Developments on IME-alkaline water electrolysis

A research programme aiming at the development of a new advanced concept in alkaline water electrolysis has been demonstrated at S.C.K.-C.E.N. under the auspices of the Commission of the European Communities. The first R&D task was the development of an alkali-compatible ion exchange membrane as a replacement of the chrysotile asbestos diaphragm. After a screening test, polyantimonic acid manufactured in thin sheets was shown to display the required ion conduction in alkaline solution. Using polysulfone as an organic binder, the sheets withstand 120°C without deterioration. Several membrane characteristics such as ionic conductance, membrane potential and Hittorf transference numbers were measured in different experimental set-ups. The temperature dependence of the membrane conductance exhibits an exponential decay when working in an alkaline solution (≤ 1 N KOH). Membrane resistance decreases from a 1.0-0.8 Δ cm² range at 25°C to a 0.25-0.15 Δ cm² range at 120°C. Gas tightness and mechanical stability were demonstrated for 1000 h of continuous operation up till now. The electrodes under investigation were mainly composed of perforated nickel plates, catalytically activated using a thermal decomposition technique. Performances up to 120°C in 50 wt % KOH for 2000 h operation were investigated for Ni, NiCo₂O₄, NiCoO₂ and La_xCoO₃ as the anode electrocatalyst. As a result of these investigations, the spinel type NiCo₂O₄ showed the best performance under the testing conditions. At the cathode, NiB, NiS_x and NiCo₂S₄ were investigated up to 120°C as the hydrogen evolution electrocatalyst. A demonstration unit of a 1 kW electrolyser has been built in order to experiment on the newly introduced components (membranes, electrodes, gaskets, etc.). It consists of a 14-cell filter press unit, each cell of 40 cm². The loop built around the stack allows an upscaling up to 10 kW.