Nanoparticles based on low-cost transition metal oxides one day could replace the expensive catalysts currently used to produce hydrogen, believe scientists at Ruhr-Universitaet-Bochum (RUB), Bochum, Germany.
“The development of non-precious-metal catalysts plays a decisive role in realizing the energy transition as only they are cheap and available in sufficient quantities to produce the required amounts of renewable fuels,” notes Kristina Tschulik, chair of analytical chemistry in the department of electrochemistry and nanoscale materials at RUB.
Her team has been studying cobalt iron oxide nanocatalysts for electrochemical water oxidation. In the past, difficulties dogged determining the reaction rates possible because the particles must be attached to the electrode using a binder and conductive additives — both of which distort the results.
Using techniques such as high-resolution bright-field transmission electron microscopy and selected area diffraction studies, the researchers now have succeeded in determining the activity and conversion rate of cobalt iron oxide nanocatalysts.
To do this, the team allows a particle to catalyze oxygen generation on the surface of the electrode and then measures the current flow. This, in turn, provides information about the reaction rate (Figure 1). “We have measured current densities of several kiloamps per square meter,” says Tschulik. “This is above the reaction rates currently possible in industry.”
Figure 1. Researchers use a shielded cell to assess nanoparticles in electrochemical experiments. Source: RUB/Kramer.
Their microscopy studies show that the nanoparticles barely change despite the high reaction rates they achieve. “Their stability under extreme conditions is exceptional,” Tschulik stresses.
The next step is the systematic study of the many properties — including particle size, composition, shape and defects — that play a role in the nanocatalyst activity. “We want to study these separately to figure out how each affects the oxygen evolution reaction,” she adds.
For this reason, the researchers for the time being are limiting their investigations to transition metal oxides: “Once we have identified the exact link between structure and reactivity, we will be able to control the synthesis of these nanocatalysts at a large scale and study their performance in large systems,” she explains.
However, Tschulik emphasizes that her team’s single particle studies themselves aren’t meant for large-scale application. Rather, they will serve as a tool for screening promising materials and identifying and optimizing their essential parameters. “Then, these intrinsically highly active nanocatalysts can be used in the conventional way for scaling up,” she concludes.