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As a cathode in aqueous zinc-ion capacitors (ZICs), nitrogen-doped carbon with a 2D bimetallic chalcogenide (NbMo6S8/NC) was used. The assembled ZIC demonstrated exceptional electrochemical stability and energy efficiency over thousands of charge–discharge cycles.

Transition metal selenides (TMS) have excellent research prospects and significant attention in supercapacitors (SCs) owing to their high electrical conductivity, superior electrochemical activity and excellent structural stability. However, the commercial utilization of TMS remains challenge due to their elaborate synthesis. Present study designed a hierarchical cobalt selenide (CoSe2) nanowire array on Ni-foam to serve as a positive electrode for asymmetric SCs (ASCs). The nanowires-like morphology of CoSe2 was highly advantageous for SCs, as it offered enhanced electrical conductivity, plenty of surface sites, and short ion diffusion. The as-obtained, CoSe2 nanowire electrode demonstrated outstanding electrochemical features, with an areal capacity of 1.08 mAh cm−2 at 3 mA cm−2, high-rate performance (69.5 % at 50 mA cm−2), as well as outstanding stability after 10,000 cycles. The iron titanium nitride@nitrogen-doped graphene (Fe-TiN@NG) was prepared as a negative electrode to construct the ASCs cell. The obtained ASCs cell illustrated an energy density of 91.8 W h kg−1 at a power density of 281.4 W kg−1 and capacity retention of 94.6% over 10,000 cycles. The overall results provide a more efficient strategy to develop redox-ambitious active materials with a high capacity for advanced energy-storage systems.

Synthesis, properties and electrochemical energy storage applications of MXenes.

A rational combination of metal cations is necessary to obtain a synergistic effect leading to improved electrochemical energy storage performance of bimetal compounds. So, the effect of concentration variation of reactants (nickel and cobalt ratio) in nickel cobalt phosphate material and their influence on physicochemical properties and electrochemical capacitive performances are investigated. The morphological evolution from microflowers (nickel phosphate) to microsheets (cobalt phosphate) is observed with increasing cobalt content in nickel cobalt phosphate thin films. The optimum nickel and cobalt composition (∼1:1) in nickel cobalt phosphate (Ni1.38Co1.62(PO4)2·8H2O) thin film electrode demonstrate maximum specific capacitance (capacity) of 1116 F g−1 (446 C g−1) at 0.5 A g−1 current density. Also, a fabricated hybrid asymmetric aqueous device consists of nickel cobalt phosphate thin film as cathode and rGO as an anode in 1 M KOH electrolyte delivers a higher specific capacitance of 120 F g−1 with a high energy density of 42.3 Wh kg−1 at a power density of 1 kW kg−1. Moreover, a hybrid asymmetric solid-state device fabricated using PVA-KOH gel electrolyte exhibits a maximum specific capacitance of 102 F g−1 with an energy density of 36.2 Wh kg−1 at 160 W kg−1 power density and 83.7 % initial capacitance retention after 4000 GCD cycles. Such excellent electrochemical capacitive performance of hybrid asymmetric devices is attributed to the synergy between nickel and cobalt species in nickel cobalt phosphate thin film electrodes, suggesting its potential application as a cathode in hybrid energy storage devices.

Electrocatalytic water splitting is a very promising and sustainable approach for generating hydrogen as a clean carbon-free fuel. To develop an efficient electrocatalyst for water splitting, the overpotential for this reaction must be minimized by using a capable electrocatalyst that can support the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we prepared a unique core–shell structure, Co-metal–organic framework (MOF) derived cobalt diselenide laminated with molybdenum diselenide (MOF-CoSe2@MoSe2) and assessed its performance as a bifunctional electrocatalyst for the HER and OER in alkaline media. The CC/MOF-CoSe2@MoSe2 core–shell structure fabricated directly on a flexible carbon cloth substrate demonstrated low overpotentials (η10) of 109.87 and 183.81 mV for the HER and OER, respectively, and a low voltage of 1.53 V for overall water splitting activity with an electrolyzer cell with symmetric CC/MOF-CoSe2@MoSe2 electrodes. The developed CC/MOF-CoSe2@MoSe2 catalyst had excellent stability over 24 h for OER, HER, and overall water splitting activity. These results suggest that lamination of MOF with a transition metal dichalcogenide is an effective route for developing the highly efficient and sustainable bifunctional electrocatalyst for overall water splitting activity.

The self-supported integrated structure of electrode consisting of heteroatoms is advantageous for high-performance energy storage applications. Herein, we developed heteroatomic Ni-Co4N nanoparticles laminated on highly conductive nitrogen-doped carbon (NC) matrix through in-situ nitridation for high energy and stable hybrid supercapacitor (HSC). The plenty of rendering electrochemically active sites, specifically, single-atom Ni, Co4N nanoparticles, and heteroatomic N-doped carbon matrix, and their several synergistic effects facilitate fast electron transfer and superior electrochemical performance. Benefiting from these merits, the resultant Ni-Co4N@NC electrode demonstrates robust electrochemical activity with high specific capacity of 397.5 mA h g−1, high rate capability of 72.4% and superior cycling stability over 10,000 cycles. The heteroatomic Ni-Co4N@NC electrode is further employed for the HSC cell beside with the activated carbon (AC) electrode, which establish the specific energy of 57.2 Wh kg−1 at a specific power of 843.8 W kg−1 and cyclic stability of 89.7% after 15,000 cycles. The present study highlights the utilization of heteroatomic self-supported metal nitrides for the high energy HSCs cell, paving the way to the expansion of highly efficient electrode materials for the future energy storage systems.