Recent advancements in supercapacitor technology

Supercapacitors have gained a lot of attention due to their unique features like high power, long cycle life and environment-friendly nature. They act as a link for energy-power difference between a traditional capacitor (having high power) and fuel cells/batteries (having high energy storage). In this perspective, a worldwide research has been reported to address this and rapid progress has been achieved in the advancement of fundamental as well as the applied aspects of supercapacitors. Here, a concise description of technologies and working principles of different materials utilized for supercapacitors has been provided. The main focus has been on materials like carbon-based nanomaterials, metal oxides, conducting polymers and their nanocomposites along with some novel materials like metal-organic frameworks, MXenes, metal nitrides, covalent organic frameworks and black phosphorus. The performance of nanocomposites has been analysed by parameters like energy, capacitance, power, cyclic performance and rate capability. Some of the latest supercapacitors such as electrochromic supercapacitor, battery-supercapacitor hybrid device, electrochemical flow capacitor, alternating current line filtering capacitor, micro-supercapacitor, photo-supercapacitor, thermally chargeable supercapacitor, self-healing supercapacitor, piezoelectric and shape memory supercapacitor have also been discussed. This review covers the up-to-date progress achieved in novel materials for supercapacitor electrodes. The latest fabricated symmetric/asymmetric supercapacitors have also been reported.

Review of supercapacitors: Materials and devices

Failed chemical reactions are rarely reported, even though they could still provide information about the bounds on the reaction conditions needed for product formation; here data from such reactions are used to train a machine-learning algorithm, which is subsequently able to predict reaction outcomes with greater accuracy than human intuition.

Machine-learning-assisted materials discovery using failed experiments

The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

Old materials with new tricks: multifunctional open-framework materials.

Metal-organic frameworks (MOFs) are typically highlighted for their potential application in gas storage, separations and catalysis. In contrast, the unique prospects these porous and crystalline materials offer for application in electronic devices, although actively developed, are often underexposed. This review highlights the research aimed at the implementation of MOFs as an integral part of solid-state microelectronics. Manufacturing these devices will critically depend on the compatibility of MOFs with existing fabrication protocols and predominant standards. Therefore, it is important to focus in parallel on a fundamental understanding of the distinguishing properties of MOFs and eliminating fabrication-related obstacles for integration. The latter implies a shift from the microcrystalline powder synthesis in chemistry labs, towards film deposition and processing in a cleanroom environment. Both the fundamental and applied aspects of this two-pronged approach are discussed. Critical directions for future research are proposed in an updated high-level roadmap to stimulate the next steps towards MOF-based microelectronics within the community.

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An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors

The literature on inorganic open-framework materials abounds in the synthesis and characterization of metal silicates, phosphates and carboxylates. Most of these materials have an organic amine as the template. In the last few years, it has been shown that anions such as sulfate, selenite and selenate can also be employed to obtain organically templated open-framework materials. This tutorial review provides an up-to-date survey of organically templated metal sulfates, selenites and selenates, prepared under hydrothermal conditions. The discussion includes one-, two-, and three-dimensional structures of these materials, many of which possess open architectures. The article should be useful to practitioners of inorganic and materials chemistry, besides students and teachers. The article serves to demonstrate how most oxy-anions can be used to build complex structures with metal–oxygen polyhedra.

Organically-templated metal sulfates, selenites and selenates

The oxygen electrocatalysis, i.e. the oxygen reduction and evolution reactions, is traditionally executed using noble metal and metal oxide-based nanostructures. However, they are associated with many disadvantages such as high cost, lower durability/selectivity and detrimental environmental effects; this motivates researchers to develop new electroactive materials. In this study, we presented the synthesis of a Co-containing metal-organic framework (Co-MOF) and explored its electrocatalytic application towards the oxygen electrocatalysis (i.e. the oxygen reduction reaction and oxygen evolution reaction). The Co-MOF efficiently catalyzes the ORR with a lower onset (0.85 V vs. RHE)/reduction potential and higher reduction current density by a four-electron reduction path. Moreover, the MOF shows higher durability with >70% performance retention after 25 hours of reaction and tolerance towards methanol; this demonstrates its potential for application in direct methanol fuel cells (DMFCs); furthermore, due to the availability of more active sites and accessible surface area, the Co-MOF performs well towards the OER with lower onset potential and small Tafel slope as compared to the commercial RuO2 nanoparticles. Moreover, it needs only 280 mV overpotential to deliver the state-of-the-art current density of 10 mA cm-2 and robust stability. It shows the high TOF value of 93.21 s-1 at the overpotential of 350 mV as compared to the reported MOF/nanoparticle-based electrocatalysts and the state-of-the-art RuO2. Therefore, we believe that the as-developed Co-MOF holds the potential to be used as both a cathode and an anode electrocatalyst in the future energy storage and conversion systems.

A cobalt metal–organic framework (Co-MOF): a bi-functional electro active material for the oxygen evolution and reduction reaction

An amine-templated iron(II) sulfate of the composition [H3N(CH2)6NH3] [FeII1.5F3(SO4)]·0.5H2O, I, representing an example of a Kagome lattice with Fe in the +2 state, has been synthesized under solvothermal conditions. Having determined the structure by single-crystal X-ray diffraction, the oxidation state of iron was established by Mossbauer spectroscopy. The magnetic properties of the Fe(II) Kagome compound are rather unusual in that it undergoes ferrimagnetic ordering below 19 K and does not exhibit spin-glass freezing.

Synthesis, Structure, and the Unusual Magnetic Properties of an Amine-Templated Iron(II) Sulfate Possessing the Kagomé Lattice

The electronic spectra, electrical conductivity, magnetism, and gas adsorption properties of the newly prepared Prussian blue analogues Fe4[Ru(CN)6]3·18H2O (2) and K1.2Ru3.6[Ru(CN)6]3·16H2O (3) are compared with those of Prussian blue itself (Fe4[Fe(CN)6]3·14H2O, 1). The increase in the degree of electronic localization for the unsymmetrical iron−ruthenium analogue 2 is reflected in a shift of the intervalence charge transfer (IVCT) band to higher energies and an increase in the electrical resistivity. In contrast, the all-ruthenium analogue 3 exhibits a lower-energy IVCT band, as well as the highest electrical conductivity, due to the combined effects of electronic delocalization and the presence of potassium ions. Unlike Prussian blue, the ruthenium and iron−ruthenium analogues show no magnetic ordering transition above 1.8 K. Nitrogen adsorption measurements at 77 K show the dehydrated forms of 2 and 3 to be microporous with BET surface areas of 670 and 325 m2/g, respectively.

Synthesis and Characterization of Ruthenium and Iron−Ruthenium Prussian Blue Analogues

1,8-Diazacubane-templated nickel(II) sulfate with the Kagome structure prepared under solvothermal conditions exhibits interesting magnetic properties.

J. N. Behera

Papers

Organically-templated metal sulfates, selenites and selenates

A cobalt metal–organic framework (Co-MOF): a bi-functional electro active material for the oxygen evolution and reduction reaction

Synthesis, Structure, and the Unusual Magnetic Properties of an Amine-Templated Iron(II) Sulfate Possessing the Kagomé Lattice

Synthesis and Characterization of Ruthenium and Iron−Ruthenium Prussian Blue Analogues

A Ni2+ (S = 1) Kagome Compound Templated by 1,8-Diazacubane