Metal–Organic-Framework-Derived N-, P-, and O-Codoped Nickel/Carbon Composites Homogeneously Decorated on Reduced Graphene Oxide for Energy Storage

Abstract

In this work, a type of high-performance electrode material of Ni/C/rGO-n [n = wt % of reduced graphene oxide (rGO)] derived from nickel-based metal−organic framework (Ni-MOF) for supercapacitors is successfully prepared. First, a hydrogen-bonding-assisted approach to continuous growth of Ni-MOFs on graphene oxide (GO) sheets is developed through the application of a hexadentate ligand, hexakis(4-carboxylphenoxy)cyclotriphosphazene (CTP-COOH), as the anchor with multiple biting points. The thicknesses of the obtained layer cakelike Ni-MOF/GO-n (n: wt % GO) nanosheet composites with GO as the filling content can be controlled by tuning the ratio between GO and Ni-MOF. During the subsequent process of thermolysis treatment of Ni-MOF/GO-n composites, GO acts as a "hard" template and thus the decomposition of loaded metal−organic frameworks (MOFs) affords highly porous metal/C composites homogeneously embedded on the rGO matrix. This highly porous structure enhances the stability of Ni/C composites profoundly. Besides, both the rGO matrix and porous metal/C composites can provide an expressway for electron transport and shorten ion diffusion paths for greatly enhanced diffusion kinetics within the electrode materials, therefore leading to a superior rate capability. Moreover, application of the hexadentate ligand CTP-COOH with a six-membered ring backbone, which consisted of N and P atoms linked together alternatively, enables self-doping of N, O, and P to the derived materials. It is proven that the electrochemical performances, especially the stability, are remarkably enhanced for the derived Ni/C/rGO-n composites compared with the bare Ni-MOF-derived Ni/C composites. More importantly, this work pioneeringly demonstrates the potential application of MOF derivatives in energy storage devices.

Metal–Organic Frameworks and Their Derived Functional Materials for Supercapacitor Electrode Application

“…The synergistic effect between different heteroatoms is conductive to good electrochemical behavior, including a large charge storage capacity (1258.7 F g −1 at 8 A g −1 ), excellent rate performance (1087.1 F g −1 at 20 A g −1 ), and superior cycling stability (110% after 50 000 cycles). [ 68 ] In another example, a Zn‐MOF constructed with 2‐ethylimidazole and 5‐methyltetrazole as a double ligand was chosen as the precursor for the preparation of a ultrahigh‐content (14.23 wt%) nitrogen‐decorated nanoporous carbon, demonstrating that pyridinic N and pyrrolic N play an important role in pseudocapacitance. [ 69 ] Generally, the nitrogen content of carbon materials is related to calcination temperatures.…”

The Application of Metal–Organic Frameworks and Their Derivatives for Supercapacitors

“…Shi et al [ 78 ] found N, P and O co-doped Co/C composites derived from Co-hexa-(4-carboxyl-phenoxy)-cyclotriphosphazene (CTP-COOH, containing C, N, O and P) can reach a maximum of 739.6 F g −1 in 6 M KOH at a current density of 1 A g −1 and keep the capacitance retention of 80.6% over 5000 cycles. Latterly, they [ 79 ] took the same organic linker, CTP-COOH, but a different salt of Co to prepare binder-free MOFs-derived carbon as a supercapacitor electrode. They [ 79 ] claimed that the electrochemical properties of MOF-derived-C/rGO (using GO as the MOFs growth template) composites are greatly enhanced compared to bare MOF-derived C. Among the obtained Ni/C, Ni/C/rGO-x (x = 2, 4 and 8 wt%), Ni/C/rGO-4 (GO: 4 wt%) exhibits the best electrochemical performance, with a maximum capacitance of 1258.7 F g −1 at a current density of 8 A g −1 and magnificent stability with capacitance retention of 110% over 50,000 cycling tests.…”

“…Latterly, they [ 79 ] took the same organic linker, CTP-COOH, but a different salt of Co to prepare binder-free MOFs-derived carbon as a supercapacitor electrode. They [ 79 ] claimed that the electrochemical properties of MOF-derived-C/rGO (using GO as the MOFs growth template) composites are greatly enhanced compared to bare MOF-derived C. Among the obtained Ni/C, Ni/C/rGO-x (x = 2, 4 and 8 wt%), Ni/C/rGO-4 (GO: 4 wt%) exhibits the best electrochemical performance, with a maximum capacitance of 1258.7 F g −1 at a current density of 8 A g −1 and magnificent stability with capacitance retention of 110% over 50,000 cycling tests. This is partially attributed to the increased surface area of Ni/C/GO-4 nanosheets (126.4 m 2 g −1 ), compared to the bare Ni/C synthesized without the presence of GO with surface area of 3.7 m 2 g −1 .…”

Ultrafine TiO2 Nanoparticle Supported Nitrogen‐Rich Graphitic Porous Carbon as an Efficient Anode Material for Potassium‐Ion Batteries

“…[32][33][34][35][36][37][38][39][40][41][42] Building on this, MOFs have been widely used as precursor materials for the generation of carbon materials hybridized with nanoscale metals and metal oxides and were used in a variety of different energy-related applications, including electrocatalytic oxygen evolution reaction/hydrogen evolution reaction, supercapacitors, and batteries. [43][44][45][46][47] Herein, we report a facile strategy for the in situ synthesis of ultrafine anatase TiO 2 nanoparticle encapsulated hierarchical nitrogen-rich graphitic carbon ( -bdc linkers and features tetrahedral and octahedral cages (6.13 and 12.55 Å) with accessible pore windows of 5-7 Å (Scheme 1). [42] We took advantage of its intrinsic porous structure to build an efficient anode material for a KIB.…”