Nanoporous graphene/CuO composite as high-performance supercapacitor electrode material

With development of portable electronics, demands for low cost, and high performance energy storage devices with enhanced energy/power density have increased. Because of intriguing features, supercapacitors have attracted great interesting to complement or replace batteries in various electronic devices. Herein, we report a high performance supercapacitor based on nanoporous graphene/CuO composite synthesized with low cost hydrothermal method. Thesynergic effects of graphene/CuO composition with its nanoporous structure have a key role in providing highly conductive surface for uniform growth of CuO nanoparticles, faster electron transfer, prevention of restacking/agglomeration, simultaneous EDLC and pseudocapacitancecontribution, facile mass transport and large accessible surface area. The nanoporous graphene/CuO electrode exhibits excellent electrochemical performance including a specificcapacitance of 575 F g−1 at 1 A g−1 and 82% retention at an ultrafast rate of 50 A g−1 and excellent cycle life (6% loss after 5000 cycles). Nanoporous structure with a high internal porosity and homogenous nanosized metal oxideswould effectively prevent the restacking and aggregation of graphene nanosheets (GNS) and consequently maintain their ion-accessible surface area.1, 2Among the various metal oxides, CuOhas attracted great interest because of its low cost and elemental abundance, easy preparation at the nanoscale, and nontoxicity.3 Graphene oxide (GO) was synthesized via chemical exfoliation (modified Hummers’ method) as reported previously.4 Nanoporous graphene/CuO was preparedas follow: 200 mg GO was ultrasonicated in 80 mL distilled water for 1 h, then the homogeneous solution was heated to 95 ◦C and 2 mL of cupric acetate aqueous solution (223 mg mL-1) was added into it under ultrasonication. After several minutes, 5 mL of ammonia solution (25%) was added to the above solution. After, 3 mL of 1% H2O2 aqueous solution was added and the mixture was transferred into a sealed Teflon-lined stainless steel autoclave and heated at 180 ◦C for 8 h.XRD, SEM and TEM images confirm the preparation of CuO nanoparticles on graphene nanosheets. Also, BET and BJH isotherms confirm nanoporous structure of sample. The half-cellelectrochemical performance of the electrode was investigated in a 3 M KOH solution. The nanoporous graphene/CuO electrode exhibits excellent electrochemical performance including a specific capacitance of 575 F g−1 at 1 A g−1 and 82% retention at an ultrafast rate of 50 A g−1 and excellent cycle life (6 % loss after 5000 cycles). This remarkable performance contrasts with nanoporous graphene/CuO made by low cost hydrothermal method, giving some insights into the design of high-performance composite electrode materials for supercapacitor applications. We envision these electrodes to be useful in a broad range of applications such as supercapacitors, lithium ion batteries, fuel cells, gas sensors, biosensors, catalysis, and other electronic devices.

Keywords:

Supercapacitor , Nanoporous , Graphene/CuO , Composite