B18-Core EXAFS
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Diamond Proposal Number(s):
[29271]
Open Access
Abstract: Photocatalytic CO2 reduction, including reaction rate, product selectivity, and longevity, is highly sensitive to the coordination structure of the catalytic active sites, and the precise design of the active site remains a challenge in heterogeneous catalysts. Herein, we report on the modulation of the coordination structure of MNx-type active sites (M = Co or Ni; x = 4 or 5) anchored on a periodic mesoporous organosilica (PMO) support to improve photocatalytic CO2 reduction. The PMO was functionalized with pendant 3,6-di(2′-pyridyl)pyridazine (dppz) groups to allow immobilization of molecular Co and Ni complexes with polypyridine ligands. A comparative analysis of CO2 photoreduction in the presence of an organic photosensitizer (4CzIPN, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) and a conventional [Ru(bpy)3]Cl2 sensitizer revealed strong influence of the coordination environment on the catalytic performance. CoN5-PMO demonstrated a superior CO2 photoreduction activity than the other materials and displayed a cobalt-based turnover number (TONCO) of 92 for CO evolution at ∼75% selectivity after 3 h irradiation in the presence of 4CzIPN. The hybrid CoN5-PMO catalyst exhibited better activity than its homogeneous [CoN5] counterpart, indicating that the heterogenization promotes the formation of isolated active sites with improved longevity and faster catalytic rate.
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Jun 2024
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I19-Small Molecule Single Crystal Diffraction
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Eman A. A.
Alkhudhayr
,
Dumitru
Sirbu
,
Miriam
Fsadni
,
Benjamin
Vella
,
Bening T.
Muhammad
,
Paul G.
Waddell
,
Michael R.
Probert
,
Thomas J.
Penfold
,
Toby
Hallam
,
Elizabeth
Gibson
,
Pablo
Docampo
Diamond Proposal Number(s):
[302080]
Open Access
Abstract: Organic–inorganic hybrid halide perovskite solar cells (PSCs) have attracted substantial attention from the photovoltaic research community, with the power conversion efficiency (PCE) already exceeding 26%. Current state-of-the-art devices rely on Spiro-OMeTAD as the hole-transporting material (HTM); however, Spiro-OMeTAD is costly due to its complicated synthesis and expensive product purification, while its low conductivity ultimately limits the achievable device efficiency. In this work, we build upon our recently introduced family of low-cost amide-based small molecules and introduce a molecule (termed TPABT) that results in high conductivity values (∼10–5 S cm–1 upon addition of standard ionic additives), outperforming our previous amide-based material (EDOT-Amide-TPA, ∼10–6 S cm–1) while only costing an estimated $5/g. We ascribe the increased optoelectronic properties to favorable molecular packing, as shown by single-crystal X-ray diffraction, which results in close spacing between the triphenylamine blocks. This, in turn, results in a short hole-hopping distance between molecules and therefore good mobility and conductivity. In addition, TPABT exhibits a higher bandgap and is as a result more transparent in the visible range of the solar spectrum, leading to lower parasitic absorption losses than Spiro-OMeTAD, and has increased moisture stability. We applied the molecule in perovskite solar cells and obtained good efficiency values in the ∼15% range. Our approach shows that engineering better molecular packing may be the key to developing high-efficiency, low-cost HTMs for perovskite solar cells.
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Nov 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21742]
Open Access
Abstract: Zn1–xSnxOy (ZTO) deposited by atomic layer deposition has shown promising results as a buffer layer material for kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Increased performance was observed when a ZTO buffer layer was used as compared to the traditional CdS buffer, and the performance was further increased after an air annealing treatment of the absorber. In this work, we study how CZTS absorber surface treatments may influence the chemical and electronic properties at the ZTO/CZTS interface and the reactions that may occur at the absorber surface prior to atomic layer deposition of the buffer layer. For this, we have used a combination of microscopy and synchrotron-based spectroscopies with variable information depths (X-ray photoelectron spectroscopy, high-energy X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy), allowing for an in-depth analysis of the CZTS near-surface regions and bulk material properties. No significant ZTO buffer thickness variation is observed for the differently treated CZTS absorbers, and no differences are observed when comparing the bulk properties of the samples. However, the formation of SnOx and compositional changes observed toward the CZTS surface upon an air annealing treatment may be linked to the modified buffer layer growth. Further, the results indicate that the initial N2 annealing step integrated in the buffer layer growth by atomic layer deposition, which removes Na–COx species from the CZTS surface, may be useful for the ZTO/CZTS device performance.
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Oct 2022
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I11-High Resolution Powder Diffraction
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Albina
Jetybayeva
,
Nino
Schön
,
Jimin
Oh
,
Jaegyu
Kim
,
Hongjun
Kim
,
Gun
Park
,
Young-Gi
Lee
,
Rüdiger-A.
