Unlocking enhanced performance and stability in graphene oxide-based capacitors through simulated sunlight irradiation

The practical application of graphene oxide (GO) in flexible energy storage is often hindered by its inherent mechanical fragility and poor stability in aqueous environments. In this study, we demonstrate that controlled simulated sunlight irradiation transforms GO membranes into robust, high-performance dielectric separators through a surface-selective modification process. Beyond systematic deoxygenation and restoration of the sp 2 carbon network confirmed by XPS, XRD, and FTIR, we report for the first time a significant light-induced enhancement in the bulk mechanical properties. Tensile testing reveals a more than twofold increase in Young’s modulus, rising from 8 GPa to 18 GPa post-treatment, alongside increased structural densification and interlayer cohesion. Notably, this modification acts as a "surface-locking" mechanism: while the core of the membrane preserves its insulating dielectric nature, the reinforced surface prevents the typical swelling and delamination of GO in water. Further electrochemical analysis reveals a remarkable "self-improving" behavior, where capacitors employing these irradiated membranes exhibit an increase in capacitance during operational cycling, a phenomenon driven by the stabilization of the hydrated GO interface. These findings highlight a green, light-driven strategy for fabricating mechanically durable and electrochemically superior energy storage devices, bridging the gap between laboratory-scale chemical tuning and macro-scale environmental reliability. Simulated sunlight drives a surface-selective modification of graphene oxide, doubling its mechanical stiffness and locking the interlayer structure. This light-induced reinforcement prevents aqueous delamination while preserving the insulating dielectric core, enabling a unique “self-improving” electrochemical behavior in robust, high-stability capacitors. • Solar-driven transformation: Simulated sunlight irradiation provides a green, non-destructive method for precise surface reduction of GO membranes. • Mechanical reinforcement: Irradiation induces a two-fold increase in Young’s Modulus (from 8 to 18 GPa), significantly enhancing structural stiffness and durability. • Interfacial stability: Removal of surface oxygen functional groups promotes π-π stacking and densification, preventing aqueous swelling and delamination. • Self-improving performance: Capacitors using treated GO films exhibit a unique electrochemical "activation," with capacitance increasing during operational cycling. • Robust energy storage: The integration of mechanical robustness and chemical tuning offers a novel strategy for high-stability, flexible electronic components.