SurfaceScience21 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 65: Poster Session V: Solid-liquid interfaces: Reactions and electrochemistry II

O 65.3: Poster

Mittwoch, 3. März 2021, 10:30–12:30, P

Surface pH estimation during electrochemical CO₂ reduction in a non-RDE setup — •David Egger, Karsten Reuter, and Christoph Scheurer — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

The electro-chemical CO₂ reduction reaction (CO₂RR) represents a promising route to renewable fuels. CO₂RR in aqueous electrolyte solutions is hampered by the loss of faradaic efficiency due to the competing hydrogen evolution reaction (HER) either by the reduction of hydronium ions or water. The latter lead to a pH increase towards the electrode surface under high current operating conditions. This shift in electrode pH can significantly influence the active catalytic state and stability of the electrode. Yet, the crucial surface pH is neither experimentally easily accessible, nor can it be simply obtained from bulk equilibrium thermodynamics.

Here, we present a semi-empirical approach to estimate the surface pH at a planar electrode from experimental electrode currents at a range of different nominal bulk pHs. By solving a 1-D simplified Poisson-Nernst-Planck equation to account for mass transport and chemical kinetics, the current approach works even outside a rotating disc electrode setup. We apply it to corresponding CO2RR data at molybdenum carbide provided alongside in situ XPS measurements and show that only after surface pH correction the XPS compositional information can be brought into agreement with the Pourbaix diagram obtained from ab initio thermodynamics.