Fig. 1. Schematic illustration of the synthetic process of samples.

Fig. 2. SEM images of (a1) Cu nanowires, (a2, a3) Cu@Co-MOF core-shell nanowires; (b1) SEM, (b2) TEM and (b3) element mappings of CuCo-SS; (c1) SEM, (c2) TEM and (c3) element mappings of CuCo-DS4; (d1) SEM, (d2) TEM and (d3) element mappings of CuCo-DS5; (e1) SEM, (e2) TEM and (e3) element mappings of CuCo-NR.

Fig. 3. XPS spectra of CuCo-SS, CuCo-DS4, CuCo-DS5 and CuCo-NR for (a) survey, (b) O 1s and (c) C 1s; XPS spectra of CuCo-DS5 for (d) Co 2p and (e) Cu 2p.

Fig. 4. (a) CV curves at 20 mV s-1, (b) GCD curves at 2 A g-1 and (c) specific capacitances of CuCo-NR, CuCo-SS, CuCo-DS4 and CuCo-DS5.

Fig. 5. Electrochemical performance of CuCo-DS5. (a) CV curves from 2 mV s-1 to 100 mV s-1. (b) GCD curves from 0.5 A g-1 to 10 A g-1. (c) Cycling stability at the constant current density of 5 A g-1. Inset: Specific capacities and specific capacitance at different current densities. (d) The plots of log(i) against log(v) at peaks of each current density. (e) Graphical illustration of the contributions of capacitive and diffuse parts at 10 mV s-1. (f) Quantitative contribution of the capacitive- and diffusion-parts at different scan rates.

Fig. 6. Graphical illustration of the hollow structure and the mechanisms of the electron/ion transfers of the CuCo-DS5.

Fig. 7. Electrochemical performance of the CuCo-DS5//AC: (a) CV curves of the CuCo-DS5 and AC electrode at 50 mV s-1. (b) CV curves of the device at 20 mV s-1 under various potential windows. (c) GCD curves with various potential windows. (d) CV curves at different scan rates. (e) GCD curves from 1 A g-1 to 10 A g-1. (f) Specific capacitance at various current densities calculated from Fig. 6e. (g) Ragone plots compared to reported Cu- and Co-based ASC devices. (h) Cycling stability of the device at 10 A g-1. Inset: Practical demonstration of CuCo-DS5//AC cell by powering a blue LED.