MXene-based O/Se-rich bimetallic nanocomposites for high performance solid-state symmetric supercapacitors

Herein, we developed a novel and high-performance supercapacitor material for by incorporating an electron-rich oxalate-modified cobalt and nickel selenide (CoNi(Ox)Se) on the surface of MXene. The formation of O/Se-loaded CoNi on the MX, affording enhanced electron transport between the electrodes. A high pseudocapacitive charge storage behavior of the CoNi(Ox)Se@MX composite is confirmed, exhibiting a specific capacitance of 1782 ​F ​g⁻¹at 5 ​mV ​s⁻¹in a KOH (1 ​M) electrolyte solution. This capacitance value is considerably higher than that of Co-based electrodes reported in the literature. Furthermore, electrochemical cyclic measurements indicated that material stability is retained after 1000 cycles at 5 ​A ​g ⁻¹. Notably, when set up as a solid symmetric capacitor, the synthesized electrodes exhibit a high energy density of 131.9 ​Wh kg⁻¹at a power density of 7.2 ​kW ​kg⁻¹, along with flexibility. The material possesses an excellent capacitance retention (95%) after 5000 cycles without loss of any metals/Se. The results indicate that the MX-based composite promoted rapid electrolyte diffusion, fast kinetics in terms of electron-transport, and high charge/discharge rates. Thus, CoNi(Ox)Se@MX structures may have the potential for the development of novel energy storage systems suitable for portable, miniaturized, and wearable power devices.