Study Of Fe³⁺/Fe²⁺ Electrolyte And Electrode Materials In Redox Battery

ABSTRACT:With the development of green energy, it is urgent to make full use of alternative energy such as water and wind energy. Due to the intermittence of these energy in time and space, it is of essential importance to realize their conversion and storage. Among various energy storage techniques, including physical and chemical approaches, redox flow batteries are of particular interest, thanks to their unique advantages like short starting time, adjustable storage capacity and fewer restrictions in region and time. So far, extensive efforts have been devoted to the researches on all-vanadium redox flow battery, zinc-cerium flow battery, zinc-bromine flow battery and so on. Regardless of their individual advantages, it is far from their large-scale applications in real industry.In this thesis, zinc-iron battery, as a novel redox flow battery, has been studied. Its electrochemical performances have been systematically investigated using aqueous FeSO4solution as the electrolyte and graphite felt as well as fabricated carbon-composite electrode as cathode materials. By means of cyclic voltammetry, electrochemical impedance spectra and dischargearge tests, the results show that1.00mol/L FeSO4is stable in0.50mol/L H2SO4, and that the redox between Fe(Ⅲ) and Fe(Ⅱ) is a quasi-reversible reaction. Specifically, the peak current achieves the highest in the electrolyte consisted of1.00mol/L FeSO4and0.50mol/L H2SO4. Meanwhile, it exhibits small electrochemical impedance with excellent dynamic performances. With zinc as the counter electrode, the dischargearge tests indicate that the standard voltage of the as-fabricated battery is higher than that of all-vanadium redox flow battery, which possesses good cycling stability up to110times. Moreover, it has high performance cost ratio and environmental friendliness. Hence, the as-proposed redox is a favorable redox couple.The graphite felt was first treated at450℃for2h, followed by acid treatment for another2h. Under the same potential, the as-treated electrode exhibited higher current density by4mA and smaller impedance by3Ω than those of the electrode without such treatments. With zinc as the counter electrode, the battery with as-treated electrode charged at1.60-1.80V and discharged at0.90-1.12V. As a result, graphite felt can be used as the cathode material for the zinc-iron battery with FeSO4as electrolyte. The thermal and acidic treatments are beneficial to enhance the electrochemical performances of the graphite felt.The redox reaction of carbon electrode is quasi-reversible reaction. Its electrochemical impedance is about3.154Ω·cm2. During dischargearge tests, the Coulombic efficiency was about78%and75%at the current density of20and30mA/cm, respectively. When the current density was higher than40mA/cm2, the Coulombic efficiency became extremely unstable.