| 1. |
- Ali-Löytty, Harri, et al.
(författare)
-
Chemical Dissolution of Pt(111) during Potential Cycling under Negative pH Conditions Studied by Operando X-ray Photoelectron Spectroscopy
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:41, s. 25128-25134
-
Tidskriftsartikel (refereegranskat)abstract
- Dissolution of a platinum catalyst is a major degradation mechanism of fuel cells, but the exact reaction mechanism has remained unclear. Here, electrochemical ambient pressure X-ray photoelectron spectroscopy (EC-APXPS) was utilized to provide direct information on chemical species on a single-crystal Pt(111) electrode under extremely low pH conditions. Measurements were conducted using a novel condensed electrolyte film electrochemical cell applying work function measurement as a loss-free probe for electrochemical potential. We show that platinum can dissolve chemically as Pt2+ ion during potential cycling and redeposit as Pt2+ at the onset potential for cathodic reactions. The dissolution of Pt does not require electrochemical oxidation via oxide place exchange. In contrast, the adsorption of oxygenated species (OH* or O*) at the onset potential for anodic reactions is a sufficient prerequisite to the dissolution. These results provide new insight into the degradation mechanism of Pt under extremely low pH conditions, predicted by the Pourbaix diagram, having practical applications to the durability of Pt-based catalysts in electrochemical energy conversion devices.
|
|
| 2. |
- Ali-Löytty, Harri, et al.
(författare)
-
The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel
- 2018
-
Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 132, s. 214-222
-
Tidskriftsartikel (refereegranskat)abstract
- Microalloying of stainless steel with reactive elements increases oxidation resistance but makes the alloy prone to microstructural changes. XPS results reveal changes in the initial oxidation mechanism on Ti-Nb stabilized ferritic stainless steel (EN 1.4521) after 120 h heat treatment at 650 °C. Age-precipitation of (FeCrSi)2(MoNb)-type Laves phase resulted in less pronounced surface segregation and oxidation of microalloying elements. Si oxidizes preferentially at the Laves precipitate locations via outward diffusion forming diffusion barrier for the other scale forming elements. Most significantly the diffusion of Mn and the formation of low volatile (Mn,Cr)3O4 spinel oxide at the surface was strongly suppressed.
|
|
| 3. |
- Boscolo Bibi, Sara, 1993-, et al.
(författare)
-
Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes
- 2024
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:3, s. 2332-2340
-
Tidskriftsartikel (refereegranskat)abstract
- Oxide-derived metals are produced by reducing an oxide precursor. These materials, including gold, have shown improved catalytic performance over many native metals. The origin of this improvement for gold is not yet understood. In this study, operando non-resonant sum frequency generation (SFG) and ex situ high-pressure X-ray photoelectron spectroscopy (HP-XPS) have been employed to investigate electrochemically-formed oxide-derived gold (OD-Au) from polycrystalline gold surfaces. A range of different oxidizing conditions were used to form OD-Au in acidic aqueous medium (H3PO4, pH = 1). Our electrochemical data after OD-Au is generated suggest that the surface is metallic gold, however SFG signal variations indicate the presence of subsurface gold oxide remnants between the metallic gold surface layer and bulk gold. The HP-XPS results suggest that this subsurface gold oxide could be in the form of Au2O3 or Au(OH)3. Furthermore, the SFG measurements show that with reducing electrochemical treatments the original gold metallic state can be restored, meaning the subsurface gold oxide is released. This work demonstrates that remnants of gold oxide persist beneath the topmost gold layer when the OD-Au is created, potentially facilitating the understanding of the improved catalytic properties of OD-Au.
|
|
| 4. |
|
|
| 5. |
- Li, Lin, et al.
(författare)
-
Operando Observation of Chemical Transformations of Iridium Oxide During Photoelectrochemical Water Oxidation
- 2019
-
Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 2:2, s. 1371-1379
-
Tidskriftsartikel (refereegranskat)abstract
- Iridium oxide is one of the few catalysts capable of catalyzing the oxygen evolution reaction (OER) in both acidic and basic conditions. Understanding the mechanism of IrOx under realistic photoelectrochemical conditions is important for the development of integrated water-splitting systems. Herein, we have developed a highly efficient OER photoanode in pH 1 aqueous solutions based on a sputtered IrOx film and a p(+)n-Si light absorber, interfaced with a sputtered Au layer. Operando high-energy-resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS) was employed to monitor the oxidation state changes of IrOx during both electrochemical and photoelectrochemical (PEC) water oxidation reactions in pH 1 aqueous solutions. We observed a gradual increase of the average oxidation state of Ir with increasing anodic potential in the precatalytic region, followed by a reduction of Ir under O-2 evolution conditions. Consistent results were obtained on dark anodes and illuminated photoanodes. However, when the thickness of IrO2 was increased to 2 and 3 nm, the spectral changes became much less pronounced, and the reduction of Ir oxidation state after the OER onset was not observed. This is due to the lower surface-to-bulk ratio, where lattice oxygen sites in the bulk are not accessible for the formation of hydroxide. More generally, the operando method developed here can be extended to other materials, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.
