Water-soluble inorganic salts with ultrahigh specific capacitance: crystallization transformation investigation of CuCl2 electrodes

Abstract

Currently, one of the biggest challenges in the field of pseudocapacitors is their capacitance value. Current knowledge on improving specific capacitance values is mainly focused on the synthesis of electrode materials with different structures and sizes. However, no studies have addressed using soluble inorganic salts directly as electrode materials. For the first time, we have reported that water-soluble CuCl₂ electrodes show a fast and reversible redox reaction of Cu²⁺ ↔ Cu⁺ and deliver a very high specific pseudocapacitance, ~5442 F g⁻¹. We have identified that the cation Cu²⁺ is responsible for achieving this big number. The chemical and crystallization transformation of the CuCl₂ electrode is presented. Commercial inorganic salts can be used directly as electrodes neglecting complex synthesis procedures, which is an easily scalable and highly economical method. This method can be extended to a large variety of commercial inorganic salt electrodes following the guideline of ionic electronegativity.