Faraday Discussions最新文献

We here describe a procedure for the calculation of PE spectra in solution, including vibrational and dynamical solvent effects. Steady-state vibronic spectra are computed in the harmonic approximation, including the effect of the electronic continuum on the cross section. Solvent effects are described in the framework of continuum polarizable models, providing an accurate assessment of dynamical solvation effects, crucial for a reliable modelling of PE processes, with a very small computational cost. Time-resolved PE spectra are computed from the nonadiabatic quantum dynamics of the electronic-vibrational wavepacket propagating on the coupled valence states, described with a linear vibronic coupling model and adopting a semiclassical approximation. Our approach provides accurate steady-state PE spectra for 9(H)adenine in the gas phase and adenosine in water. In the former case, the position, the relative energy and the dependence on the PE ejection angle for the three lowest-energy bands are in good agreement with the experimental ones. We simulated the pump-probe PE spectrum of adenosine in water using both static and dynamical approaches, obtaining spectra fully consistent with the experimental ones and getting new insights on its sub-ps photophysics. Some methodological issues in the simulation of PE spectra in solutions are also discussed.

Load-flexibility requirements of emerging P2A concepts and recent advances in ammonia synthesis catalysts challenge the established design paradigms of conventional adiabatic Haber-Bosch reactors (e.g., AICR). In particular, external direct-cooled polytropic fixed-bed reactors (EDCRs) appear to exploit modern, highly active catalysts more effectively. As catalyst activity is expected to increase further, it remains to be clarified to what extent existing reactor concepts can translate these improvements into reactor-level performance gains, or whether the reactor design itself must evolve. To address this question, a detailed model-based analysis of AICR and EDCR operation is carried out, in which catalyst improvements are represented by systematic scaling of the apparent activation energy. In this way, promising directions for future catalyst development can also be identified. The results show that increased catalyst activity improves single-pass conversion within a limited operating window; outside this range, equilibrium limitations dominate, and higher activity mainly reduces the required catalyst volume. While the operating trajectory of an AICR is fundamentally constrained by the adiabatic temperature rise and reaction ignition, the EDCR provides additional degrees of freedom and direct coupling of the operating trajectory to the reaction rate. This allows reactor operation to be aligned more closely with kinetically favorable conditions. As a result, the EDCR consistently outperforms the AICR, and even with current catalysts, single-pass conversions of up to 57% can be achieved. This indicates that reducing ammonia inhibition becomes increasingly important, since high ammonia concentrations strongly reduce reaction rates and thus limit high conversions to low space velocities. The study underscores that future catalyst development for ammonia synthesis should be coupled to reactor design, with particular emphasis on low-temperature activity, thermal catalyst stability, and reduced ammonia inhibition.

The electrochemical lithium-mediated nitrogen reduction reaction (Li-NRR) has emerged as a leading approach for ammonia electrosynthesis under mild conditions, particularly in continuous flow-cell configurations. Despite the rapid progress of this strategy, as well as the remarkable efforts in electrolyte composition engineering and solid-electrolyte-interphase layer understanding, the impact of architecture-level parameters remains unclear and is often entangled with the intrinsic process reactivity and selectivity. Here, we systematically investigate the influence of electrolyte and nitrogen-gas flow rates on Li-NRR performance in a flow cell, attempting to decouple the effect of device-level parameters from reaction chemistry in determining activity, selectivity, and stability of the system. By balancing liquid and gas flows, we demonstrate stable device operation even at high electrolyte flow rates (18 mL min^-1), allowing for a complete exchange of the electrolyte in the liquid chamber twice per minute. This electrolyte flow rate results in a simultaneous improvement of Faradaic efficiency, productivity, and ammonia recovery in the gas phase. Overall, our results highlight the critical influence of cell-architecture-related parameters on Li-NRR and emphasize the need to disentangle device engineering from electrolyte tailoring and electrochemical performance optimisation to enable a rational understanding of the mechanism understanding towards the translation of Li-NRR to a scalable process.

