Enabling extreme low-temperature proton pseudocapacitor with tailored pseudocapacitive electrodes and antifreezing electrolytes engineering

A proton pseudocapacitor, which benefits from the synergy effect between high ionic conductivity of electrolyte and pseudocapacitive electrode materials with open crystal structures to realize fast Grotthuss proton conduction, delivers a maximum energy density of 39 Wh kg−1 and a broadened electrochemical window of 0∼2.3 V at −60 °C. [Display omitted] •A lower freezing point of high-concentration phosphoric acid electrolyte is achieved owing to the broken hydrogen bond network.•Pseudocapacitive WO3 anodes and VHCF cathodes achieve excellent electrochemical performance in this electrolyte from − 60 to 25 °C.•Proton pseudocapacitor delivers a maximum energy density of 39 Wh kg−1 and a broadened electrochemical window of 0 ∼ 2.3 V at − 60 °C. A critical current challenge in the development of proton pseudocapacitors is developing antifreezing electrolytes and high-performance proton storage materials in extreme environments. Here, we design an antifreezing proton pseudocapacitor using a high-concentration phosphoric acid electrolyte and pseudocapacitive electrode materials, which delivers an outstanding rate capacity and cycle life below − 40 °C. Comprehensive physical characterization techniques and theoretical simulations demonstrate that the solvation structure of the electrolyte defines the freezing point and electrochemical stability window, which is crucial for achieving fast charge carrier mobility and avoiding side effects. The pseudocapacitive hydrated tungsten oxide anodes and Prussian blue analogue cathodes with their open crystal structures achieve fast proton transport and storage, resulting in excellent electrochemical performance from − 60 to 25 °C (1000 cycles with no capacity fading at − 40 °C). Benefiting from the synergistic effect between the electrolyte and electrode materials, the fabricated proton pseudocapacitors exhibit remarkable low-temperature electrochemical performance. It achieves a maximum energy density of 39 Wh kg−1 and a broadened electrochemical window from 1.7 V at 25 °C to 2.3 V at − 60 °C. This work provides a comprehensive strategy to develop high-performance proton energy storage devices under ultralow-temperature conditions.