Pseudocapacitive properties of polypyrrole - ferrimagnetic CoFe2O4 composites

This investigation is motivated by increasing interest in materials combining advanced electrochemical charge storage properties and spontaneous magnetization. Pseudocapacitive properties of ferrimagnetic CoFe2O4 (CFO) are observed in a potential window of-0.6 -+0.2 V in Na2SO4 electrolyte. This finding opens an avenue for the fabrication of advanced composites containing conducting polypyrrole (PPy) polymer and CFO. Composite materials show outstanding capacitive properties, which are achieved at a low resistance for electrodes with high active mass. Electrochemical studies reveal synergistic contribution of CFO and PPy. At low charging/discharging rates the composite materials exhibit higher capacitance, compared to the total contribution of individual components. At high charging/discharging rates, the capacitance of composites is significantly higher than the capacitances of PPy or CFO. The composite materials show lower resistance, than resistances of the individual components. The addition of PPy to CFO results in reduced charge transfer resistance and enables better utilization of pseudocapacitive properties of CFO. The relaxation frequency and capacitance retention decreased with increasing PPy content. The investigation of capacitive properties of the composites provides evidence of beneficial magnetohydrodynamic effect of ferrimagnetic CFO particles. The ability to enhance capacitance at high charging rates opens an avenue for the development of high power pseudocapacitors.