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Abstract Metal oxides and carbides are promising tritium permeation barrier coatings for fusion reactors. However, the thermomechanical mismatch between the coating and substrate poses a threat to their interface's integrity during fabrication and operation. To address this issue, a metallic interlayer coating was introduced followed by selective oxidation in which a compact and uniform Cr C amorphous alloy coating was successfully deposited on the stainless steel substrate by pulsed electrochemical deposition. A new composite coating of Cr x C y @Cr 2 O 3 /Al 2 O 3 was formed by subsequent controlled oxidation conversion and atomic layer deposition. The phase, morphology, chemical state and defects of the films were analyzed and compared both before and after hydrogen exposure at 300 °C. The results show that this new kind of composite coating, based on the principles of grain boundary pinning of chromic oxide with carbide and defect healing of alumina, can remarkably improve the hydrogen permeation barrier performance of these materials. Highlights • A new ceramic coating based on grain boundary pinning and passivation for hydrogen permeation barrier was proposed. • The Cr x C y @Cr 2 O 3 /Al 2 O 3 coating was successfully fabricated by selective oxidation of a Cr C alloy and atomic layer deposition. • This composite coating demonstrates improved and repair performance upon hydrogen exposure. [ABSTRACT FROM AUTHOR]