Toward a Quantitative Understanding of Crystal-Phase Engineering of Ru Nanocrystals

Thecrystal phase with a specific stacking sequence of atoms largelyaffects the catalytic performance of metal nanocrystals. Since thecontrol of the phase at the same composition is extremely difficult,the phase-dependent performance of metal nanocrystals is studied rarely.Here, we show the synthesis of Ru nanocrystals with different percentagesof face-centered cubic (FCC) and hexagonal close-packed (HCP) phasesvia kinetic control, further revealing a quantitative correlationbetween the phase percentage of Ru nanocrystals and the initial reductionrate of Ru-(III) precursors. Specifically, we manipulate the singleparameter-initial reduction rate by controlling the Ru-(III) injectionrate into the dropwise synthesis at a fixed reaction temperature andcorrelate the kinetic data with the Ru phase percentage analyzed byatomic-resolution electron microscopy and synchrotron X-ray scattering.Based on the quantitative analysis, the ranges of initial reductionrates of Ru precursors can be determined for synthesizing Ru nanocrystalswith the percentages of unusual FCC phase from 9.0 to 55.1%. We demonstratethat a low initial reduction rate corresponds to the crystallizationof the Ru HCP phase, while a high initial reduction rate favors thecrystallization of the FCC lattice. Furthermore, we also systematicallyexamine the catalytic performance of Ru nanocrystals with differentphases.