Iftikhar Hussain

Bio: Iftikhar Hussain is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Materials science & Supercapacitor. The author has an hindex of 13, co-authored 30 publications receiving 618 citations. Previous affiliations of Iftikhar Hussain include Chonbuk National University & Yeungnam University.

One-step synthesis of hollow C-NiCo2S4 nanostructures for high-performance supercapacitor electrodes.

Abstract: Carbon-containing NiCo2S4 hollow-nanoflake structures were fabricated by a one-step solvothermal method using CS2 as a single source for sulfidation and carbonization. The reaction mechanism for the hollow structure with carbon residues was explored based on the formation of a bis(dithiocarbamate)–metal complex and the Kirkendall effect during solvothermal synthesis. The NiCo2S4 nanoflake electrode exhibited a high specific capacitance of 1722 F g−1 (specific capacity 688.8 C g−1) at a current density of 1 A g−1 and an excellent cycling stability (capacity retention of 98.8% after 10 000 cycles). The as-fabricated asymmetric supercapacitor based on NiCo2S4 nanoflakes and activated carbon electrodes revealed a high energy density of 38.3 W h kg−1 and a high power density of 8.0 kW kg−1 with a capacitance retention of 91.5% and a coulombic efficiency of 95.6% after 5000 cycles, highlighting its great potential for practical supercapacitor applications.

Core–Shell Structured Nanoenergetic Materials: Preparation and Fundamental Properties

Abstract: Energetic materials, including explosives, pyrotechnics, and propellants, are widely used in mining, demolition, automobile airbags, fireworks, ordnance, and space technology. Nanoenergetic materials (nEMs) have a high reaction rate and high energy density, which are both adjustable to a large extent. Structural control over nEMs to achieve improved performance and multifunctionality leads to a fascinating research area, namely, nanostructured energetic materials. Among them, core-shell structured nEMs have gained considerable attention due to their improved material properties and combined multiple functionalities. Various nEMs with core-shell structures have been developed through diverse synthesis routes, among which core-shell structured nEMs associated with explosives and metastable intermolecular composites (MICs) are extensively studied due to their good tunability and wide applications, as well as excellent energetic (e.g., enhanced heat release and combustion) and/or mechanical properties. Herein, the preparation methods and fundamental properties of the abovementioned kinds of core-shell structured nEMs are summarized and the reasons behind the satisfactory performance clarified, based on which suggestions regarding possible future research directions are proposed.

A 3D walking palm-like core-shell CoMoO4@NiCo2S4@nickel foam composite for high-performance supercapacitors.

Abstract: Supercapacitors are one of the most promising renewable-energy storage systems. In this study, a three-dimensional walking palm-like core–shell CoMoO4@NiCo2S4@nickel foam (NF) nanostructure was synthesized using a two-step hydrothermal method for high electrochemical performance. The as-prepared composite exhibited a high areal capacitance of 17.0 F cm−2 (2433 F g−1) at a current density of 5 mA cm−2 in a three-electrode system. The results revealed outstanding cycling stability of 114% after 10 000 charge–discharge cycles. An aqueous asymmetric supercapacitor device assembled with CoMoO4@NiCo2S4@NF and activated carbon (AC)@NF as the positive and negative electrodes, respectively, showed a high capacitance of 4.19 F cm−2 (182 F g−1) and delivered a high energy density of 60.2 W h kg−1 at a power density of 188 W kg−1 and a high power density of 1.5 kW kg−1 at an energy density 29.2 W h kg−1, lighting 22 parallel-connected red light emitting diodes for over 60 s. The synergistic effects of the core–shell CoMoO4@NiCo2S4@NF electrode material highlight the potential of this composite as an effective active material for supercapacitor applications.

An oriented Ni–Co-MOF anchored on solution-free 1D CuO: a p–n heterojunction for supercapacitive energy storage

Abstract: Herein, we propose an effective strategy to enhance the electrochemical activity of a metal organic framework-based (MOF) electrode material for electrochemical capacitors. The fabrication involves the synthesis of CuO nanowires on a Cu substrate through a facile solution-free dry oxidation route followed by the deposition of an oriented Ni–Co-zeolitic imidazolate framework (Ni–Co-ZIF) on 1D CuO. This synthesis strategy benefitted from the highly exposed redox active sites of the aligned Ni–Co-ZIF, an “ion and electrolyte repository”, to assist the diffusion of electrolyte ions, and a p–n heterojunction between CuO and the Ni–Co-ZIF. ZIFs represent an emerging and unique class of MOFs. The oriented pseudocapacitive Ni–Co-ZIF@CuO composite electrode yielded excellent electrochemical merits including a high gravimetric capacitance which is 3.3- and 2.1-fold higher than those of the self-supported CuO and bulk MOF, respectively. Furthermore, we employed first principles density functional theory calculations to study the enhanced electronic conductivity and reduced work function of Ni–Co-ZIF@CuO systems upon CuO doping, which reinforced the experimental findings. Moreover, an asymmetric supercapacitor (ASC) device was assembled to evaluate the application of the as-fabricated electrode material for electrochemical capacitors. The gadget delivered a maximum energy density of 43 W h kg−1, with improved cycling stability after 10 000 cycles. The oriented Ni–Co-ZIF@CuO with remarkable electrochemical activity and mechanical flexibility inspires for next-generation MOF-based electrode materials with superior electrochemical attributes.

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

Abstract: 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.

Ultrathin NiCo-MOF Nanosheets for High-Performance Supercapacitor Electrodes

Abstract: Metal–organic frameworks (MOFs) have attracted intensive attention for high-performance supercapacitors owing to their large specific surface area and tunable pore structure. Herein, ultrathin NiCo-MOF nanosheets are fabricated by a facile ultrasonication at room temperature and employed as a supercapacitor electrode material. The unique nanosheet-like structure of NiCo-MOF provides more electroactive sites and a shorter pathway for electron transfer and electrolyte diffusion, resulting in excellent electrochemical performance with a high specific capacitance of 1202.1 F g–1 at 1 A g–1. In addition, an asymmetric supercapacitor of NiCo-MOF//activated carbon was assembled in 2 M KOH electrolyte. It delivers an energy density of 49.4 W h kg–1 at a power density of 562.5 W h kg–1 in a voltage window of 1.5 V. The results demonstrate a new method to fabricate ultrathin MOF nanosheets for high-performance supercapacitor electrode materials.