Electro-Chemical Processes

Developing advanced technologies for energy storage and conversion is widely recognized as critical to establishing a secure and sustainable U.S. energy portfolio. The full use of renewable energy resources such as solar and wind requires large-scale conversion and storage technologies to effectively manage production transients and produce fuels to replace petroleum. Electrochemical devices such as batteries, electrolyzers, and fuel cells are the most promising because of their inherently high efficiencies and compatibility with existing electricity and fuel-delivery infrastructures.

The essential physical phenomenon that occurs in all electrochemically based devices is the transfer of electrical charge across a material interface. Mechanisms that govern charge transfer are poorly understood—as are the relationships between such phenomena and device performance and reliability. Gaining this fundamental understanding would enable us to develop optimally designed electrode/electrolyte materials and interfaces, and thus more efficient or robust technologies.

In collaboration with the Advanced Light Source (located at Lawrence Berkeley National Laboratory), we have devised an experimental platform to use synchrotron-based soft x-ray techniques, such as ambient-pressure photoemission spectroscopy (APPES) and near-edge x-ray absorption spectroscopy (XAS), to directly observe local surface potential, chemical composition and elemental oxidation states at surfaces, interfaces, and in the bulk of high-temperature electrochemical devices during operation. This powerful approach is unique in the world and is capable of identifying adsorbed surface species on an electrode or electrolyte, as well as mapping the electrode overpotentials through measurement of local surface potential. This is accomplished by measuring the kinetic energies of core-level electrons generated by x-ray irradiation. Each element in the system produces electrons within a unique range of energies, thus fingerprinting that element. The magnitude or intensity of the signal is representative of the surface coverage. Furthermore, the degree to which the observed peaks in the APPES spectra shift relative to an unbiased sample is indicative of both the local bonding environment for that element (chemical shifts) and surface potential (rigid shifts). Finally, differences between bulk and surface states induced by thermochemistry and/or electrochemistry can be resolved by comparing XAS and impedance spectra with the APPES spectra, all measured simultaneously during operation.



Membrane electrode assembly sealed onto a YSZ tube creating a two-chamber, hermetically sealed environment which fully isolates anode from cathode. This device is inserted into the Advanced Light Source (ALS) end station to receive synchrotron radiation and conduct ambient-pressure photoemission spectroscopy (APPES) and electrochemical experiments.

Contact: Tony McDaniel, (925) 294-1440, amcdani@sandia.gov