Chemical Blowing of a Synthetically Green Conjugated Polymeric Network into Porous Carbon Nanosheets for Dual-Purpose Energy Storage

Abstract

Integration of multiple functionalities within a single porous carbon architecture offers an effective route to reduce material complexity, cost, and environmental impact. However, the rational synthesis of such multifunctional carbons remains challenging, as precise control over heteroatom doping and hierarchical porosity is often compromised by dopant volatilization and structural degradation at elevated pyrolysis temperatures. Herein, we report the synthesis of graphitized nitrogen- and oxygen-co-doped porous carbon nanosheets (BQPy-PCNs) via an NH4Cl-mediated chemical blowing strategy, employing a synthetically green two-dimensional (2D) benzoquinone-pyrrole conjugated polymer network (BQPy-CPN) as the precursor for dual-purpose energy storage. During pyrolysis, NH4Cl decomposes to generate reactive NH3 and HCl gases that effectively compensate and stabilize N-dopant concentration, promote in situ exfoliation, and generate hierarchical micro/mesoporosity, yielding a high surface area of up to 1208 m2 g-1. Concurrently, the resulting graphitized frameworks are enriched with electroactive pyridinic and graphitic nitrogen species, polar defect sites, and inherent pyrrolic/quinone functionalities. These synergistic structural and compositional features markedly enhance ion transport, charge storage, mass transfer, and redox kinetics. As electrodes in symmetric aqueous supercapacitors, BQPy-PCNs deliver a high specific capacitance (156 F g-1 at 0.5 A g-1), superior energy/power density (17 Wh kg-1/4500 W kg-1), and excellent cycling stability (20,000 cycles at 10 A g-1). Furthermore, BQPy-PCNs exhibit remarkable oxygen reduction reaction (ORR) activity with an onset potential of 0.94 V, rivalling commercial Pt/C. DFT calculations were performed to gain deeper insight into the mechanistic pathways underlying the superior ORR performance observed in the high-temperature sample. When integrated into Zn-air batteries, they deliver higher operating voltages, greater power densities, and enhanced durability compared to Pt/C, underscoring their strong potential as sustainable, metal-free electrodes for advanced energy storage and conversion technologies.