**2.4 Designed pore space for active materials**

The power density relies both on the active materials and pore space of the active materials. The optimization of the structure of active materials and dynamics of ions at

**Figure 2.**

*(a) and (b) CV curves and GCD curves of two different fiber electrodes, (c) CV curves under different scan rates, (d) GCD curves at different current densities of the MnOx@TiN NWs@CNT fiber electrode, (e) comparison of volumetric capacitances versus different current densities for three different fiber electrodes, and (f) cycling stability of the MnOx@TiN NWs@CNT fiber electrodes as a function of cycle number under a current density of 2.0 A cm−3 [3].*

### *Supercapacitors: Fabrication Challenges and Trends DOI: http://dx.doi.org/10.5772/intechopen.107419*

the electrode-electrolyte interface are the two promising routes for enhancing the electrochemical performance of supercapacitors [2]. The immobilized ions diffuse into the electrolyte, which not only is the key parameter for the supercapacitors, but also affect the impedance of the supercapacitors. For controlling the diffusing rate, researchers have designed and fabricated various superior architectures, including fabricating 3D structures [27], which include MXenes structures, core-sheath fibers, asymmetric fiber structures [3], and hierarchical nanoarrays. The synthetic strategy of hierarchical nanoarrays [33] can be used as a template for the epitaxial growth of secondary structures by controlling the reaction condition using a one-pot strategy to fabricate the hierarchical structure. Studies have shown that three-dimensional structures will increase the surface area considerably, especially in shape design structures. The asymmetric fiber structure has shown high potential applications because of multidimensional stacking and winding, resulting in unbelievable capacitance and power density values. **Figure 2** shows the different parameters of the supercapacitors, and **Figure 2a** and **c** shows the stability performance in the cyclic voltammetry curves at different scan rates. The charge and discharge curves of the different supercapacitors at different current densities are shown in **Figure 2b** and **d**, where the volumetric capacitances were calculated from the charge and discharge rates as a function of the current density in different capacitances (**Figure 2e**). **Figure 2f** shows the stability of supercapacitors, indicating the performance of the supercapacitors under different current and voltage values, which can be used to design the pore space and select the suitable active material.
