arXiv subjects

Kalyani Shaji

Publications and source records attributed to Kalyani Shaji.

3 recordsLinked to original sources

arXiv2026

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

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.

cond-mat.mtrl-sci↗

arXiv2025

Thermally-induced microstructural evolution in nanoparticle-based CuO, WO$_3$ and CuO-WO$_3$ thin films for hydrogen gas sensing

This study systematically investigates the microstructural evolution of nanoparticle-based CuO, WO$_3$, and composite 'CuO-WO$_3$' thin films induced by their post-deposition annealing. The films were reactively deposited using a magnetron-based gas aggregation technique, with the composite films consisting of alternating monolayers of CuO and WO$_3$ nanoparticles. After deposition, the films were annealed in synthetic air at temperatures ranging from 200 to 400$^\circ$C and characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Annealing of the CuO films led to the most pronounced changes associated with a gradual enhancement of crystallinity accompanied by significant particle growth with increasing annealing temperature, while the WO$_3$ and CuO-WO$_3$ films were more thermally stable to crystallization and particle growth. Notably, at 400$^\circ$C, the CuO--WO$_3$ films crystallized into a novel $γ$-CuWO$_4$ phase. The annealed films were further evaluated for their gas-sensing performance upon H$_2$ exposure and the obtained results were analyzed in relation to film properties and the microstructural evolution induced by annealing.

cond-mat.mtrl-sci↗

arXiv2025

New polymorph γ-CuWO4 inspired by γ-CuMoO4: experimental identification and theoretical verification

In the context of our efforts to develop hydrogen gas sensors, two samples of ternary CuWO4 with the same crystalline structure have been prepared by two different non-equilibrium techniques. We show that the materials' structure is significantly different from the known stable one, and we identify that it is very similar to that of previously reported γ-CuMoO4. We use ab initio calculations to confirm that the newly identified phase, γ-CuWO4, represents a local energy minimum. We present very similar calculated and measured lattice constants and X-ray diffractograms. We make a case that the low-temperature formation of the metastable γ-CuWO4 phase is facilitated by easier kinetics and/or by Cu-rich composition of our samples, and we show that it converts to the stable phase after annealing to 600 °C.

cond-mat.mtrl-sci↗