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18 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I20-Scanning-X-ray spectroscopy (XAS/XES)	Same FeN4 active site, different activity: how redox peaks control oxygen reduction on Fe macrocycles Silvia Favero , Ruixuan Chen , Joyce Cheung , Luke Higgins , Hui Luo , Mengnan Wang , Jesus Barrio , Maria Magdalena Titirici , Alexander Bagger , Ifan E. L. Stephens Acs Electrochemistry DOI: 10.1021/acselectrochem.4c00146 Diamond Proposal Number(s): [29842] Open Access Show Abstract ▼ Abstract: Macrocycles show high activity for the electrochemical reduction of oxygen in alkaline media. However, even macrocycles with the same metal centers and MN4 active site can vary significantly in activity and selectivity, and to this date, a quantitative insight into the cause of these staggering differences has not been unambiguously reached. These macrocycles form a fundamental platform, similarly to platinum alloys for metal ORR catalyst, to unravel fundamental properties of FeNx catalysts. In this manuscript, we present a systematic study of several macrocycles, with varying active site motif and ligands, using electrochemical techniques, operando spectroscopy, and density functional theory (DFT) simulations. Our study demonstrates the existence of two families of Fe macrocycles for oxygen reduction in alkaline electrolytes: (i) weak OH binding macrocycles with one peak in the voltammogram and high peroxide selectivity and (ii) macrocycles with close to optimal OH binding, which exhibit two voltametric peaks and almost no peroxide production. Here, we also propose three mechanisms that would explain our experimental findings. Understanding what differentiates these two families could shed light on how to optimize the activity of pyrolyzed FeNx catalysts.	Jan 2025
B18-Core EXAFS	Resolving optimal ionomer interaction in fuel cell electrodes via operando X-ray absorption spectroscopy Mengnan Wang , Jiaguang Zhang , Silvia Favero , Luke J. R. Higgins , Hui Luo , Ifan E. L. Stephens , Maria-Magdalena Titirici Nature Communications 15 DOI: 10.1038/s41467-024-53823-z Diamond Proposal Number(s): [29913] Open Access Show Abstract ▼ Abstract: To bridge the gap between oxygen reduction electrocatalysts development and their implementation in real proton exchange membrane fuel cell electrodes, an important aspect to be understood is the interaction between the carbon support, the active sites, and the proton conductive ionomer as it greatly affects the local transportations to the catalyst surface. Here we show that three Pt/C catalysts, synthesized using the polyol method with different carbon supports (low surface area Vulcan, high surface area Ketjenblack, and biomass-derived highly ordered mesoporous carbon), revealed significant variations in ionomer-catalyst interactions. The Pt/C catalysts supported on ordered mesoporous carbon derived from biomass showed the best performance under the gas diffusion electrode configuration. Through a unique approach of operando X-ray Absorption Spectroscopy combined with gas sorption analysis, we were able to demonstrate the beneficial effect of mesopore presence for optimal ionomer-catalyst interaction at both molecular and structural level.	Oct 2024
I20-EDE-Energy Dispersive EXAFS (EDE)	Deconvoluting kinetics and transport effects of ionic liquid layers on FeN4-based oxygen reduction catalysts Silvia Favero , Ifan E. L. Stephens , Maria-Magdalena Titirici Ees Catalysis DOI: 10.1039/D3EY00166K Open Access Show Abstract ▼ Abstract: The use of ionic liquid layers has been reported to improve both the activity and durability of several oxygen reduction catalysts. However, the development of this technology has been hindered by the lack of understanding of the mechanism behind this performance enhancement. In this work, we use a library of ionic liquids to modify a model FeN4 catalyst (iron phthalocyanine), to decouple the effects of ionic liquid layers on oxygen reduction kinetics and oxygen transport. Our results show that oxygen reduction activity at low overpotentials it determined by the ionic liquids’ influence on the *OH binding energy on the active sites, while oxygen solubility and diffusivity controls transport at high overpotentials. Finally, using nitrogen physisorption, we have demonstrated that the distribution of the ionic liquids on the catalyst is inhomogeneous, and depends on the nature of the ionic liquid used.	Jul 2023
