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Accurate analysis of the rich information contained within X‐ray spectra usually calls for detailed electronic structure theory simulations. However, density functional theory (DFT), time‐dependent DFT and many‐body perturbation theory calculations increasingly require the use of advanced codes running on high‐performance computing (HPC) facilities. Consequently, many researchers who would like to augment their experimental work with such simulations are hampered by the compounding of nontrivial knowledge requirements, specialist training and significant time investment. To this end, we present Web‐CONEXS, an intuitive graphical web application for democratizing electronic structure theory simulations. Web‐CONEXS generates and submits simulation workflows for theoretical X‐ray absorption and X‐ray emission spectroscopy to a remote computing cluster. In the present form, Web‐CONEXS interfaces with three software packages: ORCA, FDMNES and Quantum ESPRESSO, and an extensive materials database courtesy of the Materials Project API. These software packages have been selected to model diverse materials and properties. Web‐CONEXS has been conceived with the novice user in mind; job submission is limited to a subset of simulation parameters. This ensures that much of the simulation complexity is lifted and preliminary theoretical results are generated faster. Web‐CONEXS can be leveraged to support beam time proposals and serve as a platform for preliminary analysis of experimental data. [ABSTRACT FROM AUTHOR]

We present the coupling of two frameworks—the pseudo-open boundary simulation method known as constant potential molecular dynamics simulations (CμMD), combined with quantum mechanics/molecular dynamics (QMMD) calculations—to describe the properties of graphene electrodes in contact with electrolytes. The resulting CμQMMD model was then applied to three ionic solutions (LiCl, NaCl, and KCl in water) at bulk solution concentrations ranging from 0.5 M to 6 M in contact with a charged graphene electrode. The new approach we are describing here provides a simulation protocol to control the concentration of electrolyte solutions while including the effects of a fully polarizable electrode surface. Thanks to this coupling, we are able to accurately model both the electrode and solution side of the double layer and provide a thorough analysis of the properties of electrolytes at charged interfaces, such as the screening ability of the electrolyte and the electrostatic potential profile. We also report the calculation of the integral electrochemical double layer capacitance in the whole range of concentrations analyzed for each ionic species, while the quantum mechanical simulations provide access to the differential and integral quantum capacitance. We highlight how subtle features, such as the adsorption of potassium graphene or the tendency of the ions to form clusters contribute to the ability of graphene to store charge, and suggest implications for desalination. [ABSTRACT FROM AUTHOR]

Prussian blue is widely utilized as a cathode material in batteries, due to its ability to intercalate alkaline metal ions, including potassium. However, the exact location of potassium or other cations within the complex structure, and how it changes as a function of cycling, is unclear. Herein, we report direct insight into the nature of potassium speciation within Prussian blue during cyclic voltammetry, via operando potassium K-edge X-ray Absorption Near Edge Structure (XANES) analysis. Clear and identifiable spectra are experimentally differentiated for the fully intercalated (fully reduced Fe2+FeII Prussian white), partially intercalated (Prussian blue; Fe3+FeII), and free KNO3(aq) electrolyte. Comparison of the experiment with simulated XANES of theoretical structures indicates that potassium lies within the channels of the Prussian blue structure, but is displaced towards the periphery of the channels by occluded water and/or structural water present resulting from [Fe(CN)6]4− vacancies. The structural composition from the charge carrier perspective was monitored for two samples of differing crystallite size and electrochemical stability. Reproducible potassium XANES spectral sequences were observed for large crystallites (ca. 100 nm) of Prussian blue, in agreement with retention of capacity; in contrast, the capacity of a sample with small crystallites (ca. 14 nm) declined as the potassium became trapped within the partially intercalated Prussian blue. The cause of degradation could be attributed to a significant loss of [Fe(CN)6]–[Fe(NC)6] ordering and the formation of a potassium-free non-conducting ferrihydrite phase. These findings demonstrate the potential of XANES to directly study the nature and evolution of potassium species during an electrochemical process. [ABSTRACT FROM AUTHOR]

