Titanium bipolar plates augmented by nanocrystalline TiZrHfMoW coatings for application in proton exchange membrane fuel cells

Abstract

A TiZrHfMoW refractory high entropy alloy (RHEA) nanocrystalline coating was engineered onto a commercially pure Ti (CP-Ti) substrate to enhance its corrosion resistance for potential application as bipolar plates for use in proton exchange membrane fuel cells (PEMFCs). The as-prepared RHEA coating possesses a single-phase BCC structure with an average grain size of ∼12 nm. The electrochemical corrosion behavior of the RHEA coating in simulated PEMFC environment, with varying HF concentrations, was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), in conjunction with detection and analysis of electrochemical noise (EN). The potentiodynamic polarization and EIS measurements of the RHEA coating indicated that, at a given HF concentration, the RHEA coating exhibits a higher Ecorr, a lower icorr and a larger resistance value compared to uncoated CP-Ti. The analysis of the EN signals indicated that the RHEA coating has low correlation dimensions (below 1.4) and small instantaneous amplitudes in the Hilbert spectra, confirming that the RHEA coating was capable of maintaining a stable passive state, regardless of the HF concentrations. Furthermore, the electron work function of TiZrHfMoW RHEA was derived by first-principles calculations to unravel the physics origin of the corrosion resistance of the RHEA coating.