Zinc (Zn) ion supercapacitors (ZISCs) have attracted considerable attention as a viable energy storage technology because they are cost-effective, safe, and environmentally friendly. However, cathode materials with suitable properties are rare and need to be explored. In this regard, metal carbides (MXenes) are a good choice for capacitive energy storage, but they exhibit low capacitance. The energy storage performance of MXenes can be bossed using functionalization with heteroatom doping, e.g., nitrogen (N), to simultaneously modify ZISCs’ fundamental characteristics and electrochemical properties. Herein, we present an in-situ N-functionalization of Ti₃C₂T_x-MXene via a hydrothermal reaction with urea (denoted as N-Ti₃C₂T_x-MXene). N-functionalization into Ti₃C₂T_x-MXene raised Ti₃C₂T_x-MXene’s interlayer spacing and boosted the Zn-ion storage in 1 M ZnSO₄ electrolyte. The N-Ti₃C₂T_x-MXene electrode delivered an excellent specific capacitance of 582.96 F/g at 1 A/g and retained an outstanding cycle stability of 94.62% after 5000 cycles at 10 A/g, which is 1.8 times higher than pristine Ti₃C₂T_x-MXene at identical conditions. Moreover, the N-Ti₃C₂T_x-MXene//Zn device demonstrated a maximum capacitance of 153.55 F/g at 1 A/g, retained 92% of its initial value after 5000 cycles, and its Coulombic efficiency was ~100%. This strategy considerably reduced Ti₃C₂T_x-MXene nanosheet restacking and aggregation and enhanced electrochemical performance. Further, this research elucidated N-Ti₃C₂T_x-MXene’s charge–storage process and offered a fresh approach to the rational design of novel electrode materials for ZISCs.

The interaction between cathode and anode materials is critical for developing a high-performance asymmetric supercapacitor (SC). Significant advances have been made for cathode materials, while the anode is comparatively less explored for SC applications. Herein, we proposed a high-performance binder-free anode material composed of two-dimensional ZnFe₂O₄ nanoflakes supported on carbon cloth (ZFO-NF@CC). The electrochemical performance of ZFO-NF@CC as an anode material for supercapacitor application was examined in a KOH solution via a three-electrode configuration. The ZFO-NF@CC electrode demonstrated a specific capacitance of 509 F g⁻¹ at 1.5 A g⁻¹ and was retained 94.2% after 10,000 GCD cycles. The ZFO-NF@CC electrode showed exceptional charge storage properties by attaining high pseudocapacitive-type storage. Furthermore, an asymmetric SC device was fabricated using ZFO-NF@CC as an anode and activated carbon on CC (AC@CC) as a cathode with a KOH-based aqueous electrolyte (ZFO-NF@CC||AC@CC). The ZFO-NF@CC||AC@CC yielded a high specific capacitance of 122.2 F g⁻¹ at a current density of 2 A g⁻¹, a high energy density of 55.044 Wh kg⁻¹ at a power density of 1801.44 W kg⁻¹, with a remarkable retention rate of 96.5% even after 4000 cycles was attained. Thus, our results showed that the enhanced electrochemical performance of ZFO-NF@CC used as an anode in high-performance SC applications can open new research directions for replacing carbon-based anode materials.

It is of great significance to design electrochemical energy conversion and storage materials with excellent performance to fulfill the growing energy demand. Bimetallic cobalt/nickel-based electrode materials exhibit excellent electrical conductivity compared to mono oxides. However, their potential as electrode materials for high-performance supercapacitors (SCs) is limited because of their poor cycling stability and high-capacity fading. This work demonstrates the synthesis of binder-free bimetallic NiCo₂O₄ nano-needles supported on CC (NCO@CC) via a facile and scalable hydrothermal process. Excellent electrical conductivity and interconnected nanostructure of NCO@CC nano-needles provide the fast transfer of electrons with numerous channels for ion diffusion. Owing to such features, the binder-free NCO@CC electrode for SC discloses excellent specific capacitance (1476 Fg⁻¹ at 1.5 Ag⁻¹) with 94.25% capacitance retention even after 5000 cycles. From these outstanding electrochemical performances, it can be inferred that NCO@CC nano-needle array-structured electrodes may be potential candidates for SC applications.

Considerable efforts are underway to rationally design and synthesize novel electrode materials for high-performance supercapacitors (SCs). However, the creation of suitable materials with high capacitance remains a big challenge for energy storage devices. Herein, unique three-dimensional (3D) ZnO hexagonal cubes on carbon cloth (ZnO@CC) were synthesized by invoking a facile and economical hydrothermal method. The mesoporous ZnO@CC electrode, by virtue of its high surface area, offers rich electroactive sites for the fast diffusion of electrolyte ions, resulting in the enhancement of the SC’s performance. The ZnO@CC electrode demonstrated a high specific capacitance of 352.5 and 250 F g⁻¹ at 2 and 20 A g⁻¹, respectively. The ZnO@CC electrode revealed a decent stability of 84% over 5000 cycles at 20 A g⁻¹ and an outstanding rate-capability of 71% at a 10-fold high current density with respect to 2 A g⁻¹. Thus, the ZnO@CC electrode demonstrated improved electrochemical performance, signifying that ZnO as is promising candidate for SCs applications.

Manganese dioxide (MnO₂)-based nanostructures are promising electrode materials for supercapacitors (SCs) due to their low cost, eco-friendly nature, and high theoretical capacitance. However, the conductivity of MnO₂ is poor, which is a big problem when trying to achieve the desired capacitance value. Herein, hexagonal-phase MnO₂ nanoparticles (NPs) are directly grown on a 3D conductive carbon cloth (CC) (denoted as MnO₂-NPs@CC) as a binder-free electrode through a simple and scalable hydrothermal strategy. The results show that MnO₂-NPs@CC with a large specific surface area and high porosity could be employed as a positive electrode material for high-performance SCs. Owing to these attractive properties, the MnO₂-NPs@CC electrode delivers a high specific capacitance of 660 F/g at a current density of 2 A/g in 6 M KOH aqueous electrolytes. Moreover, the MnO₂-NPs@CC electrode demonstrates excellent cycling stability with high capacitance retention of 92.8% over 10,000 cycles. Such remarkable findings suggest that MnO₂-NPs@CC with enhanced electrochemical performance is a favorable electrode material for next-generation high-performance SCs.