Direct Observation of Heterogeneous Surface Reactivity and Reconstruction on Terminations of Grain Boundaries of Platinum

Materials
defects are very important for enhancing the catalytic
functions and applications. However, the surface defects of materials
are usually diverse, and their catalytic activity is generally measured
at the averaging level. How to directly measure/observe the catalytic
activity of the single defective site is extremely important for the
rational design of highly efficient catalysts; however, it remains
a grand challenge. Herein, we directly observe the reactivity and
simultaneously surface reconstructions of the single defective site
by “storing” catalytic trajectories and collectively
presenting reactivity profiles on solid surfaces via in situ transmission
electron microscopy using a thermally catalyzed graphitic layer growth
model reaction on terminations of grain boundaries (GBs) of platinum.
The direct in situ observation results for single defective sites
reveal that the surface reactivity decreases in the order of concave
terminations of high-angle GBs > concave terminations of low-angle
GBs > roughened edge boundaries > flat surfaces. In particular,
we
find that the heterogeneous reconstructions appear the surface-smoothening
on high-angle GBs, while the surface-roughening on low-angle GBs and
edge boundaries, which is rationalized by two competitive processes:
the release of excessive strain energy and the adsorption-induced
step formation. Comprehensively, the concave terminations of low-angle
GBs and the roughened edge boundaries represent promising catalytic
surface defects with a fine balance between reactivity and stability.
The DFT calculations result reveals a novel rhombohedral Volcano-type
Zebra-crossing plot for the structure–activity relation regarding
the improved reactivity by strained defect sites, different from a
conventional Volcano-type plot in catalysis studies. We expect the
current in situ method, direct observation of catalytic roles of surface
defects, and their in situ restructuring would assist the design and
synthesis of more nanocatalysts in the future.