Fabrication of Porous Reduced Graphene Oxide Encapsulated Cu(OH)₂ Core–shell Structured Carbon Fiber-Based Electrodes for High-Performance Flexible Supercapacitors

To explore next-generation flexible supercapacitors, lightweight, superior conductivity, low cost, and excellent capacitance are the preconditions for practical use. However, subjected to unsatisfactory conductivity, limited surface areas, and poor porosity leading to long ion transport channels, carbon fiber (CF)-based flexible supercapacitors need to further boost the electrochemical properties. Hence, a porous reduced graphene oxide encapsulated Cu(OH)₂ core–shell structured CF-based electrode was fabricated through a scalable approach. The inexpensive Cu(OH)₂ nanoarrays were controllably grown in situ on a CF substrate, with residual Cu promoting conductivity. Porous graphene oxide (PrGO), which served as the shell, was realized by Ni nanoparticle etching, which not only provided more active sites for capacitance as well as shortened accessible pathways for the ion transport but also effectively alleviated the exfoliation of the internal active materials. Moreover, thanks to this distinctive core–shell architecture, the extra space between the outer PrGO layer and the internal ordered Cu(OH)₂ nanoarrays provided increased space for capacitance storage. The assembled PrGO/Cu(OH)₂/Cu@CF electrode exhibited an excellent areal capacitance, reaching up to 722 mF cm^–2 at a current density of 0.5 mA cm^–2, attributed to its superior structure and materials advantages. The resulting PrGO/Cu(OH)₂/Cu@CF//AC//CF asymmetric flexible all-solid-state supercapacitor achieved a high energy density of 0.052 mWh cm^–2 and exhibited long-term durability. This work proposes a low-cost and effective way to fabricate hierarchically structured electrodes for wearable CF-based supercapacitors.