Interest of molecular functionalization for electrochemical storage

Despite great interests in electrochemical energy storage systems for numerous applications, considerable challenges remain to be overcome. Among the various approaches to improving the stability, safety, performance, and cost of these systems, molecular functionalization has recently been proved an attractive method that allows the tuning of material surface reactivity while retaining the properties of the bulk material. For this purpose, the reduction of aryldiazonium salt, which is a versatile method, is considered suitable; it forms robust covalent bonds with the material surface, however, with the formation of multilayer structures and sp(3) defects (for carbon substrate) that can be detrimental to the electronic conductivity. Alternatively, non-covalent molecular functionalization based on pi-pi interactions using aromatic ring units has been proposed. In this review, the various advances in molecular functionalization concerning the current limitations in lithium-ion batteries and electrochemical capacitors are discussed. According to the targeted applications and required properties, both covalent and non-covalent functionalization methods have proved to be very efficient and versatile. Fundamental aspects to achieve a better understanding of the functionalization reactions as well as molecular layer properties and their effects on the electrochemical performance are also discussed. Finally, perspectives are proposed for future implementation of molecular functionalization in the field of electrochemical storage.