Temperature-Induced Precipitation of V2O5 in Vanadium Flow Batteries—Revisited

The maximum operation temperature of the vanadium solution in vanadium flow batteries is typically limited to 40 °C to prevent the damaging thermal precipitation of V2O5. Therefore, the operation of batteries at high ambient temperatures is an important aspect to tackle for stationary storage. In the present work, a comprehensive study of the high temperature stability of redox solutions for vanadium flow batteries was performed. In particular, focus was placed on a comparison between batch and in operando precipitation experiments. It was found that, despite being a widely used method in the literature, caution should be taken when assessing the precipitation through capacity fade due to the large influence of external oxidation and cycling parameters, plausibly leading to an incorrect interpretation of the results. The in operando experiments consistently show a precipitation temperature almost 10–20 °C higher than in the batch tests at a 100% state of charge for the same time lapse.

Influence of Halide Substitution and External Stimuli on Ion Transport in Inverted MAPb(I1-xBrx)3 Perovskite Solar Cells

The coupled electronic-ionic response in various MAPb(I1-xBrx)3-based inverted perovskite solar cells (PSCs) is studied in-operando by impedance spectroscopy (IS) under varied AM1.5G light intensities and electrical biases. We show that the concentration of Br- in the composition significantly alters the capacitance and resistive response of the PSC under external stimuli. For example, we observed that the low frequency capacitance does not increase proportionally with light intensity, instead it is highly dependent on the amount of Br- in the composition. We found that the recombination resistance (Rrec) has a linear inverse relationship with light intensity in MAPbI3 and MAPbBr3 whereas, the mixed compositions show deviation. Interestingly, the deviation of Rrec from linearity also scales with the increase in Br- concentration. Upon applying an electrical bias, a large deviation of Rrec from linearity was observed all mixed halide compositions exhibited a non-linear inverse trend. We further report the diffusion coefficient (D) for each MAPb(I1-xBrx)3 composition under different light intensity. Notably, the D values decreased on changing the composition from MAPbI3 (10-7 cm2 s-1) to MAPb(I0.8Br0.2)3 and MAPbBr3 (10-8 cm2 s-1). On the other hand, mixed compositions containing more than 20% Br- concentration show faster diffusion kinetics. Overall, our results emphasize on the complex and intertwined nature of electronic and ionic response in PSC that is tunable by changing the halide composition.

One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

The valorization of CO2 via renewable energy sources allows one to obtain carbon-neutral fuels through its hydrogenation, like methane. In this study, Ni0.05Ce0.95O2−δ catalysts were prepared using a simple one-pot hydrothermal method yielding nanorod and nanocube particles to be used for the methanation reaction. Samples were characterized by XRD, BET, TEM, H2-TPR, and H2-TPD experiments. The catalytic activity tests revealed that the best performing catalyst was Ni0.05Ce0.95O2−δ, with nanorod morphology, which gave a CO2 conversion of 40% with a selectivity of CH4 as high as 93%, operating at 325 °C and a GHSV of 240,000 cm3 h−1 g−1. However, the lower activation energy was found for Ni0.05Ce0.95O2−δ catalysts with nanocube morphology. Furthermore, an in operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed flowing CO2:H2 or CO:H2 mixture, showing that the main reaction pathway, for the CO2 methanation, is the direct hydrogenation of formate intermediate.

Beamline K11 DIAD: a new instrument for dual imaging and diffraction at Diamond Light Source

The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source is a new dual-beam instrument for full-field imaging/tomography and powder diffraction. This instrument provides the user community with the capability to dynamically image 2D and 3D complex structures and perform phase identification and/or strain mapping using micro-diffraction. The aim is to enable in situ and in operando experiments that require spatially correlated results from both techniques, by providing measurements from the same specimen location quasi-simultaneously. Using an unusual optical layout, DIAD has two independent beams originating from one source that operate in the medium energy range (7–38 keV) and are combined at one sample position. Here, either radiography or tomography can be performed using monochromatic or pink beam, with a 1.4 mm × 1.2 mm field of view and a feature resolution of 1.2 µm. Micro-diffraction is possible with a variable beam size between 13 µm × 4 µm and 50 µm × 50 µm. One key functionality of the beamline is image-guided diffraction, a setup in which the micro-diffraction beam can be scanned over the complete area of the imaging field-of-view. This moving beam setup enables the collection of location-specific information about the phase composition and/or strains at any given position within the image/tomography field of view. The dual beam design allows fast switching between imaging and diffraction mode without the need of complicated and time-consuming mode switches. Real-time selection of areas of interest for diffraction measurements as well as the simultaneous collection of both imaging and diffraction data of (irreversible) in situ and in operando experiments are possible.