From a recent successful experiment which was noted as “sorely needed by the electrochemistry community", the CLF's Paul Donaldson, Gaia Neri and Alex Cowen (both of whom are from the University of Liverpool) made a second surprising discovery – one that has been picked up by Nature Catalysis.
During their experiment using the Ultra laser facility, the team took a laser technique commonly used for surface observation and applied it to electrochemistry. However, they were struggling to achieve any results.
Dr Paul Donaldson explained: “When we had our first beamtime we spent two weeks trying to use an electrochemical system that didn't work. It was frustrating because we knew that if this experiment was successful it could be an important discovery for the electrochemistry community."
“We were using an unusual electrode and we just couldn't get any signals from it. However, on the last day of experiment, Alex suggested we try out a manganese catalyst that he had happened to bring along with him."
The electrodes are pieces of gold imbedded in a plastic sheath and are conductors through which electricity enters or leaves an object, substance or region. To the team's surprise, the moment they installed the electrode, they got the results they were looking for.
“It was the first time for us to ever see SFG signals from electrocatalysts," Paul said. “And for one day we ran experiment after experiment going “Wow" because we'd never seen these signals from the interface before."
Following the elation of this discovery, the team promptly reapplied for beamtime. A few months later they returned to continue.
However, despite setting up the experiment exactly how they had previously, once again they were getting no results whatsoever.
“We couldn't get any signal at all, so we spent two weeks trying to get it. We would get some signal, but it didn’t give reproducible clear signals on Au, so the signal would die overtime. It was so disheartening because to our knowledge we weren't doing a single thing different," Paul explained.
On their last day of what had been a very frustrating experiment, the team decided to try a different sample. Alex had brought along a molybdenum compound as a backup, and the moment it was installed the team observed a rich pattern of SFG signals that began a scientific journey which resulted in the molybdenum compound's data being published in JACS.
The mystery remained, however: Why did the experiment work with the manganese sample, then not work, and then work again when a molybdenum sample was used?
What was possibly different about the samples experiment to experiment?
The team tried to solve this in a number of ways. For example, they thought that, possibly, it was the laser because they had changed the setup is between experiments. Paul exposed the electrodes to the previous beam just in case there was something about that laser that triggered the great results. However, nothing worked until one major realisation.
“It turns out that Gaia prepares her electrodes by hand polishing them. She'll spend around half an hour grinding the surface of the electrode with finer and finer grains," Paul divulged.
“In the second beamtime, she used brand new electrodes in preparation for getting the best data she could out of the experiment. However, it turns out that the re-used electrodes had been exposed to mercury during their cleaning process – mercury was the key!"
As soon as they gave the new electrodes a mercury treatment, all the incredible data returned. It appeared the mercury had either improved the electrode surfaces, stabilised the manganese compounds or allowed them to bind properly.
Because of the unlikely journey it has taken, this research using the CLF-Ultra laser has produced two papers from one series of experiments. The first being the aforementioned JACS paper, which was featured in a Young Investigators Virtual Issue for the important analysis of the molybdenum catalyst's surface interactions in an electrochemical reaction, and the second being this surprising, impactful discovery of manganese catalyst's rich surface chemistry, soon to be featured in Nature Catalysis.
Furthermore, the experiment may not end here, as there is still a question to try and answer: why does the exposure of mercury allow us to detect the signals?
Alex, Paul and Gaia are discussing looking into this as a future project.
“There are lots of possibilities as to why the pre-treatment might work, but right now we really don't know. There's a bit of a mystery to solve still," said Paul.
Impact summary (Donaldson)
The work of Neri et al provides a first glimpse of the chemistry of electrocatalysis through the 'eyes' of a powerful surface technique called Surface Sum Frequency Generation (SFG). SFG, a laser-based technique was used to probe with great specificity the layer of the catalyst molecules that exchange electrons with metal electrodes and then go on to perform chemical catalysis – a process known as electrocatalysis. SFG is a well-established, specialised technique for observing the vibrations of molecules at interfaces. Cowan (Uni. Liverpool) and Donaldson (CLF) teamed up to apply the SFG method to electrocatalysis. Few groups have to-date undertaken such research and along with electrochemists Neri, Saeed and Walsh and theorist Teobaldi, the group's first success in this area was to observe the chemical reaction of an electrocatalyst which converts CO2 to CO – an important process for both CO2 emission mitigation and generation of CO – an important industrial compound. This work was the first success of the group in electrochemical SFG and involved several years of careful experimentation, finally revealing with unprecedented detail and specificity some of the steps in the catalyst's chemical reactions and paving the way for using the SFG technique more generally in the field of electrocatalysis science.
Read more about the experiment on Nature Catalysis: https://www.nature.com/articles/s41929-018-0169-3