In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Fourier transform Infrared (FTIR) spectroscopy is a versatile technique for the characterization of materials belonging to the carbon family. Based on the interaction of the IR radiation with matter this technique may be used for the identification and characterization of chemical structures. Most important features of this method are: non-destructive, real-time measurement and relatively easy to use. Carbon basis for all living systems has found numerous industrial applications from carbon coatings (i.e. amorphous and nanocrystalline carbon films: diamond-like carbon (DLC) films) to nanostructured materials (fullerenes, nanotubes, graphene) and carbon materials at nanoscale or carbon dots (CDots). In this paper, we present the FTIR vibrational spectroscopy for the characterization of diamond, amorphous carbon, graphite, graphene, carbon nanotubes (CNTs), fullerene and carbon quantum dots (CQDs), without claiming to cover entire field.

FTIR Spectroscopy for Carbon Family Study

Supercapacitors (SCs) have great promise as the state-of-the-art power source in portable electronics and hybrid vehicles. The performance of SCs is largely determined by the properties of the electrode material, and numerous efforts have been devoted to the explorations of novel electrode materials. Recently, iron-based materials, including Fe2O3, Fe3O4, FeOOH, FeOx, CoFe2O4, and MnFe2O4, have received considerable attention as very promising electrode materials for SCs due to their high theoretical specific capacitances, natural abundance, low cost, and non-toxicity. However, most of these Fe-based SC electrodes suffer from poor conductivity and/or electrochemical instability, which seriously impede their implementation as high-performance electrodes for SCs. To settle these issues, substantial efforts have been made in improving their conductivity and cycling stability, and great processes have been achieved. Here, recent research advances in the rational design and synthesis of diverse Fe-based nanostructured electrodes and their capacitive performance for SCs are presented. Besides, challenges and prospects of Fe-based materials as advanced negative electrodes for SCs are also discussed.

Iron-Based Supercapacitor Electrodes: Advances and Challenges

Biomorphic mineralization: From biology to materials

We report the development of MOF-derived nitrogen-doped carbon/Co3O4 nanocomposites (Co3O4@NCs) with core-shell structures as an efficient electrocatalyst for the artificial nitrogen fixation at room temperature and atmospheric pressure in 0.05 M H2SO4. It exhibits a high NH3 yield of 42.58 μg h-1 mgcat.-1 and a faradaic efficiency of 8.5% at -0.2 V versus reversible hydrogen electrode. Experimental results show that the great N2 reduction reaction performance of Co3O4@NCs originates from the synergistic effects of N-doped carbon and Co3O4 with significant oxygen vacancy. In addition, we speculate that the core-shell structure can further enhance the electrochemical activity for producing NH3.

MOF-Derived Co3O4@NC with Core-Shell Structures for N2 Electrochemical Reduction under Ambient Conditions.

Heterostructured graphene@Na4Ti9O20 nanotubes for asymmetrical capacitive deionization with ultrahigh desalination capacity

Mesoporous carbon derived from ZIF-8 for high efficient electrosorption

High-quality Prussian blue/reduced graphene oxide (PB/rGO) nanohybrids were synthesized via a simple polyvinylpyrrolidone (PVP)-assisted polyol reduction method under mild conditions. The structure and composition of PB/rGO were confirmed by means of X-ray diffraction (XRD), electron microscopes (SEM and transmission electron microscopy (TEM)), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). These results indicate that ratios of starting materials allow a good control on loading and morphology of PB/graphene hybrids, and at ratio of K3Fe(CN)6/GO of 1:2, PB nanocubes get completely embedded into the defect of porous graphene matrices. Electrochemcial characterization of the PB/rGO nanocomposites with different PB/rGO weight ratios was carried out by cyclic voltammograms and galvanostatic charge–discharge in 1.0 M KNO3 electrolyte. The PB/rGO nanocomposites exhibit much higher specific capacitances than either bare PB nanocrystals or pure rGO sheets. PB/rGO (1:2) exhibits the highest specific capacitance of 251.6 F g−1 at a scan rate of 10 mV s−1 and an excellent cycling stability along with 92 % specific capacitance retained after 1000 cycle tests. The significant enhancement in electrochemical performance over PB/rGO nanocomposites can be attributed to a positive synergetic effect that the PB nanocube interlocked dispersion of rGO sheets superimposes pseudocapacitance from PB on double-layer capacitance from rGO sheets.

A novel interlocked Prussian blue/reduced graphene oxide nanocomposites as high-performance supercapacitor electrodes

Lithium–sulfur batteries have aroused great interest in the context of rechargeable batteries, while the shuttle effect and sluggish conversion kinetics severely handicap their development. Defect engineering, which can adjust the electronic structures of electrocatalyst, and thus affect the surface adsorption and catalytic process, has been recognized as a good strategy to solve the above problems. However, research on phosphorus vacancies has been rarely reported, and how phosphorus vacancies affect battery performance remains unclear. Herein, CoP with phosphorus vacancies (CoP‐Vp) is fabricated to study the enhancement mechanism of phosphorus vacancies in Li–S chemistry. The derived CoP‐Vp features a low Co‐P coordination number and the introduced phosphorus vacancies mainly exist in the form of clusters. The obtained CoP‐Vp can reinforce the affinity to lithium polysulfides (LiPSs) and thus the shuttle effect can be restrained. In addition, the reduced reaction energy barriers and the promoted diffusion of Li+ can accelerate redox kinetics. Electrochemical tests and in situ Raman results confirm the advantages of phosphorus vacancies. The S/CNT‐CoP‐Vp electrode presents outstanding cycling performance and achieves a high capacity of 8.03 mAh cm−2 under lean electrolyte condition (E/S = 5 μLE mg−1S). This work provides a new insight into improving the performance of Li–S batteries through defect engineering.

Min Luo

Papers

MOF-Derived Co3O4@NC with Core-Shell Structures for N2 Electrochemical Reduction under Ambient Conditions.

Heterostructured graphene@Na4Ti9O20 nanotubes for asymmetrical capacitive deionization with ultrahigh desalination capacity

Mesoporous carbon derived from ZIF-8 for high efficient electrosorption

A novel interlocked Prussian blue/reduced graphene oxide nanocomposites as high-performance supercapacitor electrodes

Phosphorus Vacancies as Effective Polysulfide Promoter for High‐Energy‐Density Lithium–Sulfur Batteries