Akaganeite (β-FeOOH) and hybrid active materials (akaganeite/maghemite (γ-Fe2O3)) containing carbon nanoparticles have been successfully developed through hydrothermal process using oxidation debris of graphene oxide and iron (II) chloride tetrahydrate. The obtained akaganeite sample and the hybrid material containing 29% akaganeite and 71% maghemite were confirmed using Mӧssbauer analysis. Two types of cathode made of akaganeite (β-FeOOH) and hybrid active materials supported on reduced graphene oxide (RGO) for RGO/AKA-100 and RGO/AKA-29 were taken as the main air electrode. The full-cell zinc–air battery prototypes (with 6 M KOH electrolyte) were tested for 500 cycles at room temperature. The result showed that the discharge capacity was achieved as high as 131.05 mAh/cm2 for RGO/AKA-100 and 137.26 mAh/ cm2 for RGO/AKA-29. These performances are better than that using zinc–air batteries with carbon black/MnO2 (CB/ MnO2) as air cathode, that give a discharge capacity of 115.7 mAh/cm2. The charge–discharge efficiency of RGO/AKA-100 and RGO/AKA-29 was examined in relation to their distinct catalytic activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) when incorporated into electrochemically rechargeable zinc–air batteries. In addition, the different morphology of zinc deposit and dendrite was characterized using SEM, TEM, and PXRD analysis. From this study, the high performance of active material was suggested to be due to the hybrid effect among akaganeite, maghemite, and reduced graphene oxide, which can produce a synergetic improvement.

Bifunctional active materials based on akaganeite (β-FeOOH) and maghemite (γ-Fe2O3) containing carbon nanoparticles: capacity improvement of rechargeable zinc–air batteries
    Abstract
    1 Introduction
    2 Experimental methods
        2.1 Materials
        2.2 Synthesis of reduced graphene oxide
        2.3 Synthesis of akaganeite (β-FeOOH) and hybrid (akaganeitemaghemite (γ-Fe2O3)) materials
        2.4 Synthesis of manganese dioxide (δ-MnO2)
        2.5 Material characterization
        2.6 Electrochemical measurement
    3 Results and discussion
        3.1 Characterization of reduced graphene oxide (RGO), akaganeite, and hybrid active materials
        3.2 Performance of akaganeite and its hybrid containing carbon nanoparticles as active material
    4 Conclusion
    Acknowledgements 
    References

• Bangun Satrio Nugroho(Research Center for Chemistry, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia) Corresponding author
• Muhammad Bagus Arif(Research Center for Chemistry, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Muhammad Ghozali(Research Center for Chemistry, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Sun Theo Constan Lotebulo Ndruru(Research Center for Chemistry, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Mahardika F. Rois(Research Center for Advanced Material, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Fadli Rohman(Research Center for Advanced Material, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Sudaryanto Sudaryanto(Research Center for Advanced Material, National Research and Innovation Agency (BRIN), Republik Indonesia, Kawasan Sains Dan Teknologi (K.S.T) B. J. Habibie, Tangerang Selatan 15311, Indonesia)
• Satoru Nakashima(Natural Science Center for Basic Research and Development, Hiroshima University, 1‑4‑2 Kagamiyama, Higashi‑Hiroshima 739‑8526, Japan)