Catalytic methane splitting (CMS) to hydrogen and elemental carbon is a promising route to produce COx-free hydrogen, potentially achieving net carbon-negative output when using biogenic methane as the feedstock. On transition metal nanocrystals, especially Ni, CMS proceeds at lower temperatures (<1000 K) compared to (plasma-assisted) methane pyrolysis, additionally leading to higher added-value graphitic carbon nanostructure products. Earlier work has indicated that the size of the metal nanocrystals plays a central role for hydrogen (and carbon) production rates, however, conflicting results have been reported, possibly as a result of challenges associated to the deposition of the carbon products on the catalyst surface as well as phenomena like metal particle growth, fragmentation and deactivation. Herein metal nanocrystal size effects are assessed on the methane splitting reaction rate with a series of model supported Ni catalysts. A maximum methane splitting rate is attained for Ni nanoparticles with a diameter of similar to 10 nm at the onset of the reaction. Operando synchrotron X-ray diffraction and activity-specific transmission electron microscopy studies attribute the observed size effects on reaction rate to differences in the relative contribution of Ni nanocrystals larger and smaller than ca. 10 nm. This metal nanoparticle diameter represents a threshold minimum size for the effective nucleation and growth of graphitic carbon filaments, and therefore for sustained hydrogen production, which entails the lifting of Ni nanocrystals away from the oxide support in a carbon tip-growth mechanism. Moreover, operando studies reveal metal nanocrystal growth, which is specifically driven by the earliest methane splitting events on the catalyst surface, and determinant for the metal aggregation extent and intrinsic activity of the actual working catalyst. Density Functional Theory analyses identify *C and *CH3 adspecies, emerging from CH4 splitting on neat Ni surfaces, as central mediators to attain favourable energetics for the detachment of Ni adatoms from coordinatively unsaturated sites on the metal nanocrystals and their emission onto the oxide support material, hence responsible for a catalysis-driven Ostwald ripening metal growth mechanism. The results contribute to rationalize the interplay between metal nanocrystal size and carbon-metal dynamics to define an optimal Ni nanoparticle size of similar to 10 nm for a maximum hydrogen production rate, providing a blueprint for designing optimized catalysts for low-temperature methane splitting.

This roadmap provides a comprehensive overview of the latest advancements in lead-free perovskite materials for photovoltaic and photoelectrochemical /photocatalytic applications. It highlights the urgent need for sustainable energy solutions, emphasizing the role of lead-free perovskites in addressing challenges related to toxicity, scalability, and efficiency. The roadmap is designed to guide the reader from application-driven perspectives to fundamental materials insights, characterization techniques, fabrication strategies and overreaching sustainability considerations. The document explores key material families, including tin-, bismuth-, antimony-, and copper-based perovskites, detailing their optoelectronic properties, fabrication techniques, and application potential. Special attention is given to advanced characterization methods, green processing strategies, the integration of artificial intelligence and machine learning for material design and optimization and lifecycle impact assessments to ensure environmental sustainability. By bringing together insights from global research communities, this roadmap serves as a strategic guide for advancing lead-free perovskite technology, fostering interdisciplinary collaboration, and accelerating the transition to next-generation solar energy solutions.

Metal-organic frameworks have been intensively investigated for their ability to effectively control the growth and surface chemistry of nanosized guests, with their pores acting as templates and potentially providing anchoring sites. Since the speciation, as determined by the geometry and surface chemistry of hydride-forming metals, such as Pd, under particular conditions (T, p), is controlled by their size at and beyond the nanoscale, metal-organic frameworks are a prospective matrix for speciation or phase selection. This is of relevance because the role and characteristics of the phases in hydrogenation reactions involving hydride-forming Pd catalysts are open questions. In particular, it is a matter of debate which palladium phase is the most active and most selective, as they often occur simultaneously under catalytic conditions. For the first time, our thorough investigation, including operando XAFS and computer simulations, demonstrates that by embedding Pd nanoclusters, ≤1 nm in diameter, in the pores of the NH2-UiO-66 metal-organic framework, the speciation of subnanometric Pd particles can be controlled, such that the active particles only exist in their metallic state under reaction conditions; in fact, the Pd-H2 mixture only affords surface-bound hydrogen atoms. This control of Pd speciation consequently enables the direct probing of the phase activity and selectivity in the model reaction of 1,3-butadiene hydrogenation to butenes, wherein it showed no deactivation and improved selectivity compared to conventionally prepared catalytic systems. This result shows that the metallic phase can be stabilized through subnanometric size control and that it is more selective and less prone to overhydrogenating the butadiene reactant to butane, resulting in a purer product.

