Tailored 2D conjugated polymers for pseudocapacitive proton storage

2D conjugated polymers (2D-CPs) are currently attracting substantial attention as host materials in electrochemical energy storage. They show some intriguing properties, such as high conductivity (by elevating the conjugated degree), adjustable redox activity (by controlling the monomers), and stable skeleton structure (low solubility in electrolytes). Herein, two aza-based 2D-CPs with different conjugation degrees are designed and developed for pseudocapacitive proton storage. The detailed electrochemical analysis shows that the highly conjugated 2D-CP (2D-HCP) demonstrates an inferior performance compared to partially conjugated 2D-CP (2D-PCP), especially in terms of the high-rate performance. Though combining various in-situ/ex-situ spectroscopy analyses and theoretical simulation, the reason behind this performance is revealed and is associated with the different solid-state proton diffusion kinetics in these two 2D-CPs. We believe this new understanding can be leveraged to design and develop more suitable 2D-CPs for electrochemical energy storage.