Intentional defects make for better reactions, researchers report
IMAGE: RESEARCHERS AFFILIATED WITH THE BEIJING INSTITUTE OF TECHNOLOGY RATIONALLY DESIGNED AN ELECTROCATALYST WITH BOTH AMORPHOUS AND CRYSTALLINE PHASES, AS WELL AS ABUNDANT DEFECTS, TO MORE EFFICIENTLY SPLIT WATER AND PRODUCE CLEAN-BURNING HYDROGEN GAS. view more
CREDIT: NANO RESEARCH ENERGY, TSINGHUA UNIVERSITY PRESS
A defect is not always a bad thing. In fact, when it comes to improving the electrocatalysis process that produces clean-burning hydrogen gas, it may be a very good thing. Researchers based in China engineered an electrocatalyst — which speeds up a desired reaction — with both amorphous and crystalline architectures that contains defects in the atomic structure. The defects enable the electrocatalyst to trigger “superior” reaction activity, the team reported.
They published their results on May 15th in Nano Research Energy.
“Hydrogen generation from water electrolysis — or using electric current to split water to separate hydrogen from oxygen — driven by renewable energy is a promising technology in mitigating and solving the crisis of energy and environment,” said Cuiling Li, a professor at the Chinese Academy of Sciences’ Technical Institute of Physics and Chemistry who is also affiliated with the Beijing Institute of Technology and the Binzhou Institute of Technology.
Oxygen evolution reaction is the anodic reaction of water electrolysis, in which direct current causes a chemical reaction that splits the oxygen molecules from the water molecules. However, Li called this reaction “a sluggish process,” and it limits water electrolysis as a sustainable mechanism to produce hydrogen gas. According to Li, the oxygen evolution reaction is slow because it requires a lot of power to trigger how the molecules transfer their constituents, but it could be sped up with less power if integrated with more efficient catalysts.
“Exploiting efficient electrocatalysts for the oxygen evolution reaction is paramount to the development of electrochemical devices for clean energy conversion,” Li said.
The researchers turned to ruthenium oxide, a lower cost catalyst that adheres less to reactants and intermediates than other catalysts.
“Ruthenium oxide-based nanomaterials with better oxygen evolution reaction performance in comparison to commercial products have been reported, while more sophisticated electrocatalyst design strategies to evoke more efficient catalytic performance are urgently required and largely unexplored,” Li said.
To fill this gap, the researchers synthesized ruthenium oxide porous particles. They then treated the particles to produce rationally regulated heterophases, meaning the particles contain different architectures integrated together. The porous and heterophase structure provides the defects — essentially nicks in the atomic structure — which enable more active sites for the oxygen evolution reaction to proceed with more efficiency, according to Li.
“Benefitting from the abundant defects, crystal boundaries and active site accessibility of the resultant samples, superior oxygen evolution reaction performance was demonstrated,” Li said, explaining that the engineered electrocatalysts not only produces a better oxygen evolution reaction, but it also does with less electricity powering the process. “This study demonstrates the importance of phase engineering and provides a new pathway for the design and synthesis of strategies-combined catalysts.”
Other contributors are Chengming Wang, Qinghong Geng, Longlong Fan, Jun-Xuan Li and Lian Ma, all with the Key Laboratory of Cluster Science, Ministry of Education, Beijing Key Laboratory of Photoelectronic/Electrophonic Conversion Materials, School of Chemistry and Chemical Engineering, Beijing Institute of Technology.
The Beijing Institute of Technology’s Analysis and Testing Center provided technical support for this research.
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About Nano Research Energy
Nano Research Energy is launched by Tsinghua University Press, aiming at being an international, open-access and interdisciplinary journal. We will publish research on cutting-edge advanced nanomaterials and nanotechnology for energy. It is dedicated to exploring various aspects of energy-related research that utilizes nanomaterials and nanotechnology, including but not limited to energy generation, conversion, storage, conservation, clean energy, etc. Nano Research Energy will publish four types of manuscripts, that is, Communications, Research Articles, Reviews, and Perspectives in an open-access form.
