Dendritic Core‐Frame and Frame Multimetallic Rhombic Dodecahedra: A Comparison Study of Composition and Structure Effects on Electrocatalysis of Methanol Oxidation

Abstract

The composition and structure of multimetallic nanostructures can be tailored to enhance electrocatalytic properties. This work reports a seed-mediated synthesis of novel multimetallic dendritic core-frame and frame nanostructures with a rhombic dodecahedral shape for enhanced methanol oxidation reaction (MOR). The synthesis involves in situ formation of Cu seeds and the subsequent selective deposition of Pt and Ru on the edges and vertices of the Cu seeds to generate CuPt and CuPtRu dendritic core-frame nanostructures. The core-frame nanostructures undergo a post acetic acid etching process to form the frame nanostructures. While transmission electron microscopy reveals the morphology and elemental distribution of the nanostructures, X-ray diffraction patterns confirm the alloy compositions of dendritic frames for both the core-frame and frame nanostructures. Compared to the bimetallic CuPt nanostructures, the trimetallic CuPtRu nanostructures lower the onset potential and completely suppress the peak current in the reverse scan for MOR. The CuPtRu alloyed frame nanostructures are the best to prevent Ru leaching compared to the CuPtRu core-frame nanostructures and PtRu catalysts. X-ray photoelectron spectroscopy reveals that all three elements become more electron rich in the frame nanostructures. Further refining the composition ratio of the CuPtRu alloyed dendritic frame nanostructures can lead to more efficient catalysts at a lower cost for MOR.

Tailoring the Surface Structures of CuPt and CuPtRu 1D Nanostructures by Coupling Coreduction with Galvanic Replacement

“…The Ru 3p 3/2 BE of br ‐CuPtRu was slightly upshifted compared to that of sr ‐CuPtRu, indicating that br ‐CuPtRu contained less oxidized Ru than sr ‐CuPtRu. This result suggests that Ru in the alloy is more stable than itself against oxidation and thus prevents leaching from the catalyst surface . This finding agrees with the higher stability of br ‐CuPtRu than that of sr ‐CuPtRu.…”

“…The high value of sr ‐CuPtRu had a very steep drop to 0.006 A mg Pt −1 within the first 50 s and levered at 0.005 A mg Pt −1 for the rest of the measurement up to 1800 s. The poor stability of sr ‐CuPtRu is attributed to the phase segregation of Ru on the catalyst surface which is easily leached from the catalyst surface, leaving behind the less electrochemically active bimetallic CuPt. In contrast, the high value of br ‐CuPtRu exponentially dropped to 0.025 A mg Pt −1 in 500 s, but leveled off and maintained at 0.018 A mg Pt −1 during the measurement up to 1800 s. These results suggest that the trimetallic surface alloy on br ‐CuPtRu with larger ECSA not only enhance the catalyst activity for MOR but also reduce the dissolution of Ru from the alloy for improving stability of the catalyst …”

“…Dual Cu precursors copper 2,4‐pentanedionate (Cu(acac) 2 ) and copper chloride (CuCl 2 ) at a molar ratio of 1:1 were used in the synthesis. Compared to the formation of rhombic dodecahedra, the increased amount of CuCl 2 is crucial, because chloride could stabilize both the {100} and {110} facets . Thus, the chloride ion could facilitate the formation of the nanowires by depositing Cu on {111} facets along 〈100〉 direction.…”

“…In this work, we applied a combined method of coreduction and galvanic replacement to demonstrate that the surface structures could be tailored through the competition between these two processes. As an initial example, Cu nanowires were chosen as templates for the synthesis of 1D CuPt and CuPtRu nanostructures because they could potentially be active catalysts for methanol oxidation reaction (MOR) . The synthesis involves a two‐step procedure with the formation of Cu nanowires via reduction of Cu precursors and a sequential addition of the noble metal precursors to initiate the coreduction and galvanic replacement.…”

Pt–Ni Seed-Core-Frame Hierarchical Nanostructures and Their Conversion to Nanoframes for Enhanced Methanol Electro-Oxidation

“…The open frame structures were more active catalysts than the solid nanoparticles for alcohol oxidations [16,35,36]. We demonstrated that other nanostructures with highly accessible surfaces including Pt-Cu nanodendrites [37], nanowires [38], core-frame and frame structures could enhance MOR activity [39]. In this work, we reported a seeded co-reduction method to synthesize the rhombic dodecahedral, hierarchical structure.…”