B18-Core EXAFS
|
Diego
Gianolio
,
Michael D.
Higham
,
Matthew G.
Quesne
,
Matteo
Aramini
,
Ruoyu
Xu
,
Alex I.
Large
,
Georg
Held
,
Juan-Jesús
Velasco-Vélez
,
Michael
Haevecker
,
Axel
Knop-Gericke
,
Chiara
Genovese
,
Claudio
Ampelli
,
Manfred Erwin
Schuster
,
Siglinda
Perathoner
,
Gabriele
Centi
,
C. Richard A.
Catlow
,
Rosa
Arrigo
Diamond Proposal Number(s):
[24919]
Open Access
Abstract: Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu(I)–O species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the Fe–Cu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu(I)–O is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu(II) is observed. We show that the Cu–Zn system represents the optimal active ensembles with stabilized Cu(I)–O; DFT simulations rationalize this observation by indicating that Cu–Zn–O neighboring atoms are able to activate CO2, whereas Cu–Cu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies.
|
Apr 2023
|
|
B18-Core EXAFS
|
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.
|
Apr 2023
|
|
B18-Core EXAFS
|
Jonathan
Ruiz Esquius
,
David J.
Morgan
,
Gerardo
Algara Siller
,
Diego
Gianolio
,
Matteo
Aramini
,
Leopold
Lahn
,
Olga
Kasian
,
Simon A.
Kondrat
,
Robert
Schlögl
,
Graham J.
Hutchings
,
Rosa
Arrigo
,
Simon J.
Freakley
Diamond Proposal Number(s):
[15151]
Open Access
Abstract: The oxygen evolution reaction (OER) is crucial to future energy systems based on water electrolysis. Iridium oxides are promising catalysts due to their resistance to corrosion under acidic and oxidizing conditions. Highly active iridium (oxy)hydroxides prepared using alkali metal bases transform into low activity rutile IrO2 at elevated temperatures (>350 °C) during catalyst/electrode preparation. Depending on the residual amount of alkali metals, we now show that this transformation can result in either rutile IrO2 or nano-crystalline Li-intercalated IrOx. While the transition to rutile results in poor activity, the Li-intercalated IrOx has comparative activity and improved stability when compared to the highly active amorphous material despite being treated at 500 °C. This highly active nanocrystalline form of lithium iridate could be more resistant to industrial procedures to produce PEM membranes and provide a route to stabilize the high populations of redox active sites of amorphous iridium (oxy)hydroxides.
|
Mar 2023
|
|
B18-Core EXAFS
|
Yunpeng
Zuo
,
Nikolaos
Antonatos
,
Lukáš
Děkanovský
,
Jan
Luxa
,
Joshua D.
Elliott
,
Diego
Gianolio
,
Jiří
Šturala
,
Fabrizio
Guzzetta
,
Stefanos
Mourdikoudis
,
Jakub
Regner
,
Roman
Málek
,
Zdenek
Sofer
Diamond Proposal Number(s):
[31795]
Abstract: As a fascinating innovative class of effective catalysts
for hydrogen evolution reaction (HER), transition-metal tellurides
have emerged as attractive materials, but they are still suffering
from their intrinsic activity for practical applications. Defect
engineering constitutes a promising strategy to optimize the
electronic configuration of the catalyst and further improve the
HER activity. Herein, we present the successful fabrication of
PdTe2-based catalysts with three different types of vacancies (dPdTex), including single Pd, Te defect site, and double Te defect
sites, by using a two-step method. The obtained d-PdTex
demonstrated a remarkable HER activity with an overpotential of
76 mV at 10 mA cm−2 without iR compensation, which is far lower
than that of bulk PdTe2 (259 mV). The procedure followed in this
work may be extended to generate defect sites in a range of
different two-dimensional materials, thus further expanding their potential application fields.
|
Feb 2023
|
|
B18-Core EXAFS
|
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.
|
Dec 2022
|
|
B18-Core EXAFS
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[24930, 22629]
Open Access
Abstract: The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel’s original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel’s derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling.
|
Sep 2022
|
|
B18-Core EXAFS
|
Mohamed M. M.
