Study On The Electrochemical Performance Of Co/Al-Ni/Al Hydrotalcite And Their Composite Oxides

A series of Ni/Al and Co/Al hydrotalcite which M²⁺/M³⁺ molar rations are 3 were synthesized by hydrothermal method. The layered double oxides (LDOs) were prepared through the thermal treatment of hydrotalcite. The structure and morphology of the samples were characterized by XRD, FT-IR, TG-DSC and TEM. XRD result showed that the obtained samples had nice crystal forms and high purity.The electrochemical performance of hydrotalcite modified electrode in 0.5 mol/L NaOH and K₃[Fe(CN)₆] media was investigated by cyclic voltammetry, impedance and constant current charge/discharge measurements. The analysis results indicated that the electrochemical performances of Ni/Al-Cl hydrotalcite and Ni/Al-CO₃ hydrotalcite in NaOH solution were similiar. The mechanism to explain the redox behavior of the electrode system was the electron transfer between the oxidative M²⁺ and anion located in the interlayer spacing. Furthermore, the Co/Al hydroxide modified electrode exhibited a pseudo-capacitive behaviour in 0.5 mol/L NaOH media. Such materials had good long-term capacitive performance with the highest specific capacitance value of 163.1 F/g. The Ni/Al-CO₃ hydroxide modified electrode exhibited a pseudo-capacitive behaviour in 0.5 mol/L K₃[Fe(CN)₆] media. Cyclic voltammetry results demonstrated that electrochemical reaction occured under semi-infinite linear diffusion conditions and the electrode reaction was controlled by the diffusion of OH^- and [Fe(CN)₆]^3-.In addition, the electrochemical performance of LDOs was examined by cyclic voltammetry, impedance and constant current charge/discharge measurements. It was found that the clear faradaic pseudocapacitance behavior existed in all the samples. NiAl-Cl hydrotalcite calcined at 450℃displayed excellent capacitive properties within the potential range of 0.15～0.50 V in 0.5 mol/L NaOH electrolyte. Charge/discharge behaviors were observed with the highest specific capacitance value of 419.0 F/g at the large current density of 50 mA/cm² and approximately 4.3 % loss of specific capacitance after 400 cycles. Moreover, the highest septic capacitance values of 265.5 F/g could be achieved with Co/Al hydrotalcite calcined at 300℃.