Carbon influence on hydrogen absorption and adsorption on Fe-C alloy surfaces

Abstract

Electrochemical experiments and first-principle calculations were conducted in this study to investigate the impact of carbon doping on the adsorption and absorption on Fe-C alloy surfaces. The generalized Iyer-Pickering-Zawenzaden model was adopted to determine the kinetics related to hydrogen adsorption/absorption. Discharge rate constant k1 was found increased with the presence of carbon, suggesting the promotion of the H2O ionization process and more hydrogen atoms were generated on the surface. Meanwhile, the recombination rate constant k2 decreased on carbon doping surface, indicating recombination process of hydrogen atoms were inhibited. Results also showed the hydrogen surface coverage dropped with increasing carbon content. Additionally, EIS results indicate that the distance between the adsorbed hydrogen atoms and the sample surfaces is reduced by carbon doping. All experimental results are in accordance with the first-principle calculation results which demonstrate that the presence of carbon elevated the binding energy for hydrogen adsorption while lowering the energy barrier for diffusion. Thus, carbon solutes reduce the stability for hydrogen atoms to adsorb on the surface and facilitate their diffusion into the bulk.