Electrochemical growth of a corrosion-resistant multi-layer scale to enable an oxygen-evolution inert anode in molten carbonate

Abstract

An in-situ formed three-layered scale consisting of a Cu-rich layer and two oxide layers on the surface of Ni10Cu11Fe alloy enables an inert anode for oxygen evolution reaction in molten Na2CO3-K2CO3. The outermost layer is mostly NiFe2O4, the middle layer mainly consists of NiO, and the innermost is a Cu-rich metal layer. The dense NiFe2O4 layer is resistant to molten salts and prevents O2− diffusing inwards, the middle NiO layer conducts electrons and functions as a buffer layer to increase the mechanical robustness of the whole scale, and the third copper-rich layer could help to slow down the oxidation rate of the alloy. This low-cost inert anode with a multi-layered scale is able to survive for more than 600 h in molten Na2CO3-K2CO3 electrolysis cell, generating O2 and thereby enabling a carbon-free electrometallurgical process.