B07-B-Versatile Soft X-ray beamline: High Throughput
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Álvaro
Tolosana-Moranchel
,
Alvaro
Garcia
,
Álvaro
García-Corral
,
José F.
Marco
,
Laura
Pascual
,
Dalia
Liuzzi
,
Mohamed A.
Salam
,
Pilar
Ferrer
,
Jorge
Torrero
,
David C.
Grinter
,
Georg
Held
,
Daniel
García Sánchez
,
K. Andreas
Friedrich
,
Maria
Retuerto
,
Sergio
Rojas
Diamond Proposal Number(s):
[30338]
Open Access
Abstract: The overall performance of proton exchange membrane fuel cells is limited by the sluggish kinetics of the oxygen-reduction reaction (ORR). Among the most active PGM-free ORR electrocatalysts are metal-nitrogen-carbon (M-N-C), such as Fe–N–C. The Fe–N4 ensembles in these PGM-free catalysts, present in different configurations, are proposed to be the active sites for the ORR in acid. In this work, we have synthesized a Fe/N/C catalyst via thermal treatment of a polymeric CxNy precursor obtained by the wet-polymerization of melamine (a nitrogen rich molecule) and terephthaldehyde. The materials obtained (Im-FeNC-1HT and Im-FeNC-2HT) display high ORR activity in acid electrolyte compared to other Fe–N–C catalysts prepared with precursors different than 2-methylimidazole or ZIF-8. Characterization data indicate the formation of high- and low-spin Fe-Nx ensembles, with a site density of 4.4·1019 sitesFe·g−1 estimated by electrochemical stripping of NO. The ORR activity was evaluated in a RRDE configuration in 0.1 M HClO4 and in MEA configuration in a single cell.
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Sep 2023
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B07-B-Versatile Soft X-ray beamline: High Throughput
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Dmitry
Galyamin
,
Jorge
Torrero
,
Joshua D.
Elliott
,
Isabel
Rodríguez-García
,
Daniel
García Sánchez
,
Mohamed Abdel
Salam
,
Aldo Saul
Gago
,
Mohamed
Mokhtar
,
José Luis
Gómez De La Fuente
,
Samba Violeta
Bueno
,
Diego
Gianolio
,
Pilar
Ferrer
,
David C.
Grinter
,
Georg
Held
,
Maria
Retuerto
,
Sergio
Rojas
Diamond Proposal Number(s):
[28150]
Open Access
Abstract: The demand of green hydrogen, that is, the hydrogen produced from water electrolysis, is expected to increase dramatically in the coming years. State-of-the-art proton exchange membrane water electrolysis (PEMWE) uses high loadings of platinum group metals, such as Pt in the electrode where hydrogen is produced. Alternative electrodes based on phosphides, sulfides, nitrides, and other low-cost alternatives are under investigation. Herein, a simple process for the preparation of RuP electrodes with high activity for the hydrogen evolution reaction (HER) in acidic electrolyte is described. A straightforward one-pot synthesis that yields RuP nanoparticles with fine-tuned composition and stoichiometry is presented, as determined by multiple characterization techniques, including lab- and synchrotron-based experiments and theoretical modeling. The RuP nanoparticles exhibit a high activity of 10 mA cm−2 at 36 mV overpotential and a Tafel slope of 30 mV dec−1, which is comparable to Pt/C. Moreover, a RuP catalyst-coated membrane (CCM) with a low Ru loading of 0.6 mgRu cm−2 is produced and tested in a PEMWE cell configuration, yielding 1.7 A cm−2 at 2 V.
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Jun 2023
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B18-Core EXAFS
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Dmitry
Galyamin
,
Jorge
Torrero
,
Isabel
Rodríguez
,
Manuel J.
Kolb
,
Pilar
Ferrer
,
Laura
Pascual
,
Mohamed Abdel
Salam
,
Diego
Gianolio
,
Veronica
Celorrio
,
Mohamed
Mokhtar
,
Daniel
Garcia Sanchez
,
Aldo Saul
Gago
,
Kaspar Andreas
Friedrich
,
Miguel A.
