Gallium-based nascent electrode materials towards promising supercapacitor applications: a review

To meet the energy requirement of the modern era, supercapacitors are promising candidates for energy storage devices, which possess the potential to compete with the future battery technology. To accomplish this pivotal task, it is vital to choose electrode materials that have high power and energy density as well as superb electrochemical stability. For the past few years, the use of gallium-based materials for energy storage applications has attracted attention because of their excellent activity towards electrochemical energy storage applications despite the single oxidation state (i.e., +3 which is redox inactive and does not contribute towards pseudo capacitance). Recently, research on gallium-based materials has started and will be continued further owing to the fact that gallium-based materials possess numerous excellent properties such as fast charge and discharge rate, high power density, long cycle life, stability over a wide range of temperatures, excellent electron velocity, superior chemical and physical stabilities and high voltage application capability, which make them a potential class of electrode materials for supercapacitors. The enhancement in the electrochemical performance upon the introduction of gallium into the system can make it a futuristic candidate for electrochemical energy storage devices. Herein, we systematically outline the synthesis and characterization of gallium-based materials and their composites as explored by esteemed researchers focusing only on their supercapacitive performance via electrochemical techniques. For a better understanding, the underlying charge storage mechanism and identified characteristics are presented to give a crystal-clear idea about the field. In addition, the key challenges and impending perspectives of gallium-based electrodes for supercapacitor applications are debated.

GaOOH-modified metal-organic frameworks UiO-66-NH2: Selective and sensitive sensing four heavy-metal ions in real wastewater by electrochemical method

Heavy metal pollution in the environment poses a serious threat to the ecosystem and human health, which has attracted widespread attention. In this study, an octahedral structure composite composed of UiO-66-NH₂ MOFs and semiconductor GaOOH materials has been prepared and used as electrode materials successfully. These composites can be used for the real-time and online determination of Cd²⁺, Cu²⁺, Hg²⁺, and Pb²⁺ in real water samples simultaneously or alone via an electrochemical method. Zr-MOF has a large and unique surface area that is beneficial to the adsorption and preconcentration of heavy metal ions. The experiment parameters such as pH, deposition potential, and deposition time were optimized. Under the optimized conditions, the electrochemical performances and practical applications of Zr-MOF composites modified electrode have been investigated, which shows excellent wider linear range and lower detection limit (LOD). The results demonstrated excellent selectivity, reproducibility, stability and applicability for the detection of four metal ions. These superior features stem from the synergistic reaction mechanism of UiO-66-NH₂ and GaOOH. In addition, it has been established a new detection strategy for heavy metal ions through the form of metal-organic framework (MOF) composite in this work. It may provide a novel platform for the quantitative determination of heavy metal ions in various environmental samples.

Three-Dimensional Fibrous Iron as Anode Current Collector for Rechargeable Zinc–Air Batteries

A three-dimensional (3D) fibrous structure with a high active surface and conductive pathway proved to be an excellent anode current collector for rechargeable zinc–air batteries (ZABs). Herein, a cost-effective and highly stable zinc (Zn) electrode, based on Zn electrodeposited on iron fibers (Zn/IF), is duly examined. Electrochemical characteristics of the proposed electrode are seen to compete with a conventional zinc/nickel foam (Zn/NF) electrode, implying that it can be a suitable alternative for use in ZABs. Results show that the Zn/IF electrode exhibits an almost similar trend as Zn/NF in cyclic voltammetry (CV). Moreover, by using a Zn/IF electrode, electrochemical impedance spectroscopy (EIS) demonstrates lower charge transfer resistance. In the application of a rechargeable ZAB, the fibrous Zn/IF electrode exhibits a high coulombic efficiency (CE) of 78%, close to the conventional Zn/NF (80%), with almost similar capacity and lower charge transfer resistance, after 200 charge/discharge cycles. It is evident that all the positive features of Zn/IF, especially its low cost, shows that it can be a valuable anode for ZABs.

Boosting the performance of cobalt molybdate nanorods by introducing nanoflake-like cobalt boride to form a heterostructure for aqueous hybrid supercapacitors

Binary transition metal oxides have received extensive attention because of their multiple oxidation states. However, due to the inherent vices of poor electronic/ionic conductivities, their practical performance as supercapacitor material is limited. Herein, a cobalt molybdate/cobalt boride (CoMoO₄/Co-B) composite is constructed with cobalt boride nanoflake-like as a conductive additive in CoMoO₄ nanorods using a facile water bath deposition process and liquid-phase reduction method. The effects of CoMoO₄/Co-B mass ratios on its electrochemical performance are investigated. Remarkably, the CoMoO₄/Co-B composite obtained at a mass ratio of 2:1 shows highly enhanced electrochemical performance relative to those obtained at other ratios and exhibits an optimum specific capacity of 436 F g^-1 at 0.5 A g^-1. This kind of composite could also display great rate capacity (294 F g^-1 at 10 A g^-1) and outstanding long cycle performance (90.5% capacitance retention over 10 000 cycles at 5 A g^-1). Also, the asymmetric supercapacitor device is prepared by using CoMoO₄/Co-B composite as the anode with the active carbon as the cathode. Such a device demonstrates an outstanding energy density of 23.18 Wh kg^-1 and superior long-term stability with 100% initial specific capacity retained after 10,000 cycles. The superior electrochemical properties show that the CoMoO₄/Co-B electrode material has tremendous potential in energy storage equipment applications.

A high-performance histidine-functionalized MWCNT-GONR/Co–Ni LDH flower cluster structural composite via a microwave synthesis for supercapacitors

A flower cluster structural histidine-functionalized multi-walled carbon nanotube-graphene oxide nanoribbon/Co–Ni LDH (His-MW/LDH) composite was synthesized via the microwave method.