|
|
| 6. |
- Liu, Maning, et al.
(författare)
-
Lattice Engineering via Transition Metal Ions for Boosting Photoluminescence Quantum Yields of Lead-Free Layered Double Perovskite Nanocrystals
-
Ingår i: Small. - 1613-6829.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Lead-free layered double perovskite nanocrystals (NCs), i.e., Cs4M(II)M(III)2Cl12, have recently attracted increasing attention for potential optoelectronic applications due to their low toxicity, direct bandgap nature, and high structural stability. However, the low photoluminescence quantum yield (PLQY, <1%) or even no observed emissions at room temperature have severely blocked the further development of this type of lead-free halide perovskites. Herein, two new layered perovskites, Cs4CoIn2Cl12 (CCoI) and Cs4ZnIn2Cl12 (CZnI), are successfully synthesized at the nanoscale based on previously reported Cs4CuIn2Cl12 (CCuI) NCs, by tuning the M(II) site with different transition metal ions for lattice tailoring. Benefiting from the formation of more self-trapped excitons (STEs) in the distorted lattices, CCoI and CZnI NCs exhibit significantly strengthened STE emissions toward white light compared to the case of almost non-emissive CCuI NCs, by achieving PLQYs of 4.3% and 11.4% respectively. The theoretical and experimental results hint that CCoI and CZnI NCs possess much lower lattice deformation energies than that of reference CCuI NCs, which are favorable for the recombination of as-formed STEs in a radiative way. This work proposes an effective strategy of lattice engineering to boost the photoluminescent properties of lead-free layered double perovskites for their future warm white light-emitting applications.
|
|
| 7. |
- Liu, Maning, et al.
(författare)
-
Water-Resistant Perovskite-Inspired Copper/Silver Pnictohalide Nanocrystals for Photoelectrochemical Water Splitting
- 2023
-
Ingår i: Electrochimica Acta. - 0013-4686. ; 462
-
Tidskriftsartikel (refereegranskat)abstract
- Lead halide perovskites (LHPs) photoelectrodes for photoelectrochemical (PEC) water splitting are promising candidates for solar-to-fuel conversion. However, the poor stability of LHPs in aqueous electrolyte media, together with the toxicity of lead, restricts the practical application of LHP photoelectrodes. Herein, we report the first-ever colloidal synthesis of quaternary Cu1.4Ag0.6BiI5 nanocrystals (NCs), a new lead-free perovskite-inspired nanomaterial, by a facile hot injection method. The Cu1.4Ag0.6BiI5 NCs exhibit an extraordinary water resistance, due to the well-defined coverage of hydrophobic ligands on the surface of NCs with unique layered cation disordered structure. Together with their high structural stability, the Cu1.4Ag0.6BiI5 NCs-based photoanode displays a maximum photocurrent density of 4.62 mA cm−2 at 1.23 V vs. reversible hydrogen electrode, and an applied bias photo-to-current efficiency of 2.94% without any protective layer. Our study highlights the great potential of lead-free Cu1.4Ag0.6BiI5 NCs-based photoelectrodes for a wide range of low-cost, eco-friendly, and high-performance PEC applications.
|
|
| 8. |
- Palmolahti, Lauri, et al.
(författare)
-
Pinhole-resistant nanocrystalline rutile TiO2 photoelectrode coatings
- 2022
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 239
-
Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposited (ALD) TiO2 thin films have a wide range of applications in photonics which are, however, limited by the chemical instability of the amorphous as-deposited TiO2. Post-deposition annealing is required for improving the performance by inducing phase transitions and oxide defects. ALD precursor traces remaining in the TiO2 film affect the thermally-induced processes but the understanding of the effect of growth temperature on precursor traces in the film as well as on the thermally-induced processes is weak. In this study 30 nm ALD TiO2 was grown on Si wafer from tetrakis(dimethylamido)titanium and water at 100–200 °C. TiO2 was subsequently annealed in vacuum at 200–500 °C. Increasing the growth temperature decreased the amount of N bearing precursor traces and thus makes the TiO2 more easily reducible. The reduction takes place simultaneously with the crystallization and formation of O1− defects. Vacuum annealing of TiO2 with less than 0.3 at% of N results in nanocrystalline rutile whereas samples with more N containing traces crystallized as microcrystalline anatase. Nanocrystalline rutile TiO2 was chemically stable and resistant to the dissolution at the grain boundaries under alkaline conditions making it a suitable material for protective photoelectrode coatings used in artificial photosynthesis.
|
|
| 9. |
- Saari, Jesse, et al.
