Optimizing Polyoxometalate Electrodes for Energy Storage via Cation Design and Thermal Activation

Abstract

Polyoxometalates (POM) are promising materials for electrochemical applications, such as supercapacitors. However, their stability in aqueous electrolytes is compromised due to POM cluster leaching. To mitigate this issue, POM can be combined with organic counter cations, which reduce their solubility in water and influence interactions with carbon support materials. Nevertheless, further research is needed to determine the optimal characteristics and electrode design for maximizing performance. In this work, a synergistic methodology to investigate POM compounds bearing cations with three core functionalities (ammonium, imidazolium, and pyridinium) and varying alkyl side chain lengths, is developed in order to elucidate and optimize the effects of hydrophobicity on the structure of organic–inorganic hybrid materials, electrode films, and their electrochemical performance. The results show that, although cations with long alkyl chains exhibit lower capacitance, they can be activated through molecular rearrangement in the solid state, facilitated by the flexibility of these chains within the structure. By combining thermal and electrochemical techniques, the electrode materials are optimized. These findings demonstrate that the careful selection of counter-cations with the appropriate molecular structures, followed by a thermal activation protocol, is key to developing more efficient and durable energy storage systems.