Understanding the interplay between surface chemistry, electronic structure, and reaction mechanism of catalysts at the electrified solid/liquid interface will enable the design of more efficient systems for sustainable energy production. The substantial progress in operando characterization, particularly using synchrotron based X-ray spectroscopies, provides the opportunity to uncover surface chemical and structural transformations under various (photoelectro)chemical reaction environments. In this talk, we will focus and review the main results obtained at the Advanced Light Source coupling Hard X-ray Photoelectron Spectroscopy (HAXPES) and ambient pressure conditions to access to the operando study of solid/liquid electrified interfaces. By using the “dip and pull” procedure and ambient pressure X-ray photoelectron spectroscopy (APXPS), we were able to simultaneously probe ~20-30 nm of aqueous electrolyte (at the equilibrium with its vapor) and ~10 nm of the electrocatalyst, while undergoing electrochemical reactions at the solid/liquid electrified interface. As first example of the potentialities of such innovative technique, we will show the results obtained on the investigation of the electrochemical double layer at the solid/liquid junction. By coupling numerical simulations of the electric field at the interface and the photoelectron spectra of the solvent (water) and a spectator neutral molecule used as local probe, we discerned the shape of the electrochemical double layer profile. In addition, we determined how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential. In the second part of the talk, we will show the application of the technique to two paradigmatic materials for oxygen evolution reaction: Pt and a biphasic catalyst composed of a Co3O4/Co(OH)2 layered structure. For both materials, we studied the surface and sub-surface chemical and structural evolution as a function of the applied potential, and in particular at potentials able to drive water splitting. Based on the experimental findings, we were able to propose a catalytic cycle for both systems under oxygen evolution conditions. Finally, we will portray some future perspectives/developments of APXPS within a more general operando multi-technique approach, with the aim of opening up fruitful discussions at the workshop among the AP community.

Understanding solid/liquid electrified interfaces using ambient pressure x-ray photoelectron spectroscopy

254th National Meeting (2017)

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