B18-Core EXAFS
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Diamond Proposal Number(s):
[34632]
Open Access
Abstract: Understanding and tuning the local coordination environment of Fe−N4 macrocyclic catalysts are essential for advancing non-precious metal oxygen reduction reaction (ORR) electrocatalysis. Here, we present a comprehensive experimental and theoretical investigation of three structurally distinct Fe macrocycles, iron(tetraphenylporphyrin) chloride (FeTPP), iron(II) phthalocyanine (FePc), and iron aza-bridged bis-1,10-phenanthroline hexaaza-macrocycle (Fe(Phen2N2)), to unravel how bridging atom identity and coordination geometry impact ORR activity in alkaline media. These measurements identified FePc/CNT as the most active catalyst, followed closely by Fe(Phen2N2)/CNT, with FeTPP/CNT exhibiting the lowest performance. Density functional theory simulations further demonstrated that shorter Fe−N bonds and more electronegative bridging atoms correlate with weaker *OH adsorption and higher theoretical limiting potentials. Axial coordination can alter the adsorption energetics of ORR intermediates, thereby enhancing ORR activity. Together, these results highlight the critical influence on the ORR mechanism of macrocycle bridging atoms, coordination symmetry, and axial ligation, providing molecular-level insights to guide the rational design of Fe−N4 catalysts for alkaline fuel cell applications.
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May 2026
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
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Youli
Yu
,
Yifeng
Wang
,
Hanzhi
Ye
,
Sid
Halder
,
Guangmeimei
Yang
,
Boxi
Ye
,
Santosh
Kumar
,
Georg
Held
,
James R.
Durrant
,
Maria-Magdalena
Titirici
,
Reshma R.
Rao
Diamond Proposal Number(s):
[37550, 39622]
Open Access
Abstract: Glycerol oxidation reaction (GOR) is a promising valorization route to upgrade the biodiesel by-product while coproducing green hydrogen at the cathode in electrolyzers. However, the working mechanism of transition-metal-based catalysts such as Ni(OH)2 remains poorly understood. Here, we employed a multioperando spectroelectrochemical approach combining UV–vis optical spectroscopy, X-ray absorption spectroscopy, and time-resolved stepped-potential spectroscopy to investigate the active oxidizing species and charge-transfer dynamics under OER and GOR conditions. We identified NiOOH (Ni3+) as the active species for GOR, whereas the formation of higher-valent NiOO (Ni4+) species is completely suppressed in the presence of glycerol. The accumulation of surface-adsorbed glycerol molecules is the rate-determining step (τ ∼ 27.9 s at 1.47 VRHE), occurring slower than the intrinsic catalytic step of glycerol reaction (τ ∼ 3.2 s at 1.47 VRHE), which involves oxidation and bond cleavage. In contrast, the kinetics of the OER are significantly slower (τ ∼ 167 s at 1.47 VRHE), resulting in the dominance of GOR and suppression of oxygen evolution in the presence of glycerol. The potential-independent production of formic acid during GOR follows an apparent first-order dependence on NiOOH concentration, suggesting continuous C–C bond cleavage activated by reactive *O species. These findings link oxidizing species with charge-transfer dynamics, providing insight for the rational design of Ni-based catalysts for glycerol and other biomass-derived molecule oxidations.
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Apr 2026
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I15-1-X-ray Pair Distribution Function (XPDF)
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Zhenyu
Guo
,
Kang
Wang
,
Yuanzhu
Zhao
,
Gang
Cheng
,
Yichen
Huang
,
Connor
Wright
,
Zonghao
Shen
,
Hossein
Yadegari
,
Jinglin
Jiang
,
Kaitian
Zheng
,
Cecilia
Mattevi
,
Carla
Molteni
,
Peter D.
Haynes
,
Mary P.
Ryan
,
Maria-Magdalena
Titirici
,
Fei
Xie
Diamond Proposal Number(s):
[36797]
Open Access
Abstract: Potassium-ion batteries (KIBs) with graphite anodes are emerging as a highly promising “beyond lithium” technology driven by battery demands, potassium's abundant reserves and the inherent similarities in intercalation chemistry to lithium-ion systems. Despite this potential, a understanding of potassium intercalation into graphite, particularly concerning early intercalation stages and the in-plane ordering of K+ within graphite intercalation compounds (GICs), lacks sufficient elucidation. Herein, we employed a multi-modal, operando characterisation approach to elucidate the correlation of electrochemical potassiation and structural evolution in graphite, hence unravelling the specific mechanisms of K-ion storage. Operando electrochemical dilatometry precisely quantifies the macroscopic volume expansion of a graphite electrode during potassiation. Meanwhile, operando synchrotron X-ray diffraction (XRD) records ordered phase transitions during early-stage intercalation, detailing the formation of distinct GIC phases. Furthermore, Raman spectroscopy and density-functional theory (DFT) reveal the in-plane ordering of K+ within the graphite gallery and stacking modes. Operando optical microscope and UV-vis spectroscopy together provide insights into the changing optical properties, linking these changes to different GICs and electronic structural changes. This comprehensive study offers fundamental mechanistic insights into K-ion storage in graphite, paving the way for the rational design of high-performance KIB anodes.
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Nov 2025
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I13-2-Diamond Manchester Imaging
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Mengzheng
Ouyang
,
Zhenyu
Guo
,
Luis E.
Salinas-Farran
,
Siyu
Zhao
,
Mengnan
Wang
,
Feiran
Li
,
Yan
Zhao
,
Kaitian
Zheng
,
Hao
Zhang
,
Guangdong
Li
,
Xinhua
Liu
,
Shichun
Yang
,
Fei
Xie
,
Paul
Shearing
,
Maria-Magdalena
Titirici
,
Nigel
Brandon
Diamond Proposal Number(s):
[34782]
Open Access
Abstract: Sodium-ion batteries (SIBs) are cost-effective alternatives to lithium-ion batteries (LIBs), but their low energy density remains a challenge. Current electrode designs fail to simultaneously achieve high areal loading, high active content, and superior performance. In response, this work introduces an ideal electrode structure, featuring a continuous conductive network with active particles securely trapped in the absence of binder, fabricated using a universal technique that combines electrospinning and electrospraying (co-ESP). We found that the particle size must be larger than the network's pores for optimised performance, an aspect overlooked in previous research. The free-standing co-ESP Na2V3(PO4)3 (NVP) cathodes demonstrated state-of-the-art 296 mg cm-2 areal loading with 97.5 wt.% active content, as well as remarkable rate-performance and cycling stability. Co-ESP full cells showed uncompromised energy and power densities (231.6 Wh kg-1/7152.6 W kg-1), leading among reported SIBs with industry-relevant areal loadings. The structural merit is analysed using multi-scale X-ray computed tomography, providing valuable design insights. Finally, the superior performance is validated in the pouch cells, highlighting the electrode’s scalability and potential for commercial application.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[29842]
Open Access
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.
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Jan 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[29913]
Open Access
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.
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Oct 2024
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Open Access
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.
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Jul 2023
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Open Access
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.
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Jul 2023
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Xiaoqiang
Liang
,
Sen
Wang
,
Jingyu
Feng
,
Zhen
Xu
,
Zhenyu
Guo
,
Hui
Luo
,
Feng
Zhang
,
Wen
Chen
,
Lei
Feng
,
Chengan
Wan
,
Maria-Magdalena
Titirici
Diamond Proposal Number(s):
[28663]
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.
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Apr 2023
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[25787, 27541, 29157]
Open Access
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.
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Jan 2023
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