I20-Scanning-X-ray spectroscopy (XAS/XES)	Atomically dispersed Fe in a C2N-derived matrix for the reduction of CO2 to CO Saurav C. Sarma , Jesus Barrio , Mengjun Gong , Angus Pedersen , Anthony Kucernak , Magda Titirici , Ifan E. I. Stephens Electrochimica Acta 11 DOI: 10.1016/j.electacta.2023.142855 Open Access Show Abstract ▼ Abstract: Carbon-supported single metal atoms coordinated to nitrogen have recently emerged as efficient electrocatalysts for the electrochemical CO2 reduction reaction (CO2RR) to CO; although the presence of aggregated metallic species can decrease Faradaic efficiency, catalyst utilization and promote the hydrogen evolution reaction. In this work, we employ our recent synthetic protocol for producing single and dual Fe atoms in a high surface area C2N-derived nitrogen-doped carbon and test the catalysts for CO2 reduction. The higher resolution of the X-ray absorption spectroscopy that we employed herein, relative to our previous report, allowed us to more accurately pinpoint the dominant site as pentacoordinated Fe single atoms. The material displays high active site utilization of 25.1 ± 1.2% (based on in situ nitrite stripping experiments). Additionally, a Faradaic efficiency of 98% for the CO2RR to CO was obtained, with a turnover frequency of 2.5 e− site−1 s−1, at -0.56 V vs a reversible hydrogen electrode (RHE); on par with state-of-the-art Au catalysts.	Jul 2023
I20-EDE-Energy Dispersive EXAFS (EDE)	Structural transformation of metal–organic frameworks and identification of electrocatalytically active species during the oxygen evolution reaction under neutral condition Xiaoqiang Liang , Sen Wang , Jingyu Feng , Zhen Xu , Zhenyu Guo , Hui Luo , Feng Zhang , Wen Chen , Lei Feng , Chengan Wan , Maria-Magdalena Titirici Inorganic Chemistry Frontiers DOI: 10.1039/D2QI02436E Diamond Proposal Number(s): [28663] Show Abstract ▼ Abstract: Electrocatalytic oxygen evolution reaction (OER) under neutral or near-neutral conditions has attracted research interest due to its environmental friendliness and economic sustainability in comparison with currently available acidic and alkaline conditions. However, it is challenging to identify electrocatalytically active species in the OER procedure under neutral environments due to non-crystalline forms of catalysts. Crystalline metal-organic framework (MOF) materials could provide novel insights into electrocatalytical active species because of their well-defined structures. In this study, we synthesized two isostructural two-dimensional (2D) MOFs [Co(HCi)2(H2O)2·2DMF]n (Co-Ci-2D) and [Ni(HCi)2(H2O)2·2DMF]n (Ni-Ci-2D) (H2Ci = 1H-indazole-5-carboxylic acid, DMF = N, N-Dimethyl-formamide) to investigate their OER performance in a neutral environment. Our results indicate that Co-Ci-2D holds a current density of 3.93 mA cm-2 at 1.8 V vs. RHE and a OER durability superior to the benchmark catalyst IrO2. Utilizing the advantages of structural transformation of MOF materials which are easier to characterize and analyze compared to ill-defined amorphous materials, we found out that a mononuclear coordination compound [Co(HCi)2(H2O)4] (Co-Ci-mono-A) and its isomer (Co-Ci-mono-B) were proven to be active species of Co-Ci-2D in the neutral OER process. For Ni-Ci-2D, mononuclear coordination compounds similar to structures of the cobalt material (Ni-Ci-mono-A and Ni-Ci-mono-B) together with NiHPO4 formed by the precipitation were confirmed as active species for the neutral OER catalysis. Additionally, the difference in OER activities between Co-Ci-2D and Ni-Ci-2D, approximately one order of magnitude, originates primarily from the opposite tendency of bond length changes in coordination octahedron after being treated by the PBS solution. These findings contribute to a better comprehension of the OER procedure in the neutral media.	Apr 2023