Ultrafast electron diffraction (UED) provides direct information on changes in molecular structure following photoexcitation. However, identifying the individual vibrational motions contributing to these structural dynamics remains challenging from time-dependent electron scattering and pair distribution functions alone, particularly when multiple vibrational motions contribute over similar internuclear distances. Moreover, the ∼100 fs temporal resolution of current gas-phase UED experiments further limits the vibrational dynamics that can be resolved. In this work, we introduce frequency-resolved UED, where Fourier transformation of the time-dependent difference pair distribution function (ΔPDF) along the pump-probe delay axis gives a two-dimensional frequency-distance representation of the photoinduced structural dynamics. To demonstrate the utility of frequency-resolved UED, we study the ultrafast vibrational dynamics in allene and its methylated derivative 1,2-butadiene following photoexcitation to its S₁(ππ*) state at 200 nm. We simulate the electron scattering signals from previously-published ab initio multiple spawning (AIMS) trajectories (S. P. Neville et al., J. Chem. Phys., 2016, 144, 014305). Through the frequency-distance representation, we identify the CC stretching and CCC bending motions in both molecules and their internuclear distances over which these frequency components contribute. We further separate overlapping CH₂ vibrational motions and identify contributions from multiple vibrational frequencies at the same internuclear distance. We show the delay times at which specific frequency components contribute during the excited-state dynamics by changing the pump-probe delay range used for the Fourier transform of the ΔPDF signal. In both molecules, the CCC bending motion contributes predominantly before substantial S₁ → S₀ population transfer occurs by 70-90 fs, whereas the CC stretching motion persists at all delays. We find that methyl substitution reduces the CC stretching and CCC bending frequencies, while an additional frequency component appears in 1,2-butadiene and contributes primarily during the first 90 fs. Finally, we investigate the impact of the total instrument response function (IRF) on the retrieval of these frequency components and show the importance of reaching sub-20-fs, and ultimately few-femtosecond, temporal resolution. Frequency-resolved UED therefore provides a route to identify the vibrational frequencies that contribute to photoinduced structural dynamics, the internuclear distances associated with these frequencies, and the reaction times at which they are present.

We present a combined theoretical and experimental study of the three diazine isomers pyrazine, pyrimidine, and pyridazine by means of resonant inelastic X-ray scattering (RIXS) at the nitrogen K-edge, employing fully time-dependent quantum dynamics simulations to understand the role of nuclear motion in core-excited states. The RIXS process is simulated by wave-packet propagation in both the valence- and core-excited state manifolds, carried out with the (multilayer) multiconfigurational time-dependent Hartree [(ML-)MCTDH] method. We use linear vibronic coupling Hamiltonians with up to 22 electronic states and compare a full-dimensional (24-mode) and a reduced six-mode model. We find good agreement between experiment and theory for all three molecules. In particular, our study highlights the essential role of nuclear motions during the population of short-lived intermediate core-excited states. Specifically, we show that ultrafast non-adiabatic transitions induce symmetry distortion that leads to additional emission bands, while interstate vibrational dynamics lead to vibrational progressions in the inelastic scattering spectra. These results establish a dynamical picture of the RIXS process in diazines that emphasises the importance of including nuclear dynamics in the calculations of resonant Raman processes.

This paper offers a personal perspective on the 2026 Faraday Discussions meeting on emerging materials for optoelectronics applications. Common themes of the meeting included hybrid perovskites, BaZrS₃ and related chalcogenide materials, low-dimensional materials, and data-driven science including self-driving laboratories and accelerated calculations. Discussion highlights included debate on which properties should be measured or calculated for emerging materials, the role of impurities and approximations, and the balanced interface point between theory and experiment for the case of emerging materials for optoelectronics applications. The paper also considers a possible definition of an emerging material for optoelectronics applications. It reflects on lessons learned from working in emerging materials, including the importance of pursuing open problems, articulating the result significance clearly, and sharing both positive and negative results. In addition, it provides a perspective on the role of AI in emerging materials research. It offers a personal view on how Faraday Discussions can both benefit from and contribute to AI-enabled science, while preserving the central role of human discussion and reasoning. This paper is adapted from a transcript of the concluding remarks made at the meeting.