(författare)
-
Tunable Ti 3+ -Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO 2
- 2022
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:9, s. 4542-4554
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous titania (am.-TiO2) has gained wide interest in the field of photocatalysis, thanks to exceptional disorder-mediated optical and electrical properties compared to crystalline TiO2. Here, we study the effects of intrinsic Ti3+ and nitrogen defects in am.-TiO2 thin films via the atomic layer deposition (ALD) chemistry of tetrakis(dimethylamido)titanium(IV) (TDMAT) and H2O precursors at growth temperatures of 100-200 °C. X-ray photoelectron spectroscopy (XPS) and computational analysis allow us to identify structural disorder-induced penta- and heptacoordinated Ti4+ ions (Ti5/7c4+), which are related to the formation of Ti3+ defects in am.-TiO2. The Ti3+-rich ALD-grown am.-TiO2 has stoichiometric composition, which is explained by the formation of interstitial peroxo species with oxygen vacancies. The occupation of Ti3+ 3d in-gap states increases with the ALD growth temperature, inducing both visible-light absorption and electrical conductivity via the polaron hopping mechanism. At 200 °C, the in-gap states become fully occupied extending the lifetime of photoexcited charge carriers from the picosecond to the nanosecond time domain. Nitrogen traces from the TDMAT precursor had no effect on optical properties and only little on charge transfer properties. These results provide insights into the charge transfer properties of ALD-grown am.-TiO2 that are essential to the performance of protective photoelectrode coatings in photoelectrochemical solar fuel reactors.
|
|
| 10. |
- Vuori, Leena, et al.
(författare)
-
Improved corrosion properties of hot dip galvanized steel by nanomolecular silane layers as hybrid interface between zinc and top coatings
- 2017
-
Ingår i: Corrosion: Journal of science and engineering. - : NACE International. - 0010-9312. ; 73:2, s. 169-180
-
Tidskriftsartikel (refereegranskat)abstract
- Thin organic coatings (TOC) or paints on hot dip galvanized steel (HDGS) improve the corrosion properties and create visually pleasing surfaces. Delamination of these coatings leads to corrosion and peeling of the paints. Hence, a novel method for improved adhesion and corrosion properties for HDGS surfaces is introduced. It is shown how the fabrication of a nanomolecular silane film as an interfacial layer between the HDGS and TOC or paint improves the corrosion properties of HDGS in different pH regimes. Understanding the corrosion behavior of ultra-thin silane layers under differing pH is crucial, as subsequent coatings have different pHs. By varying the silanization parameters, two different nanomolecular surface structures of aminopropyl trimethoxysilane (APS) on HDGS were fabricated: well-ordered monolayers with approximately 1 nm thickness and highly clustered APS films with a thickness in the range of 5 nm to 8 nm. To verify the nanomolecular APS structures, photoelectron spectroscopy and contact angle measurements were used. The corrosion properties of HDGS and silanized HDGS were studied with linear sweep voltammetry and electrochemical impedance spectroscopy. It is shown that at pH 5 and 7, passivation behavior is observed on silanized samples, but the most significant improvement in corrosion resistance is found at pH 10, where the corrosion currents of silanized samples are up to two orders of magnitude lower than on uncoated metallic samples. Also, it is demonstrated that the corrosion inhibition of APS is not only dependent on the thickness of the silane film, but also the molecular ordering at the surface. The thin, well-ordered APS monolayer is more resistant toward corrosion in NaCl solution (pH 7) than thicker clustered APS layer. This indicates that the highly ordered nanomolecular surface structure protects the HDGS/silane interface from the Cl- adsorption better than the thicker, but more randomly ordered, APS layers. Nanomolecular interfacial silane films for enhanced corrosion and adhesion properties on HDGS are transferrable to industrial production lines providing a low cost and environmentally friendly method for improved HDGS products.
|
|
