Search

One key process involving single atom catalysts (SACs) is the electroreduction of CO2 to fuels. The chemistry of SACs differs largely from that of extended catalytic surfaces, presenting an opportunity to improve the ability to activate very stable molecules, such as CO2. In this work, we performed a density functional theory (DFT) study of CO2 activation on a series of SACs, focusing on the role played by the adopted functional in activity predictions. The role of the exchange-correlation functional has been widely investigated in heterogenous catalysts, but it is less explored in SACs. We tested the widely used PBE and the PBE+U corrected functionals against the more robust hybrid PBE0 functional. The results show that PBE is reliable if one is interested in qualitative predictions, but it leads to some inaccuracies in other cases. A possible way to attenuate this effect is by adopting the PBE+U framework, as it gives results that are very similar to PBE0 at an acceptable computational cost. The results of this study further underline the importance of the computational framework adopted in predicting the activity of SACs. The work suggests that one needs to go beyond PBE for quantitative estimates, an important consideration when performing screening and high-throughput calculations.

Hybrid DFT calculations are employed to compare the adsorption and stabilization of Cu, Ag, and Au atoms on graphitic C3N4 and on the heterojunction formed by g- C3N4 and TiO2. While Cu and Ag can be strongly chemisorbed in form of cations on g- C3N4, Au is only weakly physisorbed. On g- C3N4/TiO2, all coinage metal adatoms can be strongly chemisorbed, but, while Cu and Ag forms cations, Au form an Au− species. Ab Initio Molecular Dynamics simulations confirm that the metal adatoms on g-C3N4 are highly mobile at room temperature, while they remain confined in the interfacial spacing between C3N4 and TiO2 on the heterojunction, being both stably bound and reachable for the reactants in a catalytic cycle. Doping g- C3N4/TiO2 with metal single atoms permits thus to generate catalytic systems with tunable charge and chemical properties and improved stability with respect to bare C3N4. Moreover, the changes in the electronic structure of g- C3N4/TiO2 induced by the presence of the metal single atoms are beneficial also for photocatalytic applications.

Composite polymer electrolytes are systems of choice for future solid-state lithium metal batteries (LMBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is among the most interesting matrices to develop new generation quasi-solid electrolytes (QSEs). Here it is reported on nanocomposites made of PVDF-HFP and pegylated SiO2 nanoparticles. Silica-based hybrid nanofillers are obtained by grafting chains of poly(ethylene glycol) methyl ether (PEG) with different molecular weight on the surface of silica nanoparticles. The functionalized nanofiller improves the mechanical, transport and electrochemical properties of the QSEs, which show good ionic conductivity values and high resistance against dendrite penetration, ensuring boosted long and safe device operation. The most promising result is obtained by dispersing 5 wt% of SiO2 functionalized with short PEG chains (PEG750, Mw = 750 g mol−1) in the PVDF-HFP matrix with an ease solvent-casting procedure. It shows ionic conductivity of 0.1 mS cm−1 at 25 °C, more than 250 h resistance to stripping/plating, and impressive results during cycling tests in LMB with LiFePO4 cathode.

The activity of catalysts is mainly dictated by the adsorption strength of reaction intermediates at their surfaces. For electrocatalysts in solution, the adsorption strength is not only determined by the intrinsic properties of catalysts and reactants, but also by the solvation energy of reaction intermediates, which is difficult to capture with theoretical methods. Here, we report the impact of different explicit solvation approaches in estimating the stability of oxygenates on the (111) surface of platinum, widely used in oxygen electrocatalysis. We simulate the adsorption of OH, O, and OOH intermediates, relevant for oxygen reduction and oxygen evolution reactions, on Pt(111) with different solvation environments. We apply the static water bilayer model, typically adopted to calculate solvation energies on Pt(111) in computational studies. We then study the trend of solvation energies under different microsolvation environments, by adsorbing the intermediates in presence of an increasing number of water molecules. Last, we use a dynamic approach based on ab-initio molecular dynamics (AIMD) to account for dynamic effects. Our results indicate that the stabilities of oxygenates approach those of the water bilayer when the number of molecules increases from zero to three, but the free energies are affected in a not trivial way by the morphology and size of the water cluster, due to the increased complexity and configurational space. Moreover, static methods imply overcorrected free energies. The adoption of a molecular dynamics approach, based on single-run AIMD simulation of the Pt(111)/H2O interface, allows retrieval estimates close to the experimental observation, including dynamic effects, and is highly transferrable. These results suggest that i) when using a microsolvation scheme, it is recommended to include a few water molecules, up to three to resemble the picture of the static bilayer model; ii) dynamic effects are important and can be included with a sin

The attention toward single-atom catalysts (SACs) for electrochemical processes is growing at an impressive pace. Electronic structure calculations play an important role in this race by providing proposals of potentially relevant catalysts based on screening studies or on the identification of descriptors of the chemical activity. So far, almost all of these predictions ignore a crucial aspect in the design of a catalyst: its stability. We propose a simple yet general first-principles approach to predict the stability of SACs under working conditions of pH and applied voltage. This is based on the construction of a thermodynamic cycle, where part of the information is taken from experiment and the rest from density functional theory (DFT) calculations. In particular, we make use of the formalism of Pourbaix diagrams to investigate the stability of SACs in reductive or oxidative conditions and we identify those that show a pronounced tendency to dissolve or to form other chemical species. Applying the procedure to four transition metal atoms, Cr, Mn, Fe, and Co, and to three supports, N-doped graphene, carbon nitride, and covalent organic frameworks, we show that a key factor in determining the final stability is the binding energy of the free metal atom to the support. The results show that several potentially very good catalysts in key electrochemical reactions are, in fact, dramatically prone to dissolution or transformation in other chemical species, suggesting that every prediction of the SAC’s catalytic activity should be accompanied by a parallel investigation of the stability.

