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.

PtCoFe nanowires with different alloying compositions are chemically prepared and acted as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) with Ru(II)-based dyes. Due to their superior − − I 3 reduction activity, PtCoFe nanowires with rich (111) facets enhance the performance of DSSCs. Hence, N719 DSSCs with PtCoFe nanowires, respectively, produce better power conversion efficiency (PCE) of 8.10% for Pt 33 Co 24 Fe 43 nanowire, 8.33% for Pt 74 Co 12 Fe 14 nanowire, and 9.26% for Pt 49 Co 23 Fe 28 nanowire in comparison to the PCE of Pt CE (7.32%). Further, the PRT-22 DSSC with Pt 49 Co 23 Fe 28 nanowire exhibits a maximum PCE of 12.29% with a certificated value of 12.0%, which surpass the previous PCE record of the DSSCs with Ru(II)-based dyes. The photovoltaic and electrochemical results reveal the composition-dependent activity along with a volcano-shaped trend in the I − / − − I 3 redox reaction. Theoretical work on the adsorption energies of I 2 , the desorption energies of I − , and the corresponding absolute energy demonstrates that the − − I 3 reduction activity followed in the order of Pt 49 Co 23 Fe 28 (111) plane > Pt 74 Co 12 Fe 14 (111) plane > Pt 33 Co 24 Fe 43 (111) plane, proving Pt 49 Co 23 Fe 28 nanowire to be a superior cathode material for DSSCs.

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In polycrystalline materials, grain boundaries are known to be a critical microstructural component controlling material’s mechanical properties, and their characters such as misorientation and crystallographic boundary planes would also influence the dislocation dynamics. Nevertheless, many of generally used mechanistic models for deformation twin nucleation in fcc metal do not take considerable care of the role of grain boundary characters. Here, we experimentally reveal that deformation twin nucleation occurs at an annealing twin (Σ3{111}) boundary in a high-Mn austenitic steel when dislocation pile-up at Σ3{111} boundary produced a local stress exceeding the twining stress, while no obvious local stress concentration was required at relatively high-energy grain boundaries such as Σ21 or Σ31. A periodic contrast reversal associated with a sequential stacking faults emission from Σ3{111} boundary was observed by in-situ transmission electron microscopy (TEM) deformation experiments, proving the successive layer-by-layer stacking fault emission was the deformation twin nucleation mechanism, different from the previously reported observations in the high-Mn steels. Since this is also true for the observed high Σ-value boundaries in this study, our observation demonstrates the practical importance of taking grain boundary characters into account to understand the deformation twin nucleation mechanism besides well-known factors such as stacking fault energy and grain size.

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