Understanding the Charge Storage Mechanism and Electrochemical Performance on the Poly[Ni(salen)]-modified Electrode Electropolymerized with Different Sweep Rate

Abstract

Poly[Ni(salen)] films were electropolymerized on multiwalled carbon nanotubes (MWCNTs) in tetrabutylammonium perchlorate/acetonitrile by cyclic voltammetry method. And the employed scan rates were 5, 10, 20 and 40 mV s⁻¹. The effect of sweep rate on the growth of poly[Ni(salen)] was investigated by the apparent surface coverage (Γ) analysis, in which Γ increased almost proportionally with the scan number for all applied scan rates. Fourier transform infrared spectroscopy and field-emission scanning electron microscope images verified the successful deposition of poly[Ni(salen)]. It demonstrated that Ni(salen) were oxidized at the interface between the electrolyte and substrate surface and then the oxidized monomers were cross linked on the substrate. The galvanostatic charge/discharge plots displayed the specific capacitance of 62.8, 78.8, 161.4 and 135.1 F g⁻¹ for 5, 10, 20 and 40 mV s⁻¹ (0.05 mA g⁻¹), respectively. Poly[Ni(salen)] grown at 20 mV s⁻¹ possessed the maximum capacity and decreased as the scan rate increased because the monomer diffusion impeded the growth of poly[Ni(salen)]. The charge diffusion coefficient (D) was found highest with the sweep rate of 20 mV s⁻¹. The excellent electrochemical performance of poly[Ni(salen)] electropolymerized at 20 mV s⁻¹ is ascribed to the better conductivity and superior diffusion ability according to the kinetics.