E02-JEM ARM 300CF	Single-atom iridium on hematite photoanodes for solar water splitting: catalyst or spectator? Qian Guo , Qi Zhao , Rachel Crespo-Otero , Devis Di Tommaso , Junwang Tang , Stoichko D. Dimitrov , Maria-Magdalena Titirici , Xuanhua Li , Ana Belén Jorge Sobrido Journal Of The American Chemical Society DOI: 10.1021/jacs.2c09974 Diamond Proposal Number(s): [25787, 27541, 29157] Open Access Show Abstract ▼ Abstract: Single-atom catalysts (SACs) on hematite photoanodes are efficient cocatalysts to boost photoelectrochemical performance. They feature high atom utilization, remarkable activity, and distinct active sites. However, the specific role of SACs on hematite photoanodes is not fully understood yet: Do SACs behave as a catalytic site or as a spectator? By combining spectroscopic experiments and computer simulations, we demonstrate that single-atom iridium (sIr) catalysts on hematite (α-Fe2O3/sIr) photoanodes act as a true catalyst by trapping holes from hematite and providing active sites for the water oxidation reaction. In situ transient absorption spectroscopy showed a reduced number of holes and shortened hole lifetime in the presence of sIr. This was particularly evident on the second timescale, indicative of fast hole transfer and depletion toward water oxidation. Intensity-modulated photocurrent spectroscopy evidenced a faster hole transfer at the α-Fe2O3/sIr/electrolyte interface compared to that at bare α-Fe2O3. Density functional theory calculations revealed the mechanism for water oxidation using sIr as a catalytic center to be the preferred pathway as it displayed a lower onset potential than the Fe sites. X-ray photoelectron spectroscopy demonstrated that sIr introduced a mid-gap of 4d state, key to the fast hole transfer and hole depletion. These combined results provide new insights into the processes controlling solar water oxidation and the role of SACs in enhancing the catalytic performance of semiconductors in photo-assisted reactions.	Jan 2023
E01-JEM ARM 200CF I20-EDE-Energy Dispersive EXAFS (EDE)	Role of Ni in PtNi bimetallic electrocatalysts for hydrogen and value-added chemicals coproduction via glycerol electrooxidation Hui Luo , Victor Y. Yukuhiro , Pablo S. Fernández , Jingyu Feng , Paul Thompson , Reshma R. Rao , Rongsheng Cai , Silvia Favero , Sarah J. Haigh , James R. Durrant , Ifan E. L. Stephens , Maria-Magdalena Titirici Acs Catalysis 5, 14492 - 14506 DOI: 10.1021/acscatal.2c03907 Diamond Proposal Number(s): [28663, 25476] Open Access Show Abstract ▼ Abstract: Pt-based bimetallic electrocatalysts are promising candidates to convert surplus glycerol from the biodiesel industry to value-added chemicals and coproduce hydrogen. It is expected that the nature and content of the elements in the bimetallic catalyst can not only affect the reaction kinetics but also influence the product selectivity, providing a way to increase the yield of the desired products. Hence, in this work, we investigate the electrochemical oxidation of glycerol on a series of PtNi nanoparticles with increasing Ni content using a combination of physicochemical structural analysis, electrochemical measurements, operando spectroscopic techniques, and advanced product characterizations. With a moderate Ni content and a homogenously alloyed bimetallic Pt–Ni structure, the PtNi2 catalyst displayed the highest reaction activity among all materials studied in this work. In situ FTIR data show that PtNi2 can activate the glycerol molecule at a more negative potential (0.4 VRHE) than the other PtNi catalysts. In addition, its surface can effectively catalyze the complete C–C bond cleavage, resulting in lower CO poisoning and higher stability. Operando X-ray absorption spectroscopy and UV–vis spectroscopy suggest that glycerol adsorbs strongly onto surface Ni(OH)x sites, preventing their oxidation and activation of oxygen or hydroxyl from water. As such, we propose that the role of Ni in PtNi toward glycerol oxidation is to tailor the electronic structure of the pure Pt sites rather than a bifunctional mechanism. Our experiments provide guidance for the development of bimetallic catalysts toward highly efficient, selective, and stable glycerol oxidation reactions.	Nov 2022
