Detecting oxygen binding to the catalyst by near ambient pressure X-ray Photoelectron Spectroscopy

What is it about?

The first step of oxygen reduction reaction that occurs at the cathode of the fuel cell is oxygen binding to the surface of the catalyst. XPS is a spectroscopic method that provides chemical composition from the very top surface. XPS is sensitive to the interactions such as hydrogen bonding or intermolecular coordination. Synchrotron-based XP spectrometers provide an opportunity to detect the changes in chemical composition at the surface of materials upon binding of reactants such as oxygen. In this study, we studied materials that are promising alternatives to expensive and rare platinum group metal catalysts used in fuel cells. The materials from the family of transition-metal-nitrogen composites were analyzed by synchrotron-based XPS in the presence of oxygen and water vapor. We followed the changes in the chemistry of nitrogen upon oxygen binding and suggested the types of chemical structures that may serve as active sites for oxygen reduction. DFT calculations confirmed the shifts in spectra observed upon oxygen and hydroxyl binding.

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Why is it important?

The role of different nitrogen, transition metal and carbon species in oxygen reduction reaction is heavily debated. This study provides clear observation of oxygen binding to specific structures existing at the surface of the catalyst.

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