Q: What initially drew you to the APS?

Tao: I first became aware of the APS as a postdoctoral researcher at Argonne more than 20 years ago, although I didn’t fully appreciate at the time what it could offer my own research. My first real engagement came after I joined Northern Illinois University and was sparked by an unexpected laboratory observation.

We were investigating lithium-based hydrogen storage materials when we noticed that molten lithium was dissolving the platinum crucible we were using. It raised an intriguing question: Could this process break bulk platinum down to individual atoms, and could those atoms act as catalysts? 

Answering it required looking beyond conventional X-ray diffraction. An APS scientist introduced me to X-ray absorption spectroscopy, which gave us a way to probe the material at the atomic scale.
 

Q: Can you describe the research you’ve conducted at the APS? 

Tao: My research at the APS has evolved step by step, with each answer leading to a more ambitious question. We began by asking how far our metal-in-lithium method could break down bulk metals: into nanoparticles, small clusters, or ultimately individual atoms.

Using X-ray absorption spectroscopy at Sectors 10 and 20, we could probe the local atomic environment around specific metals. Once we showed the approach could work with a single metal, we moved to bulk alloys. Using palladium-silver as a model system, our measurements showed that the resulting nanoparticles retained a local alloy structure similar to the bulk material.

From there, we began exploring whether separate bulk metals could be dispersed to the atomic level and reassembled into new nanoalloys. 
 

Q: What role did the APS play in enabling or advancing your work? 

Tao: The APS allows us to probe the electronic state and local atomic structure of catalytic centers under actual reaction conditions. Conventional techniques can tell us what a catalyst looks like before and after a reaction, but the structure we synthesize may not be the structure actually performing the chemistry.

Using operando X-ray absorption spectroscopy, we can observe a catalytic center while an electrochemical reaction is taking place. X-ray Absorption Near-Edge Structure (XANES) lets us follow changes in its electronic or oxidation state, while Extended X-ray Absorption Fine Structure (EXAFS) provides information about the surrounding atoms and local coordination environment.

We can then connect the state of the catalytic center with catalytic activity and product selectivity. In catalysis, what matters is not simply the material placed in the reactor, but the active structure that exists while the reaction is occurring. 
 

Q: Has anything unexpected come out of your work with the APS, either in your results or in the process itself?

Tao: One of the biggest surprises was discovering just how dynamic a catalytic center can be. We began with individual copper atoms dispersed on a carbon support. If we had examined the catalyst only before and after the reaction, we might have concluded that those isolated atoms were the active centers.

Operando measurements revealed a different picture. Under the reaction potential, the copper atoms assembled into tiny clusters of approximately three or four atoms associated with the formation of ethanol from carbon dioxide. When the potential was removed, the clusters dissociated toward the original single-atom state.

The result changed how I think about catalyst design. Rather than designing only static structures, we can consider catalysts that form the desired active center dynamically under operating conditions.
 

Q: What impact has your research at the APS had on your work so far? What are you excited about exploring next?

Tao: My work at the APS has continually pushed me toward understanding materials at shorter length scales and faster timescales. We began by determining atomic structures, then moved to operando measurements that let us watch catalytic centers evolve during reactions.

Now we’re extending that approach into quantum materials. In collaboration with APS scientists, we are beginning to use time-resolved X-ray absorption spectroscopy and X-ray diffraction following ultrashort light excitation. We want to understand how photoexcitation changes electronic and local atomic structure on ultrafast timescales, how those changes interact with electron spin states, and ultimately how spin influences quantum coherence.

My research with the APS has progressed from understanding what a material is, to seeing how it functions, to watching it evolve in real time. APS scientists have been an important part of that progression, collaborating closely with us and helping teach and support my students along the way.