Accelerated hot-carrier cooling in MAPbI3 perovskite by pressure-induced lattice compression

Hot-carrier cooling (HCC) in metal halide perovskites in the high-density regime is significantly slower compared to conventional semiconductors. This effect is commonly attributed to a hot-phonon bottleneck but the influence of the lattice properties on the HCC behaviour is poorly understood. Using pressure-dependent transient absorption spectroscopy (fs-TAS) we find that at an excitation density below Mott transition, pressure does not affect the HCC. On the contrary, above Mott transition, HCC in methylammonium lead iodide (MAPbI3) is around two times as fast at 0.3 GPa compared to ambient pressure. Our electron-phonon coupling calculations reveal about two times stronger electron-phonon coupling for the inorganic cage mode at 0.3 GPa. However, our experiments reveal that pressure promotes faster HCC only above Mott transition. Altogether, these findings suggest a change in the nature of excited carriers in the high-density regime, providing insights on the electronic behavior of devices operating at such high charge-carrier density

Lattice compression increases the activation barrier for phase segregation in mixed-halide perovskites

The bandgap tunability of mixed-halide perovskites makes them promising candidates for light emitting diodes and tandem solar cells. However, illuminating mixed-halide perovskites results in the formation of segregated phases enriched in a single-halide. This segregation occurs through ion migration, which is also observed in single-halide compositions, and whose control is thus essential to enhance the lifetime and stability. Using pressure-dependent transient absorption spectroscopy, we find that the formation rates of both iodide- and bromide-rich phases in MAPb(BrxI1-x)3 reduce by two orders of magnitude on increasing the pressure to 0.3 GPa. We explain this reduction from a compression-induced increase of the activation energy for halide migration, which is supported by first-principle calculations. A similar mechanism occurs when the unit cell volume is reduced by incorporating a smaller cation. These findings reveal that stability with respect to halide segregation can be achieved either physically through compressive stress or chemically through compositional engineering

Perovskite escape room: Which photons leave the film, and which are trapped inside?

Although halide perovskite materials hold great promise for optoelectronics, defect-assisted recombination still limits their efficiency. In the April issue of Matter, Fassl et al. present an open-source model for analyzing the photoluminescence spectra of perovskite films, showing a much lower internal quantum efficiency than previously thought in the field

Transforming inactive coke molecules into active intermediates in zeolites

Generating active intermediates from deactivating coke molecules by a regeneration process that produces valuable syngas as a by-product almost sounds too good to be true. In a recent publication in Nature Communications, Zhou and co-workers demonstrated this innovative approach by converting coke molecules into active naphthalenic cations by steam cracking in the industrially used SAPO-34 material, after it was active in the methanol-to-olefins (MTO) reaction. In this way, the nature of the commonly found hydrocarbon pool species was altered resulting in an enhanced ethylene selectivity. Their finding has been confirmed by the use of advanced characterization methods and computational calculations

Combined in Situ X-ray Powder Diffractometry/Raman Spectroscopy of Iron Carbide and Carbon Species Evolution in Fe(-Na-S)/α-Al2O3Catalysts during Fischer-Tropsch Synthesis

A Na-S promoted Fe-based Fischer-Tropsch synthesis (FTS) catalyst converts a H2/CO gas mixture into hydrocarbons with enriched C2-C4 olefin content. Above 300 °C, the carbon-depositing Boudouard reaction competes with the FTS reaction for CO as reactant. By making use of a combined in situ X-ray powder diffractometry (XRPD)/Raman spectroscopy setup, the simultaneous evolution of the FexOy/α-Fe/FexC phases and various formed carbon species has been monitored at 340 °C and 10 bar. CO carburized, Na-S promoted and unpromoted Fe(-Na-S)/α-Al2O3 catalysts were investigated. The various Fe phases present were quantified with Rietveld quantitative phase analysis (R-QPA) from the in situ collected XRPD patterns. The observed D- A nd G-bands in the in situ Raman spectra were analyzed for their relative intensities, band widths, and positions and compared to reference carbon materials. It was found that amorphous carbon with C sp3 and C sp2 in chain-like ordering evolved toward carbon nanofiber-like structures during FTS. Na-S promotion and initial CO carburization at temperatures ≥340 °C led to an increased amount of cyclic sixfold C sp2 species. Preliminary carbon deposits present in the catalysts decreased the initial fast increase of the Raman band intensities, while Na-S promotion increased Raman band intensity growth after the initial fast increase period. The carbon species evolution was unaffected by the presence of specific Fe carbides or by carbide-to-carbide transitions. Na-S promotion aided in the reduction of Fe3O4 by (H2:)CO to carbon-depositing Fe carbides. The results obtained add to our further understanding on the role of Fe and carbon species during a high-temperature FTS reaction