Single atom catalysis is relatively new frontier in catalysis with potential application in several critical chemical processes, such as water splitting reactions. Single atom catalysts (SACs) are analogues of coordination chemistry compounds, opening the way to the formation of unconventional intermediates compared to extended metal or oxide catalyst surfaces. In this work we show by means of density functional theory (DFT) calculations that the formation of unconventional adsorbates on SACs in the oxygen evolution reaction (OER) leads to complex scaling relationships, that differ from the scaling relations observed on extended surfaces. The evidence of new scaling relations directly impacts the expected catalytic activity and provides a further example of the importance of including in the modelling species beyond those that form on classical electrodes.

The evolution of nanotechnology has facilitated the development of catalytic materials with controllable composition and size, reaching the sub-nanometer limit. Nowadays, a viable strategy for tailoring and optimizing the catalytic activity involves controlling the size of the catalyst. This strategy is underpinned by the fact that the properties and reactivity of objects with dimensions on the order of nanometers can differ from those of the corresponding bulk material, due to the emergence of quantum size effects. Quantum size effects have a deep influence on the band gap of semiconducting catalytic materials. Computational studies are valuable for predicting and estimating the impact of quantum size effects. This perspective emphasizes the crucial role of modeling quantum size effects when simulating nanostructured catalytic materials. It provides a comprehensive overview of the fundamental principles governing the physics of quantum confinement in various experimentally observable nanostructures. Furthermore, this work may serve as a tutorial for modeling the electronic gap of simple nanostructures, highlighting that when working at the nanoscale, the finite dimensions of the material lead to an increase of the band gap because of the emergence of quantum confinement. This aspect is sometimes overlooked in computational chemistry studies focused on surfaces and nanostructures.

In this work we present a computational study of alkaline earth oxides (001) surfaces interfaced with water by means of density functional theory (DFT) in conjunction with ab initio molecular dynamics (AIMD) calculations. We studied the nature of MgO, CaO, SrO, and BaO (001) surfaces in contact with water. Results show that water dissociation is promoted as the alkaline earth metal becomes heavier. Similarly, the coordination number of the cation atoms with water molecules follows the same trend, indicating a more favorable interaction. The combined analysis of rumpling and pair distribution functions allows to provide a correspondence between reactivity of atoms on the surface and capability to coordinate water molecules. Except for MgO, the remaining surfaces display strong structural changes upon hydration, a relevant message when modelling hydrated surfaces. We also investigated the effect of the water thickness by adsorbing a water monolayer and bilayer to the surface. The findings of the study and the adopted approach could be of help for future studies of more complex systems or to provide fundamental rationalizations.

A computational screening of Single Atom Catalysts (SACs) bound to titanium nitride (TiN) is presented, for the Hydrogen Evolution Reaction (HER), based on density functional theory. The role of fundamental ingredients is explored to account for a reliable screening of SACs. Namely, the formation of H2-complexes besides the classical H* one impacts the predicted HER activity, in line with previous studies on other SACs. Also, the results indicate that one needs to adopt self-interaction-corrected functionals. Finally, predicting an active catalyst is of little help without an assessment of its stability. Thus, it is included in the theoretical framework the analysis of the stability of the SACs in working conditions of pH and voltage. Once unconventional intermediates and stability are considered in a self-interaction corrected scheme, the number of potential good catalysts for HER is strongly reduced since i) some potentially good catalysts are not stable against dissolution and ii) the formation of unconventional intermediates leads to thermodynamic barriers. This study highlights the importance of including ingredients for the prediction of new systems, such as the formation of unconventional intermediates, estimating the stability of SACs, and the adoption of self-interaction corrected functionals. Also, this study highlights some interesting candidates deserving of dedicated work.

Cross-coupling reactions are of great importance in chemistry due to their ability to facilitate the construction of complex organic molecules. Among these reactions, the Ullmann-type C−O coupling between phenols and aryl halides is particularly noteworthy and useful for preparing diarylethers. However, this reaction typically relies on homogeneous catalysts that rapidly deactivate under harsh reaction conditions. In this study, we introduce a novel heterogeneous catalyst for the Ullmann-type C−O coupling reaction, comprised of isolated Cu atoms chelated to a tetraethylenepentamine-pyrrole ligand that is immobilized on graphite nanoplatelets. The catalytic study reveals the recyclability of the material, and demonstrates the crucial role of the pyrrole linker in stabilizing the Cu sites. The work expands the potential of single-atom catalyst nanoarchitectures and underscores the significance of ligands in stabilizing metals in cationic forms, providing a novel, tailored catalyst for cross-coupling chemistries.

This work evaluates the feasibility of alkaline hydrogen evolution reaction (HER) using Pt single-atoms (1.0 wt %) on defect-rich ceria (Pt1/CeOx) as an active and stable dual-site catalyst. The catalyst displayed a low overpotential and a small Tafel slope in an alkaline medium. Moreover, Pt1/CeOx presented a high mass activity and excellent durability, competing with those of the commercial Pt/C (20 wt %). In this picture, the defective CeOx is active for water adsorption and dissociation to create H* intermediates, providing the first site where the reaction occurs. The H* intermediate species then migrate to adsorb and react on the Pt2+ isolated atoms, the site where H2 is formed and released. DFT calculations were also performed to obtain mechanistic insight on the Pt1/CeOx catalyst for the HER. The results indicate a new possibility to improve the state-of-the-art alkaline HER catalysts via a combined effect of the O vacancies on the ceria support and Pt2+ single atoms.

