Design of high-performance proton batteries by reducing interstitial water molecules in copper-iron Prussian...

Prussian blue analogues (PBAs) are considered to be a potentially beneficial cathode material in proton batteries. Among them, Cu,Fe based-Turnbull's blue analogue (CuFe-TBA) stands out in proton batteries because of its unique crystal structure and continuous hydrogen bond lattice network, which promotes the Grotthuss mechanism and enhances the reaction kinetics of proton conduction. However, in the process of preparing CuFe-TBA by co-precipitation method, the crystal water content of the product cannot be controlled, and excessive lattice water will affect the cycle stability. To solve these problems, we employ a chemical inhibition strategy using polyvinylpyrrolidone (PVP) to regulate the nucleation and crystal growth rate of CuFe-TBA. This strategy effectively reduces the crystalline water content, thereby ensuring that the PBAs remain electrically conductive while maintaining their electrochemical stability and safety over the operating voltage range. The appropriate amount of PVP modified CuFe-TBA (CuFe-TBA-PVP-3) has the characteristics of large specific surface area and moderate crystal water and has high discharge specific capacity and long cycle stability. CuFe-TBA-PVP-3 shows the high specific capacity of 80.9mAh g^-1 at a current density of 0.1 A g^-1, demonstrating exceptional charge/discharge specific capacity. Furthermore, the capacity retention rate is 91.23 % at 5 A g^-1 after 50,000 cycles. Therefore, CuFe-TBA-PVP-3 provides new insights and directions for the development of next-generation aqueous proton batteries.