Interface engineering for efficient charge transfer in polyaniline hybrid supercapacitors: a mini review

A very attractive prototypical pseudocapacitive polymer is polyaniline (PANI), which has extremely high theoretical capacitance, can be intrinsically conductive, and is easily synthesized at a relatively low cost. However, the actual device performance is limited by kinetic losses, large interfacial resistance, instability of the doping, pore blocking, and volume fluctuation, which cause large capacity fades. Deliberate interface engineering, such as the hybridization of PANI with carbons, metal oxides, metal sulfides, MXenes, or 3D scaffolds, is a useful approach to alleviate such problems as long as a deliberate design of the interfaces is performed. Here, we concentrate primarily on the interface design as the main design parameter and, categorize the strategies for interface design based on the charge-transfer function, not on the host material. We focus on the PANI–host and PANI–electrolyte interfaces of PANI hybridized with carbon nanostructures, transition-metal oxides and chalcogenides, MXenes, and polymeric/3D scaffolds that have been published in the last 5 years. Each design choice at the interfaces is correlated with measurable charge-transfer metrics, and five types of recent advances are distinguished: chemical anchoring and functional group design, electronic coupling and percolation network architectures, morphology-controlled access to ions, mechanical buffering architectures, and electrolyte–electrode coupling. Practical measures for charge transfer at the interface are also summarized, which offer clear transferable guidelines for future-generation hybrid supercapacitors based on PANI. This mini-review is the first to classify PANI composites based on their function and to provide a quantitative diagnostic, normalization, and scaling framework of interfacial charge transfer.