Percolation Theory for Gas Electrode of Fuel Cells

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In order to apply the statistical percolation theory to a gas electrode of fuel cells, model catalyst layers composed of wet-proofed particles and wet-susceptible particles were used for percolation experiments last year. The real catalyst layer of phosphoric acid fuel cells was used for acid percolation tests in this year.It was found that the acid could penetrate through the real catalyst layer within a short hour under acid fill level of lower than 30% in which acid could exist statistically as dispersed spots. It showed that the acid immovable critical point did not appear if the wet-susceptible catalysts were connected and linked.Acid transfer along the electrode surface was investigated using actual carbon substrates collected from the long operated phosphoric acid fuel cell. Due to the effect of the difference between progressive and drawing back wetting contact angle, acid stopped to move in spite of the large difference of the acid fill level distribution. This phenomena appeared remarkably when a new wet-proofed substrates were used.The acid could move quickly with the increase of acid fill level, but was immovable when the acid fill level became lower than 30%. This phenomena is supported by our estimated results of the percolation theory. These experimental and theoretical results can be useful for improving the reliability and the life of phosphoric acid fuel cell.