Electrochemical Energy Storage Of Transition Metals-polypyrrole Coordinated Polymer

Polypyrrole can be used as electrode materials for supercapacitor because of its unique advantages,such as simple preparation,high specific capacitance,high specific energy,reversible doping,environment friendly and good film-forming.It is expected to make more superior comprehensive performance for supercapacitor.However,polypyrrole has relatively high charge transfer resistance and low cycle life,which leads to the poor performance and cycle performance in supercapacitors.For electrochemical energy storage elements,stability is undoubtedly one of the most important factors.In this paper,several methods are adopted to improve the electrochemical stability of polypyrrole electrode materials for supercapacitors.Firstly,PPy-Ru was synthesized through the coordinated efforts between the noble metal of Ru³⁺and the pyrrole monomers.The tetrahedral structure could restraine the volume swelling or shrinking of PPy during the charge-discharge process,accordingly improving the electrochemical cycling stability.Secondly,CQDs/PPy-Fe was synthesized through the coordinated efforts between the conventional metal of Fe²⁺and the pyrrole monomers and the incorporation polymerization with CQDs.The pyrrole-Fe monomers kept tetrahedron structure could restrain volume swelling or shrinkage of PPy during the charge/discharge process,accordingly leading to improved cycling stability.In addition,the modification of CQDs could enhance the electrical conductivity of PPy and further improved rate capability of PPy.By integrating advantages from the coordination and incorporation approaches,the rate capability and cycling stability of PPy could be improved.Thirdly,PPy-CuCo was synthesized through the coordinated efforts between the bimetallic ions of Cu²⁺and Co²⁺and the pyrrole monomers.The PPy-CuCo involved the alternating linear chain-like and tetrahedron structures.The linear chain-like structure could promote the electron transfer,accordingly improving the conductivity and rate capability of PPy.The tetrahedron structure could reinforce the polymer chain strength of PPy.The restrained volume swelling or shrinkage of PPy during the charge/discharge process caused the improved electrochemical cycling stability.Through changing the material structure of pyrrole and controlling the coordination degree of two metal ions,it was to achieve the advantage balance of the two structures.PPy-CuCo could effectively maintain the high rate capability and cycle stability at high current density.The research work of this paper includes the following aspects:?1?The synthesis and electrochemical performance study of PPy-RuPPy-Ru was synthesized through two-step method,which included coordinative efforts and polymerization.The first step reaction formed the monomers of pyrrole-Ru between pyrrole and Ru³⁺by direct coordination method.Secondly,the pyrrole-Ru monomers conducted electropolymerization to obtain the coordinated polymer of PPy-Ru.The coordination reaction between the pyrrole monomer and Ru³⁺led to the formation of a tetrahedral structure that restrained volume swelling or shrinking of PPy during the charge-discharge process,accordingly causing improved electrochemical cycling stability.The specific capacitances of PPy and PPy-Ru were 249 and 618 F g^-1 at the current density of 1.0A g^-1.The results of cycling test over 2000 times at the current density of 20 A g^-1 indicated that the capacitive retention of PPy electrode was 79.4%.While PPy-Ru kept the capacitive retention of 91.4%,which exhibited good cycling stability.Based on the Polyvinyl Alcohol-sulfuric acid gel electrolyte,the all-solid-state symmetric PPy-Ru supercapacitor was assembled.According to the electrochemical test,the specific capacitance of the all-solid-state symmetric PPy-Ru supercapacitor was 122 F g^-1 at the current density of 2 A g^-1.The capacitance retention of PPy-Ru supercapacitor at the current density of 2 A g^-1 over 500 cycles charge/discharge was 82.8%.After the all-solid-state symmetric PPy-Ru