON ELECTROCOAGULATION WITH ENHANCED CATHODIC REDUCTION FOR THE REMOVAL OF AQUEOUS CONTAMINANT MIXTURES

This study presents enhanced reduction of soluble contaminants in a modified electrocoagulation process that is capable of treating a mixture of aqueous contaminants. By incorporating an iron foam cathode, the process can remove aqueous trichloroethylene (TCE) by 99.1% and nitrate ions by 98.2%, which represents 58.1 and 20 percent higher than the removal rates achieved by iron plate cathode, respectively. pH and ORP measurements indicate the development of a reducing electrolyte condition due to the ferrous generation from an iron anode, which facilitates the reduction of soluble contaminants because the competition from O2 reduction is eliminated in the system. Both iron foam and vitreous carbon foam electrodes are compatible with polarity reversal, without any deterioration in the efficiency of electroreduction of TCE and nitrate. The modified iron electrolysis process demonstrates versatility for the treatment of mixtures of contaminants, including a binary mixture of TCE and dichromate, a mixture of selenate and nitrate and a mixture of phosphate and nitrate. The ferrous species generated from the iron anode can reduce and (or) co-precipitate certain aqueous contaminants such as dichromate, selenate and phosphate, while the cathodic process can directly reduce contaminants like TCE and nitrate. Compared with the conventional electrocoagulation system that consists of two planar electrodes, the proposed process is not only more effective, but also suitable for the development of integrated and versatile process for the treatment of co-contaminated wastewater or groundwater.

Effect of mesocelluar carbon foam electrode material on performance of vanadium redox flow battery

Languid reaction rate of VO2+/VO2+ redox couple is a problem to solve for improving performance of vanadium redox flow battery (VRFB). To facilitate the slow reaction materials including large pore sized mesocellular carbon foam (MSU-F-C and Pt/MSU-F-C) are used as new catalyst. Their catalytic activity and reaction reversibility are estimated and compared with other catalysts, while cycle tests of charge–discharge and polarization curve tests are implemented to evaluate energy efficiency (EE) and maximum power density (MPD). Their crystal structure, specific surface area and catalyst morphology are measured by XRD, BET and TEM. The new catalysts indicate high peak current ratio, small peak potential difference and high electron transfer rate constant, proving that their catalytic activity and reaction reversibility are superior. Regarding the charge–discharge and polarization curve tests, the VRFB single cells including new catalysts show high EE as well as low overpotential and internal resistance and high MPD. Such excellent results are due to mostly unique characteristics of MSU-F-C having large interconnected mesopores, high surface area and large contents of hydroxyl groups that serve as active sites for VO2+/VO2+ redox reaction and platinums (Pts) supporting the MSU-F-C. Indeed, employment of the catalysts including MSU-F-C leads to enhancement in performance of VRFB by facilitating the slow VO2+/VO2+ redox reaction.

Deposition of boron doped diamond and carbon nanomaterials on graphite foam electrodes

Abstract Boron doped diamond (BDD) has remarkable physical and chemical properties, that makes it an attractive material for electrochemical applications. In this study, deposition process of BDD on porous carbon foam electrodes was performed by HFCVD method. After depositions, the substrates were not homogenously covered by the BDD thin film only. Depending on the deposition temperature, foam porosity and distance from heated filaments, different carbon nanomaterials were synthesized. The boron doped diamond, graphite nanosheets, carbon nanowalls and its composites occurred on the foams outer and inner surfaces. Two new observed types of carbon structures, the carbon nanowalls – boron doped diamond composite and graphite nanotips are analyzed and described. Analyses were made by SEM and Raman spectroscopy. The influence of deposition conditions on the growth process is discussed.

Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries: a study of structure and electrochemical performance.

In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sol-gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4 nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm(-2) at 0.1 mA cm(-2) (lowest rate) and 1.1 mA h cm(-2) at 6 mA cm(-2) (highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.

1.5 V battery driven reduced graphene oxide–silver nanostructure coated carbon foam (rGO–Ag–CF) for the purification of drinking water

A porous carbon foam (CF) electrode modified with a reduced graphene oxide–Ag (rGO–Ag) nanocomposite has been fabricated to purify water. It can perform as an antibacterial device by killing pathogenic microbes with the aid of a 1.5 V battery, with very little power consumption. The device is recycled ten times with good performance for long term usage. It is shown that the device may be implemented as a fast water purifier to deactivate the pathogens in drinking water.

Up-Scaled Microfluidic Fuel Cells With Porous Flow-Through Electrodes

In this work, an experimental microfluidic fuel cell is presented with a novel up-scaled porous electrode architecture that provides higher available surface area compared to conventional microfluidic fuel cells, providing the potential for higher overall power outputs. Our proof-of-concept architecture is an up-scaled flow-through fuel cell with more than nine times the active electrode surface area of the flow-through architecture first proposed by Kjeang et al. (2008, “A Microfluidic Fuel Cell With Flow-Through Porous Electrodes,” J. Am. Chem. Soc., 130, pp. 4000–4006). Formic acid and potassium permanganate were employed as the fuel and oxidant, respectively, both dissolved in a sulfuric acid electrolyte. Platinum black was employed as the catalyst for both anode and cathode, and the performances of carbon-based porous electrodes including cloth, fiber, and foam were compared to that of traditional Toray carbon paper (TGP-H-120). The effects of catalyst loading were investigated in a microfluidic fuel cell containing 80 pores per linear inch carbon foam electrodes. A discussion is also provided of current density normalization techniques via projected electrode surface area and electrode volume, the latter of which is a highly informative means for comparing flow-through architectures.

Characterization of a microbial fuel cell with reticulated carbon foam electrodes

A microbial fuel cell with open-pore reticulated vitreous carbon electrodes is studied to assess the suitability of this material in a batch mode, in the perspective of flow-through reactors for wastewater treatment with electricity generation. The cell shows good stability and fair robustness in regards to substrate cycles. A power density of 40W/m3 is reached. The cell efficiency is mainly limited by cathodic transfers, representing 85% of the global overpotential in open circuit. Through impedance spectrocopy, equivalent circuit modeling reveals the complex nature of the bioelectrochemical phenomena. The global electrical behavior of the cell seems to result in the addition of three anodic and two cathodic distinct phenomena. On the cathode side, the Warburg element in the model is related to the diffusion of oxygen. Warburg resistance and time are respectively 2.99kΩcm2 and 16.4s, similar to those published elsewhere.

Temperature‐Triggered Capture of Dispersed Particles Using a Laponite‐Poly(NIPAM) Temperature‐Responsive Surface

In this study a new method is investigated that enables a conductive surface to be modified so as to capture dispersed particles when the temperature is increased. Poly(NIPAM) (NIPAM is N‐isopropylacrylamide) was grafted from electrodeposited Laponite RD particles using surface‐initiated atom transfer radical polymerization (ATRP) to give a temperature‐responsive surface. This was used to capture dispersed polystyrene particles. In the first part of the study the conditions used to electrodeposit Laponite onto a carbon foam electrode were determined. The ability of the temperature‐responsive surface to capture dispersed polystyrene particles was investigated between 20 and 50°C. Temperature‐triggered particle capture was reversible or irreversible depending on the conditions used during ATRP. A high surface concentration of poly(NIPAM) on the particle electrodes is believed to increase the extent of polystyrene particle capture and also reversibility. A theoretical analysis in terms of interaction energy–distance curves is presented for the capture behavior. It is concluded that the temperature‐responsive surface has both electrostatic and steric contributions to the total interaction energy. The steric component (which originates from poly(NIPAM)) is temperature‐dependent and provides the basis for temperature‐triggered particle capture.