RuO2 and IrO2 are among the most active catalysts for the Oxygen Evolution Reaction (OER). Recently, it was demonstrated that the catalytic surface of these oxides plays a role in the reaction, where a hydrogen bond with a neighbor OH group stabilizes an unconventional −OO intermediate (−OO–H), prior to O2 evolution. Quantum chemical calculations neglecting solvation effects indicated that this intermediate is more stable than the conventional −OOH, and that deprotonation of the stabilizing −OH is the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water molecules on the relative stability of −OOH and −OO–H oxygenates on RuO2 (110) by means of density functional theory calculations combined with ab initio Molecular Dynamics simulations (AIMD). We show that the two intermediates participate in a hydrogen bonding network with water to a similar extent, but leading to different interfacial water structures, with possible implications on interfacial proton dynamics and reaction kinetics. Moreover, −OOH can spontaneously convert to −OO–H through a process mediated by water, demonstrating the critical role of explicitly including water in the model. This study provides further mechanistic insights on the role of the oxide surface chemistry in the OER mechanism and highlights the importance of explicitly treating the catalyst/water interfaces including dynamical aspects to assess the stability and the interconversion mechanism of key surface species, since the adoption of static solvation approaches tends to overestimate the energetic difference between −OOH and −OO–H reaction intermediates.

Background: The SARS-CoV-2 pandemic compromised the mental health of COVID-19 patients and their family members. Due to social distancing and lockdown measures, a remote, tele-psychotherapy program for former or current COVID-19 patients and their relatives was implemented. Objective: The primary goal of this project was to evaluate intervention feasibility. The secondary aim was to assess the impact of the intervention by means of pre-post psychological changes. Methods: After a phone-based eligibility screening and remote neuropsychological testing, participants completed online self-reports assessing baseline COVID-related psychopathology. Next, participants attended eight tele-psychotherapy sessions. After treatment, the online self-reports were completed again. Results: Of 104 enrolled participants, 88 completed the intervention (84.6 % completion rate). Significant pre-post improvements were observed for generalized anxiety (d = 0.38), depression (d = 0.37), insomnia (d = 0.43), post-traumatic psychopathology (d = 0.54), and general malaise (d = 0.31). Baseline cluster analysis revealed a subgroup of 41 subjects (47.6 %) with no psychopathology, and a second subgroup of 45 subject (52.3 %) with moderate severity. Thirty-three percent of the second group reached full symptom remission, while 66 % remained symptomatic after treatment. Conclusions: Remote brief tele-psychotherapy for COVID-19 patients and their first-degree relatives is feasible and preliminary efficacious at reducing COVID-related psychopathology in a subgroup of patients. Further research is needed to investigate distinct profiles of treatment response.

Background: Across a range of age, educational and clinical characteristics, adults experiencing depression and anxiety already use digital technology to manage their symptoms. Although several reviews and meta-analyses indicated feasibility and efficacy for adults with depression and anxiety, digital treatments are poorly accessed and disseminated. This review illustrates potentials and limitations of interventions that specifically leveraged unique features of digital technology and were grounded in the principles of Cognitive Behavioral Therapy (CBT). Methods: This systematic review followed the PRISMA guidelines. An electronic database search was conducted in October 2021. Peer-reviewed, English-language studies were included if i) they reported data from RCTs for adults aged 18+ who engaged with CBT-informed digital interventions targeting primarily depression and anxiety; ii) they used at least PHQ-9 or GAD-7 as standardized and validated assessment self-report measures for depression and anxiety. Results: Findings from 35 RCTs examining 33 interventions (25 internet-based, 6 mobile-based, a2 mobile/web) are discussed. The quality of the evidence differed widely as many small-scale RCTs reported only short-term feasibility and preliminary efficacy. Effects of CBT-informed digital interventions were substantially larger when compared to waitlist than active control conditions. Greater therapeutic benefits were observed for interventions that offered clinical assistance or were used in combination with other treatments. Conclusions: CBT-informed digital interventions have accumulated enough scientific evidence to be positioned today as: i) a low-intensity tool for those with subclinical levels of symptoms; ii) a first step in a stepped-care approach to service delivery iii) a low-cost, easily accessible option for targeted preventive programs.

Although visible-light-driven dual photoredox catalysis, a method that combines photoabsorbers and transition metals, has become a powerful tool to conduct coupling reactions, resource economical and scalability issues persist, owing to the use of catalysts and light absorbers that exploit critical raw materials (such as iridium complexes), and are homogeneous in nature. Here we report the merger of metallic single-atom and photoredox catalysis, in the form of a Ni atom-supported carbon nitride material, for the C–O coupling of carboxylic acids and alkyl halides. This operationally straightforward system, composed of only earth-abundant components, exhibits a wide functional group tolerance. Additionally, short reaction times, facile recovery and high catalyst stability make this method highly attractive for industrial applications.

Single-atom catalysts (SACs) are heterogenous catalysts with elements in common with coordination compounds. We discuss some fundamental elements required for the successful computational modeling of SACs for electrocatalytic applications. The first two aspects are the role played by the exchange-correlation functional adopted within a given DFT approach and the role of the local coordination of the active transition metal atom. Next, we discuss new intermediates that can form on SACs and that are not present on extended metal electrodes and how to model solvation, with particular emphasis on the fact that on SACs water can not only act as a solvent but also as a ligand. Finally, we discuss challenges related to the inclusion of pH and voltage in the models and some open issue concerning the rational design of new SACs.

