| 1. |
- Botella, Romain, et al.
(författare)
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Polarized ATR-IR spectroscopy for the identification of material structure : The case of graphene oxide
- 2022
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Ingår i: Materials letters (General ed.). - : Elsevier. - 0167-577X .- 1873-4979. ; 320
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Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) is a layered structure similar to graphite, whose planes of carbon atoms are decorated by oxygen-containing groups. These groups bring hydrophilicity and reactivity to GO, as they are present on its basal plane or at the edges. Thus, their identification is essential to determine the chemical properties of GO. Amongst the possible analytical techniques, infrared spectroscopy is suitable to identify these groups. In this work, an advanced spectroscopic method, polarized attenuated total reflectance infrared spectroscopy, was used to obtain a more in-depth analysis of these reactive groups. This new approach has allowed to refine the description of the functional groups at the surface and could be used to follow the evolution surface processes in material chemistry (e.g. grafting reactions).
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| 2. |
- Fan, Junpeng, et al.
(författare)
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β-Mo2C Nanoparticles Produced by Carburization of Molybdenum Oxides with Carbon Black under Microwave Irradiation for Electrocatalytic Hydrogen Evolution Reaction
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:11, s. 12270-12277
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of electrochemically active β-Mo2C nanoparticles for hydrogen production was achieved by a fast and energy-efficient microwave-assisted carburization process from molybdenum oxides and carbon black. With the use of microwave-based production methods, we aim to reduce the long-time high-temperature treatments and the use of hazardous gases often seen in traditional molybdenum carbide synthesis processes. In our process, carbon black not only serves as a carbon source but also as a susceptor (microwave absorber) and conductive substrate. The irradiation power, reaction time, and Mo:C ratio were optimized to achieve the highest electrocatalytic performance toward hydrogen production in an acidic electrolyte. A complete transformation of MoO3 to β-Mo2C nanoparticles and an additional graphitization of the carbon black matrix were achieved at 1000 W, 600 s, and Mo:C ratio above 1:7.5. Under these conditions, the optimized composite exhibited an excellent HER performance (η10 = 156 mV, Tafel slope of 53 mV·dec–1) and large turnover frequency per active site (3.09 H2·s–1 at an overpotential of 200 mV), making it among the most efficient non-noble-metal catalysts. The excellent activity was achieved thanks to the abundance of β-Mo2C nanoparticles, the intimate nanoparticle-substrate interface, and enhanced electron transport toward the carbon black matrix. We also investigated the flexibility of the synthesis method by adding additional Fe or V as secondary transition metals, as well as the effect of the substrate.
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| 3. |
- Kagkoura, Antonia, et al.
(författare)
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Bifunctional nanostructured palladium/MoSx electrocatalyst for cathode hydrogen evolution reaction PEM water electrolysis and oxygen reduction reaction
- 2023
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Ingår i: Advanced Sustainable Systems. - : Wiley-VCH Verlagsgesellschaft. - 2366-7486. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- The creation of effective Pd-based architectures with numerous electrocatalytic active sites and efficient charge transfer is of key importance for improving the electrocatalytic performance in water electrolyzer and fuel cell applications. On the other hand, MoS2, possessing multiple electrocatalytic active sites, can act both as support and booster to Pd-based electrocatalytic structures. Herein, MoSx@Pd hybrids were successfully synthesized by using a one-pot liquid phase solvothermal strategy with stoichiometric excess of Pd. The optimized MoSx@Pd proves to be an excellent bifunctional electrocatalyst for both hydrogen evolution reaction and oxygen reduction reaction (ORR). Optimized MoSx@Pd operates the process for hydrogen evolution at the same potential as Pt/C and achieves a low overpotential of 76 mV at −10 mA cm−2 due to improved reaction kinetics and charge transfer processes between Pd and MoS2. On top of that, MoSx@Pd exhibits excellent performance and stability as cathode electrocatalyst in a polymer electrolyte membrane water electrolyzer. Simultaneously, the bifunctional electrocatalyst shows enhanced electrocatalytic ORR activity and stability by maintaining 93% of its initial activity outperforming commercial Pt/C. Finally, rotating ring disk electrode analysis reveals that ORR proceeds through the energy efficient 4e− pathway, with water being the main product, rendering MoSx@Pd a promising component for fuel cells.
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| 4. |
- Piñeiro-García, Alexis, et al.
