I20-Scanning-X-ray spectroscopy (XAS/XES)
|
Diamond Proposal Number(s):
[21526]
Open Access
Abstract: Herein, the influence of iron on nanocasting of cobalt oxide nanowires and the performance of these materials for the oxygen evolution reaction (OER) are investigated. Pristine Co3O4 and mixed cobalt iron oxide nanowires with a diameter of 7 nm have been synthesized via a nanocasting route by using SBA 15 silica as a template. A small amount of iron added during the synthesis results in a decrease in the nanowires’ array length and induces the formation of a bimodal pore size distribution. Raman Spectroscopy, X-ray emission and high-energy resolution X-ray absorption spectroscopies further show that Fe incorporation alters the electronic structure by increasing the average distortion around the cobalt centers and the amount of Co2+ in tetrahedral sites. These affect the OER activity significantly; the overpotential of pristine Co3O4 at 10 mA/cm2 decreases from 398 to 378 mV, and the current density at 1.7 V increases from 107 to 150 mA/cm2 with the addition of iron at Co/Fe atomic ratio of 32. Furthermore, post-reaction characterization confirmed that both the morphology and electronic structure of nanowires remain intact after a long-term stability test.
|
Aug 2020
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[14937]
Open Access
Abstract: In this study in situ wide angle X-ray scattering (WAXS) has been measured during the spin coating process used to make the precursor films required for the formation of thin films of perovskite. A customized hollow axis spin coater was developed to permit the scattered X-rays to be collected in transmission geometry during the deposition process. Spin coating is the technique most commonly used in laboratories to make thin perovskite films. The dynamics of spin casting MAPbI3-xClx and FAPbI3-xClx films have been investigated and compared to investigate the differences between the dynamics of MAPbI3-xClx and FAPbI3-xClx film formation. In particular we focus on the crystallization dynamics of the precursor film formation. When casting MAPbI3-xClx we observed relatively fast 1D crystallization of the intermediate product MA2PbI3Cl. There was an absence of the desired perovskite phase formed directly; it only appeared after an annealing step which converted the MA2PbI3Cl to MAPbI3. In contrast, slower crystallization via a 3D precursor was observed for FAPbI3-xClx film formation compared to MAPbI3-xClx. Another important finding was that some FAPbI3-xClx perovskite was generated directly during spin casting before annealing. These findings indicate that there are significant differences between the crystallization pathways for these two perovskite materials. These are likely to explain the differences in the lifetime of the resulting perovskite solar cell devices produced using FA and MA cations.
|
Jun 2020
|
|
I09-Surface and Interface Structural Analysis
|
Andrew J.
Naylor
,
Ida
Kallquist
,
David
Peralta
,
Jean-Frederic
Martin
,
Adrien
Boulineau
,
Jean-Francois
Colin
,
Christian
Baur
,
Johann
Chable
,
Maximilian
Fichtner
,
Kristina
Edstrom
,
Maria
Hahlin
,
Daniel
Brandell
Diamond Proposal Number(s):
[20870]
Open Access
Abstract: Promising theoretical capacities and high voltages are offered by Li-rich disordered rocksalt oxyfluoride materials as cathodes in lithium ion batteries. However, as has been discovered for many other Li-rich materials, the oxyfluorides suffer from extensive surface degradation, leading to severe capacity fading. In the case of Li2VO2F, we have previously determined this to be a result of detrimental reactions between an unstable surface layer and the organic electrolyte. Herein, we present the protection of Li2VO2F particles with AlF3 surface modification, resulting in a much enhanced capacity retention over 50 cycles. While the specific capacity for the untreated material drops below 100 mA h g-1 after only 50 cycles, the treated materials retain almost 200 mA h g-1. Photoelectron spectroscopy depth profiling confirms the stabilisation of the active material surface by the surface modification and reveals its suppression of electrolyte decomposition.
