Understanding the Role of Water Flow and the Porous Transport Layer on the Performance of Proton Exchange Membrane Water Electrolyzers

Abstract

In this article, we have brought a different perspective to the topic of mass transport losses in a proton exchange membrane (PEM) water electrolyzer, particularly regarding the role of water flow and the dominant mass transport mechanism in the porous transport layer (PTL). We conducted permeation experiments on a sintered Ti PTL, where we measured the pressure loss of gas that flows through its pores; furthermore, we presented a model based on the van Genuchten–Mualem capillary pressure and the Carman–Kozeny gas permeability, and we report an increase in the pressure loss with respect to the water flow, which we reported as an increase in the apparent tortuosity of the pores in the PTL. From this we conclude that the water flow exerts a shear stress on the gas flowing through the PTL, proportional to its kinetic energy, and that the gas permeation is the dominant transport mechanism within a PTL, in contrast to a one- or two-phase flow, which is more energy demanding. Finally, we propose that further work be carried out, in particular by comparing these results to in situ measurements on an operating PEM electrolyzer.