Techniques for interpreting electrochemical impedance spectroscopy of different flowing slurry electrodes configurations are presented based upon models developed for macrohomogeneous porous electrodes. These models are discussed with regards to three different slurry systems; particles in deionized water, in supporting electrolyte without redox active species (akin to electrochemical flow capacitors), and in electrolytes supporting aqueous redox couples (akin to redox flow batteries). Through investigating each of these systems, the individual properties of a slurry can be determined. It was found that traditional overpotential descriptions, (ohmic, activation, and mass transfer) were insufficient to fully describe the impedance and polarization of the slurry electrodes. An overpotential due to the distributed current distribution in the slurry electrode was considered in the frequency range of activation overpotentials that depends on the exchange current density and the ratio of the electronic and ionic conductivities. In slurry electrodes made with multi-wall carbon nanotube particles supporting the ferric/ferrous redox couple, the distributed overpotential was found to be about the same order of magnitude as the activation overpotential and the total voltaic efficiency was over 80% at 200 mA/cm 2 .
The all-Iron flow battery utilizes the iron II/III redox couple at the positive electrode and the iron II/0 reaction at the negative electrode. The standard reduction potential of the iron II/0 reaction is at −0.44 V vs. NHE, suggesting that hydrogen evolution could be a significant factor in coulombic losses on the negative electrode. Methods of increasing the coulombic efficiency of iron plating are considered, such as anion concentration and electrolyte additives. The use of a chloride anion containing electrolyte showed less hydrogen evolution rates and faster plating kinetics than an electrolyte containing the same concentration of sulfate anions. Increasing the chloride concentration significantly reduced the hydrogen evolution observed on an iron electrode, and plating efficiencies of 97% were demonstrated on a rotating rod electrode. The effect of complexing ligands on plating and hydrogen evolution was also investigated.As renewable energy sources increasingly become a part of the grid, the need for large scale energy storage grows alongside. 1,2 One such storage technology is the redox flow battery (RFB), typically involving redox couples dissolved in an externally stored electrolyte. [3][4][5] Traditional redox flow batteries, such as the all-vanadium 6 and ironchromium 7 chemistries use redox couples as both the anode and cathode, and the electrolyte is pumped through a battery stack, where the electrochemical reactions occur, decoupling the energy and power of the battery. The amount of energy storage is solely based on the reservoir of electrolyte, and the power delivery is determined by the size of the battery stack, making scale up of redox flow batteries convenient. The all-iron flow battery utilizes the Fe II/III redox reaction at its positive electrode, and the negative reaction involves the plating and stripping of iron. 8,9 The plating reaction occurs in the stack, so the energy and power of the battery are no longer decoupled: the energy storage density is dependent on the plated iron.The standard reduction potential of the iron II/0 reaction is −0.44 V vs. NHE, well negative of the thermodynamic potential for hydrogen evolution. As such, the coulombic efficiency of iron plating will depend on the pH of the electrolyte, as well as the pH at the electrode surface. 10,11 Increasing the pH of the electrolyte will shift the equilibrium potential for hydrogen evolution more negative and decrease the diffusion limited current. 10 However, Fe 2+ will precipitate as a hydroxide species before the pH is sufficiently high to completely avoid hydrogen evolution in the potential range for iron plating. If the hydrogen evolution current is large enough, bubbles can cling to the electrode surface and cause the deposit to form around the bubble. 12 Corrosion researchers have investigated the effect of anions on the kinetics of iron corrosion. 13,14 The presence of specifically adsorbed halide ions was found to alter the mechanism by which iron corrodes. 13 The concentration of halide ions in electrolyte wa...
The ability of an electrochemical hydrogen pump cell employing a polybenzimidazole membrane imbibed with phosphoric acid to purify hydrogen rich streams has been investigated. It has been found that pure hydrogen can be produced from diluted hydrogen and from typical reformate feeds with less than 5 kW-hrs required per kilogram of hydrogen pumped. The performance of these cells does not degrade under pure hydrogen over 24 hours for current densities up to 0.4 A/cm2. However, in less than 10 hours, the polarization effects had increased by 10% under pure hydrogen at 1.0 A/cm2 and by 50% under reformate at 0.2 A/cm2. However, the performance degradation caused by the presence of CO was observed to be reversible by switching the cell polarization and flows.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.