Two birds with one stone: cobalt/silicon species encapsulated in MOF-derived nitrogen-doped carbon as an integrated electrode for next-generation symmetric pseudocapacitors with energy density over 100 W h kg−1

Abstract

Symmetric pseudocapacitors (SPCs) have the ability to provide an extended operating life-span with high power density; however, their energy density is not sufficient for various critically vital applications. To reduce the overall cost and complexity of fabrication of SPCs while simultaneously increasing their energy density, we present a “two birds with one stone” approach. Herein, to prove this idea, low-cost silicon (Si) embedded in metal–organic framework (MOF)-derived cobalt nano-sized particles/nitrogen-doped carbon (Si/Co-NC) was prepared as an integrated electrode material which works at positive and negative potential windows simultaneously. The optimized electrode with 30% Si content (Si/Co-NC1) achieved a remarkable capacitance of 845.41 F g⁻¹ at 1 A g⁻¹ in a broader potential window range (−1.0–0.4 V) and 97% of the capacitance was retained after 10 000 cycles. According to the charge storage analysis, the Si/Co-NC1 electrode works on the basis of a pseudocapacitive charge storage mechanism and possesses 79.8% capacitive contribution at 1 mV s⁻¹. Moreover, a symmetric pseudocapacitor, Si/Co-NC1‖Si/Co-NC1-SPC, shows a broader operating potential window range (0.0–1.8 V), exhibits an excellent capacitance of 277 F g⁻¹ at 2 A g⁻¹, maintains a capacitance of 96.8% after 50 000 cycles and achieves ∼100% coulombic efficiency. Additionally, the Si/Co-NC1‖Si/Co-NC1-SPC provides an ultrahigh energy density of 125.43 W h kg⁻¹ at 1804.32 W kg⁻¹, which is the greatest energy density for symmetric SCs to date.