Abstract
In the first paper of this series, the bulk, surface and transport properties of porous transport layer materials (PTL) for polymer electrolyte water electrolysis cells (PEWE) are characterized. A systematic PTL matrix of Ti fiber materials with 3 fiber diameters and 2 nominal porosities as well as a state of the art sintered powder material are investigated to get a better understanding of the governing parameters in electrolysis cells. X-ray tomographic microscopy analysis of ex situ PTL structures and post operando membrane electrode assemblies is performed. On the tomographic structures, bulk (porosity, pore/solid size distributions, fiber orientation), mass transport (diffusivity, permeability, conductivities) and surface parameters (roughness, membrane deformation, PTL surface area and interfacial contact area) are determined. The second paper of this series will correlate the structural parameters with in-depth electrochemical analysis. The new insights into the effect of PTL properties on PEWE performance allow to isolate governing key parameters. From know-how obtained on the fiber based materials fundamental design guidelines for optimization of PTL structures are deduced.
Highlights
To limit the greenhouse gases based global temperature increase by 2050 to 2°C, average CO2 emissions per unit of final energy supplied of 90 kg GJ−1 has to be reduced to 19.5–37.0 kg GJ−1.2 a transition to net zero CO2 renewable energy carriers is inescapable
This study aims at providing the missing link between the surface and bulk structures of Polymer electrolyte water electrolysis (PEWE) and the three main losses for PEWE operation, induced by charge transport, mass transport and electrochemical kinetics
All materials have a thickness of 1 mm. 3D-renderings of cubes with an edge length of 0.6 mm are given in Figure 1, with the Ti solid phase shown in gray
Summary
To limit the greenhouse gases based global temperature increase by 2050 to 2°C, average CO2 emissions per unit of final energy supplied of 90 kg GJ−1 has to be reduced to 19.5–37.0 kg GJ−1.2 a transition to net zero CO2 renewable energy carriers is inescapable. Screening processes of a wide range of different porous transport layers such as Ti sheets,[5,8] foams,[9] grids[10] and sintered structures[5,11,12,13] have been conducted to characterize their suitability and performance. Bulk characteristics such as pore and particle size distributions and transport parameters were related to electrochemical performance data in various studies. They proposed an universal empirical correlation between conductivity and permeability of the PTL‘s dry structure
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