Holey graphene oxide-templated construction of nano nickel-based metal—organic framework for highly efficient asymmetric supercapacitor

Metal—organic frameworks (MOFs) with redox-active metal sites and controllable crystalline structures make it possible to access the merits of highly-efficient electrode materials in electrochemical energy storage systems. However, most MOFs suffer from low capacitance and poor cycling stability that largely thwart their application. Herein, we present the holey graphene oxide (HGO) template strategy to prepare nano two-dimensional Ni(BDC) with HGO as both template and capping agent (denoted as Ni(BDC)-HGOx, x = 10, 20, 30, and 40 according to the added HGO amount). Structural analyses reveal that HGO can significantly inhibit the Ni(BDC) agglomeration, thus offering a high ion-accessible surface area. Ni(BDC)-HGO30 with well-exposed active sites exhibits a high capacitance of 1,115.6 F·g−1 at 1 A·g−1 in 6 M KOH aqueous, 1.8 times that of bulk Ni(BDC). An asymmetric supercapacitor with Ni(BDC)-HGO30 as a positive electrode and activated carbon as the opposing electrode delivers an energy density of 52.5 W·h·kg−1 and a power density up to 18.0 kW·kg−1, with 92.5% capacitance retention after 10,000 cycles. Galvanostatic intermittent titration technique and in situ electrochemical—Raman measurements were exploited to elucidate the electrochemical behavior of Ni(BDC)-HGO30. These results pave the way for the development of rationally tuned MOF materials for enhancing supercapacitor performances.