Tuesday, 23 September 2008

Impermeable Membrane Design Considerations

Suggestions for materials used for the design of a membrane/separator without using noble metals or catalyst.
A hydrogen and oxygen gas impermeable membrane spaced between the cathode plate and anode plate.

This membrane would be used for electrolysis of water.

Factors to be considered in designing the separator

The considerations that are important may influence the selection of the separator include the following:

# Electronic insulator
# Minimal electrolyte (ionic) resistance
# Mechanical and dimensional stability
# Sufficient physical strength to allow easy handling
# Chemical resistance to degradation by electrolyte, impurities, and electrode reactants and products
# Effective in preventing migration of particles or colloidal or soluble species between the two electrodes
# Readily wetted by electrolyte
# Permeable/impermeable to gas molecules or selective based on molecular size
# Uniformity in thickness
# Flexibility or rigidity
# Porosity
# weight

Separator types:

# microporous films
# woven
# nonwovens
# ion exchange membranes
# supported liquid membranes
# solid polymer electrolytes
# solid ion conductors
# bonded/laminates
# solid and gelled electrolyte/separator combined

My research has led me to believe that Nonwovens are widely utilized as separators for several types of batteries (NiCd’s) which are not dissimilar, comparable with a water electrolysis cell using a Potassium Hydroxide (KOH) or Sodium hydroxide (NaOH) electrolyte solution.
For example lightweight, wet laid nonwovens made from cellulose, poly(vinyl alcohol), and other fibers have achieved considerable success as separators for popular primary alkaline cells of various sizes.
The key nonwoven attributes include consistently uniform basis weight, thickness, porosity and resistance to degradation by electrolytes.

I plan to make use of some high quality fabric Nonwoven roofing sheet (pin-holed) impregnated with PVA to allow ionic transfer but which should also be impermeable to Oxygen.

Any thoughts?

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