V. Van Speybroeck

Generating a Stable Higher-Symmetry CsPbI3 Perovskite Phase in Ambient Conditions: Unveiling the Stabilization Mechanism

R.A. Saha, A. Papadopoulou, R. Ariza, G. Degutis, I. Skvortsova, T. Braeckevelt, F. De Angelis, E. Solano, J. P. de Sousa Gouveia dos Anjos, M. I. Pintor Monroy, I. Mongilyov, B. God, J. Rubio-Zuazo, J. Genoe, C. Meneghini, J.A. Steele, S. Bals, V. Van Speybroeck, J. Hofkens
ACS Nano
19, 31, 28540–28553
2025
A1

Abstract 

Black-phase cesium lead iodide (CsPbI3) is a promising candidate for high-efficiency perovskite optoelectronics, but its instability under ambient conditions remains a major challenge. Among several strategies, dimethylammonium iodide (DMAI) has emerged as a potential stabilizer; however, inconsistencies in phase stability (3–7 days) and lower solar power conversion efficiencies (∼20 vs ∼27% for hybrid perovskites) highlight the need for further improvements. This study not only demonstrates enhanced stabilization of the high-symmetry black phase of CsPbI3 and improved film morphology through optimized composition and annealing conditions but also more importantly provides detailed mechanistic insights obtained from comprehensive experimental and theoretical analyses. Systematic tuning of the DMAI concentration (1.2 M), annealing temperature (200 °C, 1 min), and Cs+ substitution (12–15%) significantly extends phase stability to 7 days under ambient conditions (35–52% relative humidity) and maintains stability even after 16 months in a drybox environment by reducing orthorhombic strain and octahedral tilting. Additionally, a minor (∼5%) zero-dimensional (0D) Cs4PbI6 phase fills pinholes, enhancing the film quality. Optimized photodiodes exhibit a low dark current (∼1 μA/cm2), high external quantum efficiency (∼80% at −2 V), and a ≥100 dB linear dynamic range. These findings provide mechanistic insights into the stabilization of the black phase of CsPbI3, advancing the development of more stable and efficient perovskite-based optoelectronic devices.

DOI 

http://dx.doi.org/

High-performance hydrophobic MOFs for selective acetone capture under humid conditions

S. Grigoletto, K. Karami, I. Maye, A. Padunnappattu, S. Ravichandran, M. Wahiduzzaman, L. Vanduyfhuys, V. Van Speybroeck, M. Thommes, J.F.M. Denayer, N. Stock, G. Maurin
Journal of Materials Chemistry A
13, 26401-26412
2025
A1

Abstract 

Capturing acetone, a major indoor air pollutant, under humid conditions is a longstanding challenge in materials science. The key obstacle lies in finding porous adsorbents that simultaneously exhibit strong affinity for acetone and intrinsic hydrophobicity, a rare and elusive pairing. Leveraging the structural and chemical versatility of metal-organic frameworks (MOFs), we first explored a diverse set of MOFs using force field Monte Carlo and density-functional theory calculations. This computational strategy identified CAU-11(Al) as a top performer: a hydrophobic, small pore MOF that enables both high acetone affinity and uptake at trace concentrations with excellent selectivity over water. Experimental validation through gas-phase pulse chromatography, adsorption measurements, and breakthrough studies confirmed the outstanding performance of this sorbent under competitive acetone/water conditions. These results position CAU-11(Al) as a promising material for real-world acetone capture in humid indoor environments.

Gold Open Access

DOI 

http://dx.doi.org/

Dynamic Evolution and Stability of Ketenes in MAPO-18 (M = Si or Mg): Molecular Insights into the Reaction Mechanism for CO2-to-Hydrocarbons

