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

• The boron chemical potential were calculated as a function of temperature, pressure and gas composition. • The bulk and surface stabilities of six iron borides are determined by the boron chemical potential. • The evolution of surface structure and morphology under dynamic conditions were predicted. • CO adsorption is weakened by surface doping of boron atom due to its electronegativity. 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 (Δ μ 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 Δ μ B , while all the Fe-rich facets of iron borides are favorable at low Δ μ 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. [ABSTRACT FROM AUTHOR]