The transition to an economy based on renewable energy sources requires the use of electrochemical methods to convert electrical energy into chemical energy and raw materials. A group of researchers from the Berlin Polytechnic, the Zurich Polytechnic, the Materials Workshop Institute of the National Research Council of Trieste and led by the Fritz Haber Institute in Berlin has discovered the reaction mechanism of one of these bottlenecks. processes, the oxygen evolution reaction.
One of the fundamental steps in the transition to an economy based on renewable energy sources is the development of new materials for the electrocatalytic evolution of oxygen, a crucial moment in the electrolysis of water. Electrolysis is a process that uses electricity to split water into its constituent elements, oxygen and hydrogen, through chemical reactions. These reactions take place on the surface of the catalysts, elements that are used to accelerate or promote a chemical reaction. In a study published in Nature, the group composed of researchers from the Institute of Materials Workshop of the National Research Council (Cnr-Iom), based in the Area Science Park, Berlin Polytechnic, Zurich Polytechnic and the Fritz Haber Institute in Berlin, explains the functioning of one of the best classes of catalysts for the oxygen evolution reaction: iridium oxides.
“The importance of oxygen electrocatalysis is explained by reference to the problem of the storage of renewables. In fact, especially for non-programmable energies, such as solar and wind power, the problem of storage becomes crucial to absorb power fluctuations and to ensure a reliable energy supply. The strategy is therefore to convert electricity into chemical fuels through the use of protons and electrons produced with the electrolysis of water “, explains Simone Piccinin of Cnr-Iom. This method is one of the most promising for storing non-programmable renewables, because it is very flexible, since fuels can be used when and where they are needed.
An obstacle to this approach, however, is the identification of electrocatalysts for the oxidation of water to molecular oxygen, or the reaction that provides the protons and electrons needed to produce these fuels. “In an attempt to develop new electrocatalysts, experts in the field have always thought that the electrocatalytic reaction of oxygen evolution could be explained using a well-known theory, developed decades ago,” continues the CNR-Iom researcher. “Our group decided to test these assumptions and, surprisingly, found that the oxygen evolution reaction is actually more similar to traditional thermal catalysis than previously thought. This allows, for the first time, to apply tools and concepts developed to describe traditional thermal catalysis also to electrochemical catalysis ”.
“To improve electrocatalysts it is important to understand the fundamental science behind them. It was becoming increasingly clear to us that the traditional description of what moves electrocatalytic reactions is incomplete, ”explains Peter Strasser of the Berlin Polytechnic. “Researchers usually assume that the oxygen evolution reaction is directly controlled by the action of the electric potential on the reaction coordinate. This is a very different scenario from thermal catalysis, where the creation and breaking of chemical bonds controls the rate of reaction through the surface chemistry”.
“From our work it emerges instead that the role of the potential is to oxidize the surface and that the charge accumulation induced by this oxidation controls the reaction rate, in a similar way to thermal catalysis”, adds Detre Teschner of the Fritz Haber Institute. . “These studies have made us realize that the reaction is controlled by surface chemistry, despite what was previously believed. By developing a laboratory method capable of quantifying charge accumulation and using theoretical simulations with quantum mechanics techniques, our group was able to study different materials and found that they all exhibited the same behavior”, concludes Piccinin.