Author Correction: Chemical targets to deactivate biological and chemical toxins using surfaces and fabrics

Correction to: Nature Reviews Chemistry https://doi-org.proxy.library.uu.nl/10.1038/s41570-021-00275-4, published online 05 May 2021. The originally published article contained an incomplete acknowledgements section, which now reads as: This work is part of the Advanced Research Center for Chemical Building Blocks, ARC CBBC, which is co- founded and co- financed by the Netherlands Organisation for Scientific Research (NWO) and the Netherlands Ministry of Economic Affairs and Climate Policy. This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands and the US Army Research Office (ARO), and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska- Curie grant agreement no. 801359. The authors thank T. Hartman (Utrecht University) for the graphical illustrations. This has been corrected in the HTML and PDF versions of the manuscript

Chemical targets to deactivate biological and chemical toxins using surfaces and fabrics

The most recent global health and economic crisis caused by the SARS-CoV-2 outbreak has shown us that it is vital to be prepared for the next global threat, be it caused by pollutants, chemical toxins or biohazards. Therefore, we need to develop environments in which infectious diseases and dangerous chemicals cannot be spread or misused so easily. Especially, those who put themselves in situations of most exposure - doctors, nurses and those protecting and caring for the safety of others - should be adequately protected. In this Review, we explore how the development of coatings for surfaces and functionalized fabrics can help to accelerate the inactivation of biological and chemical toxins. We start by looking at recent advancements in the use of metal and metal-oxide-based catalysts for the inactivation of pathogenic threats, with a focus on identifying specific chemical bonds that can be targeted. We then discuss the use of metal-organic frameworks on textiles for the capture and degradation of various chemical warfare agents and their simulants, their long-term efficacy and the challenges they face

Mechanistic Insights into the Lanthanide-Catalyzed Oxychlorination of Methane as Revealed by Operando Spectroscopy

Commercialization of CH4 valorization processes is currently hampered by the lack of suitable catalysts, which should be active, selective, and stable. CH4 oxychlorination is one of the promising routes to directly functionalize CH4, and lanthanide-based catalysts show great potential for this reaction, although relatively little is known about their functioning. In this work, a set of lanthanide oxychlorides (i.e., LnOCl with Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) and Er- and Yb-based catalysts were synthesized, characterized, and tested. All lanthanide-based catalysts can directly activate CH4 into chloromethanes, but their catalytic properties differ significantly. EuOCl shows the most promising catalytic activity and selectivity, as very high conversion levels (>30%) and chloromethane selectivity values (>50%) can be reached at moderate reaction temperatures (∼425 °C). Operando Raman spectroscopy revealed that the chlorination of the EuOCl catalyst surface is rate-limiting; hence, increasing the HCl concentration improves the catalytic performance. The CO selectivity could be suppressed from 30 to 15%, while the CH4 conversion more than doubled from 11 to 24%, solely by increasing the HCl concentration from 10 to 60% at 450 °C. Even though more catalysts reported in this study and in the literature show a negative correlation between the S CO and HCl concentration, this effect was never as substantial as observed for EuOCl. EuOCl has promising properties to bring the oxychlorination one step closer to an economically viable CH4 valorization process

Identification of Iron Carbides in Fe(−Na−S)/α-Al2O3 Fischer-Tropsch Synthesis Catalysts with X-ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H2 reduced Fe(−Na−S)/α-Al2O3 catalyst materials, with and without Na−S promotion, were carburized under CO at 240–440 °C to form Fe carbides. X-ray Powder Diffractometry (XRPD) with Rietveld Quantitative Phase Analysis (R-QPA) and Mössbauer Absorption Spectroscopy (MAS) were used to identity and quantify the formed Fe carbide phases. The Fe carbides formed in order of increasing temperature are ϵ-Fe3C, η-Fe2C, χ-Fe5C2 and θ-Fe3C. θ-Fe7C3 and a distorted χ-Fe5C2 phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ-Fe5C2 over θ-Fe3C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process