Supercapacitors, at the forefront of energy storage, bridge the gap between traditional capacitors and batteries, renowned for high power densities, rapid charge/discharge rates, and extended cycle life. MXenes, two-dimensional transition metal carbides, nitrides, and carbonitrides, have emerged as promising supercapacitor electrode materials due to remarkable electrical conductivity and tunable surface properties. This chapter explores MXene-based supercapacitors, detailing synthesis methods, electrochemical performance, and potential applications. MXene-based supercapacitor performance, covering specific capacitance, energy density, power density, and cycling stability, is discussed. The chapter also addresses challenges in MXene-based supercapacitor development, including scalability, cost-effectiveness, and long-term stability, applications in portable electronics, wearables, and electric transportation. Providing a comprehensive overview, this chapter inspires further exploration and utilization of MXene-based supercapacitors for next-gen energy storage solutions.

A highly sensitive and selective electrochemical sensor for Cu²⁺ ions was fabricated by modifying a glassy carbon electrode (GCE) with a CdS/rGO nanocomposite. The structural and morphological characteristics of the synthesized materials were thoroughly investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These analyses confirmed the synthesis of the CdS/rGO nanocomposite via a hydrothermal synthesis route. The electrochemical performance of the modified electrode was systematically evaluated using cyclic voltammetry (CV), differential pulse anodic stripping voltammetry (DPASV), and electrochemical impedance spectroscopy (EIS). The CdS/rGO-modified electrode exhibited enhanced electrocatalytic activity, with well-defined anodic and cathodic peak currents that demonstrated a linear relationship with the square root of the scan rate over the range of 50–250 mV s⁻¹. Under optimized conditions, the sensor demonstrated appropriate analytical performance over a Cu²⁺ concentration range of 10–100 nM, with a remarkably low limit of detection (LOD) of 2.83 nM. Furthermore, the sensor exhibited good selectivity toward Cu²⁺ in the presence of various interfering ions, along with good reproducibility and long-term operational stability. Its practical applicability was further demonstrated through the successful determination of Cu²⁺ ions in water samples and complex matrices, yielding satisfactory recovery values. These results highlight the potential of the CdS/rGO-based sensor as a reliable and sensitive platform for the practical electrochemical detection of Cu²⁺ ions.