PIPOXS stands for “Photon-In, Photon-Out X-ray Spectroscopy.” The beamline focuses on two types of x-ray spectroscopy in order to investigate chemical catalysts. “Photon-in” in the beamline’s name refers to x-ray absorption spectroscopy - examining the energies that a sample absorbs when hit with x-ray photons. This allows researchers to learn about an atom’s geometry, oxidation state, and length of its chemical bonds. The other type of x-ray spectroscopy used at PIPOXS is x-ray emission spectroscopy, the “photon-out” portion of the name. X-ray emission spectroscopy involves exciting electrons in a sample with photons, then waiting to see what energies of x-rays the sample eventually emits. This type of spectroscopy can provide information about an atom’s bonding partners and spin state.
Catalysts are common in nature, such as in synthesizing DNA, and are also often used in man-made processes, like producing industrial fertilizer. Catalysts are extremely efficient, especially in natural processes, so understanding how they work and attempting to recreate these processes can be very useful. The challenge is that we often don’t know how they work on a molecular level, making it difficult for us to mimic nature’s efficient catalysts, improve existing catalysts, or design new ones. The goal at PIPOXS, Pollock explains, “is to be able to study chemical catalysts, ideally under operating conditions, so that we know how they function, or how their structures might change during a chemical reaction, so that we can then learn from that and design new and better catalysts from what we currently have.”
Since catalysts function in a wide variety of processes, the PIPOXS beamline had to be designed with a very flexible end-station to accommodate a range of samples and environments. Scientists bring research to PIPOXS that investigates everything from heterogeneous catalysts on industrial scales all the way down to enzymes in cells.
The beamline’s flexibility comes from a range of built-in factors. The first is the energy range available at PIPOXS, which allows nearly the entire periodic table, from calcium to uranium, to be reached. Researchers can bring a variety of sample environments to be studied at the beamline as well. Users have brought liquids in solution, electrochemical cells with applied voltage, and samples frozen at 10 K. In addition, the beam at PIPOXS can be tuned with a wide beam for a large sample, down to about 100 by 200 microns for a very small sample.
Another built-in feature of PIPOXS is the spectrometers that are available, some of which are unique to CHESS. The spectrometers at PIPOXS allow both emission and absorption spectroscopy, but also allow for the combination of the two techniques into complicated 2-dimensional methods. This allows Pollock to tailor experiments to help users answer whatever chemical questions they may have.
One area of research often conducted at PIPOXS revolves around in situ electrochemistry. Researchers studying batteries and fuel cells are able to study the charge and discharge of their materials and monitor the oxidation states of different elements within the sample. Using x-ray absorption and emission spectroscopy, and looking at each element sequentially, scientists can see where a charge is coming from and going to during charge and discharge cycles. This kind of information would be difficult or impossible to learn without the x-ray tools available at PIPOXS.
This type of research has a broad impact on society, as we work to improve our energy economy. “We have a lot of research that goes into electrochemical systems: fuel cells, batteries, different electrochemical catalysis" says Pollock.
"[This research] can change the way that we both generate and store electrical power, it can make these processes more efficient.”
Research being conducted at PIPOXS could change the types of materials used in these systems. Right now, batteries and fuel cells often use expensive and/or hazardous materials. By studying how these systems work, the hope is to be able to replace those materials with more abundant, cheaper, and more environmentally friendly materials. “That could have a big impact on how we use energy as a society.”
Biological systems are another focus of PIPOXS research - looking at how enzymes function. Nature carries out incredibly complex, challenging chemical reactions, many of which can’t currently be replicated in a lab. Learning how these reactions are performed can inspire scientists to design catalysts that can mimic these natural processes or improve drug design.
Pollock and his team are always trying to adapt and approach new challenges at PIPOXS. One such upcoming improvement will allow wider temperature control of samples. Another improvement will allow users to look at heterogeneous catalysts during reactions - a new capability. Another project involves improvements to the way PIPOXS does energy scans that will take the time required to do a scan from five or ten minutes down to about thirty seconds. This will save users time and allow more experiments. Beyond that, “we’re always just trying to push the envelope in terms of how low of a concentration can we measure, how quickly can we scan, and how low of a signal can we actually measure, So we’re constantly trying to push the boundaries of what’s possible.”
Since 2020, access to the PIPOXS beamline has been remote. A dedicated effort by the CHESS IT and technical staff has allowed researchers to log in to the station and control everything that they could if they were physically at the beamline. Pollock explained that remote access has gone very well. “Our users have been really enthusiastic about trying this out.” Samples have come from as far away as Germany with successful remote runs. “Looking forward,” says Pollock,” I think that particularly for new user groups, the ability to do remote experiments really lowers the barrier to doing synchrotron experiments. Even once the restrictions from Covid are lifted, I think remote operations will remain an important part of our user program, simply because they allow more people to do these experiments that they wouldn’t necessarily be able to.”
The beamline’s flexibility makes it an exciting place for Pollock to work. “I’m always encountering new challenges, and new problems, and new science,” he relishes. “One week I could be working on a metalloenzyme, the next I could be working with a user on a fuel cell component, and the next I could be looking at a small-molecule catalyst. There’s always something new, there’s always something exciting going on, and I’m always learning new things at this beamline. It’s a fun place to be doing science!”