Solid-liquid-gas three-phase systems are central to chemistry, biology, physics, engineering, and even botany. Representative examples range from gas-evolving reactions at (photo)electrodes to hydrophobic interactions between proteins. Although these processes occur on the nanoscale, they are often interpreted using empirical principles extrapolated from macroscopic laws. Here we show, by means of atomistic simulations, that regularly distributed atomic- or molecular-scale chemical heterogeneities can give rise to counterintuitive behavior: the contact angle of an heterogeneous hydrophobic surface is maximized when the surface is decorated with a ∼20% atomic-level hydrophilic particle (with fixed interaction force). Similarly, a maximum in the contact angle is observed, at fixed hydrophilic particles geometry, when the difference in interaction force between the hydrophobic and hydrophilic spots is Δ ∼ 40%. We demonstrate that such atomistic-level heterogeneities can pin the solid-liquid-gas contact line. These findings have several implications. First, they rationalize the high hydrophobicity of materials that nonetheless contain a significant fraction of hydrophilic sites, Cu2(tebpz), a metal-organic framework whose pores host Cu nodes, being a notable example. Second, if our results are experimentally confirmed for more general, nonregularly patterned surfaces, they will add a new evidence for the need of overcome the asymptotic homogenization, widely used for describe heterogeneous surfaces from individual component, such as protein surfaces with amino-acid hydrophobicity scales or nanoporous materials.

With the increasing demand for indoor photovoltaics (IPV) to power autonomous and low-power electronic devices, lead-free perovskite-inspired materials (PIMs) have gained significant attention. Among the many lead-free alternatives, bismuth oxyiodide (BiOI) displays an electronic structure similar to that of high-performance lead-halide perovskites, but without the same toxicity limitations. However, its photoconversion efficiency (PCE) under indoor conditions is limited to 4.0-4.4%. A leading cause for such low efficiency is the contact between flake-like BiOI crystallites and electron and hole transport layers (ETL and HTL respectively). In this work, we thoroughly investigated an experimentally motivated (110) BiOI/ETL interface by means of density functional theory (DFT) calculations, to uncover the structural, mechanical and electronic characteristics of this heterostructure, identifying the atomistic origins of the sub-optimal performance of BiOI in photovoltaic applications. We focused on zinc oxide (ZnO) as an ETL, a material that attracted interest for its low annealing temperature (Tann = 100-300 degrees C) and higher electron mobility (& micro; = 5-30 cm2 V-1 s-1), compared to the prototypical TiO2 ETL (Tann similar to 500 degrees C; & micro; = 0.5-8 cm2 V-1 s-1). Our calculations reveal that a suitable orientation between the surfaces exists that induces limited strain on BiOI, potentially allowing the formation of an ideal heterostructure. Nevertheless, severe reconstruction occurs at the interface between BiOI and ZnO due to undercoordination of the I and O atoms of the terminal layer of the two solids. This reconstruction is observed to introduce states deep within the band gap. A trace of electron energy from the bulk of BiOI to the bulk of ZnO reveals a minimum at the BiOI/ZnO interface, which can hinder extraction and consequently reduce the PCE. Thus, we report for the first time the atomistic origins of limited PCE of BiOI/ZnO based photovoltaic devices and offer design principles to engineer more efficient interfaces.