(författare)
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A Quaternary mixed oxide protective scaffold for ruthenium during oxygen evolution reaction in acidic media
- 2023
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Ingår i: Communications Engineering. - : Springer Nature. - 2731-3395. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Proton exchange membrane water electrolysis is widely used in hydrogen production, but its application is limited by significant electrocatalyst dissolution at the anode during the oxygen evolution reaction (OER). The best performing electrocatalysts to date are based on ruthenium and iridium oxides, but these experience degradation even at moderate cell potentials. Here we investigate a quaternary Sn-Sb-Mo-W mixed oxide as a protective scaffold for ruthenium oxide. The acid-stable mixed oxide consists of an interconnected network of nanostructured oxides capable of stabilizing ruthenium into the matrix (Ru-MO). In combination with titanium fibre felt, we observed a lower degradation in the oxygen evolution reaction activity compared to unprotected ruthenium oxide after the electrochemical stress test. The superior stability of Ru-MO@Ti is attributed to the presence of MO which hinders the formation of reactive higher valence ruthenium (Ru+8). Our work demonstrates the potential of multi-metal oxides to extend the lifetime of the OER active metal and the titanium support.
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| 5. |
- Piñeiro-García, Alexis, et al.
(författare)
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Benchmarking molybdenum-based materials as cathode electrocatalysts for proton exchange membrane water electrolysis : can these compete with Pt?
- 2023
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:20, s. 7641-7654
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Tidskriftsartikel (refereegranskat)abstract
- Proton exchange membrane water electrolysis (PEMWE) is a promising technology to produce high-purity renewable hydrogen gas. However, its operation efficiency is highly dependent on the usage of expensive noble metals as electrocatalysts. Replacing, decreasing, or simply extending the operational lifetime of these precious metals have a positive impact on the hydrogen economy. Mo-based electrocatalysts are often praised as potential materials to replace the Pt used at the cathode to catalyse the hydrogen evolution reaction (HER). Most electrocatalytic studies are performed in traditional three-electrode cells with different operational conditions than those seen in PEM systems, making it difficult to predict the expected material’s performance under industrially relevant conditions. Therefore, we investigated the viability of using three selected Mo-based nanomaterials (1T′-MoS2, Co-MoS2, and β-Mo2C) as HER electrocatalysts in PEMWE systems. We investigated the effects of replacing Pt on the catalyst loading, charge transfer resistance, kinetics, operational stability, and hydrogen production efficiency during the PEMWE operation. In addition, we developed a methodology to identify the individual contribution of the anode and cathode kinetics in a PEMWE system, allowing to detect the cause behind the performance drop when using Mo-based electrocatalysts. Our results indicate that the electrochemical performance in three-electrode cells might not strictly predict the performance that could be achieved in PEMWE cells due to differences in interfaces and porosity of the macroscopic catalyst layers. Among the catalysts studied, 1T′-MoS2 is truly an excellent candidate to replace Pt as an HER electrocatalyst due to its low overpotential, low charge transfer resistance, and excellent durability, reaching a high efficiency of ∼75% at 1 A cm-2 and 1.94 V. Our study highlights the importance of a continuous development of efficient noble-metal free HER electrocatalysts suitable for PEMWE systems.
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| 6. |
- Piñeiro-García, Alexis, et al.
(författare)
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Functionalization and soft photoreduction of graphene oxide triggered by the photoinitiator during thiol-ene radical addition
- 2022
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Ingår i: FlatChem. - : Elsevier. - 2452-2627. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Thiol-ene radical addition (TERA) is a powerful reaction for the chemical functionalization of the reactive alkenes of GO with thiols. To trigger TERA, a photoinitiator (PI) is added to ensure high yields associated with fast conversion rates. However, the inappropriate use of PIs might affect the GO functionalization leading to photoreduction as well as low conversion rates. Herein, we explored the GO functionalization with cysteamine (CA) by TERA and its reduction influenced by Irgacure® 369, a commercial PI. We focused to analyze the reaction conditions that promote an orthogonal GO functionalization finding the limits where the photoreduction began. UV-spectroscopy, Raman spectroscopy, fluorescence labeling and XPS were used to characterize the functionalized GO. The data indicate three possible scenarios depending on the PI/CA molar ratio: i) orthogonal GO functionalization by TERA, ii) side reactions between GO and the radicals formed upon the PI photocleavage, and iii) soft photoreduction of the GO with alcohols and carboxylic acids as the functional groups mainly affected. However, we found that the GO functionalization by TERA was still occurring, but in less favorable conditions despite the side reactions and by-products. Therefore, photo-initiated TERA was confirmed as a powerful reaction to functionalize the reactive alkenes of GO, and by tuning the PI/CA molar ratio an orthogonal GO functionalization can be achieved, limiting side reactions and particularly GO reduction.
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| 7. |
- Piñeiro-García, Alexis, et al.
