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Purpose: The purpose of this paper is to investigate the interfacial conductivity and corrosion resistance of the Ni–P/Ti4O7 composite coating that is deposited on a carbon steel substrate as bipolar plates for proton exchange membrane fuel cells. Design/methodology/approach: The Ni–P/Ti4O7 coating was prepared by electroless plating. Scanning electron microscopy, white light interference, energy dispersive spectrometry and X-ray diffraction were used, respectively, to study the surface morphology, chemical composition and phase composition of coated samples. Electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization were used to test the electrochemical performance and corrosion behavior. The interfacial contact resistance (ICR) was measured via the standard method. Findings: The surface of the Ni–P/Ti4O7 coating is complete and dense and without obvious defects. The electrochemical test results show that the Ni–P/Ti4O7 coating provides better corrosion resistance than the Ni–P coating and substrate. Compared with the Ni–P coating, the ICR of the Ni–P/Ti4O7 coating is lower by about 82.7%. This is because the coating has more conductive contact points. The more exciting thing is that the ICR of the Ni–P/Ti4O7 coating only increases to 12.38 mΩ·cm2 after 5 h of polarization. Originality/value: This paper provides a method for achieving surface modification of metal bipolar plates. Introducing Ti4O7 particles in the Ni–P layer reduces the contact resistance before and after polarization while ensuring good corrosion resistance. [ABSTRACT FROM AUTHOR]

• The PAM gels is a new corrosion-triggered inhibiting structure. • The inhibitor ions Ce4+ could change the morphology of the products film. • The absorption and bridging of PAM gels about the corrosion product. Biomaterial polyacrylamide (PAM) hydrogel was first studied for self-healing coatings of Mg alloys. In this work, a PAM gel with Ce4+ inhibitor was in-situ composited on the surface of micro-arc oxidation treated AZ31 Mg alloy. The results indicated that the scratched samples with the composite coating could avoid pitting corrosions and self-heal in neutral salt spray test (NSST). XPS and SEM-EDS analysis reveal that the self-healing performance was ascribable to the inhibition of Ce4+ and the bridge adsorption of PAM gels. Moreover, the results of open circuit potential and polarization curve indicate that the self-healing product film has good corrosion resistance. [ABSTRACT FROM AUTHOR]