Sami Khan1 Kripa Varanasi1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Composite liquid-impregnated surfaces (LIS), whereby a thin stable film of liquid is held inside a textured solid by capillary forces, have been garnering widespread attention recently with applications in anti-fouling and anti-scaling. Corrosion and hydrogen embrittlement are broad problems in several industries, and developing surfaces that resist corrosion has been an area of great interest since the last several decades. Superhydrophobic surfaces that combine hydrophobic coatings along with surface texture have been shown to improve corrosion resistance by creating voids filled with air that minimize the contact area between the corrosive liquid and the solid surface. However, these air voids can incorporate corrosive liquids over time, and any mechanical faults such as cracks can compromise the coating and provide pathways for corrosion. In this work, we systematically study electrochemical activity and anti-corrosion properties of textured surfaces impregnated with a liquid. Since corrosion resistance depends on the area and physico-chemical properties of the material exposed to the corrosive medium, we optimize the design of liquid-impregnated surfaces based on the surface tension, viscosity and chemistry of the impregnating liquid and its spreading coefficient on the solid. We perform all corrosion experiments in a standard three-electrode cell using iron, which readily corrodes in a 3.5% sodium chloride solution, and we impregnate using Krytox, silicone oil and ionic liquids. In order to obtain textured iron surfaces, we sputter-coat thin films (~500 nm) of iron on silicon wafers textured using photolithography, and impregnate them with lubricants. We show that the corrosion rate on LIS is greatly reduced, and offers an over hundred-fold improvement in corrosion protection. Furthermore, we show that the spreading characteristics of the liquid is significant in ensuring corrosion protection: a spreading liquid that covers both inside the texture as well as the top of the texture provides a two-fold improvement in corrosion protection as compared to a non-spreading lubricant that does not cover texture tops. We also show that an increase in viscosity of the liquid scales with greater corrosion protection. We finally provide broader insights into designing liquid-impregnated electrodes specifically for electrochemical applications using ionic liquids, and study the electrochemical interactions at the three-phase catalyst-liquid-liquid interface.