Single proton anti-freezing hydrogel electrolyte with enhanced ion migration number enabling high-performance supercapacitor

Compared with traditional binary ion electrolytes, single-ion electrolytes have higher ion migration number and can avoid concentration polarization. In this work, single proton hydrogel electrolytes were prepared by one-step free radical polymerization of acrylamide and 2-acrylaminoamido-2-methyl-1-propane sulfonic acid in ethylene glycol (EG)/water binary solvent. The electrolyte possesses good mechanical strength and excellent anti-freezing ability. A high conductivity of 1.28 mS cm⁻¹ at −40 °C is achieved by adjusting monomer ratio and EG content. The proton hopping along the ion channel formed by the anionic polymer chain and the Grotthuss transport are responsible for the high conductivity. An extremely high ion migration number of 0.87 is obtained. The fixed anionic group endows the hydrogel electrolyte with good anticorrosion ability. The hydrogel electrolyte assembled supercapacitor (SC) exhibits excellent electrochemical performance in a wide temperature range from −40 °C to 60 °C and can be stored at −30 °C for 10 months without capacitance attenuation. The capacitance retention rate of the SC is as high as 92% after 15,000 cycles at both room temperature and − 40 °C. The single proton hydrogel electrolyte provides a new route for the further development of storage device based proton transport.