Graphene quantum dot/Co(OH)2 electrode on nanoporous Au-Ag alloy for superior hybrid micro-supercapacitors

Recent years have witnessed a surge of research in using nanostructured hybrid composites as electrode materials for micro-supercapacitors (micro-SCs). Herein, we synthesized a graphene quantum dot (GQD)/Co(OH)(2) composite by one-step co-deposition on nanoporous Au-Ag alloy wires, focusing on the effect of the GQDs on the operating performance of supercapacitors. We observed the formation of an interconnected network structure with Co(OH)(2) nanosheets grown on Au-Ag alloy, and GQDs were uniformly distributed in the interior of Co(OH)(2). Electrochemical measurements showed an enhanced specific capacity of 273 mC cm(-2) at 1.0 mA cm(-2) for GQD/Co(OH)(2) as compared to 151 mC cm(-2) for pure Co(OH)(2). A wire-shaped, quasi-solid-state hybrid supercapacitor device was fabricated by using the GQD/Co(OH)(2) composite as the positive electrode and active carbon as the negative electrode, which exhibits an excellent capacitance retention rate of 99.5% after 10 000 cycles at a current density of 2 A cm(-3) and can withstand bending tests nearly without degradation of the electrochemical performance. We further performed systematic first-principles calculations on GQD/Co(OH)(2) to explore its atomic electronic properties associated with the interface. Due to the addition of GQDs, we revealed increased electronic states that spread over the entire energy gap of Co(OH)(2), which are closely related to the electrical conductivity and device performance. We expect these findings to shed new light on using novel hybrid composites for future construction of high-performance and flexible energy-storage devices.