Porous carbons have several advantageous properties with respect to their use in energy applications that require constrained space such as in electrode materials for supercapacitors and as solid state hydrogen stores. The attractive properties of porous carbons include, ready abundance, chemical and thermal stability, ease of processability and low framework density. Activated carbons, which are perhaps the most explored class of porous carbons, have been traditionally employed as catalyst supports or adsorbents, but lately they are increasingly being used or find potential applications in the fabrication of supercapacitors and as hydrogen storage materials. This manuscript presents the state-of-the-art with respect to the preparation of activated carbons, with emphasis on the more interesting recent developments that allow better control or maximization of porosity, the use of cheap and readily available precursors and tailoring of morphology. This review will show that the renewed interest in the synthesis of activated carbons is matched by intensive investigations into their use in supercapacitors, where they remain the electrode materials of choice. We will also show that activated carbons have been extensively studied as hydrogen storage materials and remain a strong candidate in the search for porous materials that may enable the so-called Hydrogen Economy, wherein hydrogen is used as an energy carrier. The use of activated carbons as energy materials has in the recent past and is currently experiencing rapid growth, and this review aims to present the more significant advances.

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Energy storage applications of activated carbons: supercapacitors and hydrogen storage

In this study, we fabricated an aqueous Li-ion hybrid capacitor (LHC) using LiMn2O4 and sonochemically reduced graphene as the positive and negative electrodes, respectively. The X-ray diffraction pattern and Raman analyses were performed to identify the phase, crystalline and bonding nature of the prepared LiMn2O4 and sonochemically reduced graphene. The electrochemical characterization such as cyclic voltammetry and electrochemical impedance spectroscopy for the LiMn2O4 and graphene were analysed using a three electrode configuration. Further, asymmetric LiMn2O4║graphene LHC was fabricated and tested for its device performance. The galvanostatic charge-discharge analysis shows that the fabricated LiMn2O4║graphene LHC device delivered a high specific capacitance of 59.45 F/g at a constant discharge current density of 0.4 A/g with a better coulombic efficiency of 97.9 %. The LiMn2O4║graphene LHC device delivered a high specific energy of 39.96 Wh/kg at a power of 440 W/kg with better capacitance retention of 90.24 % even after 1000 cycles.

Fabrication of High‐Performance Aqueous Li‐Ion Hybrid Capacitor with LiMn2O4 and Graphene

Fabrication of high energy Li-ion hybrid capacitor using manganese hexacyanoferrate nanocubes and graphene electrodes

O3-Type layered oxides are widely studied as cathodes for sodium-ion batteries (SIBs) due to their high theoretical capacities. However, their rate capability and durability are limited by tortuous Na+ diffusion channels and complicated phase evolution during Na+ extraction/insertion. Here we report our findings in unravelling the mechanism for dramatically enhancing the stability and rate capability of O3-NaNi0.5Mn0.5-xSbxO2 (NaNMS) by substitutional Sb doping, which can alter the coordination environment and chemical bonds of the transition metal (TM) ions in the structure, resulting in a more stable structure with wider Na+ transport channels. Furthermore, NaNMS nanoparticles are obtained by surface energy regulation during grain growth. The synergistic effect of Sb doping and nanostructuring greatly reduces the ionic migration energy barrier while increasing the reversibility of the structural evolution during repeated Na+ extraction/insertion. An optimized NaNMS-1 electrode delivers a reversible capacity of 212.3 mAh g-1 at 0.2 C and 74.5 mAh g-1 at 50 C with minimal capacity loss after 100 cycles at a low temperature of -20 °C. Such electrochemical performance is superior to most of the reported layered oxide cathodes used in rechargeable SIBs.

A High-Rate, Durable Cathode for Sodium-Ion Batteries: Sb-Doped O3-Type Ni/Mn-Based Layered Oxides.

Sewage sludge derived magnetic biochar effectively activates peroxymonosulfate for the removal of norfloxacin

Aqueous lithium ion capacitors (LICs) with LiFePO4 positive electrodes and activated carbon (AC) negative electrodes were developed and their electrochemical performances were investigated by cyclic voltammetry, galvanostatic charge/discharge, and ac impedance spectroscopy at various temperatures. It is found that the stable voltage window for the aqueous LICs is 0–1.7 V and the optimized mass ratio between the positive electrode and negative electrode is 1:1. The rate capability of the LIC is much higher than that of the LiFePO4 electrodes. The Ohmic resistance and electrochemical impedance of the LiFePO4 and AC electrodes decrease with increasing the temperature, leading to high rate capability of the LIC. The performance of the LIC is deteriorated when it is cycled at 70 °C which is caused by the reduction of Fe2+ in LiFePO4.

Electrochemical performance of lithium ion capacitors using aqueous electrolyte at high temperature

Transition metal (TM) single atomic catalysts (MSAC-N-C) derived from doped zeolite imidazolate frameworks (ZIF-8) are considered attractive oxygen reduction reaction (ORR) catalysts for fuel cells and metal-air batteries due to their advantages of high specific surface area, more active catalytic sites, adjustable pore size, and coordination topology features. This review provides an updated overview of the latest advances of MSAC-N-C catalysts derived from ZIF-8 precursors in ORR electrocatalysis. Particularly, some key challenges, including coordination environments regulation of catalysis center in MSAC-N-C, the active sites loading optimization and synergistic effects between TM nanoclusters/nanoparticles and the single atoms on MSAC-N-C catalysis activity, as well as their adaptability in various devices, are summarized for improving future development and application of MSAC-N-C catalysts. In addition, this review puts forward future research directions, making it play a better role in ORR catalysis for fuel cells and metal air batteries.

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Research Progress in ZIF-8 Derived Single Atomic Catalysts for Oxygen Reduction Reaction

ZIF-derived zinc decorated cobalt nanoparticles for efficient oxygen reduction and Zn-air batteries

With the development of society, sodium-ion batteries (SIBs) attract more and more attention and are expected to be the next generation of daily energy storage devices. Among the previously reported cathode materials for SIBs, the layered transition metal oxides are considered to be the most competitive cathode materials due to their high specific capacities, simple synthesis process, and many similar advantages to the successful Li transition metal oxides in lithium-ion batteries (LIBs). This review summarizes the recent progress of layered transition metal oxide cathode materials for SIBs, which mainly include Mn-based, Ni/Mn-based, Ni/Co/Mn-based, and Ni/Fe/Mn-based layered cathode materials. The remaining challenges and future developments for the layered transition metal oxide cathode materials are also discussed. This review is expected to provide some insights into the development of layered transition metal oxide cathodes for high-performance SIBs. 

Yuanyuan Sun

Papers

Electrochemical performance of lithium ion capacitors using aqueous electrolyte at high temperature

Research Progress in ZIF-8 Derived Single Atomic Catalysts for Oxygen Reduction Reaction

ZIF-derived zinc decorated cobalt nanoparticles for efficient oxygen reduction and Zn-air batteries

Recent developments of layered transition metal oxide cathodes for sodium‐ion batteries toward desired high performance

Natural wood-derived charcoal embedded with bimetallic iron/cobalt sites to promote ciprofloxacin degradation