Thin Sputtered Titanium Nitride Layers for Corrosion Protection of 316L Stainless Steel Under PEM Water Electrolyzer Anode-like Conditions

Abstract

Proton exchange membrane water electrolyzers (PEMWE) electrochemically split the water molecule in order to produce high-purity oxygen (at the anode) and hydrogen (at the cathode). When coupled to a renewable energy source (such as wind or sun), green hydrogen can be synthesized, which may contribute to a massive reduction in carbon dioxide emissions in the so-called “hard-to-abate” industrial sectors, like steel and cement manufacturing.Yet, the elevated capital expenditures (capex) deriving from the use of expensive corrosion-resistant materials undermine the economic competitiveness of the PEMWE technology compared to the main hydrogen production processes, like steam reforming. To date, on the PEMWE anode side, metallic bipolar plates (BPP) and porous transport layers (PTL), are essentially made of titanium coated with precious metal layers (platinum, gold) so as to withstand the corrosive and oxidizing environment. Consequently, BPP and PTL account for more than 60% of the capex of the PEMWE stack [1,2]. Without corrosion protection, the harsh operating anodic conditions may lead to performance-killing release of cationic elements from the BPP and PTL into the catalyst layer and the polymer electrolyte [3]. It may also cause the growth of resistive oxide layers at the BPP and PTL surfaces and the development of undesired interfacial contact resistance (ICR).This contribution will focus on the corrosion protection of the anode side of BPP and will first briefly review the most recent investigations driven by capex reduction, notably based on the replacement of titanium by stainless steels and the application of novel, more cost-effective anti-corrosion coatings [3].In a second part, results on the corrosion protection of 316L stainless steel by thin layers of titanium nitride prepared by DC magnetron sputtering will be presented. The thin TiN coatings were deposited on glass, silicon and 316L stainless steel substrates using a titanium target reacting with nitrogen gas. The crystalline phase, the nanostructure and the composition of the thin films were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray reflectivity, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. The corrosion resistance of the TiN-coated stainless steel was evaluated ex situ using open-circuit potential monitoring and electrochemical impedance spectroscopy in dilute H2SO4 solution in a three-electrode electrochemical cell. The interfacial contact resistance was assessed before and after corrosion testing. The protective properties of titanium nitride coatings on 316L under PEMWE anode-like conditions will be discussed.Acknowledgements The authors gratefully acknowledge the financial support of the French National Research Agency (agreement ANR-22-PEHY-0009 under the France 2030 program as well as agreement ANR-22-CE93-0008-01).