Electrodeposition and Characterization of Platinum Coatings on Titanium Porous Transport Layers for PEM Electrolyzers

Hydrogen production by electrolysis offers significant advantages over established and more common processes such as steam reforming with regard to carbon dioxide emissions, in particular through the use of electrical energy from renewable sources and the establishment of a decentralized supply structure. The advantages of PEM (proton exchange membrane) electrolysis include high power density, scalability, and the high purity of the produced hydrogen. However, so far the manufacturing of PEM electrolyzers is time consuming, which makes their widespread use difficult and is a significant cost driver for this technology. A promising strategy for the cost-effective production of the cell components is functionalization of low-cost materials with protective coatings. In the framework of the publically funded flagship project H2Giga, coating systems for the bipolar plates (BPP) and porous transport layers (PTL) are developed and tested under real conditions in an electrolyzer stack. The anode PTL is facing very low pH and high anodic potentials as it is in close proximity to the anode catalyst layer. Therefore, the PTL is made of titanium which is proven to be long term stable under these conditions. However, titanium forms a passive layer under anodic polarization leading to an increase of contact resistance and ohmic drop in the cell. The passivation can be suppressed by electrodeposition of platinum at the interface to the catalyst layer. To ensure a good adhesion of the platinum and low material loss during electrolyzer operation, a pretreatment of the titanium surface is crucial. A state-of-the-art fluoride-containing etching solution was compared to fluoride-free processes in terms of stability of the subsequent platinum coating. Investigations on the morphology by SEM and FIB show a good correlation to polarization experiments. The results are further validated by operando testing in a five cell test stack. The fluoride-free solutions are very promising for industrial applications, but so far only provide limited activation of the titanium surface and need to be further optimized to ensure a reliable coating adhesion.