Less is more: Why an economical Iridium catalyst works so well
In the future, climate-neutral energy systems will require hydrogen to store energy, as a fuel and as a feedstock for the chemical industry. Ideally, it should be produced in a climate-neutral way, using electricity generated through the electrolysis of water using solar or wind energy. In this regard, proton exchange membrane water electrolysis (PEM-WE) is currently considered a key technology. Both electrodes are coated with special electrocatalysts to speed up the desired reaction. Iridium-based catalysts are most suitable for anodes where a slow oxygen evolution reaction occurs. However, iridium is one of the rarest elements on Earth, and one of the main challenges is to drastically reduce the demand for this precious metal. A rough analysis shows that in order to meet the world’s demand for hydrogen transported using PEM-WE technology, iridium-based anode materials should contain no more than 0.05 mg of iridium.and/cm2. Currently, the best commercially available catalysts are made from iridium oxide, which contains about 40 times this target.
P2X-Catalyst requires less iridium
But new options are already brewing: In the Kopernikus P2X project, the Heraeus Group has developed a new high-efficiency iridium nanocatalyst, consisting of a thin layer of iridium oxide deposited on a nanostructured titanium dioxide support. The so-called “P2X catalyst” requires only a tiny amount of iridium, which significantly reduces the precious metal loading (four times less than the best commercial materials currently available).
The team at HZB is led by Dr. Raul Garcia-Diez, Ph.D., Professor of Engineering. Together with colleagues at the ALBA Synchrotron in Barcelona, Marcus Bär studied a P2X catalyst that shows excellent stability even in long-term operation and compared its catalytic and spectral characteristics with benchmark commercial crystalline catalysts.
BESSY II OPERATING MEASUREMENTS
The HZB team thoroughly studied commercial benchmark catalysts as well as BESSY II’s P2X catalyst (operate Measurement). “We wanted to observe how two different catalyst materials undergo structural and electronic changes during the electrochemical oxygen evolution reaction, using operate Go to L3“Edge X-ray absorption spectroscopy (XAS),” says Marianne van der Merwe, a researcher in Bär’s team. They also developed a new experimental protocol to ensure that the results were measured in both samples at exactly the same rate of oxygen production. This allows comparison of the two catalysts under identical conditions.
Explore different chemical environments
“Based on the measurement data, we concluded that the OER mechanisms of the two types of iridium oxide catalysts are different, which is driven by the different chemical environments of the two materials,” van der Merwe said. The measurement data also show why the P2X catalyst is more crystalline than performs better compared to the benchmark: in the P2X sample, the bond length between iridium and oxygen at the OER relevant potential is significantly reduced compared to the reference catalyst. This reduction in Ir-O bond length may be related to the involvement of defective environments, which are considered key players in the highly active pathway of the oxygen evolution reaction.
“In addition, electron state observations are also related to local geometric information,” van der Merwe points out. “Our work provides valuable key information on the different mechanisms of iridium oxide-based electrocatalysts during oxygen evolution reactions and deepens our understanding of catalyst performance and stability, while our newly proposed in situ spectroelectrochemical protocol method Generally applicable to all studied anode materials are the relevant OER conditions.
2024-12-06 21:21:22