Carbon Structures with Hollow Internal Cavity as Charge Storage Materials to Achieve High Energy Density

Hollow porous carbon spheres (HPCS) havebeen synthesizedby using spherical silica nanoparticles (S-SiO ( 2 )) as templates. S-SiO ( 2 ) nanoparticles have been coated first withthe polymer of phloroglucinol/1,4-phenylenediamine/formaldehyde (PPF), followed by a second layer of SiO2, and againwith PPF as the third layer. After each step of coating,the sample has been pyrolyzed under nitrogen and S-SiO ( 2 ) has been removed to obtain HPCS-I, HPCS-II, and HPCS-III, from the first,second, and third coated samples, respectively. The synthetic strategyrelies on the use of a hard template to create void spherical coresand space confinement to develop shells of the hollow spheres. Allof the materials show a uniform spherical morphology with a hollowinner core generated by the removal of the SiO2 template.The samples have been characterized by thermal analysis, powder X-raydiffraction, nitrogen adsorption/desorption studies, electron microscopy,and X-ray photoelectron spectroscopy. Among the samples, the structuralformation of HPCS-II is found to be superior and it isalso manifested in its electrochemical properties. While all of thesamples exhibit near-rectangular cyclic voltammograms, the specificcapacitance of HPCS-II is found to be the highest. Galvanostaticcharge/discharge (GCD) studies also support the observation, and thespecific capacitance is found to be 592 F center dot g(-1) at a current density of 1 A center dot g(-1), which isretained at 444 F center dot g(-1) even at a very high currentdensity of 100 A center dot g(-1). The major contributiontoward such electrochemical behavior is believed to arise from electricaldouble-layer capacitance (EDLC). HPCS-II is found tobe highly stable, retaining 100% of its capacitance value at leastup to 5000 GCD cycles. The power density of HPCS-II isnearly thrice the power target value projected by the Partnershipfor a New Generation of Vehicles (PNGV), and it shows an outstandingenergy density value.

Automated summary

Hollow porous carbon spheres (HPCS) were synthesized using spherical silica nanoparticles as templates. The samples were characterized and HPCS-II showed the highest specific capacitance and superior electrochemical stability. The synthetic strategy involved using a hard template to create void spherical cores and space confinement to develop shells. The electrochemical behavior of HPCS-II is believed to be mainly due to electrical double-layer capacitance.