  Despite decades of research, metallic corrosion remains a long-standing
challenge in many engineering applications. Specifically, designing a material
that can resist corrosion both in abiotic as well as biotic environments
remains elusive. Here we design a lightweight sulfur-selenium (S-Se) alloy with
high stiffness and ductility that can serve as a universal corrosion-resistant
coating with protection efficiency of ~99.9% for steel in a wide range of
diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7
orders of magnitude lower than bare metal in abiotic (simulated seawater and
sodium sulfate solution) and biotic (sulfate-reducing bacterial medium)
environments. The coating is strongly adhesive and mechanically robust. We
attribute the high corrosion resistance of the alloy in diverse environments to
its semi-crystalline, non-porous, anti-microbial, and viscoelastic nature with
superior mechanical performance, enabling it to successfully block a variety of
diffusing species.
