Nickel-iron and iron-air batteries are attractive for large-scale-electrical-energy storage because iron is abundant, low-cost and non-toxic. However, these batteries suffer from poor charge acceptance due to hydrogen evolution during charging. In this study, we have demonstrated iron electrodes prepared from carbonyl iron powder (CIP) that are capable of delivering a specific discharge capacity of about 400 mAh g −1 at a current density of 100 mA g −1 with a faradaic efficiency of about 80%. The specific capacity of the electrodes increases gradually during formation cycles and reaches a maximum in the 180 th cycle. The slow increase in the specific capacity is attributed to the low surface area and limited porosity of the pristine CIP. Evolution of charge potential profiles is investigated to understand the extent of charge acceptance during formation cycles. In situ XRD pattern for the electrodes subsequent to 300 charge/discharge cycles confirms the presence of Fe with Fe(OH) 2 as dominant phase.
Beneficial effects of carbon grafting into the iron active material for rechargeable alkaline-iron-electrodes with and without Bi 2 S 3 additive is probed by in situ X-ray diffraction in conjunction with Extended X-ray Absorption Fine Structure (EXAFS) and electrochemistry. EXAFS data unravel that the composition of pristine active material (PAM) for iron electrodes comprises 87% of magnetite and 13% of α-iron while carbon-grafted active material comprises 60% of magnetite and 40% of α-iron. In situ XRD patterns are recorded using a specially designed electrochemical cell. XRD data reflect that magnetite present in PAM iron electrode, without bismuth sulfide additive, is not reduced during charging while PAM iron electrode with bismuth sulfide additive is partially reduced to α-Fe/Fe(OH) 2 . Interestingly, carbon-grafted-iron electrodes with bismuth sulfide exhibit complete conversion of active material to α-Fe/Fe(OH) 2 . The ameliorating effect of carbon grafting is substantiated by kinetic parameters obtained from steady-state potentiostatic polarization and Tafel plots. The mechanism for iron-electrode charge -discharge reactions are discussed in the light of the potential -pH diagrams for Fe -H 2 O, S -H 2 O and FeS ads -H 2 O systems and it is surmised that carbon grafting into iron active material promotes its electrochemical utilization.
Iron-based alkaline rechargeable batteries are promising candidates for large-scale energy storage applications owing to their low cost, robustness and environmental-friendliness. However, the widespread deployment of iron-based batteries has been limited by the low charging efficiency and poor discharge rate capability of the iron electrode. Our previous efforts on iron electrodes based on carbonyl iron powder and iron (II) sulfide have shown promise in overcoming these limitations. With the goal of understanding the role of sulfide additives, in this study, we have compared the performance of iron electrodes with iron (II) sulfide, iron (II) disulfide, copper (I) sulfide and zinc sulfide. The electrode containing zinc sulfide outperformed all other electrodes with a remarkable faradaic efficiency of 95% at C/2 rate and a specific discharge capacity close to 0.24 Ah g−1 at 1 C rate. The electrode did not lose any capacity for 750 cycles of repeated deep discharge at C/2 charge and discharge rates. Further, these electrodes could be cycled at 55 degrees Celsius with no noticeable change in performance. We attributed the excellent performance of zinc sulfide containing electrode to the low solubility of zinc sulfide in the electrolyte and the stability of zinc sulfide towards electro-reduction under the operating conditions of the iron electrode. These insights indicate that zinc sulfide is a promising additive for designing highly efficient and robust iron electrodes for alkaline nickel-iron and iron-air batteries.
The use of three-dimensional porous nickel foam as the current collector of the nickel hydroxide electrode adds significantly to the cost of the nickel-based alkaline rechargeable batteries. Although iron is considerably less expensive than nickel, iron corrodes at the operating potential of the nickel hydroxide electrode. We have found that a 70–100 nm thick thermal coating of cobalt ferrite spinel protects the iron from corrosion. Such a coated iron substrate was found to be stable against corrosion even when polarized anodically at 10 mA cm−2 in 30% potassium hydroxide electrolyte for 1000 h. While the thermal coating of cobalt ferrite protected iron against corrosion, incorporation of lithium ions into the coating was found to enhance the electrical conductivity of the coating. XPS and EXAFS studies confirmed that the enhanced conductivity resulted from an increase in the population of Co3+ in the ferrite spinel lattice. An inexpensive iron (steel) substrate protected by such a coating when used as a nickel hydroxide battery electrode exhibited a specific capacity of 0.25 Ah g−1 at C/5 discharge rate, comparable to a nickel hydroxide electrode based on a relatively expensive nickel foam substrate. The steel-based electrode also exhibited no noticeable degradation over 150 cycles at C/2 rate. This demonstration of a robust and economical steel substrate presents a unique opportunity for reducing the cost of the nickel hydroxide battery electrode in alkaline batteries.
The nickel-iron battery is particularly attractive for large-scale energy storage because of its relatively low cost and extreme robustness. The application of this battery can be expanded substantially if sealed cells can be constructed. To achieve a sealed cell, the oxygen and hydrogen produced in the cell during charge must be recombined. Consequently, understanding the process of oxygen recombination is of immense interest. In this study, we have focused on the kinetics of oxygen reduction on the charged iron electrode. Results of rotating disk electrode experiments demonstrate that the oxygen recombination on the iron electrode is a mass-transport-limited process involving a four-electron reduction process. On the iron battery electrode, the recombination reaction is an electrochemical process accompanied by the electro-oxidation of iron. We have measured the rate of the oxygen recombination from the decrease in the discharge capacity and also by measuring the steady-state current under potentiostatic conditions. A recombination rate as high as C/16 can be observed for iron electrodes in the "semi-flooded" configuration. The products of the recombination reaction are found to be electrochemically rechargeable. While the semi-flooded configuration allows for a high recombination rate, the utilization of the electrode is impacted by poor electrolyte distribution.
In the present study, cost-intensive Ni electrode is replaced by high surface-area activated carbon (AC) cathode and the possibility of the Fe anode, used in Ni-Fe battery, to function as Fe-C hybrid capacitor has been examined. The electrochemical properties of Fe-C hybrid capacitor assembly are studied using cyclic voltammetry (CV) and galvanostatic charge-discharge cycles. Over 100 galvanostatic charge-discharge cycles for Fe-C hybrid capacitor are carried out and a maximum capacitance of 24 F g -1 is observed.
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.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.