Characterization of Advanced PTL structures for PEM Electrolyzers at High Temperatures and elevated Current Densities

Abstract

Even though environmental measures are being taken around the world, the CO2 emissions keep rising and establishing new goals in areas such as energy power supply. This industry searches for technologies that can satisfy all benefits from renewable energy sources as electrolysers. This solution called Power-to-X technology is used to convert electrical energy to chemical energy in form of hydrogen by proton exchange membrane electrolysis (PEMWE). Even though state of the art carries studies using a current density of 2.0 A·cm-2, the research for PEM at reduced investment costs focuses now on standards of 4.0 or even 6.0 A·cm-2 and the need to improve the efficiency of the cell at these current densities. In this study it is described the characterization of titanium porous transport layers at 2.0, 4.0 and 6.0 A·cm-2, consisted of a mesh structure and a microporous layer. The study on the compression pressure applied at the assembly was done at 0.2 N·m, 0.45 N·m, 1.0 N·m, 2.2 N·m and 3.0 N·m, and it was concluded that the optimum value was 1.0 N·m, since this is the value that offers a higher efficiency and minimizes overpotentials. The limitations dominated by the slow rate of activation of the OER decrease up to 1.0 N·m. Nevertheless, at higher compression pressures the mechanical stress becomes too intense and creates holes in the MEA. After studies on the physical characterization of coated PTLs, the focus on electrochemical characterization determines how the morphology of these materials performs at elevated temperatures and current densities. As a result, Ti-GKN performed better than other PTLs during the recording of polarization curves, achieving 2.70 V at 4.0 A·cm-2. Electrochemical impedance spectroscopy registered the lowest ohmic resistances and mass transportation limitation with Ti-GKN, supporting its ohmic resistance at 159 mΩ·cm², while the ohmic resistances of Ti mesh and sintered Ti are approximately 165 mΩ·cm² and 182 mΩ·cm², respectively. The characterization concludes that a coated PTL has improved mass transport losses at low and high current densities. The Ti-GKN PTL shows optimal electron and mass transport throughout the range of current densities, even though the overpotentials generated at the uncoated PTL prevent an economical cell voltage. In a parallel study, a simulation work was carried out using SEM images and GeoDict as a material property characterization software. Images of Ti-Ti/Nb, Ti-GKN and Ti mesh were imported and the following properties predicted: bubble point, tortuosity factor and the capillary pressure curve.