Cobalt coordinated carbon quantum dots boosting the performance of NiCo-LDH for energy storage

Transition metal layered double hydroxides have extremely high specific capacitances but suffer from poor rate performance and cycling stability due to their low conductivity and structural stability. In this study, cobalt-coordinated carbon quantum dots (CoCQDs) were designed and synthesized to enhance the energy storage performance of nickel-cobalt layered double hydroxides (NiCo-LDH). Nickel and cobalt ions were co-electrodeposited with the CoCQDs to form a NiCo-LDH based composite electrode (denoted as CoC@LDH). Since the CoCQDs participated in the formation of the NiCo-LDH, the carbon quantum dots could be strongly bonded to the NiCo-LDH nanosheets through coordination interactions. Thus, the conductivity as well as the structure stability of the NiCo-LDH was effectively improved, which greatly boosted the cycle stability and rate performance of the NiCo-LDH. Several CoCQDs with different Co contents (nCoCQDs, n = 0.5, 1.0, 2.0) were fabricated and their effects on the performance of the resultant electrodes nCoC@LDH were investigated. The 1.0CoC@LDH electrode exhibited an impressive specific capacitance of 1867 F g^-1 at 1 A-g^-1, along with a significantly enhanced capacitance retention of 84.6 % after 6000 cycles at 5 A g^-1 (benchmark 49.5 %). This ingenious design provides a new avenue for fabricating pseudo-capacitive materials with unprecedented high performance.