Engineering 2D/2D oxygen vacancy-rich CoAl LDH/rGO sheet-on-sheet heterostructures with improved charge storage for supercapacitors

Layered double hydroxides (LDHs) as electrode materials for supercapacitors still suffer from limited actual specific capacities and unsatisfactory cycling performance owing to their poor intrinsic electrical conductivity and insufficient electroactive sites. Herein, oxygen vacancy (Ov)-rich CoAl-LDH nanosheets are attached onto reduced graphene oxide (rGO) nanosheets to form 2D/2D Ov-CoAl-LDH/rGO sheet-on-sheet heterostructures via a facile precipitation-reduction reaction followed by hydrothermal treatment. The introduction of rich Ov defects in CoAl-LDHs enhances the electrical conductivity, while the attachment of Ov-CoAl-LDH nanosheets on the surface of rGO nanosheets not only reduces the aggregation of Ov-CoAl-LDH nanosheets and thus exposes abundant electroactive sites, but also maintains good structural stability. Theory calculations indicate that the Fermi-level difference of two components triggers interfacial charge separation while creating a built-in electric field at the Ov-CoAl-LDH/rGO interface, which favors rapid electron/ion migration and accelerates charge storage kinetics. The optimized Ov-CoAl-LDH/rGO nanocomposites deliver specific capacities of 984 C g−1 at 3 A g−1 and 708 C g−1 at 20 A g−1 and retain an initial capacity of 90 % after 10,000 cycles at 10 A g−1. These findings showcase a feasible strategy to endow 2D/2D LDHs/graphene heterostructures with enhanced charge storage performance.