Electronic structure calculations represent an essential complement of experiments to characterize single-atom catalysts (SACs), consisting of isolated metal atoms stabilized on a support, but also to predict new catalysts. However, simulating SACs with quantum chemistry approaches is not as simple as often assumed. In this work, the essential factors that characterize a reliable simulation of SACs activity are examined. The Perspective focuses on the importance of precise atomistic characterization of the active site, since even small changes in the metal atom's surroundings can result in large changes in reactivity. The dynamical behavior and stability of SACs under working conditions, as well as the importance of adopting appropriate methods to solve the Schrödinger equation for a quantitative evaluation of reaction energies are addressed. The Perspective also focuses on the relevance of the model adopted. For electrocatalysis this must include the effects of the solvent, the presence of electrolytes, the pH, and the external potential. Finally, it is discussed how the similarities between SACs and coordination compounds may result in reaction intermediates that usually are not observed on metal electrodes. When these aspects are not adequately considered, the predictive power of electronic structure calculations is quite limited.

Single Atom Alloys (SAAs) represent one of the most promising classes of heterogeneous catalysts. They are based on isolated transition metal (TM) atoms stabilized in a host metal matrix. Among others, SAAs are widely studied for processes involving hydrogen, such as water splitting or hydrogenation reactions. On a metal surface the H2 molecule forms either weakly physisorbed species (H2phys) or dissociates with formation of chemisorbed H atoms (H*). In electrochemical processes, the adsorption free energy of the H* intermediate is normally used as a descriptor of the catalyst reactivity. Recently, it has been shown that on Single Atom Catalysts (SAC) embedded in carbon-based, sulfide, or oxide supports other species can form, where two H atoms are stably bound to the SAC, forming dihydrogen or dihydride (H*H*) surface species reminiscent of the classical Kubas's transition metal complexes in coordination chemistry. In this work we show, based on density functional theory calculations, that dihydrogen and dihydride complexes can also form on SAAs and, depending on the nature of the host metal, can be even more stable than two separated chemisorbed H* species (2H*). These new stable intermediates have not been considered so far in the analysis of the mechanism and kinetics of the reaction. The work shows that the possible formation of dihydrogen and dihydride complexes is not limited to SACs but is also valid for SAAs and needs to be considered in the study of hydrogen-based reactions on these systems.

In this work we present a computational study of the nature of a Single Atom Catalyst (SAC) consisting of a Pt1 atom anchored on a C3N4 support, and of its reactivity in the water splitting semi-reactions, the Hydrogen Evolution (HER) and Oxygen Evolution (OER) Reactions. The work is motivated by the intense research in designing catalytic materials for water splitting characterized by a low amount of noble metal species, maximization of active phase, and stability of the catalyst. C3N4-based SACs are promising candidates. The results indicate that the chemistry of a single atom is complex, as it can be anchored to the support in different ways resulting in a different stability. The reactivity of the most stable structure in HER and OER has been considered, finding that Pt1@C3N4 is more reactive than metallic platinum. Furthermore, unconventional but stable intermediates can form that differ from the intermediates usually found on extended catalytic surfaces. The work highlights the importance of considering the complex chemistry of SACs in view of the analogies existing with coordination chemistry compounds.

Single Atom Catalysts (SACs) bridge homo- and heterogenous catalysis and are promising for several chemical processes of interest, including water splitting. SACs can form reaction adducts that do not likely form on conventional metal catalysts. Besides the typical supporting matrices made by carbon-based materials, Covalent Organic Frameworks (COFs) are gaining attention because of the possibility to design the hosting cavity to stably bind the active metal site. We performed a density functional theory (DFT) study of a set of SACs made by transition metal atoms embedded in a recently synthesized COF material. We explored their reactivity in Hydrogen and Oxygen Evolution Reactions (HER and OER, respectively). SACs@COF can form several intermediates with no counterpart on the classical metal electrodes, with important implications on the reaction mechanism. The results are useful for the design of novel catalytic materials and for the identification of interpretative/predictive activity descriptors.

RuO2 and IrO2 are among the most active catalysts for the Oxygen Evolution Reaction (OER). Recently, it was demonstrated that the catalytic surface of these oxides plays a role in the reaction, where a hydrogen bond with a neighbor OH group stabilizes an unconventional −OO intermediate (−OO-H), prior to O2 evolution. Quantum chemical calculations neglecting solvation effects indicated that this intermediate is more stable than the conventional −OOH, and that deprotonation of the stabilizing −OH is the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water molecules on the relative stability of −OOH and −OO-H oxygenates on RuO2 (110) by means of density functional theory calculations combined with ab initio Molecular Dynamics simulations (AIMD). We show that the two intermediates participate in a hydrogen bonding network with water to a similar extent, but leading to different interfacial water structures, with possible implications on interfacial proton dynamics and reaction kinetics. Moreover, −OOH can spontaneously convert to −OO-H through a process mediated by water, demonstrating the critical role of explicitly including water in the model. This study provides further mechanistic insights on the role of the oxide surface chemistry in the OER mechanism and highlights the importance of explicitly treating the catalyst/water interfaces including dynamical aspects to assess the stability and the interconversion mechanism of key surface species, since the adoption of static solvation approaches tends to overestimate the energetic difference between −OOH and −OO-H reaction intermediates.

The interaction of CaO and Ca(OH)2 with solvated or gaseous SO2 plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO2 from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO2 with a CaO(001) single crystal. First, the surface chemistry of SO2 was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO2 solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas.

