Hydroxylation strategy unlocking multi-redox reaction of manganese hexacyanoferrate for aqueous zinc-ion battery

Prussian blue analogues (PBAs), as one of the most promising cathodes due to their open framework and high working voltage (similar to 1.75 V vs Zn/Zn-2+) for rechargeable aqueous zinc ion batteries (RAZIBs), commonly suffer from poor reversible capacity owing to single redox center. Here, a hydroxylation strategy is proposed for activating inactive redox pair of Mn(II)/Mn(III) in manganese hexacyanoferrate (MnHCF) to supply extra capacity. As a result, OH - rich MnHCF cathode renders a high discharge capacity of 136.1 mAh/g (at 100 mA g(-1)) and a considerable energy density of 228.8 Wh kg(-1) benefiting from the unlocked multi-redox reaction, which is much better than the OH - poor MnHCF (58.3 mAh/g and 52.6 Wh kg(-1), respectively). Furthermore, the abundant hydroxyl in OH-rich MnHCF can continuously activate the multi-redox centers to provide high capacity in the subsequent cycles. Density functional theory (DFT) calculation reveals that abundant hydroxyl functional group favors to capture Zn2+ on the sites near Mn atoms, thereby facilitating the activation of Mn-redox reaction. This study offers new opportunities for exploiting cathodes with both high working voltage and discharge capacity for RAZIBs.

Automated summary

A hydroxylation strategy is proposed to activate the inactive redox pair of Mn(II)/Mn(III) in manganese hexacyanoferrate (MnHCF), which significantly improves the discharge capacity and energy density of the cathode, offering new opportunities for cathodes with high working voltage and discharge capacity for rechargeable aqueous zinc ion batteries (RAZIBs).