supercapacitor was charged,it could light the red diodes,indicating that PPy-Ru can be used as the electrode material for supercapacitors.?2?The synthesis and electrochemical performance study of CQDs/PPy-FeCQDs/PPy-Fe was synthesized through two-step method,which included coordinative efforts and the incorporation of polymerization.The first step reaction formed the monomers of pyrrole-Fe between pyrrole and Fe²⁺by direct coordination method.Secondly,the pyrrole-Fe monomers incorporated by CQDs conducted electropolymerization to obtain the coordinated polymer of CQDs/PPy-Fe.The pyrrole-Fe monomers kept tetrahedron structure could restrain volume swelling or shrinkage of PPy during the charge/discharge process,accordingly leading to improved cycling stability.In addition,the modification of CQDs could enhance the electrical conductivity of PPy and further improved rate capability of PPy.By integrating advantages from the coordination and incorporation approaches,CQDs/PPy-Fe is expected to exhibit high conductivity and excellent electrochemical stability.The specific capacitances of PPy and CQDs/PPy-Fe were 249 and 581 F g^-1 at the current density of 1.0 A g^-1.CQDs/PPy-Fe showed lower capacity decay ratio of 45.4%than PPy?59.1%?from 1.0 to20.0 A g^-1.The capacitance retention ratio after 2000 cycles of CQDs/PPy-Fe and PPy was94.6%and 79.4%at 20.0 A g^-1,respectively.CQDs/PPy-Fe exhibited good electrochemical stability.Based on the Polyvinyl Alcohol-sulfuric acid gel electrolyte,the all-solid-state symmetric CQDs/PPy-Fe supercapacitor was assembled.According to the electrochemical test,CQDs/PPy-Fe supercapacitor showed the capacitance of 78 F g^-11 at 5.0 A g^-1 and the capacitance retention ratio of 70.1%after 1000 cycles.The CQDs/PPy-Fe supercapacitor exhibited highest energy density of 52 Wh kg^-1 at power density of 900 W kg^-1.CQDs/PPy-Fe can be used as the electrode material for supercapacitors.?3?The synthesis and electrochemical performance study of PPy-CuCoPPy-CuCo was synthesized through two-step method,which included coordinative efforts and electrochemical copolymerization.The first step reaction formed the monomers of pyrrole-Cu and pyrrole-Co between pyrrole and Cu²⁺and Co²⁺by direct coordination method.Secondly,the pyrrole-Cu and pyrrole-Co monomers conducted electrochemical copolymerization to obtain the coordinated polymer of PPy-CuCo.The PPy-CuCo involved the alternating linear chain-like and tetrahedron structures.The linear chain-like structure could promote the electron transfer,accordingly improving the conductivity and rate capability of PPy.The tetrahedron structure could reinforce the polymer chain strength of PPy.The restrained volume swelling or shrinkage of PPy during the charge/discharge process caused the improved electrochemical cycling stability.Through changing the material structure of pyrrole and controlling the coordination degree of two metal ions,it was to achieve the advantage balance of the two structures.PPy-CuCo could effectively maintain the high rate capability and cycle stability at high current density.While single metallic-coordinated polymers of PPy-Cu and PPy-Co were difficult to solve the two problems.The specific capacitances of PPy,PPy-Cu,PPy-Co and PPy-CuCo were 249,609,521 and 618 F g^-1 at the current density of 1.0 A g^-1.The rate capability of PPy-Cu,PPy-Co and PPy-CuCo from 1.0 to 20.0 A g^-1 were 51.5%,55.1%and 51.8%,respectively.The capacitance retention ratio after 2000 cycles at 20.0 A g^-1 were 80.5%,91.4%and 90.0%,respectively.PPy-CuCo exhibited better electrochemical rate capability and cycling stability.Based on the Polyvinyl Alcohol-sulfuric acid gel electrolyte,the all-solid-state symmetric PPy-CuCo supercapacitor was assembled.According to the electrochemical test,PPy-CuCo supercapacitor showed the capacitance of 72 F g^-11 at 5.0 A g^-1 and the capacitance retention of69.4%after 1000 cycles.The supercapacitor supercapacitor exhibited highest energy density of 32.5 Wh kg^-1 at power density of 750 W kg^-1.PPy-CuCo can be used as the electrode material for supercapacitors.