A cellulose fibers-supported hierarchical forest-like cuprous oxide/copper array architecture as a flexible and free-standing electrode for symmetric supercapacitors

Herein, we for the first time develop two facile and fast steps (including magnetron sputtering and electrooxidation) to grow a hierarchical forest-like Cu2O/Cu array architecture onto the three-dimensional fiber framework of cellulose paper. The Cu rods serve as the trunk and the oxidation product (Cu2O) acts as branches. When utilized as a flexible and free-standing electrode, the unique architecture made full use of a large interfacial area from the hierarchical multi-scale structure of the forest-like array, numerous channels for rapid diffusion of electrolyte ions from the porous fiber skeleton of hydrophilic cellulose paper, and fast electron transport and high electrochemical activity from the Cu2O/Cu complex. These merits endowed the electrode with a high specific capacitance of 915 F g(-1) (238 mF cm(-2)) at 3.8 A g(-1), a large specific energy of 53.7 W h kg(-1) at 1.25 kW kg(-1), superior rate capability, and excellent cycling stability with a capacitance retention of 91.7% after cycling 10 000 times. More importantly, an easy interesting strategy was proposed to assemble a symmetric supercapacitor based on the Cu2O/Cu/cellulose hybrid paper, that is, growing the forest-like Cu2O/Cu array onto the two surfaces of cellulose paper. The device delivered a high specific capacitance of 409 F g(-1) (213 mF cm(-2)) at 1.9 A g(-1), a superior specific energy of 24.0 W h kg(-1) at 0.625 kW kg(-1) and good cycling stability (90.2% capacitance retention after 10 000 cycles). These fascinating results unveil the potential of the hybrid paper as a high-performance electrode material for flexible energy storage devices and portable electronics.