Density functional theory study of H2 adsorption on the (1 0 0), (0 0 1) and (0 1 0) surfaces of Fe3C

Spin-polarized density functional theory has been used to characterize hydrogen adsorption on the Fe3C(1 0 0), Fe3C(0 0 1) and Fe3C(0 1 0) surfaces. It is found that hydrogen adsorbs dissociatively on the three surfaces. On the Fe3C(1 0 0) surface, the most stable surface species is CH at 1/3 or 2/3 monolayer, and CH4 at 1 monolayer; in contrast on the Fe3C(0 0 1) surface the most stable surface intermediates are 3-fold H at 1/3 monolayer, and CH at 2/3 monolayer, and CH4 at 1 monolayer. On the metallic Fe3C(0 1 0) surface, hydrogen adsorbs at 2-fold or 3-fold sites. The computed energetic order of hydrogen adsorption is Fe3C(1 0 0) > Fe3C(0 1 0) > Fe3C(0 0 1), and this differs from that of CO adsorption (Fe3C(0 1 0) > Fe3C(1 0 0) > Fe3C(0 0 1)).

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