Eichel
,
Karin
Kleiner
,
Florian
Hausen
,
Seungbum
Hong
Diamond Proposal Number(s):
[19772]
Open Access
Abstract: LiNi0.6Co0.2Mn0.2O2 (NCM622) undergoes crystallographic and electronic changes when charging and discharging, which drive the cathode material close to or even beyond its stability window. To unravel the charge compensation mechanism of NCM622, spatially resolved atomic force microscopy (AFM) measurements in electrochemical strain microscopy (ESM) and conductive AFM (C-AFM) modes are obtained, and the spectroscopic information and crystallographic information are compared. All experiments are performed with two sets of samples: state-of-the-art samples that are composed of a binder, a conductive additive, and an active material and polished samples for single-particle analysis. Near-edge X-ray absorption fine structure spectroscopy shows that ionic Ni2+ reacts to give Ni3+ when charging and forms covalent bonds with its oxygen neighbors. A Ni2+/Ni3+ gradient across the particles balances out with the increasing state of charge, as verified by ESM. Therefore, the results also provide an important view that improves the mechanistic understanding of ESM in electrode materials. Finally, the interplay between the electronic and ionic conductivities and the crystallinities of NCM622 cathodes is elaborated and discussed.
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Jan 2022
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Abstract: Cathode materials that have high specific energies and low manufacturing costs are vital for the scaling up of lithium-ion batteries (LIBs) as energy storage solutions. Fe-based intercalation cathodes are highly attractive because of the low cost and the abundance of raw materials. However, existing Fe-based materials, such as LiFePO4, suffer from low capacity due to the large size of the polyanions. Turning to mixed anion systems can be a promising strategy to achieve higher specific capacity. Recently, antiperovskite-structured oxysulfide Li2FeSO has been synthesized and reported to be electrochemically active. In this work, we perform an extensive computational search for iron-based oxysulfides using ab initio random structure searching (AIRSS). By performing an unbiased sampling of the Li–Fe–S–O chemical space, several oxysulfide phases have been discovered, which are predicted to be less than 50 meV/atom from the convex hull and potentially accessible for synthesis. Among the predicted phases, two anti-Ruddlesden–Popper-structured materials Li2Fe2S2O and Li4Fe3S3O2 have been found to be attractive as they have high theoretical capacities with calculated average voltages of 2.9 and 2.5 V, respectively, and their distances to hull are less than 5 meV/atom. By performing nudged-elastic band calculations, we show that the Li-ion transport in these materials takes place by hopping between the nearest neighboring sites with low activation barriers between 0.3 and 0.5 eV. The richness of materials yet to be synthesized in the Li–Fe–S–O phase field illustrates the great opportunity in these mixed anion systems for energy storage applications and beyond.
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Jan 2022
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I13-2-Diamond Manchester Imaging
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Melanie Cornelia
Paulisch
,
Marcus
Gebhard
,
David
Franzen
,
Andre
Hilger
,
Markus
Osenberg
,
Shashidhara
Marathe
,
Christoph
Rau
,
Barbara
Ellendorff
,
Thomas
Turek
,
Christina
Roth
,
Ingo
Manke
Diamond Proposal Number(s):
[21813]
Abstract: Understanding how gas diffusion electrodes are working is crucial to improve their performance and cost efficiency. One key issue is the electrolyte distribution during operation. Here, operando synchrotron imaging of the electrolyte distribution in silver-based gas diffusion electrodes is presented. For this purpose, a half-cell compartment was designed for operando synchrotron imaging of chronoamperometric measurements. For the first time, the electrolyte distribution could be analyzed in real time (1 s time resolution) even in individual pores as small as a few micrometers. The detailed analyses of dynamic filling processes are an important step for understanding and improving electrodes.
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Jul 2021
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[20757]
Open Access
Abstract: Understanding the kinetics of the crystallization process for organometal halide perovskite formation is critical in determining the crystalline, nanoscale morphology and therefore the electronic properties of the films produced during thin film formation from solution. In this work, in situ grazing incidence small-angle X-ray scattering (GISAXS) and optical microscopy measurements are used to investigate the processes of nucleation and growth of pristine mixed halide perovskite (MAPbI3–xClx) crystalline films deposited by bar coating at 60 °C, with and without additives in the solution. A small amount of 1,8-diiodooctane (DIO) and hydriodic acid (HI) added to MAPbI3–xClx is shown to increase the numbers of nucleation centers promoting heterogeneous nucleation and accelerate and modify the size of nuclei during nucleation and growth. A generalized formation mechanism is derived from the overlapping parameters obtained from real-time GISAXS and optical microscopy, which revealed that during nucleation, perovskite precursors cluster before becoming the nuclei that function as elemental units for subsequent formation of perovskite crystals. Additive-free MAPbI3–xClx follows reaction-controlled growth, in contrast with when DIO and HI are present, and it is highly possible that the growth then follows a hindered diffusion-controlled mechanism. These results provide important details of the crystallization mechanisms occurring and will help to develop greater control over perovskite films produced.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Ashok S.
