The pseudocapacitance mechanism of graphene/CoAl LDH and its derivatives: Are all the modifications beneficial?

Cobalt-Aluminum layered double hydroxide (CoAl LDH) is a hopeful electrode material due to the advantage of easy modifiability for preparing LDH-based derivatives. However, there is short of modification methods to prepare the Co-based derivatives from CoAl LDH and also short of an intuitive perspective to analyze the pseudocapacitance mechanism of CoAl LDH and its derivatives. Herein, Graphene/CoAl LDH and its derivatives including Graphene/CoS, Graphene/CoS-1, Graphene/CoOOH, Graphene/CoP were prepared by reasonably using alkali etching treatment, sulfofication and phosphorization. The specific capacitance of Graphene/CoAl LDH, Graphene/CoS, Graphene/CoS-1, Graphene/CoOOH, Graphene/CoP at 1 A g−1 are 260.7, 371.3, 440.8, 61.4 and 122.2 F g−1, especially. The pseudocapacitance mechanism of Graphene/CoAl LDH and its derivatives was analyzed. Due to the positive effect of sulfofication on the electrical conductivity of GO and cobalt sulfide, the Graphene/CoS and Graphene/CoS-1 exhibit the optimal electrochemical performance and superior rate capability. In addition, due to the repulsion effect between Graphene and OH−, the Graphene/CoAl LDH exhibits optimal cycling stability of 224.1% capacitance retention after 20000 cycles. Besides, the reason of terrible specific capacitance of Graphene/CoOOH is that the presence of H bond in interlayer of CoOOH inhibits the interaction between Co3+ and OH− species. Hence, not all modifications will increase the specific capacitance of the electrode materials. Overall, this work provides us with a detailed analysis of the electrochemical mechanism and correlation of CoAl LDH and its derivatives from the perspective of crystal structure and composition.