Faraday Discussions最新文献

Converting intermittent renewable energy, like wind or solar, into hydrocarbons faces challenges where the classic chemical processes involved often demand expensive energy storage solutions, high conversion costs, and scalability issues. Induction heated catalyst systems offer promising efficiency in using intermittent power for chemical processes, as they can rapidly respond to fluctuating energy inputs. Their fast activation and deactivation reduce energy waste, making them ideal for integrating with renewable sources. This flexibility enhances their potential in sustainable hydrocarbon and hydrogen production from variable power. Here, we report a Magnetic Induction heated Catalytic (MagIC) system that couples rapid, high-temperature induction heating with a maghemite-functionalised SBA-15 catalyst (MagSBA) to valorise polypropylene waste into methane, hydrogen and solid carbon without tar byproducts or detectable CO_x. MagSBA was selected for its magnetic heating responsiveness, thermal stability at elevated temperatures and proven catalytic activity. With rapid induction heating to 750 °C, the MagIC configuration showed different product distribution relative to non-catalytic thermal treatment. In the absence of catalyst, the process yielded 82.9 wt% gas and 17.7 wt% solid, dominated by CH₄ (50.5 at%) and containing 29.2 at% H₂. Introduction of MagSBA increased solid production to 66.7 wt% and reduced gaseous output to 33.0 wt%, while driving the gas composition toward hydrogen. The catalytic run produced 54 mmol H₂ g_PP^-1, representing a 45% enhancement in H₂ formation relative to the blank test and approaching the theoretical hydrogen yield for polypropylene; gaseous CH₄ and C2-C4 hydrocarbons fell to ≤25 at% of the gas stream. These results demonstrate that MagIC with MagSBA enables efficient dehydrogenation/cracking pathways for organic feedstock concurrent with carbon capture in solid form, providing a promising, low-emission route for chemical storage of intermittent energy.

This paper presents the time-resolved X-ray photoelectron spectroscopy (TR-XPS) setup at the Swiss Free-Electron Laser (SwissFEL) Maloja endstation for investigating the ultrafast dynamics of gas-phase molecules with site-specificity. As a case study, we investigate the dissociative photoionization of glycine. By tracking the C 1s, N 1s, and O 1s core-level edges, we resolve the site-specific dynamics following multiphoton ionization. Guided by ab initio theory, the measurements are modeled using a global kinetic fit. Using this model, we report a glycine parent cation lifetime of 395 ± 25 fs, consistent with the theoretically predicted barrier to C-C bond rupture. We track fragment separation in real time via carboxyl red-shifts, which signal the relaxation of coulombic repulsion between the COOH and the iminium ion (CH₂NH₂⁺). Finally, we address fundamental technical challenges, including the temporal limitations imposed by laser-induced optical sidebands in the presence of high-intensity fields, understanding the modulated ground-state bleach signal, and the complexities of the theoretical framework that couples ab initio molecular dynamics with high-level quantum-chemical calculations of core-level binding energies.

The chalcogenide perovskite BaZrS₃ has recently emerged as a promising material for photovoltaic energy conversion, composed of earth-abundant elements. Unlike its halide counterpart, BaZrS₃ has not yet demonstrated strong photoluminescence (PL). The excitation-intensity and temperature dependence of radiative emission in thin films of chalcogenide perovskite BaZrS₃ were studied using PL spectroscopy. Oxide precursors with compositional gradients (0.4 < [Ba]/([Ba] + [Zr]) < 0.6) were prepared with pulsed laser deposition followed by sulfurization in a tube furnace at different H₂S in Ar concentrations, as well as temperatures ranging from 900 °C to 1000 °C. As the radiative emission at room temperature was not detectable, low temperature measurements were performed, revealing a high defect density both of shallow and deep levels, related to both free-bound as well as donor-acceptor transitions. Broad emissions were detected near 1.11 eV, 1.2 eV, 1.33 eV and 1.42 eV. We compared theoretical defect level calculations from literature with the detected emissions. The dependence of some defects on sulfur partial pressure during the sample preparation could be corroborated by comparing the transitions of libraries prepared at different H₂S concentrations.