Peña
,
José Antonio
Alonso
,
Federico
Calle-Vallejo
,
Maria
Retuerto
,
Sergio
Rojas
Open Access
Abstract: The production of green hydrogen in water electrolyzers is limited by the oxygen evolution reaction (OER). State-of-the-art electrocatalysts are based on Ir. Ru electrocatalysts are a suitable alternative provided their performance is improved. Here we show that low-Ru-content pyrochlores (R2MnRuO7, R = Y, Tb and Dy) display high activity and durability for the OER in acidic media. Y2MnRuO7 is the most stable catalyst, displaying 1.5 V at 10 mA cm−2 for 40 h, or 5000 cycles up to 1.7 V. Computational and experimental results show that the high performance is owed to Ru sites embedded in RuMnOx surface layers. A water electrolyser with Y2MnRuO7 (with only 0.2 mgRu cm−2) reaches 1 A cm−2 at 1.75 V, remaining stable at 200 mA cm−2 for more than 24 h. These results encourage further investigation on Ru catalysts in which a partial replacement of Ru by inexpensive cations can enhance the OER performance.
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Apr 2023
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B18-Core EXAFS
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Maria
Retuerto
,
Laura
Pascual
,
Jorge
Torrero
,
Mohamed Abdel
Salam
,
Alvaro
Tolosana-Moranchel
,
Diego
Gianolio
,
Pilar
Ferrer
,
Paula
Kayser
,
Vincent
Wilke
,
Svenja
Stiber
,
Veronica
Celorrio
,
Mohamed
Mokthar
,
Daniel García
Sanchez
,
Aldo Saul
Gago
,
Kaspar Andreas
Friedrich
,
Miguel Antonio
Peña
,
José Antonio
Alonso
,
Sergio
Rojas
Diamond Proposal Number(s):
[27733]
Open Access
Abstract: Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr2CaIrO6 achieves 10 mA cm−2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO6 octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr2CaIrO6 as anode and low Ir loading (0.4 mgIr cm−2). The cell achieves 2.40 V at 6 A cm−2 (overload) and no loss in performance at a constant 2 A cm−2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.
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Dec 2022
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B07-B-Versatile Soft X-ray beamline: High Throughput
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Isabel
Rodríguez-García
,
Dmitry
Galyamin
,
Laura
Pascual
,
Pilar
Ferrer
,
Miguel A.
Peña
,
David
Grinter
,
Georg
Held
,
Mohamed
Abdel Salam
,
Mohamed
Mokhtar
,
Katabathini
Narasimharao
,
Maria
Retuerto
,
Sergio
Rojas
Diamond Proposal Number(s):
[28150]
Open Access
Abstract: Ru mixed oxides are the most active catalysts for the oxygen evolution reaction (OER) in acid electrolyte. However, their stability is seriously compromised during the reaction. In this work we show that it is possible to enhance both OER activity and durability of SrRuO3 mixed oxide by the partial doping with K+ in Sr2+ sites. Sr1-xKxRuO3 perovskites (x = 0.00, 0.05, 0.10 and 0.20) have been synthesized by wet chemistry. The partial doping with K+ cations led to oxides with Ru atoms in a higher oxidation state. In addition, K-doping resulted in perovskites with slightly higher symmetry. The performance of the K-doped perovskites for the OER was assessed in acid electrolyte. Clearly, the K-doped materials, especially Sr0.80K0.20RuO3, display higher activity (lower E10) and significantly higher durability than the undoped sample SrRuO3. The results indicate that chemical modifications on Ru perovskites can be a suitable strategy to improve the stability of Ru phases during the OER.
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Feb 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[24881]
Open Access
Abstract: A nitrogen-containing covalent organic framework obtained from the polymerization of 1,3-dicyanobenzene has been used as a starting material for the synthesis of Fe/N/C catalysts for the oxygen reduction reaction (ORR). In this work we report the effect of the thermal treatments on the nature and catalytic properties of the catalysts obtained after the thermal treatments. After the first thermal treatment, the catalysts obtained contain metallic iron and iron carbide particles, along with a minority fraction of inorganic FeNx sites. After acid leaching and a second thermal treatment, FeNx sites remain in the catalysts, along with a minor fraction of graphite-wrapped Fe3C particles. Both catalysts display high activity for the ORR, with the catalyst subjected to acid leaching and a second thermal treatment, 2HT-1,3DCB, displaying higher ORR activity and a lower production of H2O2. This observation suggests that iron particles, such as Fe3C, display ORR activity but mainly toward the two-electron pathway. On the contrary, FeNx ensembles promote the ORR via the four-electron pathway, that is, via H2O formation.
