Master thesis presentation Varun Satish Ballary, MPSES

Abstract: The reduction of costs for proton exchange membrane (PEM) electrolyser components is a critical consideration. This research explores the application of cost-effective non-noble materials, coated with anti-corrosive layers, onto state-of-the-art porous transport layers made from both titanium and stainless steel. Niobium and tungsten were utilized to replace platinum or other coatings for this purpose. This study focuses on assessing the corrosion resistance properties of pure metallic titanium, as well as titanium and stainless steel coated with niobium, tungsten, and a thin layer of platinum, all within a simulated PEM electrolyser environment. A corrosion test protocol was established, encompassing electrochemical impedance spectroscopy measurements and potentiodynamic polarization from -0.3 V up to 2 V vs. RHE, followed by potentiostatic polarization at 2 V vs. RHE for 24 hours. All tests were conducted in oxygen-saturated acid solutions at 80 $\deg C$ in a three-electrode corrosion cell setup to replicate the conditions on the anode side of PEM electrolysers. Furthermore, light microscopy examinations of the samples and ICP-MS analysis of the electrolyte solution were conducted before and after the corrosion test. The thin layers of niobium and platinum coated onto stainless steel using PVD sputtering exhibited electrochemical instability and failed to effectively protect the stainless-steel substrate, resulting in peeling of coatings. In contrast, a slightly thicker layer of tungsten coated using the APS method displayed electrochemical stability and effectively shielded the stainless-steel substrate from corrosion. However, some tungsten was dissolved into the electrolyte, as indicated by ICP-MS analysis. Meanwhile, thin layers of niobium and platinum coated onto titanium using PVD sputtering, as well as the slightly thicker layer of tungsten coated on titanium using the APS method, demonstrated electrochemical stability. However, both niobium and tungsten coatings exhibited oxidation based on electrochemical measurements. Thus, completely replacing platinum with non-noble metals is not reliable. Instead, reducing the thickness of the platinum coating on titanium may not adversely affect the PEM electrolyser, as it serves as an anode porous transport layer, potentially contributing to reduced system costs.

Examiner: Björn Wickman
Supervisor: Sarah Zerressen
Opponents: Abhie Sanjay Dhait, Avinash Pramode, Dineshkumar Balakrishnan Asokan