Enhancing the performance and stability of NiCo ₂ O ₄ nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo ₂ O ₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo ₂ O ₄ /Ni@NF)shows the superior specific capacity of 1142 C g ⁻¹ at 1 A g ⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g ⁻¹ . These values are about 3.7 times higher than that of the electrode (NiCo ₂ O ₄ @NF)without a seed layer, which shows the specific capacity of 305 C g ⁻¹ @1 A g ⁻¹ with cycle stability of 84% even at a lower current density of 1 A g ⁻¹ . The enhanced performance of the NiCo ₂ O ₄ /Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo ₂ O ₄ /Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe ₂ O ₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo ₂ O ₄ /Ni20@NF//rGO-Fe ₂ O ₃ @NF asymmetric solid state device delivers an areal capacitance of 446 mF cm ⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm ⁻² (at 3.58 kW cm ⁻² )and power density of 14.88 kW cm ⁻² (at 31.41 Wh cm ⁻² ).