Tin Oxide/Vertically Aligned Graphene Hybrid Electrodes Prepared by Sonication-Assisted Sequential Chemical Bath Deposition for High-Performance Supercapacitors

Abstract

Hybrid electrodes comprising metal oxides and vertically aligned graphene (VAG) are promising for high-performance supercapacitor applications because they enhance the synergistic effect owing to the large contact area between the two constituent materials. However, it is difficult to form metal oxides (MOs) up to the inner surface of a VAG electrode with a narrow inlet using conventional synthesis methods. Herein, we report a facile approach to fabricate SnO₂ nanoparticle-decorated VAG electrodes (SnO₂@VAG) with excellent areal capacitance and cyclic stability using sonication-assisted sequential chemical bath deposition (S-SCBD). The sonication treatment during the MO decoration process induced a cavitation effect at the narrow inlet of the VAG electrode, allowing the precursor solution to reach the inside of the VAG surface. Furthermore, the sonication treatment promoted MO nucleation on the entire VAG surface. Thus, the SnO₂ nanoparticles uniformly covered the entire electrode surface after the S-SCBD process. SnO₂@VAG exhibited an outstanding areal capacitance (4.40 F cm^-2) up to 58% higher than that of VAG electrodes. The symmetric supercapacitor with SnO₂@VAG electrodes showed an excellent areal capacitance (2.13 F cm^-2) and a cyclic stability of 90% after 2000 cycles. These results suggest a new avenue for sonication-assisted fabrication of hybrid electrodes in the field of energy storage.

Figure 1

Schematic illustration of preparation of the VAG electrodes decorated with SnO₂ nanoparticles using the S-SCBD process.

Figure 2

FE-SEM images of the top-view morphology of (a) VAG electrode, (b) SnO₂@VAG-15 fabricated by the sequential CBD process without the sonication process, (c) SnO₂@VAG-15 produced by the S-SCBD process, (d) edges of SnO₂@VAG-15 [part A in (c)], (e) inside the surface of SnO₂@VAG-15 [part B in (c)], and (f) magnified inside the surface of SnO₂@VAG-15 [part C in (e)].

Figure 3

(a) TEM image of SnO₂@VAG-15 (inset: HRTEM image of SnO₂@VAG-15 showing the interlayer spacing). (b) XRD patterns of VAG, SnO₂@VAG-15, and SnO₂ according to the JCPDS file no. 41-1445. (c) Raman spectra and (d) FT-IR results of the VAG electrodes and SnO₂@VAG-15.

Figure 4

(a) XPS survey spectrum of SnO₂@VAG-15. (b) High-resolution O 1s and (c) Sn 3d spectra of SnO₂@VAG-15 with deconvoluted components.

Figure 5

(a) CV curves and (b) GCD curves of VAG electrodes and SnO₂@VAG with different decorating times obtained at a scanning rate of 200 mV s^–1 and a current density of 2 mA cm^–2. (c) Variation of the areal capacitance of SnO₂@VAG with decorating time obtained at a current density of 2 mA cm^–2. (d) CV curves and (e) GCD curves of SnO₂@VAG-15 at different scanning rates from 20 to 200 mV s^–1 and current densities from 2 to 20 mA cm^–2. (f) Variation of the areal capacitance of the VAG electrode and SnO₂@VAG-15 with current densities.

Figure 6

(a) CV curves and (b) GCD curves of SnO₂@VAG-15 with the sonication process and SnO₂@VAG-15 without the sonication process acquired at a scanning rate of 200 mV s^–1 and a current density of 4 mA cm^–2.

Figure 7

(a) CV curves of the supercapacitor device using SnO₂@VAG-15 at different scanning rates from 20 to 200 mV s^–1. (b) GCD curves of the supercapacitor device at different current densities from 2 to 20 mA cm^–2. (c) Variation of the areal capacitance of EDLC and supercapacitor devices by current densities. (d) Capacitance retention and Coulombic efficiency of EDLC and supercapacitor device after 2000 cycles.

Figure 8

(a) Nyquist plot and electrical equivalent circuit (inset) of the supercapacitor devices. (b) Energy and power density comparison of the supercapacitor device using SnO₂@VAG-15 and other hybrid electrodes.