Chemists normally work rigorously to exclude impurities from their reactions. This is especially true for scanning tunneling microscopy (STM) experiments that can produce atomic-scale images of surfaces. Using STM to investigate processes such as catalysis usually requires pristine substrates—any flaws or foreign particles in the surface can critically interfere with the test study.
Preconceptions about interface defects and catalysis are about to change, however, thanks to recently published research led by Yousoo Kim and Maki Kawai at the RIKEN Advanced Science Institute in Wako.
Through a series of high-level computer simulations, the researchers found that the catalytic splitting of water molecules occurs faster on an ultrathin insulating film containing misplaced atoms than on a non-defective surface. Because water splitting reactions are one of the easiest ways to generate hydrogen fuel, this finding could be a boon to future fleets of hybrid vehicles.
Recently, Kim, Kawai, and colleagues discovered that depositing insulating magnesium oxide (MgO) onto a silver (Ag) substrate enabled extraordinary control over water dissociation reactions. By injecting electrons into the MgO/Ag surface with an STM tip, they were able to excite absorbed water molecules and cause them to sever hydrogen and hydroxide ions. Optimizing the MgO film thickness was a key part of this approach; only ultrathin layers could direct water splitting owing to its enhanced electronic interaction strength.
This relationship between insulator thickness and chemical reactivity suggested to the researchers that the oxide–metal interface plays a crucial role in directing catalytic reactions. Engineering specific flaws into the ultrathin interface could be one way to heighten the electronic control over the water-splitting process. However, since artificially manipulating oxide atoms is a difficult experimental procedure, they used density functional theory simulations, based on quantum mechanics, to analyze the role of structural imperfections in MgO.
Surprisingly, the researchers found that three different types of defects—oxygen and magnesium impurities, as well as an oxygen vacancy—improved water adsorption and substantially lowered dissociation energy barriers compared to an ideal MgO film. Further analysis revealed that the oxide defects accumulate charges injected into the substrate, creating an electronic environment that speeds up the catalytic water splitting. “In the presence of these defects, the film’s chemical reactivity can be greatly enhanced,” says Kim.
The next goal for the researchers is to find systematic techniques to control interface imperfections on these novel catalytic films—an objective best achieved by the team’s unique combined experimental–theoretical approach, notes Kim.
Jung, J., Shin, H.-J., Kim, Y. & Kawai, M. Activation of ultrathin oxide films for chemical reaction by interface defects. Journal of the American Chemical Society 133, 6142–6145 (2011).
Shin, H.-J., Jung, J., Motobayashi, K., Yanagisawa, S., Morikawa, Y., Kim, Y. & Kawai, M. State-selective dissociation of a single water molecule on an ultrathin MgO film. Nature Materials 9, 442–447 (2010)
Jung, J., Shin, H.-J., Kim, Y. & Kawai, M. Controlling water dissociation on an ultrathin MgO film by tuning film thickness. Physical Review B 82, 085413 (2010).
Not of Divided Mind
19.01.2017 | Hertie-Institut für klinische Hirnforschung (HIH)
CRISPR meets single-cell sequencing in new screening method
19.01.2017 | CeMM Forschungszentrum für Molekulare Medizin der Österreichischen Akademie der Wissenschaften
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
19.01.2017 | Earth Sciences
19.01.2017 | Life Sciences
19.01.2017 | Physics and Astronomy