Preparation And Electrochemical Investigation Of ZIF-Derived Porous Carbons

Nowdays, the severe environment pollution and energy shorage are needed to develop new sustainable and renewable energy technologies. Among the newly developed materials, porous carbons play an important role especially in application to fuel cells, supercapacitors, lithium-sulfur batteries and so on. As a new class of porous materials, metal-organic frameworks (MOFs) are composed of the organic ligand containing oxygen or nitrogen atoms with the transition metal or rare earth metal linked by self-assembly, which attract widespread attention in recent years. Recently, MOFs were selected as outstanding template and/or precursor to prepare nanoporous carbon materials with new structure and properties based on their high surface areas, controllable structures and abundant organic species in their scaffolds. Zeolitic Imidazolate Frameworks (ZIFs), a sub-family of MOFs, consist of transition metal ions and imidazolate linkers, which can form3D tetrahedral frameworks resembling zeolite topologies. The exceptional thermal and chemical stability and contain rich nitrogen source in imidazolate ligands, which make ZIFs be an ideal precursor for construction of N-doped porous carbons.In this work, we successfully fabricate ZIF-derived in situ nitrogen-doped porous carbon materials (ZIF-derived porous carbons) by using ZIF-7as a precursor and different additional carbon sources. We explores the various factors for affecting the structure and morphology of the material in the process of preparing the ZIF-based porous carbon, such as the mixed mode of ZIF-7with additional carbon sources (solid mixing and liquid mixing), carbonization temperature (750,850,950and1000℃), the amount of additional carbon (0.2,0.5and0.8mol/L glucose solution), different precursors (ZIF-7and ZIF-8) and different additional carbon source (glucose, ethylene glycol, glycerol and furfuryl alcohol).ZIF-derived porous carbons as electrodes materials were used in supercapacitors. Through cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopic (EIS) study its electrocaptive performance. Results indicate that the ZIF-7/glucose composite-derived Carbon-L-950as an electrode for electrochemical capacitor exhibits high specific capacitance of228F g-1in6mol/L KOH at a current density of0.1A g-1, even178F g-1at a high current of10A g-1and good stability over5000cycles. Moreover, the conductive agent (like acetylene black) is not required in the preparation process of the working electrode, which not only lowers the preparation costs but also is favorable for stability and performance.Besides, ZIF-derived in situ nitrogen-doped porous carbons act as metal-free electrocatalyst for cathode oxygen reduction reaction (ORR) in the fuel cells. Carbon-L-950, as metal-free electrocatalyst, shows excellent electrocatalytic activity (the onset and half-wave potentials are0.86and0.70V vs. RHE, respectively) and nearly four electron selectivity (the electron transfer number is3.68at0.3V), which is close to commercial20%Pt/C. Moreover, when methanol was added, the Pt/C catalyst would be poisoned while the Carbon-L-950would be unaffected. By exploring the current-time chronoamperometric response in25000seconds, we found that the duration stability of Carbon-L-950is much better than the commercial20%Pt/C. Thus, Carbon-L-950exhibit excellent ability to avoid methanol crossover effects, and long-term operation stability superior to the Pt/C catalyst. This facile fabrication of ZIF-derived porous carbons may open a new avenue for producing new family of porous carbon materials for advanced energy storage devices,such as fuel cells, supercapacitors and lithium batteries.