PtFe alloy nanostructures enclosed by differently oriented facets, including polyhedrons, concave cubes, and nanocubes, were synthesized through the fine adjustment of specific surfactant−crystal facet bindings. PtFe nanostructures with various alloy compositions were then employed as the counter electrodes (CEs) for the redox reaction of iodide/ tri-iodide (I − /I 3 − ) in dye-sensitized solar cells. Devices with the Pt 9 Fe 1 polyhedrons and Pt 9 Fe 1 concave cubes produced better photovoltaic conversion efficiency (PCE) of 8.01% and 7.63% in comparison to the PCE of 7.24% achieved with Pt CE. The superiority is attributed to the rapid charge transfer, higher limit current, and better electronic conductivity and catalytic activity with respect to the Pt CEs. The photovoltaic and electrochemical results indicated the shape-and composition-dependent activity in the I − /I 3 − redox reaction, which obeys the sequence of polyhedrons > concave cubes > nanocubes and Pt 9 Fe 1 nanostructures > Pt 7 Fe 3 nanostructures. Further theoretical work indicated that the I 3 − reduction activity of the nanosurfaces was in the order of Pt 9 Fe 1 (111) > Pt(111) > Pt 9 Fe 1 (100). The combination of experimental and theoretical work thus clearly demonstrates the shape-and composition-dependence of PtFe nanostructures in terms of the I 3 − reduction activity.

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Our calculations with spin-polarized density functional theory were carried out to characterize the adsorption and dissociation of the NH3 molecule on the Fe(111) surface. The molecular structures and adsorbate/substrate interaction energies of NH3/Fe(111), NH2/Fe(111), NH/Fe(111), N/Fe(111), and H/Fe(111) configurations were predicted. In these calculations, four adsorption sites, such as top (T), bridge (B), 3-fold-shallow (S), and 3-fold-deep (D) sites, of the Fe(111) surface, were considered. It was shown that the barriers for the stepwise NH3 dissociation reaction, NH3(g) -> N-(a) + 3H((a)), are 28.32 kcal/mol (for H2N-H bond activation), 28.49 kcal/mol (for HN-H bond activation), and 25.34 kcal/mol (for N-H bond activation), and the entire process is 20.08 kcal/mol exothermic. To gain insight into the catalytic activity of the Fe(111) surface for the dehydrogenation of NH3, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis