Novel Approach to Measure Key Structural Parameters of PEM Fuel Cell Catalyst and Gas Diffusion Layer Based on Archimedes Principle

Commercialization of fuel cells and demand for large scale manufacturing of their components necessitates the design of novel characterization methods which produce consistent results in a timely and cost efficient manner. In this work, we report a simple approach to measure the porosity, pore volume and thickness of catalyst and gas diffusion layers based on the principle of buoyancy in different fluids. Moreover, the method allows for obtaining the ionomer content of the catalyst layer. By applying this method on a porous PTFE substrate with known pore surface area and varying ionomer content, we are able to measure the density of the ionomer film vs. thickness at high (nm) resolution. Water sorption measurements on these model samples yield the maximum water content as a function of ionomer thickness. Water sorption measurements made on individual components of the catalyst layer (Pt/C and bulk ionomer) were also compared against those made on a catalyst layer. We observed a discrepancy between water uptake of individual constituents and catalyst layer. We utilized such difference in measured and expected water uptake to estimate the thickness of ionomer in the catalyst layer. This is the first attempt to estimate the thickness of ionomer in catalyst layer using a bulk scale ex-situ method. Overall, we show that this method is a lower cost and faster technique for measuring key characteristics of porous layers when compared with alternative methods such as electron microscopy and spectroscopy techniques. Furthermore, it can be easily adopted by industry and large manufacturing divisions.