W. Chen (Wei - CMM), M. Bocus, U. Olsbye, V. Van Speybroeck
Chinese Journal of Catalysis
2026
A1

Abstract 

AEI topology molecular sieves (MAPO-18) have shown promising properties as components of OX-ZEO type tandem catalysts, where the Brønsted acid sites (BAS) introduced by different framework substitutions lead to distinct catalytic mechanisms using ketene as key intermediates in the CO2-to-hydrocarbons conversion. This study provides molecular-level insights into the reactions of three ketenes (ketene, methyl ketene, and dimethyl ketene) with the BAS in MAPO-18 (M = Si, Mg) molecular sieves at operando conditions through firstprinciples molecular dynamics (FPMD) simulations combined with enhanced sampling techniques. Free energy surfaces constructed from FPMD simulations revealed distinct kinetic and thermodynamic preferences, linking them to different reaction routes for the production of olefins. Prior studies suggested that ketenes and their protonated analogues are key intermediates in two different pathways to olefins formation, and the three ketenes exhibited higher kinetic stability than their protonated forms in H-SAPO-18 compared to H-MgAPO-18, suggesting a high tendency for olefin production via the (cyclo)addition-decarboxylation route in H-SAPO-18. In contrast, the increased stability of the cationic intermediates and low protonation barrier for methyl and dimethyl ketenes in MgAPO-18 favor their direct decarbonylation to olefins. Surface-bound species displayed decreasing stability from surface acetate to surface propionate to surface isobutyrate, aligning with established trends for surface alkoxides. Moreover, a comparison with static calculations demonstrates their limited ability to capture the entropic contributions and dynamic effects that dominate the behavior of active intermediates under realistic reaction conditions, highlighting the necessity of MD approaches for accurate mechanistic modeling of catalytic reactions. Overall, this study provides key steps of ketene reactivity in zeolite frameworks, bridging computational and experimental insights into CO2-to-hydrocarbon conversion pathways. These results emphasize how subtle variations in the framework composition and substituents dictate the reaction mechanisms, offering guidance for the rational design of molecular sieves tailored for selective catalytic transformations.

DOI 

http://dx.doi.org/

Design of a Tunable, High-performance Mixed Matrix Membrane Platform for Gas Separations

T. Xiaoyu, S. Robijns, A. Lamaire, R. Goeminne, N. De Witte, M. Dickmann, R. Verbeke, T. Van der Donck, R. de Oliveira Silva, Q. Ke, Y. Li, I. Aslam, C. Van Goethem, T. Donckels, R. Helm, D. Sakellariou, T. Van Assche, V. Van Speybroeck, M. Dusselier, I. Vankelecom
Advanced Materials
37(34): 2502393
2025
A1

DOI 

http://dx.doi.org/10.1002/adma.202502393

Understanding the entanglement between diffusion and reaction by probing the mobility of ketene in chabazites

W. Chen (Wei - CMM), P. Cnudde, V. Van Speybroeck
Journal of Catalysis
453, 116546
2026
A1

Abstract 

In zeolite catalysis, diffusion and reaction are generally viewed as separate processes that independently affect catalytic performance due to the significant variation in timescales for diffusion and reaction. Nevertheless, this study reveals that reaction and diffusion can be intertwined, a phenomenon hitherto unexplored. In particular, we highlight this complex relationship for ketene intermediates in chabazite topologies, where the diffusion properties of ketene are notably affected by the reactivity with Brønsted acid sites (BAS) and guest molecules present in the zeolite pores. Ketene is an important intermediate in zeolite catalyzed methanol-to-hydrocarbons and COx-to-hydrocarbons conversion and its diffusion and reaction behavior directly impacts the catalytic performance. Our ab initio molecular dynamics simulations reveal that ketene diffusion is significantly facilitated by hydrogen bonding interactions with BAS during the diffusion through the 8-ring windows of chabazite, and that ketene can also readily react with other guest species along the diffusion pathway. This entanglement between reaction and diffusion can be attributed to the high activity of ketene, resulting in a strong competition between reaction and diffusion, which cannot be viewed as two independent processes. Therefore, our findings concerning the complex interconnection between diffusion and reaction not only contribute to the fundamental understanding of ketene chemistry in chabazite but also have important consequences for other fields of catalysis involving highly active intermediates.

