Corrosion protection of steel in molten Li2CO3–K2CO3 and Na2CO3–K2CO3 mixtures in a hydrogen-containing atmosphere

The electrochemical behaviour of TiN-, TiN–AlN-, Cr- and CrN-coated 316L stainless steel in molten Li₂CO₃–K₂CO₃ and Na₂CO₃–K₂CO₃ melts in a reducing gaseous atmosphere (10% H₂–90% N₂) was studied using voltammetry and scanning electron microscopy combined with energy-dispersed X-ray analysis in the temperature range of 600–730 C. To facilitate the identification of the electrochemical reactions the voltammetric behaviour of stainless steel, titanium, nickel and gold was also investigated. Voltammetric characteristics obtained at AlN–TiN coated electrodes showed no anodic reactions at potentials more negative than that of CO^2– ₃ oxidation. Cr- and CrN-coated electrodes demonstrated a suppressed anodic dissolution after the first steady state voltammetric cycle. The voltammograms obtained for the other electrodes studied displayed the corresponding anodic metal-dissolution waves. TiN, AlN, Cr and CrN coatings seem to be the most promising as corrosion-resistant materials for the anodic compartments of molten carbonate fuel cells.