Co-containing metal–organic framework for high-performance asymmetric supercapacitors with functionalized reduced graphene oxide

Abstract

Nowadays, supercapacitors are the most coveted eco-friendly and sustainable next-generation energy storage devices. In this regard, developing supercapacitors with high energy density and power density has always been a challenge for researchers. Herein, we have exploited an electroactive Co-containing metal–organic framework (Co-MOF) using cheap and commercially available starting materials under refluxing conditions and explored its energy storage properties in three- and two-electrode methods. The Co-MOF exhibited a specific capacitance of 425 F g⁻¹ at 2 A g⁻¹, maintaining a capacitance of ∼78% over 2200 successive charge–discharge cycles in a three-electrode system. The two-electrode asymmetric supercapacitor (ASC) using Co-MOF as the working electrode and as-synthesized p-phenylenediamine (PPD)-functionalized reduced graphene oxide (PPD-rGO) as the counter electrode divulged a specific capacitance of 72.5 F g⁻¹ at 2 A g⁻¹ current density with ∼70% capacitive retention after 2200 successive charge–discharge cycles over a broad potential window of 0–1.6 V. Moreover, the ASC demonstrated a maximum power density of 11.9 kW kg⁻¹ at 10 A g⁻¹ and a maximum energy density of 25.8 W h kg⁻¹ at 2 A g⁻¹ current density. Owing to the stable electrochemical redox (Co²⁺/Co³⁺)-mediated pseudocapacitive behavior of the Co-MOF and the high surface area and electrical conductivity of in situ generated PPD-intercalated rGO, the fabricated ASC unveiled high-performance supercapacitive behaviors. To investigate the practical applicability of this material, solid-state (ASC) devices were fabricated by employing the Co-MOF as the positive electrode and PPD-rGO as the negative electrode in a KOH-based gel electrolyte, which could power a commercially available light-emitting diode bulb (∼1.8 V) for several seconds. Therefore, the elucidated high electrochemical energy storage performance of the prepared Co-MOF makes it a very promising electrode material for supercapacitors.