| 1. |
- Abb, Marcel J.S., et al.
(författare)
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Thermal Stability of Single-Crystalline IrO2(110) Layers : Spectroscopic and Adsorption Studies
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:28, s. 15324-15336
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of ultrathin single-crystalline IrO2(110) films with the gas phase proceeds via the coordinatively unsaturated sites (cus), in particular Ircus, the undercoordinated oxygen species on-top O (Oot) that are coordinated to Ircus, and bridging O (Obr). With the combination of different experimental techniques, such as thermal desorption spectroscopy, scanning tunneling microscopy (STM), high-resolution core-level spectroscopy (HRCLS), infrared spectroscopy, and first-principles studies employing density functional theory calculations, we are able to elucidate surface properties of single-crystalline IrO2(110). We provide spectroscopic fingerprints of the active surface sites of IrO2(110). The freshly prepared IrO2(110) surface is virtually inactive toward gas-phase molecules. The IrO2(110) surface needs to be activated by annealing to 500-600 K under ultrahigh vacuum (UHV) conditions. In the activation step, Ircus sites are liberated from on-top oxygen (Oot) and monoatomic Ir metal islands are formed on the surface, leading to the formation of a bifunctional model catalyst. Vacant Ircus sites of IrO2(110) allow for strong interaction and accommodation of molecules from the gas phase. For instance, CO can adsorb atop on Ircus and water forms a strongly bound water layer on the activated IrO2(110) surface. Single-crystalline IrO2(110) is thermally not very stable although chemically stable. Chemical reduction of IrO2(110) by extensive CO exposure at 473 K is not observed, which is in contrast to the prototypical RuO2(110) system.
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| 2. |
- Weber, Tim, et al.
(författare)
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Extraordinary Stability of IrO2(110) Ultrathin Films Supported on TiO2(110) under Cathodic Polarization
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; , s. 9057-9062
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Tidskriftsartikel (refereegranskat)abstract
- Down to a cathodic potentials of -1.20 V versus the reversible hydrogen electrode, the structure of IrO2(110) electrodes supported by TiO2(110) is found to be stable by in situ synchrotron-based X-ray diffraction. Such high cathodic potentials should lead to reduction to metallic Ir (Pourbaix diagram). From the IrO2 lattice parameters, determined during cathodic polarization in a H2SO4 electrolyte solution (pH 0.4), it is estimated that the unit cell volume increases by 1% due likely to proton incorporation, which is supported by the lack of significant swelling of the IrO2(110) film derived from X-ray reflectivity experiments. Ex situ X-ray photoelectron spectroscopy suggests that protons are incorporated into the IrO2(110) lattice below -1.0 V, although Ir remains exclusively in the IV+ oxidation state down to -1.20 V. Obviously, further hydrogenation of the lattice oxygen of IrO2(110) toward water is suppressed for kinetic reasons and hints at a rate-determining chemical step that cannot be controlled by the electrode potential.
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| 3. |
- Weber, Tim, et al.
(författare)
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In situ studies of the cathodic stability of single-crystalline IrO2(110) ultrathin films supported on RuO2(110)/Ru(0001) in an acidic environment
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:40, s. 22956-22962
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Tidskriftsartikel (refereegranskat)abstract
- We investigate with in situ surface X-ray diffraction (SXRD) and X-ray reflectivity (XRR) experiments the cathodic stability of an ultrathin single-crystalline IrO2(110) film with a regular array of mesoscopic rooflike structures that is supported on a RuO2(110)/Ru(0001) template. It turns out that the planarity of the single-crystalline IrO2(110) film is lost in that IrO2(110) oxide domains delaminate at a cathodic potential of -0.18 V. Obviously, the electrolyte solution is able to reach the RuO2(110) layer presumably through the surface grain boundaries of the IrO2(110) layer. Subsequently, the single-crystalline RuO2(110) structure-directing template is reduced to amorphous hydrous RuO2, with the consequence that the IrO2(110) film loses partly its adhesion to the template. From in situ XRR experiments we find that the IrO2(110) film does not swell upon cathodic polarization down to -0.18 V, while from in situ SXRD experiments, the lattice constants of IrO2(110) are shown to be not affected. The rooflike mesostructure of the IrO2(110) flakes remains intact after cathodic polarization to -0.18 V, evidencing that the crystallinity of IrO2(110) is retained. This journal is
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| 4. |
- Weber, Tim, et al.
