High reaction rates even without precious metals – ScienceDaily



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Non-precious metal nanoparticles could one day replace expensive catalysts for the production of hydrogen. However, it is often difficult to determine what reaction rates can reach, especially when it comes to oxide particles. This is because the particles must be connected to the electrode using a binder and conductive additives, which distort the results. With the aid of electrochemical analyzes of individual particles, researchers have now been able to determine the activity and conversion of nanocatalyst substances made from cobalt iron oxide – without any binders. The team led by Professor Kristina Tschulik of the Ruhr-Universit├Ąt Bochum has colleagues from the University of Duisburg-Essen and Dresden, Germany. Journal of the American Chemical Society, published online May 30, 2019.

"The development of non-precious metal catalysts plays a decisive role in realizing the energy transition because they are inexpensive and available in sufficient quantities to produce the required amounts of renewable fuels," says Kristina Tschulik, a member of the Cluster of Excellence Ruhr. Explore Solvation (Resolv). Hydrogen, a promising energy source, can be acquired by splitting water into hydrogen and oxygen. The limiting factor here so far has been the partial reaction in which the oxygen is produced.

Better than the reaction rates currently achieved in the industry

As efficiently the cobalt iron oxide particles are able to catalyze the generation of oxygen was investigated by the researchers in the present work. They analyzed many individual particles one after the other. Chemists allowed a particle to catalyze the generation of oxygen at the surface of the electrode and measure the current flow therefrom, which provides information about the reaction rate. "We measured current densities of several kiloamps per square meter," says Tschulik. "This is above the reaction rates currently possible in the industry."

The team showed that, for particles smaller than 10 nanometers, current flow is dependent on particle size – the smaller the catalyst particle, the lower the current. The current is also limited by the oxygen that is produced in the reaction and diffuses away from the surface of the particle.

Extremely stable despite high stress

After the catalysis experiments, the chemists observed the catalyst particles under the transmission electron microscope. "Despite the high reaction rates, that is, although the particles have created so much oxygen, they have practically not changed," Tschulik sums up. "Stability under extreme conditions is exceptional."

The analysis approach used in the current work can also be transferred to other electrocatalysts. "It is essential to find out more about the activities of nanocatalysts in order to efficiently develop non-precious metal catalysts for tomorrow's renewable energy technologies," said the Bochum-based chemist. In order to analyze the effect of particle size on catalytic activity, it is important to synthesize nanoparticles of defined size. As part of the University Alliance Ruhr, the Bochum team closely cooperates with researchers at the University of Duisburg-Essen, led by Professor Stephan Schulz, who produce the catalyst particles.

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