Abstract Solid–liquid contact electrification is widely studied using diverse experimental geometries that are often implicitly assumed to probe equivalent interfacial processes. Here, we directly test this assumption by comparing immersion–emersion, droplet-based contact, and pressure-driven intrusion–extrusion electrification using the same hydrophobic nanoporous silicon monolith and isotopically substituted liquids (H2O and D2O). Despite identical surface chemistry, isotopic substitution produces qualitatively different electrical responses depending on the wetting regime. Immersion–emersion experiments show polarity inversion between H2O and D2O, while droplet measurements reveal distinct charge evolution and periodic opposite-polarity events. In contrast, forced nanopore intrusion preserves polarity but strongly enhances electrical output for D2O. These results demonstrate that wetting of surface nanoroughness during droplet, vs immersion–emersion, vs complete nanopores wetting upon intrusion–extrusion correspond to fundamentally different electrification states. By using isotope substitution as a controlled probe, this work establishes a general framework for disentangling protocol-dependent effects in solid–liquid contact electrification and triboelectric energy conversion.

The wetting behavior of hydrophobic nanoporous materials plays a pivotal role in advanced technologies such as energy storage, molecular separations, catalysis, and biomimetic systems. A central challenge in employing these materials is the precise control of wetting (intrusion) and dewetting (extrusion) pressures. To address this, we investigated how varying the concentration of organic linkers in ZIF-7-8 (composed of Zn-methylimidazole and benzimidazole) influences the intrusion-extrusion behavior of water within its micropores. Remarkably, we noticed that even a minor substitution of organic linkers (below 3%) led to significant and systematic changes in the wetting properties. Owing to the small fraction of substituted linkers, such effect could not be explained by classical models that consider individual cages. To elucidate this phenomenon, we combined experiments with molecular dynamics simulations and stochastic modeling of the crystallites. Our results reveal that the introduction of alien linkers perturbs the hydrogen-bond network, thereby disrupting the cooperative effects fundamental to the intrusion-extrusion process.

The mesoscopic-level formation mechanism of carbon nanotube growth, particularly the transition from a graphene patch to a tube, remains unclear. Recent studies have focused on finding a complete description of this phenomenon to understand its origin and to have total control over the formation of carbon nanotubes. In this study, a thermodynamic model is proposed that follows the sharp interface model approach, in which all energy contributions to the total energy of the nanotube are identified as bulk or surface terms. This study proposes an additive model to calculate the total energy of these structures and identify the dominant energy contributions that determine whether the adsorbed carbon atoms form a growing cap on the catalyst nanoparticle or initiate a new carbon nanotube perpendicular to the surface. By comparing the total energy of these two mechanisms, the research aims to elucidate the energetic driving force behind each pathway for optimizing future nanotube growth processes. We also discuss the generality of the model introduced in this article, showing how it can incorporate temperature and disorder effects, thereby enabling the description of both vapor-solid-solid and vapor-liquid-solid mechanisms of carbon nanotube formation at relevant operating conditions. Finally, we outline a strategy for a genuine multiscale framework that combines the microscopic, atomistic picture of carbon nanotube formation with a meso/macroscopic nucleation and growth representation based on a sharp-interface model.

The wettability of nanoporous materials is a key property for a diverse range of applications. However, the heat generated in this process remains largely unexplored. Herein, the heats of intrusion/extrusion into/from ZIF-8 + water systems of various ZIF-8 crystallite sizes were measured at different temperatures. We found that decreasing crystallite size to the nanoscale resulted in a reduction of the magnitude of the heats of intrusion/extrusion. These results were mirrored in simulations, where the reduction of intrusion heat by reducing the characteristics dependent on crystallite size was comparable to the values obtained experimentally. We related this to the reduction in filling at lower pressures. We recorded the inversion of the sign of the heats of intrusion/extrusion measured at high temperatures. In addition, the heat/work ratio of the intrusion/extrusion processes was dependent on temperature while independent of crystallite size, decoupling the two parameters and making them tunable exogenously.