|
May 2020
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[14239]
Abstract: Increasing dependence on rechargeable batteries for energy storage calls for the improvement of energy density of batteries. Toward this goal, introduction of positive electrode materials with high voltage and/or high capacity is in high demand. The use of oxygen chemistry in lithium and sodium layered oxides has been of interest to achieve high capacity. Nevertheless, a complete understanding of oxygen-based redox processes remains elusive especially in sodium ion batteries. Herein, a novel P3-type Na0.67Ni0.2Mn0.8O2, synthesized at low temperature, exhibits oxygen redox activity in high potentials. Characterization using a range of spectroscopic techniques reveals the anionic redox activity is stabilized by the reduction of Ni, because of the strong Ni 3d–O 2p hybridization states created during charge. This observation suggests that different route of oxygen redox processes occur in P3 structure materials, which can lead to the exploration of oxygen redox chemistry for further development in rechargeable batteries.
|
Jan 2020
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[15487]
Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small angle X-ray scattering (GISAXS) are herein employed to determine the dye···TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes: an organic metal-free dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3, and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller inter-particle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest inter-particle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.
|
Dec 2019
|
|
I19-Small Molecule Single Crystal Diffraction
|
Wei
Zhang
,
Yong
Hua
,
Linqin
Wang
,
Biaobiao
Zhang
,
Yuanyuan
Liu
,
Peng
Liu
,
Valentina
Leandri
,
Yu
Guo
,
Hong
Chen
,
James M.
Gardner
,
Licheng
Sun
,
Lars
Kloo
Diamond Proposal Number(s):
[15819, 20805]
Open Access
Abstract: Two zinc-based coordination complexes Y3 and Y4 have been synthesized, characterized and their performance as hole-transport materials (HTMs) for perovskite solar cells (PSCs) have been investigated. The complex Y3 contains two separate ligands, and the molecular structure can be seen as a dis-connected porphyrin ring. On the other hand, Y4 consists of a porphyrin core, and therefore a more extended conjugated system as compared to Y3. The optical and redox properties of the two different molecular complexes are comparable. However, the hole-mobility and conductivity of Y4 as macroscopic material are remarkably higher than that of Y3. Furthermore, when employed as hole-transport materials in perovskite solar cells, cells containing Y4 show a power conversion efficiency (PCE) of 16.05%, comparable to the Spiro-OMeTAD based solar cells with an efficiency around 17.08%. In contrast, solar cells based on Y3 show a negligible efficiency of about 0.01%. The difference in performance of Y3 and Y4 are analyzed and can be attributed to the difference in packing of the non-planar and planar building blocks in the corresponding materials.
|
Aug 2019
|
|
|
|
Abstract: Hybrid organic–inorganic halide perovskites are promising materials for thin-film solar cells. However, the toxicity and instability of best-in-class lead–halide perovskite materials make them nonideal. To combat these issues, we replaced lead with bismuth and explored the sensitivity of these new lead-free materials to the valency and bonding of their cationic organic groups. Specifically, we synthesized and characterized the materials properties and photophysical properties of hexane-1,6-diammonium bismuth pentaiodide ((HDA2+)BiI5) and compared them to an analogue containing a more volatile organic group with half the number of carbon and nitrogen atoms in the form of n-propylammonium ((PA+)xBiI3+x, where 1 < x < 3). The full crystallographic structures of (HDA2+)BiI5 and (PA+)xBiI3+x were resolved by single-crystal X-ray diffraction. (HDA2+)BiI5 was shown to be pure-phase and have a one-dimensional structure, whereas (PA+)xBiI3+x was shown to be a mix of one-dimensional and zero-dimensional phases. Structures of the materials were confirmed by synchrotron X-ray diffraction of powders. Both (HDA2+)BiI5 and (PA+)xBiI3+x exhibit steady-state photoluminescence at room temperature. Density functional theory calculations of (HDA2+)BiI5 predict electronic absorption features and a ∼2 eV bandgap that are consistent with those observed experimentally. Structure–property relationships of the materials were examined, and moisture tolerance and film quality were found to be superior for dication-containing (HDA2+)BiI5 in relation to monocation-containing (PA+)xBiI3+x. We hypothesize that these trends are in part due to a molecular bridging effect enabled by the presence of the dicationic hexanediammonium groups in (HDA2+)BiI5. Solar cells fabricated using (HDA2+)BiI5 as the photoactive layer exhibited photovoltaic action while those containing (PA+)xBiI3+x did not, suggesting that organic dicationic groups are beneficial to light-absorber morphology and ultimately solar-cell performance.
