Enhanced electrochemical stability of CuCo bimetallic-coordinated polypyrrole

CuCo bimetallic-coordinated polypyrrole (PPy-CuCo) is designed as active electrode material of supercapacitor to improve the electrochemical stability of PPy. PPy-CuCo is synthesized by electrochemical polymerization reaction of copper-coordinated pyrrole (Py-Cu) and cobalt-coordinated pyrrole (Py-Co) monomers, which is initially formed by chemical coordination reaction between pyrrole and Cu²⁺ or Co²⁺. PPy-CuCo involves the alternating linear chain-like structure of PPy-Cu and tetrahedron structure of PPy-Co. The linear chain-like structure promotes the interchain electron transfer, accordingly improving the rate capability of PPy. The tetrahedron structure reinforces the polymer chain strength of PPy. The volume swelling or shrinkage of PPy during the charge/discharge process is restrained to improve electrochemical cycling stability of PPy. The specific capacitance increases from 249 F g⁻¹ for PPy to 556 F g⁻¹ for PPy-CuCo at 1.0 A g⁻¹. The rate capacitance retention accordingly increases from 40.9% for PPy to 48.2% for PPy-CuCo when the current density increases from 1.0 to 20.0 A g⁻¹. Moreover, the cycling capacitance retention also increases from 79.4% for PPy to 90.0% for PPy-CuCo even at 20.0 A g⁻¹ after 2000 cycles. PPy-CuCo with superior electrochemical stability presents the promising supercapacitor application for electrochemical energy storage.