Nanostructural design of a Pt-enriched layer generated on a Pt–Cr–Mn–Fe–Co–Ni high-entropy alloy thin film: electrochemical dealloying in acidic environments

We fabricated Pt–Cr–Mn–Fe–Co–Ni alloy thin films on Pt(1 1 1) substrate using the arc-plasma deposition method at 973 K in ultrahigh vacuum (≈10 −7 Pa) while maintaining (1 1 1) lattice stacking from the substrate to the surface. The fabricated thin films were subsequently electrochemically dealloyed by applying square wave potential cycling with different combinations of upper and lower potentials in N 2 -purged 0.1 M HClO 4 . The nanostructural changes induced in the film surfaces by dealloying were as follows: upper and lower potentials of 1.2 and 0.6 V, as well as 1.0 and 0.0 V vs. the reversible hydrogen electrode (RHE) generated nanoporous Pt layers with a thickness of 5 nm on the thin film surface, whereas dealloying at upper and lower potentials of 1.0 V and 0.6 V vs. RHE resulted in a roughened Pt-enriched surface of several monolayers thick. The results suggest that the resulting nanostructures, which range from roughened Pt-enriched surface to nanoporous Pt layer, can be associated to specific dissolution rates of the constituent elements at given potentials, elemental distributions of the as-fabricated film, and Cr oxide at the electrode–electrolyte interface. This study demonstrates specific nanostructures can be fabricated by tuning the dealloying conditions of high-entropy alloy thin films.