Studies on metal hydride electrodes containing no binder additives

Abstract

Electrochemical properties of hydrogen storage alloys (AB 5 type: LaMm-Ni 4.1Al 0.3Mn 0.4Co 0.45) were studied in 6 M KOHaq using Limited Volume Electrode (LVE) method. Working electrodes were prepared by pressing alloy powder (without binding and conducting additives) into a metal net wire serving as a support and as a current collector. Cyclic voltammetry curves reveal well defined hydrogen sorption and desorption peaks which are separated from other faradic processes, such as surface oxidation. Voltammograms of LVE resemble the curves obtained by various authors for single particle metal alloy electrodes. Hydrogen diffusion coefficient calculated at room temperature for LV electrodes and for 100% state of charge reaches a constant value of ca. 3.3 × 10 −9 and 2.1 × 10 −10 cm 2 s −1, for chronoamperometric and chronopotentiometric measurements, respectively. A comparison of the electrodes with average alloy particle sizes of ca. 50 and 4 μm allows us to conclude that at room temperature hydrogen storage capability of AB 5 alloy studied is independent on the alloy particle size. On the other hand, reduction of the particle size increases alloy capacity at temperatures below −10 °C and reduces time of electrochemical activation of the electrode.