Preparation And Properties Of Electrode Materials Based On MOFs Precursors

In view of current synthesis and application research status of electrode materials for energy storage and conversion devices, we have obtained heteroatoms-doped carbon materials by carbonizing the mixtures of metal-organic frameworks (MOFs) and different heteroatom sources, which were mixed by impregnation or ball-milling methods. The electrochemical performances as electrocatalysts were examined. On the other hand, the novel and fluorescent carbon nanodots (Cdots) functional MOFs composites were synthesized by a stepwise synthetic approach. Most importantly, the composites exhibited highly fluorescent sensing for nitroaromatic explosives, owing to the double effect of porous MOFs and fluorescent Cdots. The detailed achievements are given below:(1) We encapsulated urea and dimethyl sulfoxide (DMSO) into MOF-5 as precursors. After carbonization and acid etching, the nitrogen and sulfur co-doped porous carbons have been synthesized. The powder X-ray diffraction (XRD) patterns clarify that the hybrids are amorphous carbons. The mesoporous structures of these carbons are proved by the N2 sorption isotherms and pore size distributions. The XPS and EDS spectra also demonstrate that N and S heteroatoms have been successfully incorporated into the frameworks of the samples. As electrocatalysts for oxygen reduction reaction (ORR), the performances of these materials were examined. Meanwhile, the influence of the ratio of N and S on the ORR was systematically investigated. These results show that the representative NS(3:1)-C-MOF-5 catalyst shows the highest onset potential, and is even comparable to commercial Pt-C catalyst, due to the synergistic effect of N and S co-doping. In terms of long-term stability and excellent resistance to the methanol crossover effect for the ORR, NS(3:1)-CMOF-5 is superior to commercial Pt-C.(2) We have first fabricated N, P and S ternary-doped metal-free porous carbon materials using MOF-5 as a template and dicyandiamid (DCDA), triarylphosphine (TPP) and dimethyl sulfoxide (DMSO) as N, P and S precursors (designated as NPS-C-MOF-5). The performances of the carbon materials as electrocatalysts for the ORR were examined. The influences of porous carbons (C-MOF-5, C-UMCM-1, C-MOF-177) from carbonizing different MOFs (MOF-5, MOF-177 and UMCM-1) on the ORR were systematically investigated. On the other hand, using MOF-5 as precursors, the influences of porous carbons from different carbonization temperature on the ORR were also proved. On the basisi of the experimental data, the following conclusions have been drawn:the order of peak potentials of the three porous carbons is found to be C-MOF-5> C-UMCM-1> C-MOF-177, which agrees with the order of their onset potentials. C-MOF-5-900 exhibits the most positive peak potential and onset potential for the ORR among the three samples carbonizing at 700,900, and 1000℃, indicating that C-MOF-5-900 holds the most excellent electrocatalytic activity. Due to the synergistic effect of N, P and S ternary-doping, the electroneutrality of carbon atom and asymmetric spin density of heteroatoms were changed. And then, NPS-C-MOF-5 exhibits excellent catalytic activity, methanol tolerance and long-term stability.(3) The novel N-doped Fe/Fe3C@graphitic layer/carbon nanotube hybrid (Fe/Fe3C@NGL-NCNT) was successfully synthesized using MIL-101(Fe) and melamine as solid precursors after ball-milling and carbonization. The PXRD pattern shows that the hybrid is composed of Fe/Fe3C species and graphitic carbons. The EDS and XPS spectra further support the above results and demonstrat the existence of N. Then, the performances of the hybrid as electrocatalyst for the ORR and OER were investigated. On the other hand, the influences of the amount of Fe/Fe3C species and melamine, and carbonization temperature on the ORR were explored. Due to the synergistic effect of the unique architecture, a large amount of active sites, and high N concentration, the hybrid shows higher ORR activity comparable to commercial Pt-C; while methanol tolerance, OER activity and stability superior to those of commercial Pt-C.(4) The carbon dots (Cdots) functional UMCM-1 composite (Cdots@UMCM-1a) was synthesized by embedding Cdots within UMCM-1 by a stepwise synthetic approach. The PXRD pattern exhibits the framework structures remain almost intact after the encapsulation of Cdots. We investigated the applications for the H2 storage and fluorescent detection for nitroaromatic explosives of the hybrid.