Defined porosity for hydrogen production with maximized efficiency

Project description

PEM (proton exchange membrane) electrolysis is one of the most important methods for producing large quantities of hydrogen. A corresponding electrolyzer consists of the PEM, which is contacted by the electrodes on both sides. The porous transport layer (PTL) is located between the electrodes and the PEM. Currently, a wide variety of materials and manufacturing processes and combinations thereof are used for PTLs in PEM (proton exchange membrane) electrolysis, ranging from expanded metal to sintered bodies, from coated and uncoated titanium and stainless steels to carbon materials. Targeted structuring of the porosity for these materials, even across multiple size scales, has so far only been possible to a very limited extent, e.g., through the use of multilayer materials, which lead to increased contact resistance between the components. Porous components are usually manufactured using sacrificial materials, direct foaming, replication technology, or partial sintering. These conventional manufacturing processes allow only limited variation and adjustment of pore size and geometry.

This is where the CapS-PTL project comes in. The aim is to enable the porosity in PTLs to be defined and adjusted using industrial production methods. The literature already describes clear correlations between porosity, pore size, pore channels, electrical conductivity, and contact resistance with the efficiency of the electrolyzer, which have not yet been sufficiently taken into account in component design. Perforated sheets, expanded metals, metal fleeces, and incompletely sintered metal powders are commonly used as PTLs. What all these solutions have in common is that the corresponding manufacturing processes allow little to no targeted control of pore size and geometry with regard to functionality. The approach proposed here with the CapS (Capillary Suspension) process allows precise control of these parameters. At the same time, pore gradients in the component and metastructures, such as channels, can be adjusted to control mass transport. In addition, material gradients can be introduced into the porous structure. Since the process allows great freedom in the choice of starting materials, the components can be optimally adapted to the challenging conditions on the cathode and anode sides. Here, temperature, humidity, electrical potentials, and corrosive environmental conditions lead to severe degradation of the materials used. Due to the simple processing of the method, even for large structures, an increase in manufacturing efficiency can be expected. In addition to the areas of application mentioned here in electrolysers, a wide range of other applications are conceivable.

Fraunhofer IWM subproject:

Production of porous titanium electrodes (PTL) based on capillary suspensions (CapS).

• Production of bulk porous titanium electrodes using liquid forming. In this way, samples can be easily produced and examined in terms of porosity and pore size. Assembly for use in a test setup for electrolysis must be carried out subsequently.
• Production of thick-film porous titanium electrodes as a prototype for industrial scaling. This process can be easily adapted for industrial use and scaled, for example, in the form of tape casting. The samples can already be produced in suitable dimensions for characterization in a test setup.
• Production of additively manufactured porous titanium electrodes for targeted metastructuring. With the aid of a 3D printer, the capillary suspensions can be produced in highly complex geometries and structures. This is particularly interesting for specifically adjusting the functionalities of the porous titanium electrodes. In this way, concepts can be developed to further improve efficiency and operation.
• Evaluation of porous titanium electrodes using test setups for electrolysis. The different capillary suspensions and geometries of the porous titanium electrodes are characterized and evaluated in a test setup. This allows both the capillary suspensions and the geometries of the porous titanium electrodes to be specifically optimized for the application in an iterative process. This characterization takes place alongside all other developments in order to be able to evaluate the work results in concrete terms.