WATER PERMEABLE SHEET AND USES THEREOF

摘要

There is described a water permeable sheet suitable for use as a recuparator membrane in a fuel cell. The sheet is substantially impermeable to gas, and has the following properties: (a) a water vapour transmission rate (WVTR) of at least 200 g² / m² / day at 25 DEG C and 75% relative humidity; and (b) a mean dimensional stability (over 100 cycles as defined herein) for a wet or dry sheet in any direction parallel to the sheet surface of less than about 15% change in linear dimension. The sheet may be a laminate of a water permeable first layer (such as cellulose) bonded to a supporting porous layer comprising either a matrix of water insoluble fibres (such as a non-woven glass fibre mat) or a porous plastic film (such as polyethylene); or may be an impregnate of a matrix of water insoluble fibres (such as non woven glass fibre mat) impregnated with a water permeable material (such as cellulose). Laminated sheets of the invention may comprise additives (such as urethane / ethylene oxide co-polymer and/or silica) in the laminating adhesive to improve the WVTR of the laminate without significantly reducing its de-lamination strength. Optionally other additives may be added to the sheet such as anti-microbial agents (such as PHMB, titanium dioxide and silver chloride mixture and/or silver nitrate) and heat conductors (such as metal or carbon black powders). Such highly water permeable, gas impermeable and dimensionally stable sheets may be used as recuparator membranes to manage heat, water and/or humidity levels in the reactant streams of a fuel cell.