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.

Computational Optimization of Porous Structures for Electrochemical Processes

“…It is assumed that steady gas-liquid distributions are obtained at breakthrough of the gas phase to the bottom of the pore network and at disconnection of the water supply route from the bottom side to the top by further increase of the gas pressure. The model assumptions (i.e., stepwise invasion, steady-state invasion patterns) are made in accordance with experimental results reported in [46] for low capillary numbers and incompressible gas flow, as well as on the simulation results for gas permeation in [47].…”

“…It is assumed that steady gas-liquid distributions are obtained at breakthrough of the gas phase to the bottom of the pore network and at disconnection of the water supply route from the bottom side to the top by further increase of the gas pressure. The model assumptions (i.e., stepwise invasion, steady-state invasion patterns) are made in accordance with experimental results reported in [46] for low capillary numbers and incompressible gas flow, as well as on the simulation results for gas permeation in [47]. In summary, the situations studied in this work are: (1) a reference 2D network without a gradient; (2) a 2D network with a continuous LTH gradient; (3) a 3D network with a gradient identical to case 2; (4) a 3D network with the same gradient as in case 2 but in the opposite direction (i.e., HTL); (5) a 3D network with two different porosity regions (denoted as a dual-porosity pore network, similarly to Figure 2).…”

Polymer Electrolyte Water Electrolysis: Correlating Porous Transport Layer Structural Properties and Performance: Part I. Tomographic Analysis of Morphology and Topology

“…Transport parameters.-Different PTL transport properties in the void and solid phases are important for PEWE operation. 24,39,40 When a channel based flow field is used, then the through-plane properties will dominate species transport in the channel areas while a mixture of through-plane and in-plane properties is relevant for the rib areas. For energy transport the situation is inversed as heat will flow through the flow field ribs.…”

Elucidating the Performance Limitations of Alkaline Electrolyte Membrane Electrolysis: Dominance of Anion Concentration in Membrane Electrode Assembly

“…However, it is to be supposed that both HER and OER kinetic improve with increasing the KOH concertation, which should result in a reduction in activation loss . This surprising observation for the OER can be explained when considering that increasing concentration of KOH also leads to an increased viscosity, which influences hydrodynamic transport properties, like diffusion, convection, but also bubble formation and bubble detachment . Since we do not expect mass transport limitation to be significant at such low current densities we attribute the OER activity loss to the bubble formation on the electrode surface and partially active sites blockage by increasing the electrolyte viscosity at elevated KOH concentration .…”