IN-SITU STM INVESTIGATION OF METAL HYDRIDE ELECTRODES IN ALKALINE ELECTROLYTE DURING ELECTROCHEMICAL CYCLES

For more than a decade metal hydride electrodes have been investigated by ex situ methods. In situ STM (Scanning Tunnelling Microscopy) allo ws investigation of single metal hydride grains during the charge and discharge process in the electrolyte. The advantage of STM measurement s is its manifold analysing feasibility, e.g. surface morphology, surf ace conductivity and atomic forces with spatial resolution, and even s ometimes atomic resolution. Samples of alloy grains pressed into a gol d pellet and the polished surfaces of bulk alloys were investigated in concentrated alkaline electrolyte (6 M KOH) by means of STM. The volu me expansion between the metal and the hydride was measured on a singl e grain in the electrolyte. This value of Delta V/V=14.9% is very clos e to the value observed from X-ray diffraction measurements (15.4%). M ultiphase samples show a very inhomogeneous surface conductivity. The identification of the phases with different surface conductivities is a key in understanding the hydrogen absorption mechanism in the electr olyte. (C) 1997 Elsevier Science S.A.