Atomic-Scale Interface Engineering via Ultrasonic-Electrochemical Hybrid Polishing: Achieving Damage-Free NiTi Bipolar Plates with Ultra-Low Contact Resistance for Hydrogen Fuel Cells

Hydrogen fuel cell bipolar plates demand surfaces with an atomically smooth morphology and stable electrochemical interfaces to minimize contact resistance and corrosion degradation. While nickel-titanium (NiTi) alloys offer inherent advantages for this role, their practical deployment is hindered by persistent surface defects (e.g., microcracks and oxide inclusions) introduced during additive manufacturing. Here, we propose an ultrasonic-electrochemical hybrid polishing strategy that synergistically integrates in situ electrochemical dissolution with ultrasonic cavitation-induced mechanical activation, achieving dual interfacial engineering: (1) atomic-scale material removal via dislocation-mediated plasticity and (2) self-passivating oxide layer formation. Molecular dynamics simulations reveal that ultrasonic excitation reduces the critical shear stress for dislocation nucleation, enabling defect-free surfaces at specific etching depths. (3) The synergistic coupling of ultrasonic, electrochemical, and mechanical interactions facilitates the elimination of residual powdery particulates on additively manufactured NiTi bipolar plates, thereby reducing interfacial contact resistance. This work establishes a paradigm of energy-field-assisted interfacial engineering for metallic bipolar plates, bridging atomic-scale mechanisms with macroscale device performance.