DOI 

http://dx.doi.org/10.1016/j.jcat.2025.116546

Quantitative Description of Strongly Correlated Materials by Combining Downfolding Techniques and Tensor Networks

D. Vrancken, S. Ganne, D. Verraes, T. Braeckevelt, L. Devos, L. Vanderstraeten, J. Haegeman, V. Van Speybroeck
Journal of Chemical Theory and Computation
21, 16, 7830-7844
2025
A1

Abstract 

We present a high-accuracy procedure for electronic structure calculations of strongly correlated materials. To address limitations in current electronic structure methods, we employ density functional theory in combination with the constrained random phase approximation to construct an effective multiband Hubbard model, which is subsequently solved using tensor networks. Our work focuses on one-dimensional and quasi-one-dimensional materials, for which we employ the machinery of matrix product states. We apply this framework to the conjugated polymers trans-polyacetylene and polythiophene, as well as the quasi-one-dimensional charge-transfer insulator Sr2CuO3. The predicted band gaps show quantitative agreement with state-of-the-art computational techniques and experimental measurements. Beyond band gaps, tensor networks provide access to a wide range of physically relevant properties, including spin magnetization and various excitation energies. Their flexibility supports the implementation of complex Hamiltonians with longer-range interactions, while the bond dimension enables systematic control over accuracy. Furthermore, the computational cost scales efficiently with system size, demonstrating the framework’s scalability.

DOI 

http://dx.doi.org/10.1021/acs.jctc.5c00796

Cluster-Based Machine Learning Potentials to Describe Disordered MetalOrganic Frameworks up to the Mesoscale

P. Dobbelaere, S. Vandenhaute, V. Van Speybroeck
Chemistry of Materials
37, 15, 5696-5709
2025
A1

Abstract 

Metal-organic frameworks (MOFs) are highly interesting and tunable materials. By incorporating spatial defects into their atomic structure, MOFs can be finetuned to exhibit precise chemical functionalities, extending their applicability in various technological fields. Defect engineering requires a fundamental understanding of the nature of spatial disorder and consequent changes in material properties, which is currently lacking. We introduce the cluster-based learning methodology, enabling the development of state-of-the-art machine learning potentials (MLPs) from defective systems at any length scale. Our method identifies atomic interactions in bulk structures and extracts local environments as finite molecular fragments to augment the model's training data where needed. We show that cluster-based learning delivers MLPs capable of accurately describing spatial defects in mesoscopic systems with over 20 thousand atoms. Afterward, we select our best model to investigate some major mechanical properties of spatially disordered UiO-66-derived structures, elucidating the influence of defect concentration and composition on material behavior. Our analysis includes large supercell structures, demonstrating that (near-) ab initio accuracy is within reach at the mesoscale.

Gold Open Access

DOI 

http://dx.doi.org/10.1021/acs.chemmater.5c00821

Increasing the Phase Stability of CsPbI3 Nanocrystals by Zn2+ and Cd2+ Addition: Synergy of Transmission Electron Microscopy and Molecular Dynamics

I. Skvortsova, T. Braeckevelt, A. De Backer, N. Schrenker, B. Pradhan, J. Hofkens, S. Van Aert, V. Van Speybroeck, S. Bals
ACS Nano
19, 18, 17698-17708
2025
A1

Abstract 

Metal halide perovskites (MHPs) are emerging as promising materials for optoelectronic and photovoltaic applications due to their favorable electronic properties, including a tunable bandgap. However, achieving high stability for these materials remains a critical challenge, particularly for CsPbI3, whose photoactive phases spontaneously convert into a nonphotoactive yellow orthorhombic δ-phase under ambient conditions. This transformation results in a significant increase in bandgap and a loss of photoactive functionality. In this study, we investigate the impact of Zn2+ and Cd2+ dopants on the phase stability of CsPbI3 nanocrystals (NCs), emphasizing the formation of Ruddlesden–Popper (RP) planar defects, which are frequently observed during compositional tuning. Using transmission electron microscopy (TEM), we follow the temporal evolution of the phase transformation, where black-phase NCs agglomerate and form elongated microtubes with a yellow-phase crystal structure. Our observations demonstrate that doped samples are significantly more stable, while the dopants are key factors in the formation of the RP-like defects with specific atomic arrangements. Using a combination of quantitative TEM and molecular dynamics (MD) simulations we characterize the structure and composition of as-found RP-like defects and elucidate their role in stabilizing the photoactive phases of CsPbI3 through decreased phase transition kinetics.

DOI 

http://dx.doi.org/10.1021/acsnano.5c01825

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