Pd nanosheets, [11] the derivative PdCu nanosheets, [12] PtPb/Pt nanoplates, [13] and PtPdM (M = Ni, Co, and Fe) nanosheets. [1] Another strategy to improve the activity and stability of catalysts in electrocatalytic reactions is to form alloys; [14][15][16][17] and alloying with non-noble metals may help reduce the cost of the catalyst further. [18][19][20][21] Compared to the well-studied bimetallic alloys, trimetallic alloys can possess a more complex alloy lattice that has better reactivity and stability, and the extra composition could further fine-tune the properties of the catalyst. [18,[22][23][24] For instance, Xiong et al. reported a PtFeCo trimetallic tristar nanostructure with enhanced hydrogen evolution reaction activity. [23] The addition of Fe and Co lowered the d-band center of Pt, enhanced the reaction activity and reduced the cost of the catalyst. Other reported trimetallic catalysts include the PtCuCo hollow nanospheres, [25] PtPdNi nanocages, [26] and PtNiAu alloy nanostructures. [27] Previously, our group reported a solvothermal synthesis of Pd-Pt alloy nanosheets. [8] Herein, we further developed a wet chemical method to synthesize wrinkled ultrathin Pd and PdPtNi trimetallic nanosheets. Because of facile reaction conditions, the reaction process and formation mechanism of the ultrathin Pd nanosheets were comprehensively studied. It was found that the degree of wrinkling increased with the increase in temperature and the progress of reaction, and the CO formed in situ by the decomposition of the solvent N,Ndimethylformamide (DMF) is responsible for 2D growth. Trimetallic PdPtNi nanosheets were obtained by depositing Pt and Ni onto the Pd nanosheets, with the atomic composition of the PdPtNi nanosheets readily adjusted by the molar ratio of the precursors. The ORR catalytic performance of the nanosheets was demonstrated. Among all the nanosheets, the Pd 9 Pt 1 Ni 1 nanosheets showed the highest half-potential of 0.928 V (vs reversible hydrogen electrode (RHE)). The nanosheets also exhibited improved stability, with the half-potential shifted negatively only by 10.6 mV after 10 000 cycles. Results and DiscussionPd nanosheets were synthesized by using a facile wet chemical method. Typically, 4.5 mg Na 2 PdCl 4 was first dissolved in 6 mL of DMF and 4 mL of ethylene glycol (EG), followed byThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202103665.

Discovering new methods and principles in the inequivalent growth of equivalent facets is of great significance for going beyond symmetrical nanocrystals and for out-of-box exploration. In this work, we demonstrate that a middle ground exists between the traditional weak ligands and the strong ligands with unusual growth modes. By modifying the seed concentration during the growth of pentagonal Au nanorods, the typical weak ligand cetyltrimethylammonium bromide (CTAB) is made strong, leading to notches of restricted growth and even the active surface growth mode. In-depth investigation in the link between growth kinetics and ligand packing reveals the principle of their interplay --that the on-off dynamics of the ligands only allows for a certain limit of materials deposition rate. Beyond this limit, the growth materials build up and are then diverted elsewhere, leading to inequivalent growth. The fact that a freshly grown surface has few ligands promotes the active surface growth, focusing the growth materials onto a few sites. We believe that the knowhow of interfering ligand packing via growth kinetics would offer a powerful tool of synthetic control, where the facet-and curvature-dependent ligand packing is expected to be useful synthetic handles.

Surface ligands play critical roles in nanosynthesis and thus it is of great importance in expanding the scope of suitable ligands. In this work, we explore phenynyl ligands in modulating the Au-Au interface when growing Au domains on Au seeds. A patchy growth mode is observed where the emerging islands are flat-laying with holes and branches. This growth mode is distinctively different from the conventional facet-controlled growth using weak ligands, and the non-wetting island growth using strong ligands. Through manipulating the molecular structure and the packing of the phenynyl ligands on the Au seeds, the overgrown Au domains are continuously tuned, from patches to islands, extending the plasmon absorption peak into the near-infrared spectral range. We believe that the new ligand with intermediate affinity and the unusual growth mode would expand the control in both synthesis and application.