CdSe Nanoparticles Synergized with 2D Ti3C2Tx MXene as the Dual-Function Composite for Enhanced K+ Ion Storage and Water Splitting

Developing high-performance materials for energy storage and water splitting remains a significant challenge in energy research. Metal selenides, such as CdSe, exhibit excellent electrical conductivity and electrochemical activity, but they tend to form aggregates. Two-dimensional (2D) Ti₃C₂T_x MXene has good stability and conductivity but is limited by its low capacitance and electrocatalytic performance. To address these issues, CdSe@Ti₃C₂T_x composites were synthesized by a two-step large-scale hydrothermal method, where CdSe nanoparticles were uniformly grown on Ti₃C₂T_x MXene nanosheets. The composites significantly enhance the specific capacity, ion mobility, cycling stability, and catalysis activity due to the synergistic effect between Ti₃C₂T_x and CdSe nanoparticles. In a three-electrode system, the composites achieve a specific capacitance of 1847 F g^-1 at 0.125 mA cm^-2 and retain 89.2% of their capacitance after 10 000 cycles, demonstrating superior electrochemical properties compared to those of CdSe- or Ti₃C₂T_x-based electrodes. The asymmetric supercapacitor (ASC) with CdSe@Ti₃C₂T_x as the positive electrode and activated carbon (AC) as the negative electrode has a specific capacitance of 219.1 F g^-1, a capacity retention of 88.1% after 5000 cycles, and an energy density of 45.8 W kg^-1. This research also analyzes the reasons for the performance enhancement from the perspective of density of states theory. Furthermore, the CdSe@Ti₃C₂T_x composite shows catalytic potential for water splitting, with overpotentials of 201 mV for the hydrogen evolution reaction (HER) and 276 mV for the oxygen evolution reaction (OER). These results suggest that 2D MXene-based CdSe is a promising candidate for energy storage and water splitting.