(författare)
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In Situ Synchrotron-Based Studies of IrO2(110)-TiO2(110) under Harsh Acidic Water Splitting Conditions : Anodic Stability and Radiation Damages
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:48, s. 20243-20250
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Tidskriftsartikel (refereegranskat)abstract
- In situ stability studies of an IrO2(110)-TiO2(110) model electrode are carried out under acidic water electrolysis conditions, employing synchrotron-based techniques including surface X-ray diffraction (SXRD) and X-ray reflectometry (XRR) with a photon energy of 21.5 keV. These experiments are complemented by ex situ scanning electron microscopy (SEM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) experiments. Even at an anodic current density of 250 mA·cm-2during electrochemical water splitting, the IrO2(110)-TiO2(110) model electrode turned out to be stable against Ir dissolution. However, radiation-induced damages of the IrO2(110) film are observed: Part of the IrO2(110) film delaminates upon heavy exposure to the synchrotron beam, while subsequently the uncovered TiO2(110) is subject to further (photon-induced) corrosion. We propose that the X-ray photons induce oxygen vacancy formation by displacing O2-ions of TiO2from regular to interstitial sites, while the potential drop across the TiO2(110) substrate leads to a migration of interstitial O2-ions from interface toward bulk TiO2. This reduction step at the interface between IrO2(110) and TiO2(110) weakens the adhesion of the epitaxially grown IrO2(110) film to the TiO2(110) substrate so that the strained IrO2(110) film is partially delaminated. Higher X-ray photon energies of 60-90 keV mitigate this degradation process.
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| 5. |
- Weber, Tim, et al.
(författare)
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Operando Stability Studies of Ultrathin Single-Crystalline IrO2(110) Films under Acidic Oxygen Evolution Reaction Conditions
- 2021
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 11:20, s. 12651-12660
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Tidskriftsartikel (refereegranskat)abstract
- The anodic corrosion behavior of 50 Å thick single-crystalline IrO2(110) films supported on slightly bulk-reduced TiO2(110) single crystals is studied during acidic water splitting by a unique combination of operando techniques, namely, synchrotron-based high-energy X-ray reflectivity (XRR) and surface X-ray diffraction (SXRD) together with highly sensitive inductively coupled plasma mass spectrometry (ICP-MS). Corrosion-induced structural and morphological changes of the IrO2(110) model electrode can be followed on the atomic scale by operando XRR and SXRD that are supplemented with ex situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), whereas with ICP-MS, the corrosion rate can be quantified down to 1 pg·cm-2·s-1 with a time resolution on the second scale. The operando synchrotron-based X-ray scattering techniques are surprisingly sensitive to Ir corrosion of about 0.10 monolayer of IrO2(110) in ∼26 h, i.e., 0.4 pg·cm-2·s-1. The present study demonstrates that single-crystalline IrO2(110) films are much more stable than hitherto expected. Although the dissolution rate is very small, ICP-MS experiments reveal a significantly higher dissolution rate than the operando high-energy XRR/SXRD experiments. These differences in dissolution rate are suggested to be due to the different modi operandi encountered in ICP-MS (dynamic) and operando XRR/SXRD experiments (steady state), a fact that may need to be considered when hydrogen production is coupled to intermittent energy sources such as renewables.
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| 6. |
- Weber, Tim, et al.
(författare)
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Potential-Induced Pitting Corrosion of an IrO2(110)-RuO2(110)/Ru(0001) Model Electrode under Oxygen Evolution Reaction Conditions
- 2019
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 9:7, s. 6530-6539
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Tidskriftsartikel (refereegranskat)abstract
- Sophisticated IrO2(110)-based model electrodes are prepared by deposition of a 10 nm thick single-crystalline IrO2(110) layer supported on a structure-directing RuO2(110)/Ru(0001) template, exposing a regular array of mesoscopic rooflike structures. With this model electrode together with the dedicated in situ synchrotron based techniques (SXRD, XRR) and ex situ characterization techniques (SEM, ToF-SIMS, XPS), the corrosion process of IrO2(110) in an acidic environment (pH 0.4) is studied on different length scales. Potential-induced pitting corrosion starts at 1.48 V vs SHE and is initiated at so-called surface grain boundaries, where three rotational domains of IrO2(110) meet. The most surprising result is, however, that even when the electrode potential is increased to 1.94 V vs SHE 60-70% of the IrO2 film still stays intact down to the mesoscale and atomic scale and no uniform thinning of the IrO2(110) layer is encountered. Neither flat IrO2(110) terraces nor single steps are attacked. Ultrathin single-crystalline IrO2(110) layers seem to be much more stable to anodic corrosion than hitherto expected.
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