Surface structure and morphology evolution of iron borides under dynamic conditions: A theoretical study

Surface feature and its variation along with complex atmosphere are of fundamental significance to understanding the functionality of applied materials especially in heterogeneous catalysis and corrosion prevention. Here we performed a unified theoretical study on the surface structure and morphology of iron borides and their evolution under dynamic gaseous conditions by combination of density functional theory, ab initio atomic thermodynamics and Wulff construction. In particular, thermodynamic stability of iron borides and corresponding surfaces varied from the boron chemical potential (Δμ_B) of certain atmosphere, which increases with decreasing pressure and increasing temperature and concentration of boron source. The stability of boron-rich surfaces has been improved with increasing Δμ_B, while all the Fe-rich facets of iron borides are favorable at low Δμ_B condition. Accordingly, the crystallite morphology of iron borides undergoes significant evolution upon dynamic condition. Finally, the surface properties of iron borides are carefully tested by CO adsorption which indicated the activation ability of CO is closely connected with boron triggered surface charge transfer between Fe and CO. This work was expected not only to help understand the surface structure and morphology of iron borides under realistic condition, but also provides fundamental insights into rational design of corrosion resistant and catalytic materials.