Measurement of effective oxygen diffusivity in microporous media containing moisture

Abstract

The mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the cell performance of a polymer electrolyte fuel cell (PEFC). The oxygen diffusivity of paper type porous media, which is generally used as a GDL, was measured with respect to its liquid water content using experimental apparatus consisting of an oxygen sensor based on the galvanic cell. A numerical method was established to obtain the effective oxygen diffusivity of microporous test materials by calculating the oxygen concentration distribution on both sides of the test material. Experimental results indicate that the relative oxygen diffusivity of paper type GDLs increases nonlinearly as the water saturation decreases.

Characteristics of oxygen diffusivity and water distribution by X-ray radiography in microporous media in alternate porous layers of different wettability for moisture control in gas diffusion layer of PEFC

“…Park et al [5] found that it was difficult to remove water from CLs employing two materials with different pore sizes. Utaka et al [6,7] devised a method for measuring the oxygen diffusivity of a GDL containing moisture using an oxygen absorber and they evaluated its gas diffusion characteristics.…”

“…A small hole was drilled in the holder to allow air out, but it was closed off during measurements. A vacuum impregnation method [7], in which an evacuated leak-tight container containing the test material is dipped in pure water, was used to saturate the test porous material with water.…”

Precise measurement of effective oxygen diffusivity for microporous media containing moisture by review of galvanic cell oxygen absorber configuration

“…However, there have been few studies that have measured the effective diffusivity in a sample containing moisture. Through research on water management in PEFCs, the authors have developed a method to measure the oxygen diffusivity of microporous media containing moisture [13,14]. Utaka et al [13] evaluated the gas diffusion characteristics of a dry GDL using a method that employed a galvanic cell oxygen absorber, where multi-layered GDLs with a larger diffusion resistance were used to obtain the precise oxygen diffusivity.…”

“…However, diffusivity measurement of a single GDL containing moisture is required under conditions similar to those during practical operation. The galvanic cell oxygen absorber with peripheral equipment and the measurement method were further improved to evaluate the oxygen diffusion characteristics in a single GDL with/without the presence of moisture [14]. This method was demonstrated to be effective for measuring a single GDL containing moisture and the measurement error factors were also examined.…”

“…Therefore, a special method was required for deriving the diffusion coefficient with sufficient accuracy. The authors have previously developed a comparison method [14], where the apparent mass transfer conductance of a standard test sample with a known diffusion coefficient is measured consecutively under the same experimental conditions with and without the sample. Using the standard sample measurement, the effective oxygen diffusion coefficient for the test sample was determined by adopting the bulk characteristics of oxygen reaction in the galvanic cell oxygen absorber as a variation of the effective diffusion resistance.…”