Wetting-dewetting of nanoporous materials is of key importance for a wide range of natural and technological cases, which include separation, chromatography, ionic channels. Heterogeneous lyophobic systems (HLS) consisting of a lyophobic nanoporous material and a non-wetting liquid are attractive for thermomechanical energy storage, conversion and dissipation under pressure/temperature variations. In recent years, metal-organic frameworks (MOFs) are entering many fields, including those mentioned above due to their wide structural diversity, structural flexibility and high tunability. In this work, we investigate the hitherto unexplored effects of forced wetting (intrusion-extrusion) of a hybrid mixed-linker ZIF-7-8 MOF (Zn-methylimidazole0.794-benzimidazole0.206) with water. Surprisingly, despite its structural similarity to ZIF-8, the hybrid ZIF-7-8 MOF demonstrates a non-hysteretic water intrusion-extrusion cycle that is in strong contrast to both ZIF8 and ZIF-7 MOFs, which have pronounced intrusion-extrusion hysteresis. We used a combination of highpressure intrusion-extrusion experiments, neutron diffraction structural analysis and atomistic simulations to put forward several hypotheses regarding the observed transformation from shock absorber/bumper behavior of ZIF-8 and ZIF-7 to molecular spring behavior of hybrid ZIF-7-8. These results open a new route for tuning the intrusion-extrusion (wetting-dewetting) hysteresis for numerous applications.

Despite water intrusion in microporous materials being extensively investigated, obtaining a detailed overview of the intrusion mechanism in materials with more complex morphology, topology, and physical-chemical characteristics, such as metal-organic frameworks (MOFs), is far from trivial. In this work, we present a qualitative study on the mechanism of water intrusion in a crystallite of hydrophobic Cu-2(tebpz) (tebpz = 3,3 ',5,5 '-tetraethyl-4,4 '-bipyrazolate) MOF. This MOF is characterized by a complex morphology; it consists of primary (main channels) and secondary (lateral apertures) porosities. This is similar to some zeolites, such as the so-called ITT-type zeolite framework, but it presents the additional characteristics of high flexibility of the material and non-uniform hydrophobicity. Interestingly, in Cu2(tebpz), water intrusion occurs first for some of the channels lying tangent to the surface of the MOF's crystallite. This is due to hydrogen bonding bridging with bulk water across the (thin) lateral apertures of these channels. In macroscopic terms, this can be understood as a local reduction of hydrophobicity favoring intrusion. Temperature and pressure influence the average number of hydrogen bonds and the number of intruded water molecules, explaining the effect of these thermodynamic parameters on the intrusion/extrusion characteristics of this porous material. Molecular dynamics simulations allowed us to glimpse liquid intrusion in this complex hydrophobic material, highlighting how the classical models valid for mesoporous systems, namely, Young-Laplace's law, are not quite appropriate to describe intrusion in such materials.

Wetting of a porous solid by a fluid is of significant interest to many industrial processes. However, at the nanoscale, this process is complex, and little is known about its temperature dependance. In this work, we explored the intrusion-extrusion of water for a heterogeneous lyophobic system composed of a hydrophobic mesoporous silica gel and water over a wide 25-250 degrees C temperature range. The intrusion pressure was found to have a classical negative temperature dependance in the whole 25-250 degrees C temperature range. However, an unexpected non-monotonic temperature dependance was observed for the extrusion pressure. In particular, it became temperature independent above 200 degrees C. This observation suggests that dewetting of nanopores at high temperature is more complex than previously thought of and serves as experimental grounds for further theoretical exploration.

