To enhance the electrochemical performance of reduced graphene oxide (rGO) on nickel foam for use as the negative electrode in supercapacitors, rGO@TiO2 and rGO@TiN core–shell electrodes were fabricated by depositing 5 nm TiO2 or TiN thin films onto rGO using atomic layer deposition. The material properties of the electrodes were subsequently tuned using post-deposition thermal treatment, after which the electrochemical properties of the rGO@TiO2 and rGO@ TiN electrodes were systematically compared. The rGO@TiO2 electrode annealed at 300 °C had a lower charge transfer resistance (Rct) than the pristine rGO electrode, while the higher slope in the low-frequency region of the corresponding Nyquist plot indicated enhanced charge accumulation. As a result, the areal capacitance increased by 19.5% from 211.9 to 253.2 mF cm−2 at a current density of 4 mA cm−2 . 

In contrast, the rGO@TiN core–shell electrode demonstrated no significant change in Rct relative to rGO, while its solution resistance decreased. However, due to the higher electrical conductivity of TiN compared to TiO2, the capacity retention at higher current densities improved. Overall, thermally treated rGO@TiO2 was more effective than rGO@TiN as a core–shell structure designed to improve the performance of rGO-based negative electrodes.