Joined ellipsometry and voltametry investigation on the second discharge plateau in Ni(OH)2

The electrochemical properties of nickel hydroxide, produced via an electrodialysis process are studied by means of cyclic voltametry and in-situ ellipsometry methods. The Ni(OH)₂ electrodes are thin layers of nickel hydroxide powder deposited on a polished platinum substrate. Electrochemical and optical properties are investigated in a voltage domain including the so-called “second discharge process”. The reduction of nickel hydroxide proceeds at two successive potentials with a recovering of the initial optical data only after the second discharge step. The first discharge step leads to a nickel hydroxide not fully discharged while the second discharge step is coupled both to a sudden change in the nickel hydroxide properties and an agglomeration of particles phenomenon. Project financed by the E.U., program Brite Euram BRPR-CT97-0515 (NEARBY) Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.