Revolutionizing Hydrogen Production: The Future of Iridium-Based Catalysts

In the future, hydrogen will play a crucial role in a climate-neutral energy system, serving as a means to store energy, a fuel, and a raw material for the chemical industry. The ideal way to produce hydrogen in a climate-neutral manner is through electrolysis of water using electricity generated from renewable sources such as solar or wind energy. Proton Exchange Membrane Water Electrolysis (PEM-WE) is currently seen as a key technology for this purpose, with both electrodes coated with special electrocatalysts to facilitate the desired reactions.

However, one of the major challenges in this process is the use of iridium-based catalysts, particularly for the anode where the oxygen evolution reaction takes place. Iridium is a rare and precious metal, and there is a need to significantly reduce its demand in the production of hydrogen. A rough analysis has shown that to meet the global demand for hydrogen in transportation using PEM-WE technology, iridium-based anode materials should contain no more than 0.05 mgIr/cm2. Currently, the best commercially available catalyst made from iridium oxide contains about 40 times this target value.

To address this issue, the Heraeus Group has developed a new efficient iridium-based nanocatalyst known as the ‘P2X catalyst’. This catalyst consists of a thin layer of iridium oxide deposited on a nanostructured titanium dioxide support and requires only a minimal amount of iridium, reducing the loading of precious metal substantially (four times lower than the current best commercial material).

A team at the Helmholtz-Zentrum Berlin (HZB), led by Dr. Raul Garcia-Diez and Prof. Dr.-Ing. Marcus Bär, along with colleagues from the ALBA synchrotron in Barcelona, has conducted a study on the P2X catalyst. The researchers found that the P2X catalyst exhibits remarkable stability even during long-term operation and have compared its catalytic and spectroscopic properties with the benchmark commercial crystalline catalyst.

Using operando measurements at the BESSY II synchrotron, the HZB team investigated how the two catalyst materials change structurally and electronically during the electrochemical oxygen evolution reaction. The researchers developed a new experimental protocol to ensure that both samples were measured under the same oxygen production rate, allowing for a direct comparison under equivalent conditions.

The study revealed that the mechanisms for oxygen evolution reaction in the two classes of iridium oxide catalysts are different due to their distinct chemical environments. The data also showed that the P2X catalyst outperforms the benchmark catalyst, with a significant decrease in the bond lengths between iridium and oxygen at relevant potentials. This reduction in bond lengths is associated with the involvement of defective environments that play a crucial role in highly active pathways of the oxygen evolution reaction.

Overall, the research provides valuable insights into the different mechanisms of iridium oxide-based electrocatalysts during the oxygen evolution reaction, deepening our understanding of catalyst performance and stability. The newly proposed in situ spectroscopic electrochemical protocol is applicable to all anode materials studied under relevant conditions, offering a promising approach for future research in this field.