Fe-Doped NiCoSe@Pitch-Carbon on Carbon Cloth: A Synergistic Electrode for Flexible Asymmetric Supercapacitors.

Through a synergistic strategy combining cation doping and carbon hybridization, we have successfully achieved the rational design and fabrication of an Fe-doped and carbon-hybridized Fe-NiCoSe/CTPC/CC electrode. We first investigated the effect of Fe ions on the electrochemical performance by systematically varying the iron content, aiming to introduce an appropriate amount of Fe to enhance the capacitance of NiCoSe. Subsequently, we incorporated pitch-derived carbon (CTPC) to improve the material stability and also to increase the electrical conductivity. In the preliminary experiments, the control NiCoSe/CC electrode delivered a specific capacitance of 726 mF cm-2 at 1 mA cm-2, and after 5000 charge-discharge cycles, its capacitance decayed to only 50.08% of its initial value. In contrast, the optimized Fe-NiCoSe/CTPC/CC-3 electrode achieved a superior specific capacitance of 1535 mF cm-2 at the same current density and retained 84.41% of its initial capacitance after 5000 cycles, fully demonstrating the effectiveness of carbon hybridization. The flexible asymmetric supercapacitor (FASC) assembled with this material was tested within a wide voltage window of 0-1.4 V, delivering a specific capacitance of 264.9 mF cm-2. At a power density of 354.7 μW cm-2, the device achieved a high energy density of 23.55 μWh cm-2 and retained 85.41% of its initial capacitance after 10,000 cycles. To further elucidate the underlying mechanism, we performed density functional theory (DFT) calculations to compare the density of states and adsorption energies of pristine NiCoSe and Fe-doped NiCoSe. The results strongly corroborate the experimentally observed enhancements in electrical conductivity and ion adsorption behavior. Overall, both Fe doping and carbon hybridization are effective strategies to improve the electrochemical capacitance and stability of the material, respectively.