Unveiling the Growth Mechanism of Ordered‐Phase within Multimetallic Nanoplates

Abstract Tuning the crystal phase of alloy nanocrystals (NCs) offers an alternative way to improve their electrocatalytic performance, but, how heterometals diffuse and form ordered‐phase remains unclear. Herein, for the first time, the mechanism for forming tetrametallic ordered‐phase nanoplates (NPLs) is unraveled. The observations reveal that the intermetallic ordered‐phase nucleates through crystallinity alteration of the seeds and then propagates by reentrant grooves. Notably, the reentrant grooves act as intermediate NCs for ordered‐phase, eventually forming intermetallic PdCuIrCo NPLs. These NPLs substantially outperform for oxygen evolution reaction (221 mV at 10 mA cm⁻²) and hydrogen evolution reaction (19 mV at 10 mA cm⁻²) compared to commercial Ir/C and Pd/C catalysts in acidic media. For OER at 1.53 V versus RHE, the PdCuIrCo/C exhibits an enhanced mass activity of 9.8 A mg⁻¹_Pd+Ir (about ten times higher) than Ir/C. For HER at ‐0. 2 V versus RHE, PdCuIrCo/C shows a remarkable mass activity of 1.06 A mg⁻¹_Pd+Ir, which is three‐fold relative to Pd/C. These improvements can be ascribed to the intermetallic ordered‐structure with high‐valence Ir sites and tensile‐strain. This approach enabled the realization of a previously unobserved mechanism for ordered‐phase NCs. Therefore, this strategy of making ordered‐phase NPLs can be used in diverse heterogeneous catalysis.