The Atomic Intelligence of Liquid Metals.

[NNadir]

I was just discussing some interesting aspects of liquid metals with my son, specifically liquid metal alternatives to liquid sodium which has become - wrongly I think, and I believe he agrees - the default coolant for breeding fast spectrum nuclear reactors. There is a hell of a lot more to applications of liquid metals in nuclear technology than sodium, but people have the habit of doing things they way they've always been done, a mistake, I think in a changing world. (I'm a big fan of exploring the potential for liquid plutonium and its interesting series of eutectics.)

Anyway, I think a great deal about liquid metals, and in particular eutectics, a generally esoteric point, so I was pleased to come across this news item in the current issue of Science:

The atomic intelligence of liquid metals

Subtitle:

Liquid metals may deliver greener and more sustainable chemical reactions

KOUROSH KALANTAR-ZADEH , TORBEN DAENEKE, AND JUNMA TANG Science, 25 Jul 2024 Vol 385, Issue 6707 pp. 372-373.

Some excerpts:

Chemical reactions account for about 12% of global greenhouse gas emissions and a large portion of the world’s total energy consumption (1). Many contemporary chemical processes rely on multiple facilities that use solid-state catalytic materials for specific reactions. Solid catalysts normally possess fixed atomic arrangements that form active sites (2). Despite their capacity to lower energy barriers for reactions, the absence of atomic-level flexibility can limit efficiency and selectivity for certain reactions. By contrast, liquid metals—metals and alloys that are liquid near or at room temperature—can rearrange interfacial atom positions in response to processes that occur at their surface. This can guide reactions, a capacity that could be viewed as a type of innate intelligence. This intelligence involves steering freely moving liquid-state atoms into desired locations for more efficient functionalities. This behavior thus promises energy favorable reaction pathways as well as reactions that are not feasible in solid-state systems...

...Liquid metals—which constitute a family of low–melting point metals and alloys, such as mercury (Hg)– and gallium (Ga)– based liquids at near room temperature and tin (Sn) and bismuth (Bi) alloys at higher temperatures—present opportunities for diverse chemical reactions (6). Incorporating noble and transition metals into liquid metals bestows the resulting alloys with tailored catalytic properties. Liquid metals offer high surface entropy by keeping elements energetic and highly dispersed, allowing them to naturally provide a multitude of dynamically changing active sites for bond formation and dissociation reactions (7). These active sites may exhibit greater capability for driving reactions compared with solid-state surfaces, and the overall thermodynamic barriers at the liquid metal surfaces may be decreased...

Not mentioned are the elements rubidium and cesium, the latter being available in an interesting highly radioactive form, albeit cut by the natural isotope ¹³³Cs isotope, by isolation from used nuclear fuel, which is also true of the former, although the radioactivity (derived largely from the naturally occurring ⁸⁷Rb isotope) is far lower and thus perhaps less useful in many applications. These metals strike me as interesting owing to their unique properties in carbon chemistry, discussed obliquely in the full article:

...The surfaces of liquid metals naturally inhibit van der Waals attraction. Consequently, if solid species are formed as by-products on active sites as the result of a reaction, they naturally exfoliate with minimal mechanical agitation. Hence, the reactive surface remains accessible and resists having the active sites blocked by processes such as the buildup of carbon (coking) and surface reactions that inactivate the catalyst (poisoning). One investigation revealed that surface deactivation is mitigated to allow the continuous production of carbonaceous solids as the main product from CO₂ feedstock on liquid metal surfaces (11)...

I'm not a fan of the concept of "green hydrogen" - the production of hydrogen on Earth always results in the destruction of exergy, although in theory, if not in practice, it can be produced by some exergy capture from what would otherwise be waste heat via process intensification. This said, I have mused at length on thermochemical water splitting cycles relying on the properties of liquid metals. They may be impracticable, but are fun to consider.

Anyway, it's a cool little note in the current issue of Science.

I trust you're enjoying the weekend.