Low Temperature Molten Salts In Mg-based Hydrogen Storage Alloy Electrodeposition And Its Properties

The Mg-based hydrogen storage alloys are considered as one of the most promising hydrogen storage alloys,offering the combination of great hydrogen storage capacity,low density,abundant resource and low cost.The Mg-based alloys were electrodeposited in urea-acetamide-NaBr low temperature molten salts,and the electrochemical performance of the alloys was studied.The main content in this dissertation was summarized as follows:1.The electrochemical behaviours of Ni(II),Mg(II),La(III) on Cu electrode was investigated in urea-acetamide(4.27 mol·L-1)-NaBr(1.40 mol·L-1) low temperature molten salts, respectively.The reduction processes of Ni(II) were proved as one step irreversibility by cyclic voltammetry experiments.The diffusion coefficient (D0) and the transfer coefficient (α) of the Ni(II) was calculated as D0=2.03×10-7 cm2·s-1 andα=0.41 respectively. Mg(II) and La(III) could not be electrochemically reduced in this molten salts independently. The nucleation processes were three-dimentional direction and instantaneous processes which was studied by chronoamperometry methods, and the diffusion coefficient (D0) was calculated as 9.09×10-7 cm2·s-1.2.The codeposition behaviors of Mg(II),La(III) and Ni(II) were studied in low temperature molten salts by cyclic voltammetry and Energy dispersion spectrum(EDS).It was indicated that the codeposition of Ni-La,Ni-Mg and Ni-Mg-La alloys was step-by-step reduction. The codepositon mechanism was explained by the polynuclear complex of electroactive intermediates.3.The Ni-La,Ni-Mg and Ni-Mg-La alloys were prepared by constant current and potentiostatic electrodeposition. The effect of the deposition potential, current density and main salt concentration ratio on the deposits composition was investigated. The structure and surface morphology of the deposits were analyzed by EDS,Scanning Electronic Microscope(SEM) and X-ray diffraction (XRD). The results showed that the deposits were multi-phase containing amorphous phase. 4.The maximum discharge capacity and the cycle-life sequence of the deposits were both as follows: Ni-Mg-La>Ni-La>Ni-Mg. The cyclic voltammetry anodic peak current (Ip) of different alloy electrodes was decreased with increasing sweeping number,and the anodic peak area and its Ip are both proportional to electrode discharge capacity. The linear relationship between Ip and v1/2 (v is sweeping rate) indicated that the electrode discharge reaction was controlled by hydrogen atom diffusion process.