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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., Journal of the Electrochemical Society, 166 (4), ISSN:0013-4651, ISSN:1945-7111

In this work a model of an elevated pressure CO2 electrolyzer producing primarily formate or formic acid is presented. It consists of three parts: A model of the bulk electrolyte, the diffusion layer, and the electrode surface. Data from the literature was used to validate both the bulk portion of the model, as well as the overall model. Results from the literature were further explored and explained by reference to the model and faradaic efficiency is predicted very well (R-Square of 0.99 for the fitted data, and 0.98 for the non-fitted data). The primary effect of increasing the pressure on a CO2 electrolyzer is seen to be increasing the maximum attainable partial current density, while the faradaic efficiency and specific energy of formation plateau at pressures above 10-20 bar, at 95% and of 3.7 kWh/kg, respectively. Unlike the efficiencies, the profitability of running a reactor increases with pressure, following a similar trend as partial current density, showing the importance of this quantity as a performance metric of a CO2 electrolyzer. In general this work shows the utility of a model of this sort in the design, evaluation and operation of CO2 electrolyzers.