Cracking the code: why platinum electrodes corrode
An atomic vandal has finally been caught! Scientists from Leiden University and the Department of Energy’s SLAC National Laboratory have uncovered the mysterious cause behind the rapid corrosion of platinum electrodes. This breakthrough paves the way for more affordable green hydrogen production and more reliable electrochemical sensors.
It’s a strange quirk that has puzzled scientists for decades: for most metals, being negatively polarised protects against corrosion. But platinum electrodes can rapidly break down under these conditions.
That’s a problem because electrolysers and many other electrochemical devices often rely on these negatively polarised platinum electrodes submerged in an electrolyte – essentially saltwater. Although platinum is an expensive but durable and generally stable option, it doesn't stay immune to degradation in these environments. ‘Being quite stable doesn't mean it doesn't degrade at all,’ says Dimosthenis Sokaras, a senior scientist at SLAC and the SLAC team’s principal investigator.
What compounds are to blame?
‘If you take a piece of platinum and you apply a very negative potential, you can dissolve your platinum in a matter of minutes,’ says Marc Koper, Professor of Catalysis and surface chemistry at Leiden University, and the Leiden team's principal investigator.
Two prominent theories had attempted to explain this process. Some scientists thought that sodium ions from the electrolyte solution were to blame. These ions, the thinking went, pushed their way into the platinum’s atomic lattice and formed platinides – platinum atoms lugging around positively-charged sodium ions – that peel away. Others suggested a similar process but pointed the finger at both sodium and hydrogen ions – that is, protons – working together to produce platinum hydrides instead.
‘This was the only technique we could come up with that could sort of deal with the experimental conditions.’
Observing platinum corrosion in action
The research team knew they would need to somehow observe platinum as it was corroding in an electrolyte while making lots of hydrogen. To do so, the team turned to SLAC’s Stanford Synchrotron Radiation Lightsource. There, SLAC researchers have developed high-energy-resolution X-ray spectroscopy techniques that could penetrate the electrolyte and filter out other effects, allowing the researchers to focus in on subtle changes in the platinum electrode in operando, or during operation. ‘High-energy-resolution X-ray absorption spectroscopy, for us, was the only technique we could come up with that could sort of deal with the experimental conditions,’ says SLAC scientist Thom Hersbach.
In addition, the team developed a special pump and “flow cell,” Sokaras says, that could clear hydrogen bubbles that form during the electrode’s operation and interfere with the X-ray experiment.
Platinum hydrides are the culprit behind the corrosion
Using those capabilities together, the team made the first ever observations of platinum actively corroding, recording X-ray spectra from the negatively polarised electrode's surface.
Prior to running the experiment, the researchers had a hunch that hydrides were to blame for the corrosion, but it took several years of analysing the data before they could prove this hypothesis. ‘It just took loads and loads of different iterations of trying to figure out “how do we accurately capture what's going on?”’ Hersbach says.
Using computational models of platinum hydrides and platinides, the researchers simulated the spectra they would expect to see from each structure under the SSRL's X-ray beam. Comparing the numerous simulated spectra with the results of their experiment confirmed that only platinum hydride could have produced their results. ‘By advancing the frontiers of X-ray science, SSRL has developed operando methods that, combined with modern supercomputing, now allow us to tackle decades-old scientific questions,’ Sokaras says.
Now, the team's findings can be used to develop solutions for platinum corrosion in electrolysers and many other electrochemical devices. The project, Koper says, ‘shows how important in science it is to put a lot of expertise together.’
Headerimage: The culprit: Hydride formatiom at a platinum surface.
Further reading
Read the original press release at the website of SLAC National Accelorator Laboratory