Corrosion of AISI 310 and 316 in Molten Hydroxide Under Steam Electrolysis Conditions

Abstract

Steam electrolyzers, utilizing molten hydroxide electrolyte, offer potential for improvement in electrochemical efficiency, cost reduction, use of conventional materials of construction and process scale up for large scale hydrogen production. Stainless steels, used for the fabrication of cell components (current collector, gas separator, wet seals, and manifolds) experience accelerated corrosion in the presence of molten hydroxide electrolyte in both oxidizing (anodic) and reducing (cathodic) atmospheres. In this study, the corrosion behavior of AISI 310 and 316 has been studied at 600 °C using melt immersion and cyclic voltammetry tests. Melt immersion test revealed formation of the porous lithium iron oxide at the melt-oxide interface for both AISI 310 and 316. Oxide scale cross-sectional study conducted by FIB/TEM showed multi-layer oxide scale formation. Inductively Coupled Plasma (ICP) Spectroscopy analysis showed the presence of Cr in the electrolyte melt obtained from samples exposed to oxidizing atmosphere. Cyclic voltammetry tests showed the breakdown of passive metal-oxide under anodic overpotential in molten hydroxide. Mechanisms for hydroxide-induced corrosion is proposed and discussed.