Efficient electrocatalysts for direct seawater electrolysis are critical for the sustainable production of green hydrogen without straining freshwater resources. However, linking structure-property relationships to catalytic activity and stability remains challenging. Here, FeNiB electrocatalysts with tuneable crystallinity were synthesised via scalable chemical reduction and controlled thermal treatment, producing amorphous, partially crystalline (200 °C), and fully crystalline (400 °C) structures. Crystallinity strongly influenced surface morphology, electrochemically active surface area (ECSA), and charge transfer. The amorphous FeNiB showed surface fractals with the highest ECSA and double-layer capacitance, delivering the best hydrogen evolution reaction (HER) performance with an overpotential of -0.364 V vs. RHE at 100 mA cm^-2, compared to -0.416 V vs. RHE and -0.427 V vs. RHE for the 200 °C and 400 °C samples, respectively. In contrast, the partially crystalline FeNiB (200 °C) exhibited optimal oxygen evolution reaction (OER) activity, requiring 0.314 V vs. RHE at 100 mA cm^-2, outperforming the amorphous (0.364 V vs. RHE) and fully crystalline (0.402 V vs. RHE) samples. This enhanced OER performance arises from a balance between structural order and accessible active sites. The best-performing samples maintained stable operation over 24 h in alkaline saline and natural seawater with minimal degradation. These results highlight crystallinity as a key parameter for tuning electrocatalyst performance and provide design insights for practical seawater electrolysis systems.

Understanding light-activated processes in molecular rotors is essential for applications ranging from energy storage to light-emitting materials. Rotation around single bonds provides an efficient nonradiative decay pathway, leading many molecular rotors to undergo quenching across environments. Nonadiabatic dynamics simulations offer a route to disentangling competing decay channels, but the predicted mechanisms depend sensitively on the level of theory. Here, we examine how different electronic-structure methods shape the topology of conical intersections and, in turn, the photochemical behaviour of sym-triphenylcyclopropene (Ph₃C₃H), a propeller-shaped rotor exhibiting low-quantum-yield emission from a locally excited state. Using exploratory-based surface-hopping dynamics with TD-CAM-B3LYP, ADC(2), and MRSF-TD-CAM-B3LYP, we characterise the S₂-S₁ and S₁-S₀ conical intersections and relate their topographies to the observed decay pathways. Consistent with the underlying potential-energy surfaces, the trajectories computed with ADC(2) evolve to S₀ significantly faster than those obtained with TD-CAM-B3LYP and MRSF-TD-CAM-B3LYP. The S₂-S₁ intersection is peaked and bifurcating, promoting extensive population exchange, particularly for MRSF-TD-CAM-B3LYP. Two distinct S₁-S₀ intersections are identified: CI₁, consistently peaked across CASSCF and all MRSF-TDDFT functionals, and CI₂, which is sloped and single-path for all MRSF-TDDFT functionals but appears sloped and bifurcating at the MS-CASPT2 level. Across all methods, CI₁ emerges as the dominant decay channel. MRSF-TD-CAM-B3LYP dynamics yield three outcomes: reformation of the initial geometry, formation of a diradical intermediate, and production of the bicyclic photoproduct, reflecting its bifurcating topology and more reliable ground-state description relative to LR-TDDFT. A systematic analysis of exchange-correlation functional dependence within MRSF-TDDFT reveals strong consistency across functionals, with only minor deviations such as the borderline single-path behaviour of BHHLYP and DTCAM-AEE. These findings raise important questions about the reliability, limitations, and future development of black-box excited-state methods for modelling photochemical decay in molecular rotors.