Optimizing ZnSe microspheres through 2D MXene for asymmetric pseudocapacitive supercapacitors and efficient hydrogen production via water splitting

In response to the increasing demand for sustainable energy, recent efforts have focused on developing novel composites with improved crystalline structures, chemical stability, and conductivity for electrochemical applications. Self-assembled zinc selenide (ZnSe) microspheres are synthesized by a simple hydrothermal process, and their electrochemical applications as a positive electrode/electrocatalyst in asymmetric pseudocapacitive supercapacitor (APSC) and water splitting are investigated. ZnSe is integrated into the two-dimensional (2D) Ti₃C₂T_x/MXene nanosheets that serve as a physical barrier to mitigate agglomeration, prevent side reactions of Zn, provide ZnSe with more sites and a steady Zn²⁺ supply, ultimately enhancing the electrochemical performance. Composite electrode demonstrates superior specific capacitance of 1673.8 F g⁻¹ at 1 A g⁻¹, remarkable cyclic stability (98.81 % capacity retention over 10,000 cycles), and excellent pseudocapacitive performance of 88 % at 60 mV s⁻¹. Density functional theory (DFT) simulations displayed highest adsorption energy for ZnSe@Ti₃C₂T_x, showcasing stable structure and strong electron interaction. To demonstrate the commercial viability, active carbon (AC) is employed as the cathode to fabricate the AC//ZnSe@Ti₃C₂T_x-APSC device. In the water splitting assessment, ZnSe@Ti₃C₂T_x shows the lowest Tafel slopes (∼51.3 mV dec⁻¹ for oxygen evolution reaction (OER) and ∼36.9 mV dec⁻¹ for hydrogen evolution reaction (HER)). This novel approach significantly advances the overall performance of APSC and water-splitting.