In organic polymeric materials with mixed ionic and electronic conduction (OMIEC), the excess charge in doped polymers is very mobile and the dynamics of the polymer chain cannot be accurately described with a model including only fixed point charges. Ions and polymer are comparatively slower and a methodology to capture the correlated motions of excess charge and ions is currently unavailable. Considering a prototypical interface encountered in this type of materials, we constructed a scheme based on the combination of MD and QM/MM to evaluate the classical dynamics of polymer, water and ions, while allowing the excess charge of the polymer chains to rearrange following the external electrostatic potential. We find that the location of the excess charge varies substantially between chains. The excess charge changes across multiple timescales as a result of fast structural fluctuations and slow rearrangement of the polymeric chains. Our results indicate that such effects are likely important to describe the phenomenology of OMIEC, but additional features should be added to the model to enable the study of processes such as electrochemical doping. [ABSTRACT FROM AUTHOR]

Electrochemical catalysis of nitrogen to ammonia is an environmentally friendly alternative strategy to the traditional and damaging Haber–Bosch process. Nevertheless, it is limited by a low ammonia yield and faradaic efficiency due to (i) the complexity associated with the breaking of the N≡N bond and (ii) the competing hydrogen evolution reaction. Herein, we report that the electrochemical dealloying of exfoliated PdBi2 nanoflakes into palladium hydride greatly enhances the electrocatalytic nitrogen reduction reaction. The electrochemical decomposition of bismuth atoms creates vacancies in the PdBi2 crystal lattice enabling hydrogen atoms to be absorbed and instigating the initial protonation of N2 molecules necessary for the eventual NH3 formation. The average ammonia yield and faradaic efficiency were 30.06 ± 1.16 μg cm−2 h−1 and 15.25 ± 1.29% when the potential was held at −1.5 V vs. sat. Ag/AgCl after 6 h at room temperature. Our conclusions are supported by the first-principles simulations and this work emphasizes the potential implementation of palladium compounds for future N2 reduction reaction electrocatalysts. [ABSTRACT FROM AUTHOR]

Objectives: This case study reports the real-world practicalities of implementing a mixed-methods heat acclimation (HA) programme before the 2022 FIFA World Cup., Methods: One male English soccer referee (age: 44 years; height: 1.82 m; body mass: 76.0 kg) who had officiated professionally for over 17 years and had over 10 years' experience officiating in European and international matches undertook an 11-session HA programme over 22 days. On days 1 and 22, a 30 min fixed-intensity heat tolerance test (9 km.h -1 , 2% gradient, 40°C, 40% relative humidity) was performed, and physiological and perceptual responses were measured. A mixed-methods HA approach was used, including environmental chamber isothermic training, post-temperate training saunas and hot water immersion., Results: Compared with the pre-test, peak core temperature reduced by 0.40°C (38.4 vs 38.0°C; minimal detectable change (MDC) = 0.34°C), peak skin temperature reduced by 0.5°C (36.7 vs 36.2°C; MDC=0.28°C) and peak heart rate reduced by 5 b·min -1 (167 vs. 162 b·min -1 ; MDC=4 b·min -1 ) in the post-test. In the post-test, the sweat rate increased by 17% (1.94 vs 2.27 L.h -1 ; MDC=0.42 L.h -1 ). Peak thermal sensation (7 = 'hot') and the rating of perceived exertion (3 = 'moderate') were unchanged between the tests. However, peak thermal comfort (3 = 'slightly uncomfortable' vs 2 = 'uncomfortable') was rated lower in the post-test., Conclusion: The HA programme elicited positive physiological but indifferent perceptual responses, highlighting that mixed-methods HA can be implemented when a referee still has officiating, travel and training responsibilities during the HA window., Competing Interests: SB is employed by the PGMOL as Head of Physical Performance. The authors have no other competing interests to declare., (Copyright © Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Linear-scaling density functional theory simulation of methylated imogolite nanotubes (NTs) elucidates the interplay between wall-polarization, bands separation, charge-transfer excitation, and tunable electrostatics inside and outside the NT-cavity. The results suggest that integration of polarization-enhanced selective photocatalysis and chemical separation into one overall dipole-free material should be possible. Strategies are proposed to increase the NT polarization for maximally enhanced electron-hole separation.