Matter (2024). DOI: 10.1016/j.matt.2024.10.023">
Unveiling multimetallic effects: tailoring all-metal-made aerogels as self-supported electrocatalysts
The proposed mechanism of the atomic radius-induced ligament size control. Credit: Matter (2024). DOI: 10.1016/j.matt.2024.10.023
Have you ever imagined that high-density metals could be converted into an ultralight aerogel? This counterintuitive idea was presented in 2009 by Eychmüller's group, where all-metal-made aerogels, i.e., metal aerogels (MAs), were produced by assembling metal nanoparticles in a controlled manner. Since then, these special and promising materials have been explored by global scientists, gradually forming a new field in materials science.
MAs composed of more than one metal, namely multimetallic aerogels (MMAs), have received particular attention, because MMAs feature widely tunable properties stimulated by the synergy of multiple metals. For a material structured from multiple components, the first thought might be whether this material will have attributes stemming from each constituent, or if it will feature enhanced performance because of the synergy of different constituents.
Indeed, many research articles demonstrate that MMAs are often better than single-component MAs in, for example, electrocatalysis. Better performance was primarily achieved by tuning the difference in electrical conductivity, lattice parameters and electronic structure of dissimilar metals.
I am interested in controlled synthesis because I believe the synthesis ability dictates how far a material goes. Therefore, instead of the application aspect, I am concentrating on the synthesis aspect incurred by multimetallic effects. This is the motivation of our paper published in Matter titled "Manipulating multimetallic effects: Programming size-tailored metal aerogels as self-standing electrocatalysts."
In our study, we found that multimetallic effects concurrently impacted the sol-gel process of metals and the ligament size of the resulting MMAs.
We discovered an unconventional, gravity-driven gelation behavior of metal systems in a Science Advances paper five years ago. We found that the gelation process of metal systems is similar to a precipitation process. Driven by the high density of metals (e.g., the density of gold is ~19.3 g cm-3), the as-formed metal aggregates eventually settle down with the lapse of time and form a monolithic gel at the vessel bottom.
If the metal aggregate is not solely made up of gold, for example, what will happen for a gold-silver bimetallic system? The incorporation of relatively low-density silver (~10.5 g cm-3) will reduce the average density of metals and thus slow down the sedimentation process, leading to a prolonged gelation time.
This was proven by our experiments and characterizations using a variety of metal combinations (single, binary and triple metals). It not only offers a way to tune the sol-gel process but also confirms the generality of our proposed gravity-driven gelation mechanism.
The most exciting and important part is the ligament size control via multimetallic effects. The ligament size is a critical parameter for MAs, for it dictates the nano effects and thus many physicochemical properties of materials.
Historically, the ligament size is tuned by modulating the initiators or introducing ligands, which may contaminate the resulting MAs. Taking a glance at all reported MAs since 2009, one will recognize that some MAs (e.g., Au, Ag) often feature large ligament sizes while others (e.g., Pd, Pt, Ru, Rh) often feature small ligament sizes. However, almost all alloy aerogels feature small ligament sizes. Then the question arises: What happens when two metals come together?
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We thoroughly studied the ligament size change by controllably introducing different types and amounts of auxiliary metals into the main metal systems (e.g., introducing nickel sources to gold sources before conducting the gelation process). We found that 1% auxiliary metals drastically reduced the ligament size by ~ 30% to 78%, which worked for Au, Ag and Cu-based aerogels.
This impressive phenomenon was rationalized by the atomic radius mismatch between the main metal and the auxiliary metal. The mismatch will retard the layer-type deposition of metal atoms. Instead, the ligament growth will follow an island-type deposition style, thus producing more branches and thinning the ligament size (see image above). Depending on the mismatch degree and the proportion of the auxiliary metal atoms, the ligament size can be well adjusted.
Finally, using the gravity-driven gelation behavior, we developed a sedimentation-based, non-destructive strategy to boost the electrocatalytic performance of MMAs. This technique avoids the sonication-led structure destruction that was suffered by previously reported MA-based electrocatalysts.
Briefly, several pieces of carbon paper were placed at the bottom of the reaction vessel, accepting the settled metal aggregates. The in-situ-generated metal aggregates will gradually sediment and enrich on the carbon paper, thus forming a CP-supported intact gel film (the Au-Pt system was used as an example).
This CP-supported intact Au-Pt gel film was directly used as the working electrode to catalyze the alcohol oxidation reaction. Because of its well-retained network, this intact metal gel manifested record-high performance for both methanol- and ethanol- oxidation reactions.
In summary, our study not only provides a fresh viewpoint on using multimetallic effects for tuning the preparation and structure of MMAs but also solves the long-lasting challenge of preparing intact metal gel-based electrocatalysts for high-performance catalysis.
This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.
More information: Qian Cui et al, Manipulating multimetallic effects: Programming size-tailored metal aerogels as self-standing electrocatalysts, Matter (2024). DOI: 10.1016/j.matt.2024.10.023
Ran Du received his B.E. in 2011 from Beijing Institute of Technology and PhD degree in 2016 from Peking University. After successive research stays at Nanyang Technological University (2016–2017), TU Dresden (2017–2019, sponsored by Humboldt fellowship), and Hong Kong University (2020–2021), he joined the Beijing Institute of Technology as a professor in 2021. His research interest lies in the creative synthesis of advanced aerogels (e.g., metal aerogels, nanocarbon aerogels, etc.) and exploring their smart applications in catalysis, environment remediation, and smart materials.
Citation: Unveiling multimetallic effects: Tailoring all-metal-made aerogels as self-supported electrocatalysts (2024, December 9) retrieved 9 December 2024 from https://phys.org/news/2024-12-unveiling-multimetallic-effects-tailoring-metal.html
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