The wetting-dewetting of liquids in nanoporous solids is central to nanofluidics, separation, and energy storage, yet its temperature dependence under extreme conditions remains poorly understood. Here, we investigate water intrusion-extrusion in ordered mesoporous silica (SBA-15) functionalized with octyl groups (SBA-15-C8) across 25-250 °C and compare it with hydrophobized silica of disordered porosity. Intrusion pressures in both systems follow the expected negative temperature dependence described by classical capillarity. In contrast, extrusion pressures reveal a striking topology-temperature interplay. Up to 175 °C, SBA-15-C8 releases water at near-ambient pressure, unlike its disordered counterpart. Above 200 °C, however, extrusion from ordered pores converges to the high-pressure behavior of disordered silica, indicating a loss of topological distinction. Atomistic simulations suggest that this transition originates from thermally induced restructuring of the grafted layer: chain stretching effectively narrows the pores and may induce a Cassie-Baxter-like state, enhancing hydrophobicity and facilitating vapor nucleation. These findings demonstrate that pore topology ceases to govern extrusion at elevated temperatures, instead being dictated by a temperature-driven surface reconfiguration. The results contribute to a fundamental understanding of capillarity under extreme confinement and open opportunities for exploiting high-temperature wetting/dewetting in energy conversion, damping, and thermal management technologies.

High-energy-density thermochemical materials (TCMs), such as salt hydrates are ideal for low- and medium-temperature thermal energy storage applications. However, pure salt hydrates face challenges like poor thermal cyclability and control of reaction kinetics. Composite TCMs, created by integrating salt hydrates into support matrices, can improve the performance. However, condensation of water vapor in the pores of the composite can hinder hydration-dehydration reactions, leading to poor cyclability and reaction kinetics. In this work, we study the role of matrix hydrophobicity in the thermal cyclability of composite TCMs based on MgSO4·7H2O. Two silica matrices were employed: hydrophobic silica grafted with C8 chains and hydrophilic silica. Hydrophobic composites demonstrated excellent structural stability during 20 cycles with minimal morphological changes in silica and progressive salt particle size reduction. In contrast, hydrophilic matrix-based composites rapidly degraded, liquefying after only five cycles and showing complete loss of energy density. The improved performance of hydrophobic composites is attributed to the prevention of liquid water formation during thermal cycling, which otherwise accelerates salt dissolution and structural failure. These findings emphasize the critical importance of hydrophobic host materials in developing stable, high-performance thermochemical energy storage systems using salt hydrates.

Zeolitic imidazolate frameworks (ZIFs), such as ZIF-8, possess high surface area and tunable porosity, making them attractive for many applications. However, their structural flexibility can hinder performance in pressure-dependent processes like gas separation or water intrusion for energy storage. Several strategies have been proposed to control the characteristics of these materials but the general laws still remain elusive. In this study, we employ a combined theoretical/experimental approach to address this question. We focus on ZIF-8 and its derivatives to illustrate principles of endogenic and exogenic tuning with respect to processes related to intrusion of gasses and liquids in the porous system. Density functional theory and molecular dynamics simulations is used to investigate how linker swinging, the fundamental process controlling intrusion-extrusion/gas separation, depends on the endo-/exogenic modifications. These results will be tested against experimental pressure-volume-temperature liquid porosimetry data. Our results ultimately offer a design pathway for tailoring optimization of ZIF-based MOFs and, possibly, MOFs and porous materials at large.

Zeolitic imidazolate frameworks, such as ZIF-8, possess high surface area and tunable porosity, making them attractive for many applications. However, their structural flexibility can hinder performance in pressure-dependent processes like gas separation or water intrusion for energy storage and conversion. Several strategies have been proposed to control the characteristics of these materials, but the general laws still remain elusive. In this study, we employ a combined theoretical/experimental approach to address this question. We focus on ZIF-8 and its derivatives to illustrate principles of endogenic and exogenic tuning with respect to processes related to the intrusion of gases and liquids into the porous system. Density functional theory and molecular dynamics simulations are used to investigate how linker swinging, the fundamental process controlling intrusion-extrusion/gas separation, depends on the endo-/exogenic modifications. These results will be tested against experimental pressure-volume-temperature liquid porosimetry data. Our results ultimately offer a design pathway for tailoring the optimization of ZIF-based MOFs and, possibly, MOFs and porous materials in general.