Multifunctional Structural Supercapacitor Based on Urea-Activated Graphene Nanoflakes Directly Grown on Carbon Fiber Electrodes

Structural energy storage systems offer both load bearing and electrochemical energy storage capabilities in a single multifunctional platform. They are emerging technologies for modern air and ground transportation vehicles, promising considerable mass and volume savings over traditional systems. To this end, carbon fiber reinforced composites have attracted interest for structural supercapacitors (SS), emanating principally from their similar laminate design. However, carbon fiber (CF) electrodes suffer from poor electrochemical storage performance. To tackle this deficiency, carbon fiber electrodes were modified with a 3D network of radially grown graphene nanoflakes (GNFs) to enhance their degree of graphitization and active surface area. We show that the GNF surface morphology offers an ∼9 times increase in specific capacitance (Csp) of CF structural supercapacitor. Moreover, chemical activation of the GNFs/CF hybrid electrodes by urea induces a further improvement in Csp by ∼14 times, while almost maintaining the elastic modulus of the control CF-based device. It has been established that the high specific capacitance stems from the highly electroactive edge-dominated nitrogen moieties and enhanced electrical conductivity induced by urea activation. Overall, the urea-activated hybrid electrodes offer an ∼12-fold increase in energy and power densities compared to CF control structural supercapacitor devices. These findings provide important knowledge for the design of next-generation multifunctional energy storage electrodes by highlighting the importance of interfacial nanoengineering.