The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

As modern society develops, the need for clean energy becomes increasingly important on a global scale. Because of this, the exploration of novel materials for energy storage and utilization is urgently needed to achieve low-carbon economy and sustainable development. Among these novel materials, metal–organic frameworks (MOFs), a class of porous materials, have gained increasing attention for utilization in energy storage and conversion systems because of ultra-high surface areas, controllable structures, large pore volumes and tunable porosities. In addition to pristine MOFs, MOF derivatives such as porous carbons and nanostructured metal oxides can also exhibit promising performances in energy storage and conversion applications. In this review, the latest progress and breakthrough in the application of MOF and MOF-derived materials for energy storage and conversion devices are summarized, including Li-based batteries (Li-ion, Li–S and Li–O2 batteries), Na-ion batteries, supercapacitors, solar cells and fuel cells.

Metal–Organic Frameworks (MOFs) and MOF-Derived Materials for Energy Storage and Conversion

Creating oxygen-vacancies in MoO3-x nanobelts toward high volumetric energy-density asymmetric supercapacitors with long lifespan

Supercapacitors (SCs) have attracted much attention as energy storage devices due to their high power density, fast charge/discharge capability, and long cycling life. The core/shell structure design of the electrocapacitive material is one of the effective ways to achieve large surface area and high conductivity for providing more faradaic reaction sites and accelerating the charge transfer, respectively, and therefore to enhance the electrocapacitive performance of SCs. To better understand the core/shell structure, this review paper compares the material category, morphology, and synthesis methods for the core/shell structures as well as their electrochemical performances for the corresponding SCs. The electroactive materials applied in the core/shell structure include carbon materials, conducting polymers, metals, metal hydroxides, metal oxides and metal sulfides, while zero-dimensional, one-dimensional, two-dimensional, and three-dimensional structures are considered for the core/shell material. This review article outlines the most commonly used methods for making the core and shell materials over the past decade (2007–2018), and points out the most efficient combination of the material categories and morphologies for the core/shell structure. By understanding the details of the core/shell materials, more efficient design regarding the choices of material category and morphology can be achieved, and therefore better electrocapacitive performance for the resulting SCs can be realized.

A review of electrode materials based on core–shell nanostructures for electrochemical supercapacitors

Construction of magnetic lignin-based adsorbent and its adsorption properties for dyes.

Ternary ZnO/Co3O4/NiO inherited layered core-shell structure from a double template for high performanced supercapacitor

In situ hydrothermal construction of hydrogel composites by anchoring Ni(OH)2 nanoparticles onto sulfonated graphene and their application for functional supercapacitor electrode

The invention belongs to the technical field of metal-organic framework materials, and relates to a method for preparing a polynary nano-cage composite material by using a zeolitic imidazolate framework as a template. The method comprises the following steps: synthesizing a ZIF-67 framework through a solvothermal technology by using methanol as a solvent, and synthesizing a hydroxide precursor from nickel nitrate and zinc nitrate by adjusting a mass ratio of the zinc nitrate to the nickel nitrate; and sequentially centrifuging, washing, drying and calcining the hydroxide precursor to obtain the nano-cage composite material. The method has the advantages of simple process, low price, easiness in control, and low cost, and the prepared product is a nano-cage composite material having a non-spherical hollow structure, and has the advantages of large specific surface area, high crystallinity, good morphology, and easiness in realization of industrialization.

Method for preparing polynary nano-cage composite material

The invention belongs to the technical field of a metal organic composite material, relates to a method for preparing a nano-cage composite material by taking a zeolite imidazate skeleton as a template, in particular to a method for preparing a non-spherical hollow structure nano-cage composite material by taking ZIF-67 as a template. The method comprises the following steps: synthesizing a ZIF-67 nano-crystal, taking the ZIF-67 as the template, dispersing into an ethanol solution of nitrate, stirring, centrifuging and drying, and annealing in the air with the temperature of 300 to 350 DEG C and at the rate of 2 DEG C/min for 2 to 3 hours. The operation condition is easy to control, the equipment is simple, the preparation cost is low, the nano-cage composite material with the hollow structure is synthesized by adjusting the mass ratio of zinc nitrate to copper nitrate, the prepared product particles are distributed uniformly, particle diameter dispersibility is high, the fission agglomeration degree is small, and the appearance is good. The method is simple in process, easily available in raw material, low in cost, low in pollution and suitable for industrialized production.

Method for preparing non-spherical hollow structure nano-cage composite material by template method

The invention belongs to the technical field of preparation of nano materials and relates to a preparation method of a BiOCl photocatalyst, in particular to a method for preparing a BiOCl photocatalyst by a solvothermal method and application of the method. The method comprises: first, making graphite powder into graphene oxide via concentrated sulfuric acid and potassium permanganate, using Bi(NO3)3.5H2O as a Bi source, KCl as a Cl source and CTAB (cetyl trimethyl ammonium bromide) as a surfactant to prepare, with the GO (graphene oxide) doped in, the BiOCl photocatalyst through the simple solvothermal method, and degrading rhodamine B via visible light catalysis. The method has the advantages that the preparation conditions are easy, the process flow is simple, the process is easy to perform, the process provides good effect after being used in photocatalytic degradation of dyes, the environment can be protected, environmental burden can be relieved, and the method is suitable for industrial production.

Zhou Saisai

Papers

Ternary ZnO/Co3O4/NiO inherited layered core-shell structure from a double template for high performanced supercapacitor

In situ hydrothermal construction of hydrogel composites by anchoring Ni(OH)2 nanoparticles onto sulfonated graphene and their application for functional supercapacitor electrode

Method for preparing polynary nano-cage composite material

Method for preparing non-spherical hollow structure nano-cage composite material by template method

Method for preparing BiOCl photocatalyst by solvothermal method