A Voltage-Enhanced, Low-Cost Aqueous Iron− Air Battery Enabled with a Mediator-Ion Solid Electrolyte Xingwen Yu and Arumugam Manthiram* Materials Science and Engineering Program and Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States S Supporting Information *
ABSTRACT: A new type of aqueous iron−air (Fe−air) battery is demonstrated with an alkaline anode electrolyte (anolyte) and an acidic cathode electrolyte (catholyte). The anolyte and catholyte are separated by an alkali-metal-ion (Li+-ion or Na+-ion) solid-electrolyte separator in which the alkali metal ion serves as an ionic mediator to sustain the redox reactions at the anode and cathode. Coupling the acidic air cathode with the alkaline iron anode demonstrates a voltage-enhanced Fe−air battery. To reduce the cell overpotential, the Fe−air battery is operated with decoupled bifunctional air cathodes comprising an IrO2/ Ti (iridium oxide on titanium mesh) electrode for the oxygen evolution reaction and a Pt/C (carbon-supported platinum) electrode for the oxygen reduction reaction.
O2 + 2H 2O + 4e− ↔ 4OH−
fficient utilization and strategic accommodation of the intrinsic variability of the energy supply from renewable resources (e.g., solar and wind) require the development of large-scale energy storage systems with low-cost and earthabundant materials.1−5 In this regard, metal−air batteries have been attracting great attention.6,7 Among the various metal−air battery systems, aqueous zinc−air (Zn−air) batteries and nonaqueous lithium−air (Li−air) batteries are in the forefront. Although the Li−air system exhibits high operating voltage and high intrinsic electrochemical capacity, the nonaqueous Zn−air system is more practical at the current stage because of the relatively safe, low-cost, and reliable nature of the zinc−air chemistry and technology.8−10 As a common material, iron is the fourth most abundant element in the earth’s crust. Therefore, as far as the material cost and abundance are concerned, iron-anode-based air batteries (Fe−air) can offer more beneficial features than Zn−air batteries toward reducing cost.11−13 The Fe−air battery has been known since the 1970s and has been considered as a low-cost, environmentally benign electrochemical energy-storage system.14,15 The Fe−air batteries are generally operated under alkaline conditions with a theoretical voltage of 1.28 V based on the alkaline iron anode chemistry and the alkaline oxygen cathode chemistry in accordance with eqs 1 and 2. Because of the anode and cathode overpotentials during cell operation, the practical voltage of alkaline Fe−air batteries is even lower (
