Iridium-free catalysts for acid water electrolysis investigated
Scanning electron micrograph of a cobalt-based catalyst on a fibre substrate (micrograph was manually coloured) and schematic representation of a multi-technique operando material characterization indicated by artificially added light ray, bubbles and rising spectra. © Marc Tesch/MPI-CEC
Hydrogen will play an important role, both as a fuel and as a raw material for industry. However, in order to produce relevant quantities of hydrogen, water electrolysis must become feasible on a multi-gigawatt scale. One bottleneck is the catalysts required, with iridium in particular being an extremely rare element. An international collaboration has therefore investigated iridium-free catalysts for acidic water electrolysis based on the element cobalt. Through investigations with various methods, among them experiments at the LiXEdrom at the BESSY II X-ray source in Berlin, they were able to elucidate processes that take place during water electrolysis in a cobalt-iron-lead oxide material as the anode. The study is published in Nature Energy.
The oxygen evolution reaction (OER) in water electrolysis requires special catalytic support. However, iridium catalysts are probably not suitable for large-scale use due to their price and limited availability, so alternatives must be found. An international team led by Dr Alexandr N. Simonov from Monash University in Melbourne, Australia, has now investigated the acidic oxygen evolution reaction on cobalt-based catalysts and elucidated the changes at the active cobalt sites. The research teams used different methods and combined their findings to a new picture.
Processes during the Oxygen evolution reaction
The stabilisation of catalysts during OER involves the interaction of corrosion and oxidation processes and is considered key to catalyst development. ‘In this study, we have discovered that the corrosion and deposition processes are not directly linked to the catalytic process, but run in parallel,’ says Dr Marc Tesch from the Max Planck Institute for Chemical Energy Conversion, one of the authors of the study. The time-resolved measurements also show that the development of the catalyst to a stabilised active state is not a rapid process, but takes place on a time scale of minutes. X-ray spectroscopy shows that the catalytically active cobalt sites adopt an oxidation state higher than 3+ during the acidic OER and do not exhibit long-range order. This distinguishes them from previously described cobalt μ-(hydr)oxo structures, which are present in neutral and alkaline reaction environments.
International collaboration under Corona conditions
A significant part of the research was carried out at BESSY II during the coronavirus pandemic, when international travel and external access to the synchrotron facility were severely restricted. ‘The support provided by the local team at BESSY II was therefore particularly important,’ says Tesch.
The findings are helpful for developing cost-effective cobalt-based anode catalysts for use in proton exchange water electrolysers.
- Self assembling monolayer can improve lead-free perovskite solar cells tooTin perovskite solar cells are not only non-toxic, but also potentially more stable than lead-containing perovskite solar cells. However, they are also significantly less efficient. Now, an international team has succeeded in reducing losses in the lower contact layer of tin perovskite solar cells: The scienstists identified chemical compounds that self-assemble into a molecular layer that fits very well with the lattice structure of tin perovskites. On this monolayer, tin perovskite with excellent optoelectronic quality can be grown, which increases the performance of the solar cell.
- Scrolls from Buddhist shrine virtually unrolled at BESSY IIThe Mongolian collection of the Ethnological Museum of the National Museums in Berlin contains a unique Gungervaa shrine. Among the objects found inside were three tiny scrolls, wrapped in silk. Using 3D X-ray tomography, a team at HZB was able to create a digital copy of one of the scrolls. With a mathematical method the scroll could be virtually unrolled to reveal the scripture on the strip. This method is also used in battery research.
- Sodium-ion batteries: New storage mechanism for cathode materialsLi-ion and Na-ion batteries operate through a process called intercalation, where ions are stored and exchanged between two chemically different electrodes. In contrast, co-intercalation, a process in which both ions and solvent molecules are stored simultaneously, has traditionally been considered undesirable due to its tendency to cause rapid battery failure. Against this traditional view, an international research team led by Philipp Adelhelm has now demonstrated that co-intercalation can be a reversible and fast process for cathode materials in Na-ion batteries. The approach of jointly storing ions and solvents in cathode materials provides a new handle for designing batteries with high efficiency and fast charging capabilities. The results are published in Nature Materials.