|
Feb 2019
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[15151]
Abstract: Mixed and doped metal oxides are excellent candidates for commercial energy applications such as batteries, supercapacitors, solar cells and photocatalysis due to their activity, stability, tailorable band edge and bandgaps, and low cost. However, the routes commonly employed in their synthesis present synthetic bottlenecks with reliance on sacrificial materials, the use of high temperatures, long reaction times, and little ability to control morphology, thus compromising their scale-up. Herein, we present the single pot, electrochemical synthesis of high surface area, doped metal titanate nanostructures, including Na2Ti3O7 (NTO), 25 wt.% Sn:NTO, 5 wt.% Fe:NTO and 3 wt.% Cu:NTO. The synergic use of the cathodic corrosion method with suspended droplet alloying (SDA) led to materials with excellent homogeneity, presenting a promising route for the screening, production and discovery of electroactive materials. As proof of concept of the synthetic control and impact on reactivity, we found that the photoanodic oxygen evolution activity of the nanomaterials was adversely affected by Fe and Sn doping into NTO while Cu doping, at 3 wt.% displayed significant improvement. This work demonstrates the ability of the cathodic corrosion method to obtain compositionally- and structurally- controlled mixed-metal oxides in a rapid fashion, thus creating new opportunities in the field of materials engineering and the systematic study of compositional gradients on the (photo)electrochemical performance of metal oxide nanoparticles.
|
Sep 2018
|
|
I13-2-Diamond Manchester Imaging
|
Diamond Proposal Number(s):
[16110]
Open Access
Abstract: Lithium sulfur (Li-S) batteries have great potential as a successor to Li-ion batteries but their commercialization has been complicated by a multitude of issues stemming from their complex multi-phase chemistry. In-situ X-ray tomography investigations enable direct observations to be made about a battery, providing unprecedented insight into the microstructural evolution of the sulfur cathode and shedding light on the reaction kinetics of the sulfur phase. Here, for the first time, the morphology of a sulfur cathode was visualized in 3D as a function of state of charge at high temporal and spatial resolution. Whilst elemental sulfur was originally well dispersed throughout the uncycled cathode, subsequent charging resulted in the formation of sulfur clusters along preferred orthogonal orientations in the cathode. The electrical conductivity of the cathode was found not to be rate-limiting, suggesting the need to optimize the loading of conductive carbon additives. The carbon and binder domain, and surrounding bulk pore phase were visualized in the in-situ cell, and contrast changes within both phases were successfully extracted. The applications of this technique are not limited to microstructural and morphological characterization, and the volumetric data can serve as a valuable input for true 3D computational modelling of Li-S batteries.
|
Aug 2018
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[17223]
Abstract: Nanoscale morphology has been established as one of the controlling factors in the device performance of bulk heterojunction polymer solar cells. We report in this work morphology changes in both lateral and vertical directions in PffBT4T-2OD:PC71BM solar cells, as well as their effects on device performance. Thermal annealing was found to increase the crystallinity of PffBT4T-2OD and domain size of PC71BM clusters without any observable impact on vertical component redistribution, whilst methanol rinsing reduces the crystallinity of PffBT4T-2OD, encourages the migration of PC71BM towards the mixed polymer-rich phase as well as towards the film surface on both PEDOT:PSS and TiO2 substrates. The polymer-rich surface region in vacuum- and thermal annealing- treated conventional devices obstructs electron injection towards the cathode, and reduces the maximum achievable device efficiency, whilst this polymer-rich surface region is beneficial in the inverted devices. However, although a PC71BM-rich region will locate at the cathode or anode interface upon methanol rinsing treatment in conventional and inverted devices respectively, holes can still be effectively injected from both sides the device to ensure effective charge transport, as supported by a number of optoelectronic property investigations.
|
Jun 2018
|
|