TiO2 is a relevant catalytic material, and its chemistry in aqueous environment is a challenging aspect to address. Also, the morphology of TiO2 particles at the nanoscale is often complex, spanning from faceted to spherical. In this work, we study the pH- and facet-dependent surface chemistry of TiO2/water interfaces by performing ab initio molecular dynamics simulations with the grand canonical formulation of species in solution. We first determined the acid-base equilibrium constants at the interface, which allows us to estimate the pH at the point of zero charge, an important experimental observable. Then, based on simulated equilibrium constants, we predict the amount of H+, OH-, and adsorbed H2O species present on the surfaces as a function of the pH, a relevant aspect for water splitting semi-reactions. We approximated the complex morphology of TiO2 particles by considering the rutile (110) and (011), and anatase (101), (001), and (100) surfaces.

The electrochemical reduction of CO2 on single atom catalysts (SAC) has emerged as a highly promising yet intricate process, requiring an in-depth understanding of each elementary step of the reaction. Most of the theoretical studies pertaining the screening of new efficient catalysts neglect important effects such as the capability of the catalytic site to bind and activate CO2, the occurrence of competing reaction paths via formation of different isomers in the intermediate steps, and the role of water. In this work we will show that these are key aspects of the CO2 reduction reaction (CO2RR). Employing density functional theory, we investigated a series of Transition Metal atoms (Sc-Cu, Mo-Ag, W-Au) embedded in nitrogen doped graphene (TM@4N-Gr) and their activity in the CO2 reduction. Our results show that water is not only solvating the reaction intermediates, but it acts as a ligand itself, competing with CO2 when binding to the catalytic site. This coordination chemistry effect largely affects the stability of the chemical intermediates. Furthermore, only a small fraction of the investigated SACs can bind and activate CO2, and that in most cases the reaction proceeds via formation of the OCHO intermediate and not of the COOH one, as often assumed.

In this tutorial review we report the state-of-the-art of the modeling approaches of Single Atom Catalysts (SAC) for water splitting and fuel cells reactions. The discussion applies for Hydrogen Evolution Reaction (HER), Oxygen Reduction Reaction (OER), Hydrogen Oxidation Reaction (HOR), and Oxygen Reduction Reaction (ORR). The main scope of this work is to underline the relevant aspects of SACs modelling. On the one hand, the review could help computational chemists aiming to start the study of SACs. On the other hand, experimentalists could find the critical analysis of DFT results of interest to understand better the strengths and weaknesses of simulations, and how to interpret computational results. After an introductory section of SACs, we start by briefly presenting the state-of-the-art methodologies. Then, we analyze the critical aspects for a reliable prediction of the electronic properties, and we discuss the robustness of the structural models and ways to validate them. Furthermore, we discuss the main approaches to predict catalytic activity and selectivity, which is the final goal of the computational catalysis. We conclude this review with a critical analysis of the current challenges in the field, and the main limitations of the modeling approaches that are described.

We investigate the interface between carbon nitride (C3N4) and phosphorene nanosheets (P-ene) by means of Density Functional Theory (DFT) calculations. C3N4/P-ene composites have been recently obtained experimentally showing excellent photoactivity. Our results indicate that the formation of the interface is a favorable process driven by Van der Waals forces. The thickness of P-ene nanosheets determines the band edges offsets and the charge carriers’ separation. The system is predicted to pass from a nearly type-II to a type-I junction when the thickness of P-ene increases, and the conduction band offset is particularly sensitive. Last, we apply the Transfer Matrix Method to estimate the efficiency for charge carriers’ migration as a function of the P-ene thickness.

The Oxygen Evolution Reaction (OER) is a key part of water splitting. On metal and oxide surfaces it usually occurs via formation of three intermediates, M(OH), M(O), and M(OOH) (also referred to as OH*, O*, and OOH* species where * indicates a surface site). The last step consists of O2 release. So far, it has been generally assumed that the same path occurs on single atom catalysts (SACs). However, the chemistry of SACs may differ substantially from that of extended surfaces and is reminiscent of that of coordination compounds. This raises the question of whether on SACs the OER follows the classical mechanism or not. Using a DFT approach, we studied a set of 30 SACs made by ten metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Pd and Pt) anchored on three widely used 2D carbon-based materials, graphene, nitrogen-doped graphene and carbon nitride. In none of the cases examined the most favourable reaction path is the conventional one. In fact, in all cases other intermediates with higher stabilities form: M(OH)2, M(O)(OH), M(O)2, and M(O2) (OH* OH*, O* OH*, O* O*, O2* according to standard nomenclature). Therefore, the common assumption that on SACs the OER proceeds via formation of OH*, O*, and OOH* intermediates is not verified. Predictions of new catalysts based on the screening of large number of potential structures can lead to completely incorrect conclusions if these additional intermediates are not taken into consideration.

We investigated the impact of quantum confinement on the band gap of chalcogenides 2D nanostructures by means of density functional theory. We studied six different systems: MoS2, WS2, SnS2, GaS, InSe, and HfS2 and we simulated nanosheets of increasing thickness, ranging from ultrathin films to ∼10-13 nm thick slabs, a size where the properties converge to the bulk. In some cases, the convergence of the band gap with slab thickness is rather slow, and sizeable deviations from the bulk value are still present with few nm-thick sheets. The results of the simulations were compared with the available experimental data, finding a quantitative agreement. The impact of quantum confinement can be rationalized in terms of effective masses of electrons and holes and system’s size. These results show the possibility of reliably describing quantum confinement effects on systems for which experimental data are not available.

