Zinc-air flow batteries exhibit high energy density and offer several appealing advantages. However, their low efficiency of zinc utilization resulted from passivation and corrosion of the zinc anodes has limited their broad application. In this work, ethanol, which is considered as an environmentally friendly solvent, is examined as an electrolyte additive to potassium hydroxide (KOH) aqueous electrolyte to improve electrochemical performance of the batteries. Besides, the effects of adding different percentages of ethanol (0-50% v/v) to 8 M KOH aqueous electrolyte were investigated and discussed. Cyclic voltammograms revealed that the presence of 5-10% v/v ethanol is attributed to the enhancement of zinc dissolution and the hindrance of zinc anode passivation. Also, potentiodynamic polarization and electrochemical impedance spectroscopy confirmed that adding 5-10% v/v ethanol could effectively suppress the formation of passivating layers on the active surface of the zinc anodes. Though the addition of ethanol increased solution resistance and hence slightly decreased the discharge potential of the batteries, a significant enhancement of discharge capacity and energy density could be sought. Also, galvanostatic discharge results indicated that the battery using 10% v/v ethanol electrolyte exhibited the highest electrochemical performance with 30% increase in discharge capacity and 16% increase in specific energy over that of KOH electrolyte without ethanol.
Manganese oxide (MnO2) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO2) allows reversible insertion/extraction of Zn2+ ions and exhibits high storage capacity of Zn2+ ions. However, a poor conductivity of δ-MnO2, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO2 with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO2 nanoflowers and MNG were synthesized and examined using X-ray diffraction, electron spectroscopy, and electrochemical techniques. Also, performances of the batteries with the pristine δ-MnO2 nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn2+ ions with diffusion scheme and pseudocapacitive behavior. The battery using MNG cathode exhibited a high initial discharge capacity of 235 mAh/g at 200 mA/g specific current density compared to 130 mAh/g which is displayed by the pristine δ-MnO2 cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO2. The results obtained pave the way for improving the electrical conductivity of MnO2 by using graphite flake support. The graphite flake support significantly improved performances of ZIBs and made them attractive for use in a wide variety of energy applications.
Zinc-air batteries (ZABs) offer high specific energy and low-cost production. However, rechargeable ZABs suffer from a limited cycle life. This paper reports that potassium persulfate (KPS) additive in an alkaline electrolyte can effectively enhance the performance and electrochemical characteristics of rechargeable zinc-air flow batteries (ZAFBs). Introducing redox additives into electrolytes is an effective approach to promote battery performance. With the addition of 450 ppm KPS, remarkable improvement in anodic currents corresponding to zinc (Zn) dissolution and limited passivation of the Zn surface is observed, thus indicating its strong effect on the redox reaction of Zn. Besides, the addition of 450 ppm KPS reduces the corrosion rate of Zn, enhances surface reactions and decreases the solution resistance. However, excess KPS (900 and 1350 ppm) has a negative effect on rechargeable ZAFBs, which leads to a shorter cycle life and poor cyclability. The rechargeable ZAFB, using 450 ppm KPS, exhibits a highly stable charge/discharge voltage for 800 cycles. Overall, KPS demonstrates great promise for the enhancement of the charge/discharge performance of rechargeable ZABs.
Zinc-air batteries are a promising technology for large-scale electricity storage. However, their practical deployment has been hindered by some issues related to corrosion and passivation of the zinc anode in an alkaline electrolyte. In this work, anionic surfactant sodium dodecyl sulfate (SDS) and nonionic surfactant Pluronic F-127 (P127) are examined their applicability to enhance the battery performances. Pristine zinc granules in 7 M KOH, pristine zinc granules in 0-8 mM SDS/7 M KOH, pristine zinc granules in 0-1000 ppm P127/7 M KOH, and SDS coated zinc granules in 7 M KOH were examined. Cyclic voltammograms, potentiodynamic polarization, and electrochemical impedance spectroscopy confirmed that using 0.2 mM SDS or 100 ppm P127 effectively suppressed the anode corrosion and passivation. Nevertheless, direct coating SDS on the zinc anode showed adverse effects because the thick layer of SDS coating acted as a passivating film and blocked the removal of the anode oxidation product from the zinc surface. Furthermore, the performances of the zinc-air flow batteries were studied. Galvanostatic discharge results indicated that the improvement of discharge capacity and energy density could be sought by the introduction of the surfactants to the KOH electrolyte. The enhancement of specific discharge capacity for 30% and 24% was observed in the electrolyte containing 100 ppm P127 and 0.2 mM SDS, respectively.
Identifying highly stable, cost-effective, platinum-free, and efficient electrocatalysts for the oxygen reduction reaction (ORR) remains a formidable challenge. The ORR is important for advancing fuel cell and zinc-air battery (ZAB) technologies towards cost-efficiency and environmental sustainability. This work presents the utilization of economically viable materials through a straightforward synthesis process, exhibiting the development of efficient Mo2C/Fe3C-NC catalysts ingeniously derived from phosphomolybdic acid (PMA) and iron phthalocyanine (FePc). The results demonstrate that the optimized Mo2C/Fe3C-NC3 catalysts exhibit remarkable electrochemical performance, evidenced by an impressive onset potential of ∼1.0 V versus RHE, a half-wave potential of 0.89 V, and a superior current density of about 6.2 mA cm-2. As for their performance in ZABs, the optimized catalysts reach a peak power density of 142 mW cm-2 at a current density of 200 mA cm-2. This synergy, coupled with the uniform distribution of Mo2C and Fe3C nanoparticles, greatly enhances the active catalytic sites and promotes electrolyte diffusion. Our approach diverges from traditional methods by employing an in situ self-assembled heterostructure of Mo2C/Fe3C on nitrogen-doped carbon tubes, avoiding the conventional high-temperature hydrogen gas reduction process. Beyond serving as feasible alternatives to commercially available Pt/C catalysts, these materials hold promise for large-scale production owing to their affordability and the simplicity of the synthesis technique. Such a breakthrough paves the way towards the realization of sustainable energy technologies and lays the groundwork for further exploration into amplifying the scalability and efficiency of ORR catalysts.