Corrosion-resistant and conductive Ti-Nb-O coatings tailored for ultra-low Pt-loaded BPPs and PTLs in PEM electrolyzers

TL;DR

This work addresses the cost and durability challenges of metallic components in PEM electrolyzers by developing corrosion-resistant, conductive Ti–Nb–O bilayer coatings deposited via HiPIMS on stainless steel. By tuning oxygen partial pressure and Nb/Ti ratios, the authors obtain controlled oxide phases that yield resistivities around $10^{-4}$ Ω·cm and corrosion currents of $0.01$–$0.08$ μA cm$^{-2}$ after accelerated corrosion. Importantly, applying a $5$ nm Pt overlayer on these coatings enables the DOE ICR target to be met post-corrosion, while Pt loading is reduced by up to two orders of magnitude. This strategy offers a practical pathway to durable, cost-effective PEM electrolyzers with substantially less reliance on precious metals, particularly when the optimized $p_{ox}=3$ mPa and Nb ~5–8 at% are employed.

Abstract

We develop highly corrosion-resistant and conductive Ti-Nb-O coatings for metallic components -- bipolar plates (BPPs) and porous transport layers (PTLs) -- in PEM water electrolyzers. Using reactive high-power impulse magnetron sputtering (HiPIMS), we deposit compact 200 nm bilayer coatings onto SS316L substrates, systematically tailoring their composition. By precisely controlling oxygen partial pressure and Nb/Ti ratio, we adjust stoichiometry and structure, directly affecting electrical resistivity and corrosion resistance. We examine interfacial contact resistance (ICR) and electrochemical parameters before and after accelerated corrosion testing. Optimized coatings exhibit resistivity on the order of 10^-4 Ohmcm and extremely low corrosion current densities (J_corr = 0.01-0.08 uA/cm^2), well below the U.S. DOE 2026 target. Most importantly, these coatings enable the ICR target after accelerated corrosion testing with a Pt overlayer as thin as 5 nm, reducing Pt loading by up to two orders of magnitude compared to conventional approaches.

Figures (9)

• Figure 1: Schematic representation of the experimental setup for coating preparation. Sample positions 1, 2, 3, and 4 correspond to progressively closer distances to the Nb strip. For Ti--O coatings, the Nb strip was omitted.
• Figure 2: Schematic diagrams of the experimental setups for (a) the ICR measurement and (b) the auxiliary measurement of $R_{\mathrm{Au} / \mathrm{GDL}}$, representing the contact resistance between the gold-coated electrode and the GDL.
• Figure 3: The ternary plot depicts the elemental compositions of the upper layers for all prepared coatings. Black triangles, red diamonds, green circles, and purple squares represent layers prepared at oxygen partial pressures, $p_{\mathrm{ox}}$, of 0, 3, 5, and 8 mPa, respectively.
• Figure 4: X-ray diffraction (XRD) patterns of the upper layers within the examined compositional space. The patterns are grouped according to the oxygen partial pressure, $p_{\mathrm{ox}}$, applied during deposition (0, 3, 5, and 8 mPa) and are arranged vertically based on the Nb content in the metal fraction, expressed as $\mathrm{Nb}/(\mathrm{Ti} + \mathrm{Nb})$. Reflections of the hexagonal $\alpha$-Ti phase are denoted by black squares, while those of the substoichiometric cubic TiO$_x$ phase are marked by green circles. The Si substrate peak is denoted by "s".
• Figure 5: Electrical resistivity of coating upper layers visualized through a continuous color mapping within the examined compositional space. Data smoothing is applied to highlight overall trends within each panel. Triangle, diamond, circle, and square symbols indicate the elemental compositions of coatings with upper layers deposited at $p_{\mathrm{ox}}$ values of 0, 3, 5, and 8 mPa, respectively.