Symmetry-enabled multisite redox utilization in Cu-Ni cyanide coordination polymer for high-rate long-life aqueous proton batteries

Aqueous proton batteries (APBs) offer a safe and cost-effective route for grid-relevant energy storage; however, simultaneously achieving high-rate capacity and long-term stability in acidic electrolytes remains challenging. Herein, we report CuNi(CN)3, a symmetric bimetallic cyanide-bridged coordination polymer (C3─M─N3 motif) with well-defined CuNi sites, which are identified by XPS and XAS, enabling dual-metal charge storage through multisite proton-coupled electron transfer (PCET). The CuNi(CN)3 delivered 130 mAh/g at 1 A/g, retained 92% of its capacity and 98% Coulombic efficiency after 2000 cycles at 8 A/g in 0.5 M H2SO4. The full cell with MoS2@N-CQDs delivers 114 mAh/g at 1 A/g and 86 mAh/g at 8 A/g, while retaining 80% capacity over 8000 cycles at high rates. Quasi-operando XRD, FTIR, Raman, and XPS reveal preserved long-range order with reversible cyanide-environment and Cu/Ni valence evolution, supporting a topochemical proton-storage mechanism and rapid proton transport within the framework. Overall, these results establish a scalable cyanide-framework strategy for high-rate APBs in acidic media. Aqueous proton batteries offer safe, low-cost energy storage, but achieving high-rate performance and long-term stability remains challenging. Here, the authors report CuNi(CN)3, a cyanide-bridged bimetallic coordination polymer with high capacity, rate capability, and cycling stability for aqueous proton batteries.