Enhancing the efficiency of hydrogen permeation inhibition by means of the synergistic effects of inorganic and organic inhibitors

Hydrogen permeation inhibition using chemical inhibitors could be a practical and convenient method for protecting steels from hydrogen embrittlement, but its efficiency remains unsatisfactory for industrial applications. This study explores enhancing hydrogen permeation inhibition by combining chemical inhibitors with different characteristics. Inorganic inhibitors sodium nitrite (NaNO 2 ) and sodium molybdate (Na 2 MoO 4 ) were found to inhibit hydrogen permeation through mechanisms distinct from the organic inhibitor benzotriazole (BTA). NaNO 2 mitigates hydrogen permeation primarily through its self-reduction reaction, which competes with the hydrogen evolution reaction, reducing hydrogen generation and ingress into steel, achieving an inhibition efficiency of up to 52.5 % at a 0.2 M concentration. Na 2 MoO 4 reduces hydrogen permeation by forming a protective molybdenum oxide layer that blocks active sites for hydrogen evolution and hydrogen ingress, with a maximum inhibition efficiency of 50.7 % at a 0.2 M concentration. A synergistic effect was observed between Na 2 MoO 4 and BTA, significantly enhancing hydrogen permeation inhibition to 86.2 % by forming a denser, thicker composite film on the steel surface. The molybdenum oxide fills defects in the BTA film and provides additional adsorption sites for BTA. These findings suggest a prospect of developing more efficient hydrogen permeation inhibitors by leveraging the synergistic effects of film-forming inorganic and organic inhibitors. • Inhibitors show synergistic effects enhancing hydrogen permeation inhibition. • NaNO 2 and Na 2 MoO 4 inhibit hydrogen permeation by different mechanisms. • Hydrogen permeation efficiency depends on the characteristics of inhibitor films. • Local inhibitor film formation and coverage were identified by electrode arrays. • A model explains the synergistic effects of hydrogen permeation inhibition.