Evolution of an Electrochemically Inactive Metal-Organic Framework to Reticulated Porous Carbon Particles with High Supercapacitance

An iron-containing porphyrin-basedporous metal-organicframework (PPMOF) has been synthesized and subsequentlypyrolyzed to obtain the carbon structure with homogeneous distributionof nitrogen. The pyrolysis is carried out at different temperaturesand in the presence of two different environments; in argon to obtain PPMOF-Ar-700, PPMOF-Ar-800, and PPMOF-Ar-900, and in nitrogen to obtain PPMOF-N-800. The motivationhere is to study the change in the electrochemical properties thattake place on conversion of the metal-organic framework toits corresponding carbons. The materials have been characterized bypowder X-ray diffraction, nitrogen adsorption/desorption, scanningelectron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy,among others. It was observed that PPMOF almost did notshow any electrochemical response and was unstable, whereas the carbonizedframeworks showed good supercapacitive behavior and stability. Thesurface area increases from 353 to 838 m(2)center dot g(-1), when the pyrolysis gas is switched over from nitrogen to argon.It also results in the formation of uniform smooth spherical particlesin PPMOF-Ar-800, in contrast to agglomerated broken particlesin PPMOF-N-800. PPMOF-Ar-800 shows a remarkablespecific capacitance value of 500 F center dot g(-1) ata current density of 1 A center dot g(-1) which is retainedat a high value of 111 F center dot g(-1) at a very highcurrent density of 50 A center dot g(-1) in galvanostaticcharge/discharge studies, whereas for PPMOF-N-800, thespecific capacitance is 400 F center dot g(-1) at 1 A center dot g(-1) and its discharge time is also shorter than thatfor PPMOF-Ar-800. This indicates that the pyrolysis environmentplays a crucial role in the formation and stabilization of the carbonstructures.