Menon
,
Seda
Ulusoy
,
Dickson O.
Ojwang
,
Lars
Riekehr
,
Christophe
Didier
,
Vanessa K.
Peterson
,
German
Salazar-Alvarez
,
Peter
Svedlindh
,
Kristina
Edström
,
Cesar Pay
Gomez
,
William R.
Brant
Diamond Proposal Number(s):
[21804]
Open Access
Abstract: Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol–gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.
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Feb 2021
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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V.
Celorrio
,
D. J.
Fermin
,
L.
Calvillo
,
A.
Leach
,
H.
Huang
,
G.
Granozzi
,
J. A.
Alonso
,
A.
Aguadero
,
R. M.
Pinacca
,
A. E.
Russell
,
D.
Tiwari
Diamond Proposal Number(s):
[10306, 15151, 16479]
Abstract: Oxygen electrocatalysis at transition metal oxides is one of the key challenges underpinning electrochemical energy conversion systems, involving a delicate interplay of the bulk electronic structure and surface coordination of the active sites. In this work, we investigate for the first time the structure–activity relationship of A2RuMnO7 (A = Dy3+, Ho3+, and Er3+) nanoparticles, demonstrating how orbital mixing of Ru, Mn, and O promotes high density of states at the appropriate energy range for oxygen electrocatalysis. The bulk structure and surface composition of these multicomponent pyrochlores are investigated by high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption spectroscopy, X-ray emission spectroscopy (XES), and X-ray photoemission spectroscopy (XPS). The materials exhibit high phase purity (cubic fcc with a space group Fd3̅m) in which variations in M–O bonds length are less than 1% upon replacing the A-site lanthanide. XES and XPS show that the mean oxidation state at the Mn-site as well as the nanoparticle surface composition was slightly affected by the lanthanide. The pyrochlore nanoparticles are significantly more active than the binary RuO2 and MnO2 toward the 4-electron oxygen reduction reaction in alkaline solutions. Interestingly, normalization of kinetic parameters by the number density of electroactive sites concludes that Dy2RuMnO7 shows twice higher activity than benchmark materials such as LaMnO3. Analysis of the electrochemical profiles supported by density functional theory calculations reveals that the origin of the enhanced catalytic activity is linked to the mixing of Ru and Mn d-orbitals and O p-orbitals at the conduction band which strongly overlap with the formal redox energy of O2 in solution. The activity enhancement strongly manifests in the case of Dy2RuMnO7 where the Ru/Mn ratio is closer to 1 in comparison with the Ho3+ and Er3+ analogs. These electronic effects are discussed in the context of the Gerischer formalism for electron transfer at the semiconductor/electrolyte junctions.
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Jan 2021
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[19067]
Open Access
Abstract: High-end organic–inorganic lead halide perovskite semitransparent p–i–n solar cells for tandem applications use a phenyl-C61-butyric acid methyl ester (PCBM)/atomic layer deposition (ALD)-SnOx electron transport layer stack. Omitting the PCBM would be preferred for manufacturing, but has in previous studies on (FA,MA)Pb(Br,I)3 and (Cs,FA)Pb(Br,I)3 and in this study on Cs0.05FA0.79MA0.16PbBr0.51I2.49 (perovskite) led to poor solar cell performance because of a bias-dependent light-generated current. A direct ALD-SnOx exposure was therefore suggested to form a nonideal perovskite/SnOx interface that acts as a transport barrier for the light-generated current. To further investigate the interface formation during the initial ALD SnOx growth on the perovskite, the mass dynamics of monitor crystals coated by partial p–i–n solar cell stacks were recorded in situ prior to and during the ALD using a quartz crystal microbalance. Two major finds were made. A mass loss was observed prior to ALD for growth temperatures above 60 °C, suggesting the decomposition of the perovskite. In addition, a mostly irreversible mass gain was observed during the first exposure to the Sn precursor tetrakis(dimethylamino)tin(IV) that is independent of growth temperature and that disrupts the mass gain of the following 20–50 ALD cycles. The chemical environments of the buried interface were analyzed by soft and hard X-ray photoelectron spectroscopy for a sample with 50 ALD cycles of SnOx on the perovskite. Although measurements on the perovskite bulk below and the SnOx film above did not show chemical changes, additional chemical states for Pb, Br, and N as well as a decrease in the amount of I were observed in the interfacial region. From the analysis, these states and not the heating of the perovskite were concluded to be the cause of the barrier. This strongly suggests that the detrimental effects can be avoided by controlling the interfacial design.
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Jan 2021
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