Supercapacitors (SCs) have been regarded as alternative electrochemical energy storage devices; however, optimizing the electrode materials to further enhance their specific energy and retain their rate capability is highly essential. Herein, the influence of nitrogen content and structural characteristics (i.e., porous and non-porous) of the NiS/nitrogen-doped carbon nanocomposites on their electrochemical performances in an alkaline electrolyte is explored. Due to their distinctive surface and the structural features of the porous carbon (A-PVP-NC), the as-synthesized NiS/A-PVP-NC nanocomposites not only reveal a high wettability with 6 M KOH electrolyte and less polarization but also exhibit remarkable rate capability (101 C/g at 1 A/g and 74 C/g at 10 A/g). Although non-porous carbon (PI-NC) possesses more nitrogen content than the A-PVP-NC, the specific capacity output from the latter at 10 A/g is 3.7 times higher than that of the NiS/PI-NC. Consequently, our findings suggest that the surface nature and porous architectures that exist in carbon materials would be significant factors affecting the electrochemical behavior of electrode materials compared to nitrogen content.
Templates are known to serve as critical components for synthesizing porous materials; however, their removal in some cases is time-consuming and not eco-friendly. Inspired by the hydrogels, a hierarchical porous activated carbon (HPAC) material is successfully prepared in this study through a pyrolysis procedure of polyvinylpyrrolidone (PVP)-derived hydrogel under an argon atmosphere at 900 °C. The numerous water molecules captured within the PVP hydrogel matrix can be regarded as greener templates, thus significantly enhancing the specific surface area of the resultant HPAC to 2012 m 2 /g. In addition to the physicochemical and structural characterizations, the capacitive performances of hydrogel-derived HPAC electrode materials with 5.1 mg/cm 2 of mass-loading are further explored as applied to symmetric supercapacitors and lithium-ion capacitors. As the results, their remarkable reversible capacitances outputted from the former (117.5 F/g at 0.13 A/g; 77.6 F/g at 1.3 A/g) and the latter (128.7 F/g at 0.1 A/g; 73.6 F/g at 10 A/g) are revealed. Such favorable results are attributed to distinctive textural properties of hydrogel-derived HPAC and synergistic features of the resulting electrode by the presence of a hydrophobic binder and one-dimensional conductive additive.
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