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New separators for alkaline water electrolysis have been prepared and optimised, starting from long-chain aromatic polymers. With these separators the working conditions (zero gap cells) are up to 120 C with a current density of 1 A/cm2. Under the same conditions and relative to a cell working without separator, at 90 C with 30% KOH an increase of 160-250 mVolt is observed at 4 A/cm2. The most promising polymers which may be used for preparing separators are poly-p-phenylene sulphide, poly-p-xylilene and poly-m-xylilene sulphide. Obviously they must be functionalised prior to use. The methodological approach used for preparing the separator is extremely important, since when used, it governs both the ohmic drop and the gas separation efficiency. The best results are obtained starting from needle felts which have the following characteristics: 600 g/m2, thickness 1.1 mm, bubble point 25-28 cm of water. The felts have been calendered twice and thermally stabilised in air for two hours at 220-230 C, in order to provoke the occurrence of the oxidative and crosslinking reactions which markedly increase the characteristics of samples considered. The needle felts have been successively sulphonated in the gas phase with SO(3) in SO(2) at 50-60 C. The above separators have been tested in long-term experiments (2000-3000 hours) in 30-32% KOH without degradation or loss of efficiency in gas separation ( H(2) and O(2) purity always better than 99.97-99.98% and 99% respectively).

Additional information

Authors: GIUFFRE L, Politecnico di Milano (IT);MODICA G, Politecnico di Milano (IT);TEMPESTI E, Politecnico di Milano (IT)
Bibliographic Reference: EUR 12538 IT (1990) 120 pp., MF, ECU 8
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