Dual-modified graphene films via molecular and structural co-optimization for high-energy-density aqueous zinc-ion hybrid capacitors

The increasing demand for safe and long-lasting electrochemical energy storage for electric vehicles and portable electronics is driving the development of advanced aqueous zinc-ion hybrid capacitors (AZIHCs). Graphene-based cathodes offer high conductivity and stability, but their performance is hindered by nanosheet stacking and lack of active sites. To overcome this limitation, a dual-modification strategy is proposed, combining molecularly functionalized reduced graphene oxide (PrGO) and flame-reduced graphene oxide (FrGO). The p-phenylenediamine (PPDA) modified PrGO possesses abundant redox-active sites, while the wrinkled FrGO interlayer prevents π-π stacking and enhances interlayer porosity. By adjusting the FrGO/PrGO mass ratio, the composite film (PrGO/FrGO-2) achieves an interlayer-expanded architecture with balanced defect density and conductivity. As a cathode for AZIHCs, it exhibits high gravimetric/volumetric capacitances (348.25F g −1 /176.75F cm −3 ) and exceptional energy densities (107.73 Wh kg −1 ; 59.85 Wh L −1 ). The material retains 93% capacitance after 10,000 cycles. This study introduces a molecular/structural co-optimization approach for designing high-performance flexible electrodes for future energy storage solutions.