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The Unconventional Self-Healing Behavior in Noble Metal Gels

One of the most extensively researched topics in the area of material science is electrocatalysis because this process is largely involved in several major energy-associated processes, for example, the hydrogen evolution reaction (HER) for the production of green hydrogen, the oxygen reduction reaction (ORR) for fuel cells, and the oxygen evolution reaction (OER) for metal-air batteries.

Ultrafast Gel Fabrication. Image Credit: Copyright: Ran DU et al. Matter 2020.

Noble metal aerogels (NMAs) have evolved as a new group of excellent electrocatalysts because of the integrated aspects of aerogels and metals. But the advancement of such porous materials is still hampered by the slow fabrication techniques, which can stretch from several hours to even many weeks.

Moreover, noble metals have special optical properties that pose another challenge—for example, the plasmonic resonance in one such optical property that, so far, has been overlooked in NMAs, and this aspect restricts their promising high performance in electrocatalysis.

China-based Ran Du is an Alexander von Humboldt research fellow who joined the physical chemistry team of Professor Alexander Eychmüller at TU Dresden as a postdoc in 2017. Together, the researchers have recently exposed an unusual self-healing behavior in noble metal gels; such behaviors are seldom observed in the only inorganic gel systems.

Based on this, the researchers developed a counter-intuition technique to expedite the gelation speed dramatically. The team’s breakthrough discoveries were published in the popular journal, Matter.

Along with his team, Ran Du devised a counter-intuitive disturbance-promoted gelation technique, which is an unusual and theoretically new method to realize rapid gelation.

At the time of gelation, the in situ introduction of an interfering field considerably promotes mass transportation and causes accelerated reaction kinetics. When this disturbing field is removed, the ensuing pieces of gel can assemble once again to a monolith considering the self-healing property.

In this fashion, the transportation obstacle faced in the presence of conventional gelation techniques is successfully resolved, resulting in gelation at room temperature within 1 to 10 minutes and without impacting the gels’ microstructures. This gelation technique is two-to-three orders of the magnitude faster than conventional techniques.

Monte Carlo simulations also supported the mechanism. Of note, the disturbance ways can also be extended to bubbling and shaking, and the technique is relevant to numerous compositions, like rhodium (Rh), palladium (Pd), gold (Au), gold-palladium-platinum (Au-Pd-Pt), gold-palladium (Au-Pd), and morphologies, for instance, the homogeneous structure or core-shell structure.

Ran Du also leveraged the integrated catalytic and optic activities of noble metals.

We also were first to demonstrate the photoelectrocatalytic properties of NMAs by using ethanol oxidation reaction (EOR) as a model reaction, displaying an activity increase of up to 45.5 % by illumination and realizing a current density of up to 7.3 times higher than that of commercial palladium/carbon (Pd/C).

Ran Du, Postdoc and Alexander von Humboldt Research Fellow, Chair of Physical Chemistry, Technische Universität Dresden

Thus we pioneered the exploration of photoelectrocatalysis on NMAs opening up new space for both fundamental and application-orientated studies for noble metal gels and other systems,” concluded Ran Du.


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