Multi-ion Coordinated Water Network in Dilute Acid Electrolytes for Ultralow-Temperature (≤-80 °C) Proton Energy Storage.

Proton batteries/capacitors, known for fast ion diffusion kinetics, are a promising alternative for low-temperature energy storage. However, ultralow-temperature (≤-60 °C) proton energy storage devices have been impeded by the strong corrosion of high-concentration acids and the high freezing point of low-concentration acids. Here, a strong-super-cooling electrolyte with a multi-ion coordinated water network (hybrid electrolyte of dilute acid and chaotropic zinc salt) is designed for fast proton transport at low temperatures. The chaotropic zinc salt not only reduces the number of free water but also minimizes the number of strong hydrogen bonds in the electrolyte, thus inhibiting the transition of the water molecules to an ordered arrangement at low temperatures. More importantly, the formation of stable Zn-HO-ClO water molecule network, driven by strong interactions between ions, can effectively improve the proton transport to achieve the excellent rate performance of electrodes. This electrolyte also enables a long cycle life of the assembled CuHCF//α-MoO for over 15 000 cycles below -60 °C, expediting the development of proton energy storage devices at ultralow temperatures.