Fig. 3: Analysis of the passive film of the CoCrFeNiN0.07 HEAs specimens passivated for 3 h in 0.5 M H2SO4 solution at a potential of 0.7 V (within the passive region).

a A bright-field TEM images of the cross-section at passive film areas and the measured thicknesses; b Mott-Schottky plots; c calculated relative fraction of the metallic elements in the outmost surface of passive films, and d donor and acceptor densities for passive films on SLM, HIP, and CR HEAs.