RESUMO
Using graphene oxide and a cobalt salt as precursor, a three-dimensional graphene aerogel with embedded Co3 O4 nanoparticles (3D Co3 O4 -RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze-drying and thermal reduction. The obtained 3D Co3 O4 -RGO aerogel has a high specific capacitance of 660â F g(-1) at 0.5â A g(-1) and a high rate capability of 65.1 % retention at 50â A g(-1) in a three-electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6 M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5â V, the device exhibits a high energy density of 40.65â Wh kg(-1) and a power density of 340â W kg(-1) and shows a high cycling stability (92.92 % capacitance retention after 2000â cycles). After charging for only 30â s, three CR2032 coin-type asymmetric supercapacitors in series can drive a light-emitting-diode (LED) bulb brightly for 30â min, which remains effective even after 1â h.
Assuntos
Cobalto/química , Eletrodos , Géis , Grafite/química , Óxidos/química , Microscopia Eletrônica de Varredura , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
The adsorption isotherms of hydrogen on super activated carbon were measured systematically, covering a temperature range of 93-293 K at 20 K intervals and pressures up to 7 MPa. All the experimental data were linearized by adopting the coordinates ln ln(n) vs 1/(ln P). The results indicate that the adsorption limit (P(lim), n(lim)) exists virtually at high pressure and has a certain physical meaning. Based on the adsorption limit, further analyses were carried out by modeling the adsorption isotherms in the coordinates ln(n(lim)/n) vs ln(RT(ln(P(lim)/P) and a linear comprehensive adsorption model was proposed in the form n (lim)=n.exp(psi T+lambda/T-c/) (beta).[RT ln( P (lim)P )] (b) which can predict the adsorption isotherm of hydrogen on activated carbon in supercritical conditions.