E01-JEM ARM 200CF I20-EDE-Energy Dispersive EXAFS (EDE)	From haemoglobin to single-site hydrogenation catalyst Alain Y. Li , Angus Pedersen , Jingyu Feng , Hui Luo , Jesus Barrio , Julien Roman , King Kuok (mimi) Hii , Maria-Magdalena Titirici Green Chemistry 313 DOI: 10.1039/D2GC02344J Diamond Proposal Number(s): [28663, 28698] Open Access Show Abstract ▼ Abstract: Iron-based single-site catalysts hold immense potential for achieving highly selective chemical processes, with the added advantage of iron being an earth-abundant metal. They are widely explored in electrocatalysis for oxygen reduction and display promising catalytic activity for organic transformations. In particular, FeNx@C catalysts are active for the reduction of nitroarene into aromatic amines. Yet, they are difficult to mass-produce, and most preparation methods fail to avoid single site aggregation. Here we prepared FeNx@C catalysts from bio-derived compounds, xylose and haemoglobin, in a simple two-step process. Since haemoglobin naturally contains FeNx single-sites, we successfully repurposed them into hydrogenation catalytic centers and avoided their aggregation during the preparation of the material. Their single-site nature was demonstrated by aberration-corrected transmission electron microscopy and X-ray absorption techniques. They were shown to be active for transfer hydrogenation of nitroarenes into anilines, with excellent substrate selectivity and recyclability, as demonstrated by the preserved yield across seven catalytic cycles. We also showed that FeNx@C could be used to prepare 2-phenylbenzimidazole through a reduction/condensation tandem. Our work shows for the first time the viability of biomass precursors to prepare Fe single-site hydrogenation catalysts.	Sep 2022
I22-Small angle scattering & Diffraction	Disinfector-assisted low temperature reduced graphene oxide-protein surgical dressing for the postoperative photothermal treatment of melanoma Yuanhao Wu , Junyao Yang , Alexander Van Teijlingen , Alice Berardo , Ilaria Corridori , Jingyu Feng , Jing Xu , Maria-Magdalena Titirici , Jose Carlos Rodriguez-Cabello , Nicola M. Pugno , Jiaming Sun , Wen Wang , Tell Tuttle , Alvaro Mata Advanced Functional Materials 52 DOI: 10.1002/adfm.202205802 Diamond Proposal Number(s): [28002] Open Access Show Abstract ▼ Abstract: Materials that combine the functionalities of both of proteins and graphene are of great interest for the engineering of biosensing, drug delivery, and regenerative devices. Graphene oxide (GO) offers an opportunity to design GO-protein interactions but the need for harsh reduction processes to enable GO photoexcitation remains a limitation. A disinfector-assisted low temperature method to reduce GO-protein materials and fabricate surgical dressings with tuneable photothermal efficiency and bioactive properties for the postoperative treatment of melanoma is reported. The approach harnesses the capacity of 70% ethanol to penetrate the protein shell of microorganisms to infiltrate GO-protein complexes and reduce GO at low temperature (85 °C) while maintaining the material structure and bioactivity. Both experiments and coarse-grained simulations are used to describe the reduction process and assess the material properties. In vitro and in vivo validation revealed the capacity of the dressings to prevent tumor recurrence and promote healing after tumor resection.	Jul 2022
E01-JEM ARM 200CF I20-EDE-Energy Dispersive EXAFS (EDE)	Metal coordination in C2N-like materials towards dual atom catalysts for oxygen reduction Jesus Barrio , Angus Pedersen , Jingyu Feng , Saurav Ch. Sarma , Mengnan Wang , Alain Y. Li , Hossein Yadegari , Hui Luo , Mary P. Ryan , Maria-Magdalena Titirici , Ifan E. L. Stephens Journal Of Materials Chemistry A 120 DOI: 10.1039/D1TA09560A Diamond Proposal Number(s): [28663, 28698] Open Access Show Abstract ▼ Abstract: Single-atom catalysts, in particular the Fe–N–C family of materials, have emerged as a promising alternative to platinum group metals in fuel cells as catalysts for the oxygen reduction reaction. Numerous theoretical studies have suggested that dual atom catalysts can appreciably accelerate catalytic reactions; nevertheless, the synthesis of these materials is highly challenging owing to metal atom clustering and aggregation into nanoparticles during high temperature synthesis treatment. In this work, dual metal atom catalysts are prepared by controlled post synthetic metal-coordination in a C2N-like material. The configuration of the active sites was confirmed by means of X-ray adsorption spectroscopy and scanning transmission electron microscopy. During oxygen reduction, the catalyst exhibited an activity of 2.4 ± 0.3 A gcarbon−1 at 0.8 V versus a reversible hydrogen electrode in acidic media, comparable to the most active in the literature. This work provides a novel approach for the targeted synthesis of catalysts containing dual metal sites in electrocatalysis.	Feb 2022

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