High catalytic efficiency in metal nanocatalysts is attributed to large surface area to volume ratios and an abundance of under-coordinated atoms that can decrease kinetic barriers. Although overall shape or size changes of nanocatalysts have been observed as a result of catalytic processes, structural changes at low-coordination sites such as edges, remain poorly understood. Here, we report high-lattice distortion at edges of Pt nanocrystals during heterogeneous catalytic methane oxidation based on in situ 3D Bragg coherent X-ray diffraction imaging. We directly observe contraction at edges owing to adsorption of oxygen. This strain increases during methane oxidation and it returns to the original state after completing the reaction process. The results are in good agreement with finite element models that incorporate forces, as determined by reactive molecular dynamics simulations. Reaction mechanisms obtained from in situ strain imaging thus provide important insights for improving catalysts and designing future nanostructured catalytic materials.
In
this study, highly transparent conducting fluorine-doped tin
oxide (FTO) electrodes were fabricated using the horizontal ultrasonic
spray pyrolysis deposition. In order to improve their transparent
conducting performances, we carried out oxygen activation by adjusting
the ratio of O2/(O2+N2) in the carrier
gas (0%, 20%, and 50%) used during the deposition process. The oxygen
activation on the FTO electrodes accelerated the substitution concentration
of F (FO
•) into the oxygen sites in the
FTO electrode while the oxygen vacancy (VO
•
•) concentration was reduced. In addition, due
to growth of pyramid-shaped crystallites with (200) preferred orientations,
this oxygen activation caused the formation of a uniform surface structure.
As a result, compared to others, the FTO electrode prepared at 50%
O2 showed excellent electrical and optical properties (sheet
resistance of ∼4.0 ± 0.14 Ω/□, optical transmittance
of ∼85.3%, and figure of merit of ∼5.09 ± 0.19
× 10–2 Ω–1). This led
to a superb photoconversion efficiency (∼7.03 ± 0.20%)
as a result of the improved short-circuit current density. The photovoltaic
performance improvement can be defined by the decreased sheet resistance
of FTO used as a transparent conducting electrode in dye-sensitized
solar cells (DSSCs), which is due to the combined effect of the high
carrier concentration by the improved FO
• concentration on the FTO electrodes and the fasted Hall mobility
by the formation of a uniform FTO surface structure and distortion
relaxation on the FTO lattices resulting from the reduced VO
•
•
• concentration.
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