Single atom catalysts (SACs) consist of isolated metal atoms stabilized on a solid support. The name suggests that the catalytic activity is due to the nature of the metal atom, but of course the interaction with the substrate plays a role as well. But what is more important? The metal atom or its surrounding? To answer this question, we have performed numerical experiments based on density functional theory (DFT). 24 transition metal atoms have been incorporated in Nitrogen-doped graphene, and the catalytic activity in the hydrogen evolution reaction (HER) has been studied changing the metal and keeping the N-doped graphene matrix fixed. Then, one specific atom, Pt, has been embedded in the same matrix but the nitrogen neighbors of Pt have been systematically replaced by carbon or oxygen atoms generating more than 20 structures. The HER has thus been studied by keeping the metal center fixed but changing the surrounding. It turns out that the same great variability in chemical behavior can be achieved by changing the active site or the surrounding environment. This shows the importance of the local coordination in determining the catalytic activity. The consequences of this conclusion for modeling studies of SACs are discussed.

In this work, we demonstrate the essential role of the formation of superoxo and peroxo complexes on single-atom catalysts (SACs), an aspect that is often neglected in the study of these systems. By means of density functional theory calculations, we consider a representative set of 11 transition metal atoms (Sc, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, Pd, Pt) anchored on nitrogen-doped graphene, and we show that most of them form stable superoxo and peroxo intermediates when they react with molecular oxygen. Their formation has a direct impact on the oxygen evolution reaction (OER), and we develop the corresponding microkinetic models showing that this step of the reaction cannot be neglected. Depending on the transition metal atom, the inclusion of the superoxo/peroxo complexes in the analysis of the reaction profile can change the kinetics by several orders of magnitude. This work reveals the important role of dioxygen complexes species in the OER and reinforces the notion of SACs as analogs of coordination compounds

The most widely used approach to predict catalytic activity is density functional theory, whose results however depend on the adopted exchange-correlation functional. In this work, the role played by the functional in predicting the activity of single atom catalysts (SAC) in the hydrogen and oxygen evolution reactions (HER and OER) is studied. 16 transition metal (TM) atoms embedded in N-doped graphene are simulated and the performance of the widely adopted Perdew–Burke–Ernzerhof (PBE) functional against the hybrid PBE0 functional is assessed. The PBE+U approach, a computationally less complex way to correct for the self-interaction error in density functional theory, is also considered. The predictions obtained with PBE have a substantial deviation from PBE0 for first row TMs, i.e., 3d systems, while smaller deviations are found for the 4d and 5d series. The PBE+U results represent an improvement with respect to PBE, although some differences from PBE0 remain. This study underlines the importance of the choice of the DFT functional in screening new catalysts and in predicting catalytic activities. The use of PBE appears acceptable for 4d and 5d metals, while in the case of 3d systems PBE+U or PBE0 approaches are recommended, in particular for magnetic ground states.

From grain boundaries and heterojunctions to manipulating 2D materials, solid-solid interfaces play a key role in many technological applications. Understanding and predicting properties of these complex systems present an ongoing and increasingly important challenge. Over the last few decades computer simulation of interfaces has become vastly more powerful and sophisticated. However, theoretical interface screening remains based on largely heuristic methods and is strongly biased to systems that are amenable to modelling within constrained periodic cell approaches. Here we present an unconstrained and generally applicable non-periodic screening approach for systematic exploration of material’s interfaces based on extracting and aligning disks from periodic reference slabs. Our disk interface method directly and accurately describes how interface structure and energetic stability depends on arbitrary relative displacements and twist angles of two interacting surfaces. The resultant detailed and comprehensive energetic stability maps provide a global perspective for understanding and designing interfaces. We confirm the power and utility of our method with respect to the catalytically important TiO2 anatase (101)/(001) and TiO2 anatase (101)/rutile (110) interfaces.

ConspectusSingle-atom catalysis (SAC) is a fascinating and rapidly growing field in heterogeneous catalysis. In less than 20 years, this has become one of the most widely investigated subjects by the catalytic community for various good reasons: the ability to synthesize active catalysts using a minimum amount of precious metals, the expected higher selectivity of SACs compared to assemblies of nanoparticles of variable sizes, and the fact that SACs represent a bridge between homogeneous and heterogeneous catalysis. The relative simplicity of SAC structures compared to classical heterogeneous catalysts based on supported metal nanoparticles has stimulated an intense simulation activity aimed at predicting new potential catalysts from first principles, often based on machine learning algorithms. This is a very ambitious objective and ultimately represents the final goal of every modeling activity: the possibility to provide realistic predictions of new material properties and catalytic reactivity. However, one of the main reasons that theory is useful is and remains the interpretation and analysis of experimental results, with the no less crucial goal of understanding the basic principles that determine a certain functionality or reactivity. The combination of advanced characterization techniques and theoretical calculations can provide a general conceptual framework to better understand structure-function relationships. In this Account, we will address this aspect in trying to provide answers to some fundamental questions related to the structure, stability, and activity of SACs. We will start by addressing a question that arises every time a new SAC is synthesized: where are the metal atoms? What is their coordination mode with the support? Once we have shown how to address this point, we will move on to the next fundamental question: do the single atoms stay put? How does the chemical environment of a SAC depend on the preparation or reaction conditions? Next, we

