Electrochemical deposition of highly porous reduced graphene oxide electrodes for Li-ion capacitors

Electrochemical deposition (ECD) is a promising and efficient technique for film assembly and electrode fabrication in energy storage and conversion devices. Herein, reduced graphene oxide (ErGO) with high porosity was driven by high-voltage ECD to form a binder-free capacitor electrode for lithium ion capacitors (LICs). The high voltage was used to drive the continuous and constant reduction of graphene oxide as well as for generation hydrogen, which was responsible for the porous structure. The latter not only prevented the severe stacking problem of reduced graphene oxide (rGO) but also facilitated the mass transfer of the electrolyte for the capacitive adsorption/desorption. One of the advantages of ECD is that it allows controlling very well the thickness and weight of the electrochemically deposited layer. Therefore, the effect of film thickness on the capacitive performance was also investigated. We found that increasing the film thickness did not linearly increase the areal capacitance, which was attributed to the resistive electrolyte diffusion through internal pores. Furthermore, a good capacitance as high as 168 F g⁻¹ at 0.1 A g⁻¹ was obtained by combining ErGO with V₂O₅ nanoparticles, benefiting from the integration of the high surface area of ErGO and the redox activity of V₂O₅.