Local Basicity Dependent Gas-Liquid Interfacial Corrosion of Nickel Anode and Its Protection in Molten Li2CO3-Na2CO3-K2CO3

Revealing the gas-liquid interfacial corrosion mechanism of metals under anodic polarization in molten salts is crucial for the development of metallic anodes for molten carbonate electrolysis. Herein, the effects of operating temperature, gas atmosphere, applied current density and electrolysis time on the gas-liquid interfacial corrosion behaviors of nickel anodes in molten Li2CO3-Na2CO3-K2CO3 were systematically investigated. It was found that the gas-liquid interfacial corrosion of nickel anodes was accelerated with decreasing temperature and increasing CO2 content of gas atmosphere. Three distinct corrosion regions of nickel anodes can be identified: (I) the thin salt film region, (II) the meniscus region, and (III) the full immersion region. It was revealed that the formation of negative basicity gradient in the meniscus induced the dissolution/re-precipitation of NiO scale, thereby accelerating the gas-liquid interfacial corrosion of nickel anodes. Furthermore, an Al2O3 sheath was applied to shield the gas-liquid part of nickel electrodes to prevent gas-liquid interfacial corrosion, thus making Ni a stable oxygen-evolution inert anode.