One-pot three-component regioselective azide-alkyne cycloadditions are central reactions for synthesizing pharmaceuticals and fine chemicals and are also applied for in vivo metabolic labeling biotechnology. Homogeneous catalysts based on copper species coordinated with ancillary ligands are regularly used to perform this reaction, offering superior catalytic activity and selectivity compared to conventional heterogeneous counterparts based on supported copper nanoparticles. However, the challenge of catalyst recovery limits the use of these homogeneous compounds in many large-scale applications. In this work, we report the high catalytic performance of a family of Cu-based single-atom catalysts for triazole synthesis, with an emphasis on the fundamental understanding of the structure and function of the catalyst. The catalysts were prepared via tricyanomethanide polymerization to create a joint electronic structure where the mesoporous graphitic carbon nitride carrier acts as a ligand for the atomically dispersed copper species. The material properties and the precise metal location/coordination (i.e., deposited in the heptazine pore of carbon nitride, substituted in the framework of carbon nitride, hosted in a vacancy, or entrapped in sandwich-like arrangement) were characterized through a battery of spectroscopic and theoretical methods. The catalysts were employed in the synthesis of 1,2,3-triazoles employing azide-alkyne click reaction under base-free conditions. The single-atom Cu catalysts demonstrated improved activity and selectivity compared to the homogeneous reference catalyst. Density functional theory calculations corroborated the results and showed that the reaction proceeds through a barrier given by the activation of the acetylenic moiety on Cu1. The activity of this step was primarily affected by the coordination of the metal with the support. Therefore, understanding the metal coordination in single-atom catalysts is critical to further optimizing

We present an approach to determine from first principles the expected efficiency of semiconductors heterojunctions in solar light absorption and electron-hole pairs generation for photocatalysis and solar cells applications. In a composite material, upon absorption of photons of appropriate wavelength, electrons and holes can migrate towards different components of the junction, thus reducing the electron-hole recombination probability. This occurs when the bands of the two semiconductors are properly aligned. However, a favorable band alignment is not a sufficient condition to have a device able to convert efficiently solar light into chemical or electrical energy. Using the Transfer Matrix Method and Density Functional Theory calculations we evaluate the transmittance and reflectivity of the charge carriers, and we determine two descriptors, the injection efficiency and the maximum conversion efficiency, that allow us to predict in a more realistic way the performance of the device. This method is based on the explicit inclusion of surface, interface, and quantum confinement effects that can be present when the heterojunction is formed. By using the YP/TiO2 (Y = Al, Ga, In) and the CsPbX3/TiO2 (X = Cl, Br, I) systems as examples we show that the approach provides an excellent agreement with the available experimental data.

The description of the band gap of halide perovskites at the level of density functional theory (DFT) has been subject of several studies but still presents significant problems and deviations from experimental values. Various approaches have been proposed, including the use of system-specific hybrid functionals with a variable amount of exact exchange or the explicit inclusion of spin-orbit coupling (SOC) effects. In this work, we present a pragmatic recipe to compute the band gap of halide perovskites with a minimum average error. The recipe is tested on a set of 36 halide perovskites of the type ABX3 [A = Cs, methyl-ammonium (MA), and formamidinium (FA); B = Ge, Sn, and Pb; and X = Cl, Br, and I] for which experimental estimates of the band gap have been reported in the literature. Upon assessment of the accuracy of commonly used DFT functionals and the analysis of their performances based on error and statistical analysis, we suggest a strategy to compute band gaps in halide perovskites with a single functional. This is based on the use of the hybrid HSE06 functional where SOC is included exclusively for Pb-containing compounds. The results are rationalized in terms of the materials' chemical nature and are corroborated by the prediction of their expected efficiencies in solar cells. The calculated efficiencies from band gaps obtained with the proposed approach closely follow the experimental trend, demonstrating the importance of adopting a reliable but material-independent computational strategy to screen new halide perovskite materials for solar energy conversion.

Background: Motor structures involvement has been traditionally assumed to account for selective deficits of verb (V) vs. noun (N) processing in Parkinon's disease (PD) patients via action semantic impairment (Embodied Cognition Theory, ECT). Nonetheless, post-semantic accounts, as well as extra-linguistic explanations (task difficulty effects), have not been evenly endorsed. This study aimed at investigating neurocognitive underpinnings of N-V discrepanies in PD patients. Methods: PD patients with (PD+) and without (PD-) cognitive impairments were compared to healthy participants (HPs) on tasks evaluating N and V semantic as well as post-semantic processing. Effects of motor content (actionality) of Ns and Vs and of verb argument structure (VAS) complexity were assessed. Results: All groups performed worse in V than in N lexical retrieval. PD patients performed worse than HPs on both lexical and semantic tasks. By contrast, only N/V naming tasks discriminated PD-from PD + patients. PD + patients showed selective difficulties in retrieving low-actionality as well as transitive and unaccusative Vs. No associations were detected between the action semantic measure and V-naming performances. Discussion: ECT-framed explanations cannot account for N-V discrepancies in PD patients. Indeed, these patients showed semantic deficits not limited to the action domain and retrieved most easily high-actionality Vs. N-V discrepancies in PD patients would thus reflect a magnification of a differential processing demand for Vs vs. Ns - which is intrinsic to the neurocognitive system. Nonetheless, PD patients being sensitive to VAS complexity might imply fronto-striatal involvement in V post-semantic processing, possibly at the lemma level.