(författare)
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Photochemical Functionalization of Graphene Oxide by Thiol–Ene Click Chemistry
- 2020
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 59:29, s. 13033-13041
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Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) is an important platform that can be functionalized, notably because of its wide variety of functional groups. Functionalization is a critical step, leading to the production of GO-based materials for promising applications in many fields ranging from biomedicine, depollution, to energy storage. Defects introduced into the graphitic domain during graphite oxidation allow to obtain alkene groups, which can be functionalized via thiol–ene click reactions (TER). Usually, for GO functionalization by TER, thermal radical initiators have been used with disadvantages such as high reaction times and the subsequent GO reduction, losing possible oxygen functional groups that can be further used for a second functionalization. Hence, we introduce the photochemical functionalization of GO by TER, with cysteamine as the probe molecule, using a photoinitiator. The reaction was characterized by attenuated total reflection–Fourier transform infrared spectroscopy, UV spectroscopy, fluorimetry, X-ray photoelectron spectroscopy, and Raman spectroscopy. This new perspective of photoinduced TER provides advantages such as short reaction times, use of mild conditions, and avoiding a subsequent GO reduction, associated with efficient orthogonal functionalization.
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| 8. |
- Piñeiro-García, Alexis, et al.
(författare)
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The "how" and "where" behind the functionalization of graphene oxide by thiol-ene "click" chemistry
- 2023
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Ingår i: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 29:50
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Forskningsöversikt (refereegranskat)abstract
- Graphene oxide (GO) is a 2D nanomaterial with unique chemistry due to the combination of sp2 hybridization and oxygen functional groups (OFGs) even in single layer. OFGs play a fundamental role in the chemical functionalization of GO to produce GO-based materials for diverse applications. However, traditional strategies that employ epoxides, alcohols, and carboxylic acids suffer from low control and undesirable side reactions, including by-product formation and GO reduction. Thiol-ene “click” reaction offers a promising and versatile chemical approach for the alkene functionalization (−C=C−) of GO, providing orthogonality, stereoselectivity, regioselectivity, and high yields while reducing by-products. This review examines the chemical functionalization of GO via thiol-ene “click” reactions, providing insights into the underlying reaction mechanisms, including the role of radical or base catalysts in triggering the reaction. We discuss the “how” and “where” the reaction takes place on GO, the strategies to avoid unwanted side reactions, such as GO reduction and by-product formation. We anticipate that multi-functionalization of GO via the alkene groups will enhance GO physicochemical properties while preserving its intrinsic chemistry.
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| 9. |
- Piñeiro-García, Alexis, et al.
(författare)
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Tuning the nucleophilic attack and the reductive action of glycine on graphene oxide under basic medium
- 2021
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Ingår i: Materials Today Chemistry. - : Elsevier. - 2468-5194. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- Amino acids are important compounds for GO functionalization because they can improve GO properties for many applications ranging from biomedicine to depollution. However, amino acids can act as nucleophiles or as reducing agents for GO functionalization or reduction, respectively. Hence, we systematically studied the GO functionalization/reduction using glycine as a model amino acid under basic conditions at room temperature. Attenuated total reflectance–Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy, and Raman spectroscopy were used to characterize the modified GO with glycine. We found that low glycine concentrations produced an epoxide ring opening reaction, whereas an increase in glycine concentration led to GO reduction. The basic medium allowed to conserve the carboxylic acid groups, whereas the GO reduction mechanism was governed by the partial hydrolysis of epoxide groups and the subsequent reduction of carboxylic acids to carbonyls. This article opens up the opportunity to study and control the conditions in which different amino acids could be used for either GO functionalization or GO reduction.
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| 10. |
- Rafei, Mouna, et al.
(författare)
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Hydrogen evolution mediated by sulfur vacancies and substitutional Mn in few-layered molybdenum disulfide
- 2024
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Ingår i: Materials Today Energy. - : Elsevier. - 2468-6069. ; 41
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Tidskriftsartikel (refereegranskat)abstract
- MoS2 is widely praised as a promising replacement for Pt as an electrocatalyst for the hydrogen evolution reaction (HER), but even today, it still suffers from low performance. This issue is tackled by using Mn3+ as a surface modifier to trigger sulfur vacancy formation and enhance electron transport in few-layered 2H MoS2. Only 10% of Mn is sufficient to transform the semiconductive MoS2 into an active HER electrocatalyst. The insertion of Mn reduces both HER onset potential and Tafel slope which allows reaching 100 mA/cm2 at an overpotential of 206 mV, ten times larger of what undoped MoS2 can achieve. The enhanced activity arises because Mn3+ introduces electronic states near the conduction band, promotes sulfur vacancies, and increases the hydrogen adsorption. In addition to its facile production and extended shelf-life, Mn–MoS2 exhibits an efficiency of 73% at 800 mA/cm2 and 2.0 V when used in proton exchange membrane water electrolyzers.
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