Accessing Dynamic Electrochemical Interfaces
A new technique reveals ultrafast processes in electrode-electrolyte interfaces under operating conditions.
The Science
Electrodes’ surfaces drive reactions that are critical to energy conversion. In batteries, electrodes accept and release electrons. This process charges and discharges the battery. However, scientists know little about the chemistry of these surfaces during this process. Techniques that are sensitive to these surfaces require a vacuum or conditions that are incompatible with true electrochemical environments. To overcome this limitation, scientists developed a method called modulation-excitation X-ray spectroscopy (ME-XAS). This approach revealed that copper(III) species (a type of compound) forms during water oxidation. (Oxidation is an important step in water splitting.) This was the first time that scientists have directly observed this compound during this process. The technique also captured sequential oxidation events that occurred within milliseconds.
The Impact
This finding fundamentally changes how scientists can study electrochemical interfaces. The direct observation of Cu(III) resolves decades of debate. These results also reveal new principles for designing catalysts. By studying very fast surface transformations, scientists have a way to investigate mechanisms that were previously inaccessible. The methodology is also broadly applicable. Scientists can now study any interface between electrodes under working conditions. They can now observe rather than infer the chemistry of these surfaces. This capability accelerates the development of many technologies, including battery materials. Overall, this method helps transform electrochemistry from relying on trial-and-error approaches to directly designing surfaces.
Summary
Modulation-excitation X-ray absorption spectroscopy (ME-XAS) achieves what has eluded electrochemists for decades: direct, time-resolved observation of electrode surfaces during operation. The technique synchronizes periodic potential modulation with hard X-ray absorption measurements. It uses phase-sensitive detection to extract signals specific to the surface signals from bulk-dominated spectra with unprecedented sensitivity. Scientists at the Stanford Synchrotron Radiation Lightsource, a Department of Energy (DOE) Office of Science User Facility, developed the technique. With the technique, they captured the complete surface-oxidation sequence with 30-millisecond resolution. Two fundamental discoveries emerged. First, Cu(III) species form at electrode surfaces during oxygen evolution. This finding provides experimental validation of computationally predicted intermediates. Theoretical calculations performed on resources at the National Energy Research Scientific Computing Center (a DOE Office of Science User Facility), confirmed the spectroscopic assignments. Second, hydroxide adsorption precedes and templates Cu₂O formation, followed by Cu(OH)₂ growth. These kinetics reveal that initial hydroxide coordination governs all subsequent transformations. Potential applications span fundamental electrochemistry and industrial catalysis. It could apply to any setting where interfacial chemistry determines function. The methodology provides DOE researchers with unprecedented capability to understand and control electrode–electrolyte interfaces critical for energy technologies, the chemical industry, and manufacturing.
Contact
Dimosthenis Sokaras
Stanford Synchrotron Radiation Lightsource
SLAC National Accelerator Laboratory
dsokaras@slac.stanford.edu
Funding
Primary support for this research was provided by the DOE Office of Science, Office of Basic Energy Sciences through the Scientific User Facilities Division and the Chemical Sciences, Geosciences, and Biosciences Division. The research used resources at the Stanford Synchrotron Radiation Lightsource and National Energy Research Scientific Computing Center (NERSC), both DOE Office of Science User Facilities.
Publications
Garcia-Esparza, A.T., et al. "The electrode-electrolyte interface of Cu via modulation excitation X-ray absorption spectroscopy." Energy & Environmental Science, 18, 4643-4650 (2025). [DOI: 10.1039/D5EE01068C]
Basera, P., et al. "The Role of Cu³⁺ in the oxygen evolution activity of copper oxides." Journal of the American Chemical Society, 147, 16070-16083 (2025). [DOI: 10.1021/jacs.4c18147]
Related Links
The case of the missing copper species, SLAC news
Modulation to probe the interface, Nature Catalysis Editor’s Research Highlight
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Performer: University , DOE Laboratory , SSRL , NERSC
