Precise and controllable synthesis strategy of noble metal-non-noble alloy nanomaterials

On January 17, 2023, Beijing time, Professor Gao Chuanbo of Xi’an Jiaotong University and researcher Zhang Qing of ShanghaiTech University published a team entitled “Synthesis of noble/non-noble metal alloy nanostructures via an active-hydrogen involved interfacial reduction” in the journal Nature Synthesis strategy”.

This study proposes a new synthesis method for noble metal-non-noble metal alloy nanomaterials, which effectively overcomes the reduction potential difference between different metal salts through the interface reduction mechanism of active hydrogen, and realizes the synthesis of a series of different kinds of alloy nanomaterials and the precise regulation of their alloy components in a wide range of proportions.

The corresponding author of the paper is Gao Chuanbo; The first author is Liu Zhaojun.

Precious metal-non-noble alloy nanomaterials usually exhibit excellent catalytic performance and have important application value in new energy and other fields. However, there is a huge intrinsic reduction potential difference between metal salts, showing significant differences in reduction kinetics, which brings difficulties to the precise control of the alloying process, and the alloy nanomaterials prepared usually have a narrow component control window. This bottleneck restricts the study of the structure-activity relationship and the optimization of catalytic performance of alloy nanocatalysts.

In this work, Professor Gao Chuanbo’s team initiated the reactive hydrogen interface reduction process by introducing nitrite acid into the synthesis system of alloy nanomaterials, and realized the precise and controllable synthesis of a series of noble metal-non-precious metal alloy nanomaterials. Nitrite molecules form active hydrogen on the surface of crystal nuclei or seed crystals through dehydrogenation reactions. Active hydrogen exists in the form of hydrogen atoms or hydrogen radicals, and has a standard reduction potential (E°=–2.31 V) that is much lower than that of precious metal salts and most non-precious metal salts, so it can effectively overcome the reduction potential difference between different metal salts and achieve their controllable co-reduction. As a strong oxidant, nitrite also makes the solution phase exhibit strong oxidation, thereby inhibiting the solution phase reduction process of metal salts. Therefore, the transfer of metal reduction reactions from the solution phase to the seed crystal/solution interface helps to improve the controllability of alloy synthesis.

The strong oxidizing solution phase and strong reducing seed crystal surface constructed by nitrite acid enable the synthetic system to use Pd nanocube as seed crystal to realize the controllable preparation of Pt-Ni {111} nanoshell. The results of spherical aberration correction electron microscopy showed that the alloy nanoshell epitaxically grew on the surface of Pd nanocrystals, and the two elements of Pt and Ni were evenly distributed in the alloy shell.

Figure 1: Schematic diagram of the synthesis of Pt-Ni alloy nanoshells on Pd nanocrystals and characterization of products with different reaction times.

Figure 2: Structural characterization of Pt-Ni alloy nanoshells synthesized on Pd nanooctahedrals.

The synthesis mechanism study found that the presence of nitrite acid and metal seed crystals was the key to induce the noble-non-precious metal co-reduction process. The results of mass spectrometry and electron paramagnetic resonance confirmed that nitrite formed active hydrogen on the surface of the seed crystal through dehydrogenation reaction, and the active hydrogen existed in the form of hydrogen atoms or hydrogen radicals.

Figure 3: Synthesis mechanism study.

This strategy is universal and significantly improves the controllability of alloy nanomaterial synthesis. Through the adjustment of precursor types and proportions, the synthesis of nanomaterials of different noble metal-non-noble metal alloys can be realized, and the alloy components can be precisely controlled within a wide range of proportions. By selecting different types of crystals, the controllable preparation of alloy nanomaterials with different morphology/crystal plane structure can be realized.

Figure 4: Universality of synthetic strategies.

Finally, the authors examine the electrocatalytic hydrogen evolution performance of the Pd@Pt-Ni nanooctahedral synthesized by this strategy. Among the different Pt/Ni ratios, Pd@Pt1.1Ni showed the optimal catalytic hydrogen evolution activity.

Figure 5: Characterization of electrocatalytic hydrogen evolution performance of Pd@Pt-Ni nanooctahedron.

This study proposes a new paradigm for the synthesis of alloy nanomaterials, which provides conditions for the precise synthesis, performance optimization and catalyst screening of alloy nanomaterials. This work was supported by projects such as the National Natural Science Foundation of China (22071191) and the Shaanxi Provincial Key Research and Development Program (2021GXLH-Z-022). (Source: Science Network)

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