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JOURNAL
Nano Research Energy
ARTICLE TITLE
Phase engineering oriented defect-rich amorphous/crystalline RuO2 nanoporous particles for boosting oxygen evolution reaction in acid media
More complex than expected: Catalysis under the microscope
At TU Wien (Vienna, scientists use microscopy techniques to observe chemical reactions on catalysts more precisely than before yielding a wealth of detail. This made clear why some effects cannot be predicted.
Peer-Reviewed PublicationIMAGE: CATALYSIS UNDER THE MICROSCOPE view more
CREDIT: TU WIEN
Catalysts composed from tiny metal particles play an important role in many areas of technology – from fuel cells to production of synthetic fuels for energy storage. The exact behavior of catalysts depends, however, on many fine details and their interplay is often difficult to understand. Even when preparing exactly the same catalyst twice, it often occurs that these two will differ in minute aspects and therefore behave very different chemically.
At TU Wien, scientists try to identify reasons for such effects by imaging the catalytic reactions taking place on various locations on these catalysts, applying several different microscopy techniques. Such an approach yields a reliable, microscopically correct understanding of the catalytic processes.
In doing so, it appeared that even relatively “simple” catalytic systems were more complex than expected. For example, it is not only the size of the employed metal particles or the chemical nature of the support material that define the catalytic properties. Even within a single metal particle, different scenarios can prevail on the micrometer scale. In combination with numeric simulations, the behavior of different catalysts could then be explained and correctly predicted.
Not all particles are the same
“We investigate the combustion of the possible future energy carrier hydrogen with oxygen, forming pure water, by using rhodium particles as catalysts”, explains Prof. Günther Rupprechter from the Institute of Materials Chemistry at TU Wien. Various parameters play an important role in this process: How big are the individual rhodium particles? Which support material do they bind to? At which temperature and which reactant pressures does the reaction take place?
“The catalyst is made from supported rhodium particles, but it does not behave like a uniform object which can be described by a few simple parameters, as often tried in the past”, highlights Günther Rupprechter. “It soon became clear, that the catalytic behavior strongly varies at different catalyst locations. A given area on a given rhodium particle may be catalytically active, whereas another one, just micrometers away, maybe catalytically inactive. And a few minutes later, the situation may even have reversed.”
Nine catalysts at one sweep
For the experiments, the first author of the study, which was published in the prestigious journal ACS Catalysis, Dr. Philipp Winkler, prepared a stunning catalyst sample, comprising nine different catalysts with differently sized metal particles and varying support materials. In a dedicated apparatus, all catalysts could therefore be observed and compared simultaneously in a single experiment.
“With our microscopes, we can determine if the catalyst is catalytically active, it´s chemical composition and electronic properties – and this for each and every individual spot on the sample”, says Philipp Winkler. “In contrast, traditional methods usually just measure an average value for the entire sample. However, as we have demonstrated, this is often by far not sufficient.”
Even more complex than anticipated
Chemical analysis on the microscopic scale has shown that the catalyst composition can vary locally even more than expected: Even within the individual metal particles strong differences were observed. “Atoms of the support material can migrate onto or in the particles, or even form surface alloys”, states Günther Rupprechter. “At some point, there is even no clear boundary anymore, but rather a continuous transition between catalyst particle and support material. It is crucial to consider this fact – because it also affects the chemical activity.”
In a next step, the team at TU Wien will apply the gained insights and the successful methods to tackle even more complex catalytic processes, in their continuing mission to explain processes on a microscopic scale, to contribute to the development of improved catalysts, and to search for new catalysts.
JOURNAL
ACS Catalysis
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Imaging Interface and Particle Size Effects by In Situ Correlative Microscopy of a Catalytic Reaction
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