Kashbor
,
Dedi
Sutarma
,
James
Railton
,
Naoko
Sano
,
Peter J.
Cumpson
,
Diego
Gianolio
,
Giannantonio
Cibin
,
Luke
Forster
,
Carmine
D’agostino
,
Xi
Liu
,
Liwei
Chen
,
Volkan
Degirmenci
,
Marco
Conte
Diamond Proposal Number(s):
[24728]
Open Access
Abstract: In this study, we use zeolite Y as a support for the synthesis of Sn and Ga doped zeolites aimed at the isomerization of glucose to fructose. Though these materials are inactive in water, they are active in methanol and we could ascertain a reaction pathway involving a hydride shift for the interconversion of glucose to fructose and mannose, and a Brønsted acid pathway with the formation of a methyl fructoside intermediate and its hydrolysis to fructose if water was added afterwards. By using characterizations comprising: chemisorption, XPS, XRD, HAADF-STEM and EXAFS; it was possible to demonstrate that a straightforward impregnation protocol for the preparation of our catalysts, led to Sn/Y mainly consisting of small SnO2 clusters on the external surface of the zeolite, whereas Ga/Y consisting of highly dispersed Ga species mostly inside the zeolite pores; and a catalytic activity that appears to be dominated by Brønsted acid sites.
|
May 2022
|
|
B18-Core EXAFS
|
Peng
Tang
,
Hyeon Jeong
Lee
,
Kevin
Hurlbutt
,
Po-Yuan
Huang
,
Sudarshan
Narayanan
,
Chenbo
Wang
,
Diego
Gianolio
,
Rosa
Arrigo
,
Jun
Chen
,
Jamie H.
Warner
,
Mauro
Pasta
Diamond Proposal Number(s):
[26066]
Abstract: Platinum single-site catalysts (SSCs) are a promising technology for the production of hydrogen from clean energy sources. They have high activity and maximal platinum-atom utilization. However, the bonding environment of platinum during operation is poorly understood. In this work, we present a mechanistic study of platinum SSCs using operando, synchrotron-X-ray absorption spectroscopy. We synthesize an atomically dispersed platinum complex with aniline and chloride ligands onto graphene and characterize it with ex-situ electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectroscopy (XANES), and extended X-ray absorption fine structure spectroscopy (EXAFS). Then, by operando EXAFS and XANES, we show that as a negatively biased potential is applied, the Pt–N bonds break first followed by the Pt–Cl bonds. The platinum is reduced from platinum(II) to metallic platinum(0) by the onset of the hydrogen-evolution reaction at 0 V. Furthermore, we observe an increase in Pt–Pt bonding, indicating the formation of platinum agglomerates. Together, these results indicate that while aniline is used to prepare platinum SSCs, the single-site complexes are decomposed and platinum agglomerates at operating potentials. This work is an important contribution to the understanding of the evolution of bonding environment in SSCs and provides some molecular insights into how platinum agglomeration causes the deactivation of SSCs over time.
|
Feb 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[22152]
Abstract: Fe–N–C aerogel catalysts were prepared by sol–gel polycondensation of resorcinol, melamine and formaldehyde precursors in the presence of FeCl3 salt, followed by supercritical drying and thermal treatments. The effect of the mass ratio of precursors on the microstructure, iron speciation and oxygen reduction reaction (ORR) performance of the Fe–N–C aerogels was investigated by N2 sorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, CO chemisorption and rotating disk electrode in acidic medium. The best ORR performance (activity and mass transport) was obtained by an optimum balance between pore structure and active Fe-Nx species. Through acid washing, the durability of the catalyst was further improved by eliminating unstable and inactive species, particularly iron nanoparticles and iron carbide. From the CO chemisorption and turnover-frequency value, the surface sites were comparable with the highest values reported in literature. Finally, Fe–N–C aerogel catalyst was implemented a in membrane–electrode assembly with an active area of 25 cm2 and tested in single cell, emphasizing the importance of the ink formulation on the performance.
|
Dec 2021
|
|
B18-Core EXAFS
|
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.
|
Nov 2021
|
|