Conventional water electrolysis is fundamentally limited by the kinetic constraints of coupled electrode reactions, particularly the oxygen evolution reaction, which necessitate substantial overpotentials despite decades of catalyst development. Recently, spatially and temporally decoupled electrolysis has emerged as a new paradigm in which electrochemical charge storage and catalytic fuel production are separated. This decoupling enables catalysis beyond the confines of the electrode surface and fundamentally alters how electrons are delivered to the catalyst. Here, we investigate redox-mediated hydrogen evolution in strongly alkaline media, examining the interplay between dissolved redox mediators and heterogeneous hydrogen evolution catalysts. Notably, we demonstrate that separating electron transfer from catalytic hydrogen evolution minimises some of the kinetic penalty associated with the electrode-electrolyte interface, enabling hydrogen evolution at potentials approaching the thermodynamic limit, even on nickel catalysts. Nevertheless, catalyst identity remains critical in determining reaction kinetics. Comparison of platinum and Raney® nickel reveals a prolonged activation period unique to nickel, demonstrating that catalyst surface chemistry continues to govern hydrogen evolution despite the absence of direct electrode-mediated electron transfer. These findings establish decoupled electrolysis as a fundamentally distinct model for investigating the interplay between charge transfer and catalysis, providing new insight into electrocatalytic energy conversion.

Ground and excited electronic states in highly symmetric systems typically possess high degrees of spatial degeneracy as a consequence of point-group symmetry. However, many current quantum-chemical methods struggle to accurately describe the strong correlation effects inherently present in these states, thereby precluding the ability to obtain meaningful insights into the electronic structure of the underlying systems. Consequently, many of their important chemical and spectroscopic properties cannot be reliably computed and predicted. In this article, a new theoretical framework is described that unifies the symbolic treatment of non-Abelian symmetry in QSym² and the recently developed state-specific multi-reference coupled cluster theory termed Generalised Normal-Ordered Coupled Cluster (GNOCC) to describe such difficult ground and excited states in a balanced and targeted manner. This is ensured by the ability of QSym² to exploit symmetry orbits to restore any broken spatial symmetries and generate symmetry-adapted multi-determinantal wavefunctions, as well as the ability of GNOCC to dynamically correlate arbitrary spin eigenfunctions in a size-extensive and spin-free manner. To illustrate the capabilities of this framework, several ground and excited states in three model systems are examined in detail: (i) octahedral (H₆)²⁺, (ii) octahedral H₆, and (iii) tetrahedral Li₄. The results demonstrate that the proposed method can target both degenerate and non-degenerate states, while delivering improved numerical performance relative to conventional single-reference coupled-cluster approaches.

Hydrogen has become an ideal alternative energy carrier in response to the growing global energy crisis and the transition away from fossil fuel dependence. The development of effective, affordable and long-lasting electrocatalysts for water splitting to produce hydrogen remains a major challenge. In this work, a facile coprecipitation of nitrogen-doped FeCo alloy (FCN) nanoparticles in the presence of preformed WO₃ nanostructures of various quantities resulted in nitrogen-doped FeCo/WO₃-based heterostructures (FCNWO). This heterostructure engineering of electrocatalysts improves the hydrogen evolution reaction (HER) by creating interfaces that expose active sites and accelerate the charge transfer. The morphology and crystal structure of the FCNWO samples synthesised with different FCN : WO₃ ratios were characterised and electrochemical hydrogen generation activity evaluated. Among them, the FCNWO-2 catalyst, prepared with a precursor FeCo : WO₃ ratio of 1 : 0.75 exhibited optimal performance and demonstrated the best HER activity in 1.0 M KOH, with an overpotential of 275 mV at 10 mA cm^-2, a small Tafel slope of 71 mV dec^-1 and a high electrochemical surface area of 322.5 cm². These results demonstrate its promise as an effective electrocatalyst for energy conversion and storage applications.