Photoelectron spectroscopy offers detailed information about the electronic structure and chemical composition of surfaces, owing to the short distance that the photoelectrons can escape from a... Show morePhotoelectron spectroscopy offers detailed information about the electronic structure and chemical composition of surfaces, owing to the short distance that the photoelectrons can escape from a dense medium. Unfortunately, photoelectron based spectroscopies are not directly compatible with the liquids required to investigate electrochemical processes, especially in the soft X-ray regime. To overcome this issue, different approaches based on photoelectron spectroscopy have been developed in our group over the last few years. The performance and the degree of information provided by these approaches are compared with those of the well established bulk sensitive spectroscopic approach of total fluorescence yield detection, where the surface information gained from this approach is enhanced using samples with large surface to bulk ratios. The operation of these approaches is exemplified and compared using the oxygen evolution reaction on IrOx catalysts. We found that all the approaches, if properly applied, provide similar information about surface oxygen speciation. However, using resonant photoemission spectroscopy, we were able to prove that speciation is more involved and complex than previously thought during the oxygen evolution reaction on IrOx based electrocatalysts. We found that the electrified solid-liquid interface is composed of different oxygen species, where the terminal oxygen atoms on iridium are the active species, yielding the formation of peroxo species and, finally, dioxygen as the reaction product. Thus, the oxygen-oxygen bond formation is dominated by peroxo species formation along the reaction pathway. Furthermore, the methodologies discussed here open up opportunities to investigate electrified solid-liquid interfaces in a multitude of electrochemical processes with unprecedented speciation capabilities, which are not accessible by one-dimensional X-ray spectroscopies. Show less
Badiani, V.; Bajada, M.; Beller, M.; Bocarsly, A.B.; Bonnet, S.A.; Bozal-Ginesta, C.; ... ; Zwijnenburg, M. 2019
This paper summarizes our current understanding of the so-called “hydrogen region” of nanostructured platinum electrodes. While on Pt(111) sites there is indeed only hydrogen adsorption in the... Show moreThis paper summarizes our current understanding of the so-called “hydrogen region” of nanostructured platinum electrodes. While on Pt(111) sites there is indeed only hydrogen adsorption in the hydrogen region, step sites in platinum involve the replacement of adsorbed hydrogen by adsorbed hydroxyl, which interacts with co-adsorbed cations. The so-called “third hydrogen peak”, which develops on oxidatively roughened platinum electrodes, and on platinum electrodes with a high (110) step density subjected to a high concentration of hydrogen, remains one of the elusive peaks in the hydrogen region. We present evidence that the peak involves surface-adsorbed hydrogen (instead of subsurface of occluded hydrogen) on a locally “reconstructed” (110)-type surface site, which is unstable when the hydrogen is oxidatively removed. The cation sensitivity of the third hydrogen peak appears different from other step-related peaks, suggesting that the chemistry involved may still subtly different. Show less