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Nov 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
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Diamond Proposal Number(s):
[26554]
Open Access
Abstract: The nature and evolution of FeNxCy moieties in Fe/C/N catalysts has been studied by analysing Fe and N environments. TEM and Fe-XAS reveal the presence of FeNx moieties and Fe3C particles in the fresh catalyst. NEXAFS reveals the presence of two groups of (Fe)NxCy ensembles, namely (Fe)Nx-pyridinic and (Fe)Nx-pyrrolic. The architecture of the FeNxCy ensembles and their evolution during the ORR has been analysed by XAS, NEXAFS, and identical locations TEM. NxCy, FeNxCy and Fe3C species are partially removed during the ORR, resulting in the formation of Fe2O3 and Fe3O4 particles with different morphologies. The process is more severe in acid electrolyte than in alkaline one. (Fe)Nx-pyrrolic moieties are the main ones in the fresh catalysts, but (Fe)Nx-pyridinic groups are more stable after the ORR. The correlation between the evolution of the ORR activity and that of the FeNxCy ensembles indicates that FeNx-pyridinic ensembles are responsible for the ORR activity.
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Apr 2021
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Álvaro
García
,
María
Retuerto
,
Carlota
Dominguez
,
Laura
Pascual
,
Pilar
Ferrer
,
Diego
Gianolio
,
Aida
Serrano
,
Pia
Assmann
,
Daniel G.
Sanchez
,
Miguel A.
Peña
,
Sergio
Rojas
Open Access
Abstract: In this work, we report the synthesis of Fe/N/C electrocatalysts using triazine based porous organic polymers as precursors. Iron-doped triazine porous organic polymers were obtained by in situ polymerization of iron precursor and 1,2- or 1,4- dicyanobenzene (DCB). In order to obtain the actual catalyst, the polymer obtained was subjected to thermal treatment under NH3. The catalysts obtained exhibit activity and durability for the oxygen reduction reaction in acid electrolyte. Thorough characterization of the catalysts reveal the formation of several types of iron species, including metallic iron, iron carbides and Fe-Nx moieties. The latter species is the main responsible for the high activity measured for the oxygen reduction reaction in acid electrolyte. 1,2-DCB results in more active catalysts than 1,4-DCB due to the higher fraction of FeNx ensembles in the former, probably because vicinal positions of N-bearing groups are more prone to coordinate Fe atoms.
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Dec 2019
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B18-Core EXAFS
I10-Beamline for Advanced Dichroism - scattering
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María
Retuerto
,
Laura
Pascual
,
Federico
Calle-Vallejo
,
Pilar
Ferrer
,
Diego
Gianolio
,
Amaru González
Pereira
,
Álvaro
García
,
Jorge
Torrero
,
María Teresa
Fernández-Díaz
,
Peter
Bencok
,
Miguel A.
Peña
,
José Luis G.
Fierro
,
Sergio
Rojas
Open Access
Abstract: The design of active and durable catalysts for the H2O/O2 interconversion is one of the major challenges of electrocatalysis for renewable energy. The oxygen evolution reaction (OER) is catalyzed by SrRuO3 with low potentials (ca. 1.35 VRHE), but the catalyst’s durability is insufficient. Here we show that Na doping enhances both activity and durability in acid media. DFT reveals that whereas SrRuO3 binds reaction intermediates too strongly, Na doping of ~0.125 leads to nearly optimal OER activity. Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO6 octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites.
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May 2019
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B18-Core EXAFS
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María
Retuerto
,
Federico
Calle-Vallejo
,
Laura
Pascual
,
Pilar
Ferrer
,
Álvaro
García
,
Jorge
Torrero
,
Diego
Gianolio
,
José Luis G.
Fierro
,
Miguel A.
Peña
,
José Antonio
Alonso
,
Sergio
Rojas
Diamond Proposal Number(s):
[18119]
Abstract: The activity of oxides towards the oxygen evolution reaction (OER) is usually tuned by changing the transition metal components and/or the surface facets. An important yet less studied feature is the repercussion of the lattice oxygen content of the oxide in the active site's coordination and catalytic performance. This is illustrated here for the Ba-Ni-O system. We synthesized two oxides with Ni in different coordination and oxidation states, namely BaNiO2 with Ni2+ in square-planar positions, and BaNiO2.78(2) with Ni3+ and Ni4+ in octahedral positions. We show that the square-planar configuration of Ni endows BaNiO2 with high intrinsic OER activity, comparable to the best catalysts in the literature. DFT indicates that progressively lowering the lattice oxygen content from BaNiO3 to BaNiO2 increases the Ni sites' affinity for the reaction intermediates, thereby lowering the OER overpotential. Thus, oxygen content is an important parameter in oxide catalysts, as it modulates the coordination, orbital splitting, oxidation number, and catalytic activity of the active sites.
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Nov 2018
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