Designing porous transport layers for optimal bubble transport in water electrolyzers

Optimizing the design of porous transport layers (PTLs) is essential for enhanced bubble transport in polymer electrolyte membrane (PEM) water electrolyzers. This study utilized operando neutron imaging to understand multiphase bubble transport behaviour in titanium-based PTLs and identified PTL characteristics that lead to lower mass transport resistance and superior performance. For the PTLs examined in this work, the tested powder-based PTL exhibited more effective bubble removal than the tested fiber-based PTL, which was consistent with the improved electrolyzer performance and reduced mass transport resistance. This improvement was associated with a pronounced bubble saturation gradient from the PTL/catalyst layer interface to the PTL/flow field interface, indicating reduced through-plane bubble accumulation. The tested powder-based PTL also exhibited a channel/land-dependent bubble saturation distribution with lower bubble saturation in the channel regions, suggesting effective in-plane bubble removal from land to channel regions and reduced in-plane bubble accumulation. Furthermore, numerical simulations illustrated that the powder-based PTL displayed lower anisotropy in tortuosity, wherein the ratio of through-plane tortuosity to in-plane tortuosity was nearly equal to 1, compared to the fiber-based PTL which showed a ratio greater than 1. Our findings indicated that the improved mass transport behaviour in the powder-based PTL resulted from combined effects of reduced bubble accumulation, favourable through- and in-plane gas distribution, and isotropic transport properties.