## 3 Results
Among five composites, the Ni\({}_{0.9}\)Co\({}_{0.1}\)(OH)\({}_{2}\) and Ni\({}_{0.1}\)Co\({}_{0.9}\)(OH)\({}_{2}\) electrodes express large differences in specific capacitances compared with the other three samples. The poor ability under the same measured conditions is mainly due to the aggregation of material, which deteriorates the accessibility of electrolyte ions in electroactive material. Furthermore, the Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) electrode still maintains a specific capacitance of 79.2%, even when the current density increases 20-times more than the initial value, representing an excellent rate capability. What is noteworthy is that the Ni\({}_{0.3}\)Co\({}_{0.7}\)(OH)\({}_{2}\) electrode offers a slightly higher rate capability of 82% (2624 and 2622). Figure 5: Galvanostatic charge/discharge (GCD) curves at current densities from 1 to 20 A/g: (a) Ni\({}_{0.9}\)Co\({}_{0.1}\)(OH)\({}_{2}\); (b) Ni\({}_{0.7}\)Co\({}_{0.3}\)(OH)\({}_{2}\); (c) Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\); (d) Ni\({}_{0.3}\)Co\({}_{0.7}\)(OH)\({}_{2}\); (e) Ni\({}_{0.1}\)Co\({}_{0.9}\)(OH)\({}_{2}\); (f) GCD curves of the Ni\({}_{1\text{-x}}\)Co\({}_{\text{x}}\)(OH)\({}_{2}\) electrodes at current density of 1 A/g. 2151 F/g at 1 and 20 A/g) than that of the Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) sample, which highlights the advantage of nanowire morphology as a one-dimension (1D) geometry, which can better guarantee effective ion diffusion and electron transportation at high current density [44,62]. Based on Equations (2) and (3), the Ragone plots of the samples were obtained to further illustrate the electrochemical properties, as exhibited in Figure 6b. The Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) sample shows energy densities of 97.5, 95.5, 91, 84.9 and 77.2 Wh/kg at power densities of 0.25, 0.5, 1.25, 2.5 and 5 kW/kg, respectively. The EIS studies over the frequency range of 100 mHz to 100 kHz in 2 M KOH were carried out on Ni\({}_{0.7}\)Co\({}_{0.3}\)(OH)\({}_{2}\), Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\), and Ni\({}_{0.3}\)Co\({}_{0.7}\)(OH)\({}_{2}\) as optimized electrodes. Figure 7a records the typical Nyquist plots. Generally, the intrinsic resistances (electrolyte and material) and contact resistances (electrolyte/material and material/current collector) are summarized as \(R_{\rm s}\), which is valued from the intersection of the EIS plot and real axis. Figure 7b illustrates the high frequency in an enlarged view, in which the semicircle corresponds to the charge transfer resistance (\(R_{\rm cI}\)). The straight line at the low frequency portion represents the ion diffusion in the electrolyte, arising in a Warburg element (\(W\)) [61,63,64]. The Ni\({}_{0.3}\)Co\({}_{0.7}\)(OH)\({}_{2}\) electrode delivers the smallest diameter (expressing lowest \(R_{\rm cI}\)) and largest slop (suggesting fastest ion diffusion), which is consistent with its outstanding rate performance. The highest specific capacitance produced by the Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) electrode is due to: (1) the union of Ni and Co at ratio of 5:5 generating most electroactive sites from the feasible interaction of the valence state electron [54]; (2) the \(R_{\rm s}\) value of the Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) electrode being lower than the others. Overall, the EIS spectra well coincide with the aforementioned CV and GCD results. Figure 7c presents the fitting equivalent circuit, where CdI and \(C_{\rm ps}\) account for double-layer capacitance and pseudocapacitance, respectively. The long-term electrochemical stability was assessed via repetitive GCD tests at a constant current density of 20 A/g. Figure 8 displays the capacitance retentions and coulombic efficiencies of the Ni\({}_{0.5}\)Co\({}_{0.5}\)(OH)\({}_{2}\) electrode as a function of the cycle numbers (the inset depicts the GCD curves of the last 10 cycles).