Continuous hydrogen-bond networks in Prussian blue analogues enabled by transition metal tuning for efficient...

Given their inherent advantages in safety, low cost, and environmental benefits, aqueous proton batteries (APBs) have emerged as a highly promising new energy storage system. Prussian blue analogues (PBAs) are considered excellent cathode materials for APBs due to their simple preparation, open three-dimensional framework, and abundant redox sites. However, they still suffer from issues such as unstable lattice structures and poor cycling performance. To address this, a Cu-Fe-based Turnbull's blue analogue (denoted as TBACu) was synthesized via a facile co-precipitation method, demonstrating superior long-cycle cycling stability. This outstanding performance stems from two primary factors: First, the abundant crystalline water incorporated during synthesis forms a continuous hydrogen-bond network within the crystal structure, facilitating rapid proton transport via the Grotthuss mechanism. Second, the incorporation of Cu greatly enhances the stability of the lattice framework, ensuring highly reversible proton insertion/extraction during cycling. As a result, TBA-Cu exhibits an outstanding specific capacity of 73.2 mAh g^-1 at 0.1 A g^-1 and demonstrates exceptional cycling robustness, with 83% capacity retention even after 50,000 cycles at 5 A g^-1. This work provides valuable insights for the design of high-performance and long-life Prussian blue-based cathode materials for proton batteries.