The Electrochemical Hydrogen Sorption Behaviour of Zr-Cu-Al-Ni Metallic Glasses

Abstract

Amorphous Zr–Cu–Al–Ni alloys are of interest for hydrogenation studies because they consist of a combination of early and late transition metals. Potentiodynamic polarisation tests were conducted to investigate the cathodic hydrogen reduction reactions on the surface of melt-spun Zr₅₅Cu₃₀Al₁₀Ni₅ and Zr₆₅Cu_17.5Al_7.5Ni₁₀ ribbons. In the Tafel region, the electrodic desorption reaction is the rate-determining step which competes with the hydrogen absorption reaction. In the next polarisation region, the hydrogen reduction takes place under mass transfer-control. The ribbons are galvanostatically charged with hydrogen to different hydrogen-to-metal ratios in 0.1 mol/l NaOH solution. The rate of hydrogen absorption of the Zr₅₅Cu₃₀Al₁₀Ni₅ alloy is higher than that of the Zr₆₅Cu_17.5Al_7.5Ni₁₀ alloy, although the hydrogen discharge rate on the surface of the Zr₆₅Cu_17.5Al_7.5Ni₁₀ alloy is higher. Upon charging the samples at room temperature to H/M=1.3 using a low charging rate (−1 mA/cm²), the X-ray diffraction pattern show the main peaks of a Zr-hydride and Cu and/or a Cu rich phase(s) besides the amorphous phase. The potentiostatic double-pulse technique (PDP) was applied to estimate the fraction of reversibly absorbed hydrogen in the amorphous alloy samples by charging at different cathodic potentials. Subsequently, the residual hydrogen concentration (irreversibly absorbed hydrogen) was determined by hot extraction. The Zr₅₅Cu₃₀Al₁₀Ni₅ alloy was found to absorb a higher fraction of reversible hydrogen than the Zr₆₅Cu_17.5Al_7.5Ni₁₀ alloy.