Proton-Fluid Preintercalation Topochemistry for High-Rate Capacity and Ultralow-Temperature Proton Storage

Fundamental limitations in structural reversibility and electrochemical performance have rendered anode materials a critical bottleneck for proton batteries and capacitors. While the rational design of intrinsic properties for metal oxides offers a promising route for advanced proton storage, the simultaneous realization of high-power and low-temperature operability remains a grand challenge. We show that topochemical preintercalation of protons and confined lattice water in hydrated molybdenum bronze modifies host lattice rearrangement and enables ultrafast proton-coupled electron transfer. Ion-fluid cointercalation mediates electrochemical reaction pathways to an unconventional three-proton insertion mechanism, enabling a state-of-the-art specific capacity of 407 mAh g^-1, ultrahigh-rate capability exceeding 1000 C (500 A g^-1), and ultralow-temperature adaptability (194.2 mAh g^-1 at -80 °C). Comprehensive in situ crystal and interface evolution methods and theoretical calculations reveal a highly reversible and homogeneous protonation mechanism and enhanced interfacial transport, suppressing heterogeneous and unstable reaction kinetics of pristine MoO₃. The hybrid proton capacitor with such a molybdenum bronze anode shows an unprecedented ultrahigh-power and ultralow-temperature performance, with excellent stability for over 2000 cycles at -80 °C. This work highlights physicochemical insights on preintercalation topochemistry in modulating charge carrier-host interactions and provides electrode design principles for high-rate and low-temperature nonmetallic ion storage.