A high-voltage Zn-ion hybrid supercapacitor based on a conjugated polyphthalocyanine framework cathode and a Zn@Zn
Wenyun Wang1, Chao Yang1, Mingcan Chen1
1School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China.
Abstract:
Aqueous Zn-ion hybrid supercapacitors have shown extraordinary promise for electrochemical energy storage, due to low cost, high security, large power density and acceptable energy density. Rational optimization of electrodes and electrolytes has always been the key for boosting the electrochemical energy storage performances of aqueous Zn-ion hybrid supercapacitors. We propose a pH-decoupling Zn-ion hybrid supercapacitor based on a conjugated polyphthalocyanine (PPc) framework cathode and a Zn@Zn phthalocyanine (Pc) anode. Many structural characterizations indicate that the porous PPc framework possesses the different chemical structure from the symmetrical intermediate. The PPc electrode provides higher gravimetric specific capacitances in the ZnSO4/H2SO4 electrolyte than those in the ZnSO4 electrolyte and the H2SO4 electrolyte. Compered to the Zn anode, the Zn@ZnPc anode exhibits the longer cycle life of Zn-ion hybrid supercapacitors, more obvious suppression on hydrogen evolution reaction, better infiltration property of the electrolyte and the larger adsorption energy for the chemisorption of a bare Zn2+ ion. Electrochemical kinetics analysis of the pH-decoupling PPc//Zn@ZnPc supercapacitor confirms the predominant capacitive-controlled capacity for energy storage, due to physical adsorption and chemical adsorption of electrolyte ions for producing electric double layer capacitance and pseudocapacitance respectively. Additionally, theoretical calculation confirms the appropriate adsorption energy of the bridging N atoms for the highly reversible adsorption/desorption of Zn(H2O)62+. This assembly strategy of the pH-decoupling PPc//Zn@ZnPc supercapacitor opens up a new avenue for exploiting high-performance aqueous Zn-ion hybrid supercapacitors.
