Development of mesoporous silica-based inorganic proton exchange membrane for fuel cells

Abstract

Due to the certain performance limitations present in the current Nafion based electrolyte membrane for proton exchange membrane (PEM) fuel cell, many attempts have been made to develop better alternative materials based electrolyte membrane. One such approach is the composite membrane, which comprise a matrix interpenetrated with a proton-conducting polymer. In this report, the matrix using mesoporous silica based material and the proton-conducting polymer using phosphotungstic acid (HPW), was prepared as the composite membrane and was studied for the application of high temperature fuel cells. Mesoporous silica was prepared with various pore sizes by hydrothermal treatment method and different crystal structures by chemical synthesis, and HPW was penetrated into the channels of silica matrix by vacuum impregnation method to form the composite membrane as test samples. Material characterization tests were carried out to reveal the success preparation of mesoporous silica with various pore sizes and different crystal structures, and the success impregnation of HPW particles uniformly into the silica matrix, without losing its proton conductivity function. Tests also reveal that the composite consisting of the smaller pore size silica as matrix has a higher thermal stability, better in retaining water content as compared to the larger pore size counterparts. Similarly composite with silica having a 3D face-centered crystal structure, Im3m as the matrix also has higher thermal stability over the temperature operating range of 0~200oC. Electrochemical characterization tests were carried out to reveal that silica with various pore sizes as the matrix has an influence on the overall composite membrane proton conductivity and stability. The small pore size silica based matrix has higher proton conductivity stability as compared to the larger pore size. The small pore size silica based matrix was recorded to have steady proton conductivity value of 0.078 Scm-1 over a time period of 24 hour. Other results include the maximum proton conductivity of composite membrane consisting of 3D cubic bi-continuous crystal structure as the matrix and HPW as the proton carrier measured at 0.1 Scm-1 at operating temperature about 80~90oC in comparison with Nafion 117, 0.065 Scm-1. This suggests that the silica/HPW composite membrane could be used as an effective proton exchange membrane for high temperature fuel cell.