Hydrothermal Synthesis of Humate‐Layer‐Based Bimetal Organic Framework Composites as High Rate‐Capability and Enery‐Density Electrode Materials for Supercapacitors

Abstract

Abstract A humate‐layer‐based bimetal organic framework (HA‐NiCo‐BPDC) material is successfully synthesized using humate layers obtained by ultrasonic‐hydrothermal peeling as a substrate and BPDC as a ligand via a hydrothermal approach. It exhibits a porous composite structure in which flower‐like NiCo‐BPDC nanosheets are loaded on humate layers, originating a guiding effect of humate layers on the NiCo‐BPDC growth. HA‐NiCo‐BPDC owns a similar crystal structure to NiCo‐BPDC, in which humate and BPDC ions have coordinated with nickel or cobalt ions to form carboxylates. Nickel and cobalt ions present positive divalent states, and they have close ability to coordinate with BPDC or humate ions. Owing to unique hierarchical architectures and fascinating synergetic effects between NiCo‐BPDC nanosheets and humate layers, HA‐NiCo‐BPDC has high specific capacitance and rate capability, and low internal resistance and charge transfer resistance. It exhibits better rate capability than NiCo‐BPDC and larger specific capacitance than HA−Ni(Co)‐BPDC. Moreover, HA‐NiCo‐BPDC//rGO asymmetric supercapacitor has wide operating potential window, high energy density and cycling stability. All those show that HA‐NiCo‐BPDC composites are a promising electrode material for supercapacitors. This study exploits a novel way for value‐added applications of humates and their natural sources “humic acids”.