The global warming crisis has sparked a series of environmentally cautious trends in chemistry, allowing us to rethink the way we conduct our synthesis, and to incorporate more earth-abundant materials in our catalyst design. “Single-atom catalysis” has recently appeared on the catalytic spectrum, and has truly merged the benefits that homogeneous and heterogeneous analogues have to offer. Further still, the possibility to activate these catalysts by means of a suitable electric potential could pave the way for a true integration of diverse synthetic methodologies and renewable electricity. Despite their esteemed benefits, single-atom electrocatalysts are still limited to the energy sector (hydrogen evolution reaction, oxygen reduction, etc.) and numerous examples in the literature still invoke the use of precious metals (Pd, Pt, Ir, etc.). Additionally, batch electroreactors are employed, which limit the intensification of such processes. It is of paramount importance that the field continues to grow in a more sustainable direction, seeking new ventures into the space of organic electrosynthesis and flow electroreactor technologies. In this piece, we discuss some of the progress being made with earth abundant homogeneous and heterogeneous electrocatalysts and flow electrochemistry, within the context of organic electrosynthesis, and highlight the prospects of alternatively utilizing single-atom catalysts for such applications.

One of the objectives of electronic structure theory is to predict chemical and catalytic activities. This is a challenging target due to the large number of variables that determine the performance of a heterogeneous catalyst. The complexity of the problem has reduced considerably with the advent of single atom catalysts (SACs) and, in particular, of graphene-based SACs for electrocatalytic reactions such as the oxygen reduction (ORR), the oxygen evolution (OER), and the hydrogen evolution (HER) reactions. In this context we assist with a rapidly growing number of theoretical studies based on density functional theory (DFT) and with proposals of universal descriptors that should provide a guide to the experimentalist for the synthesis of efficient catalysts. In this Perspective we critically analyze some of the current problems connected with the prediction of the activity of SACs: accuracy of the calculations, neglect of important contributions in the models used, physical meaning of the proposed descriptors, not to mention some problems of reproducibility. It follows that the "rational design"of a catalyst based on some of the proposed universal descriptors should be considered with caution.

The application of a mechanical strain to a 2D material can create pseudo-magnetic fields and lead to a quantized valley Hall effect. However, measuring valley-resolved effects remains a challenging task due to their inherent fragility and dependence on the sample’s proper design. Additionally, non-local transport probes based on multiterminal devices have often proven to be inadequate in yielding conclusive evidence of the valley Hall signal. Here, we introduce an alternative way of detecting the quantized valley Hall effect, which entirely relies on local density measurements, performed deep in the bulk of the sample. The resulting quantized signal is a genuine Fermi sea response, independent of the edge physics, and reflects the underlying valley Hall effect through the Widom-Středa formula. Specifically, our approach is based on measuring the variation of the particle density, locally in the bulk, upon varying the strength of the applied strain. This approach to the quantized valley Hall effect is particularly well suited for experiments based on synthetic lattices, where the particle density (or integrated density of states) can be spatially resolved.

This essay opposes the idea that contemporary critical events like pandemics, global warming, environmental deterioration, et cetera, are to be considered as affecting humanity in a uniform way. Instead of seeing these phenomena like abstract universal threats, I propose to look at them through the lens of my concept of differential harm. By drawing on interdisciplinary sources, this concept aims at covering a series of processes that are best described in differential, rather than absolute, terms. By the same token, differential harm is a matter of scale. Moreover, this essay also suggests that macroscopic critical processes are better understood as instances of harm, rather than violence. Instead of framing macroscopic disruptive phenomena as simple calamities or crises, my approach also aims at acknowledging their social, political, and psychological dimensions.

What if I told you that they knew everything? And that they have known it for a very long time? On January 13 of this year, 2023, in the journal Science, perhaps the most important article to date on climate change was published. In political, social, and ethical terms, this article represents the equivalent of a nuclear bomb, despite the fact that (as is sadly obvious to expect) no one in mainstream news channels (and very few in academia) has mentioned it.

Part of ISBN 9781450394222QC 20230801

The application of a mechanical strain to a 2D material can create pseudo-magnetic fields and lead to a quantized valley Hall effect. However, measuring valley-resolved effects remains a challenging task due to their inherent fragility and dependence on the sample’s proper design. Additionally, non-local transport probes based on multiterminal devices have often proven to be inadequate in yielding conclusive evidence of the valley Hall signal. Here, we introduce an alternative way of detecting the quantized valley Hall effect, which entirely relies on local density measurements, performed deep in the bulk of the sample. The resulting quantized signal is a genuine Fermi sea response, independent of the edge physics, and reflects the underlying valley Hall effect through the Widom-Středa formula. Specifically, our approach is based on measuring the variation of the particle density, locally in the bulk, upon varying the strength of the applied strain. This approach to the quantized valley Hall effect is particularly well suited for experiments based on synthetic lattices, where the particle density (or integrated density of states) can be spatially resolved., SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

The development of high-performance Lithium-ion batteries has long been at the forefront of energy technologies, given the urgent need for large-scale deployment of renewable energy sources, together with the electrification of transportation. The electrolyte, which is a fundamental component of such electrochemcal systems, is often the limiting factor directly affecting the performance and safety of the battery [1,2]. In this context, Poly(vinylidene difluoride)-based electrolytes have attracted huge attention due to their interesting ionic conductive properties and capability to overcome safety issues by replacing flamable organic liquid electrolytes [3]. Despite the interest in these polymer electrolytes, the mechanism of Li-ion diffusion in PVDF-based electrolyte is not well understood. Recent experimental studies [4] have argued that residual DMF solvent, which is used during the electrolytes preparation to dissolve the polymer-salt system, solvates Li+ and contributes to the ionic diffusion. Here we have used Density Functional Theory (DFT) to elucidate the role of DMF in the solvation and diffusion of Li+. The interaction of Li+ with DMF molecules and PVDF chains has been computed by constructing Li+(DMF)n(PVDF)m complexes. In addition, molecular dynamics simulation has been performed in order to obtain additional insights on the diffusion of Li+(DMF)n(PVDF)m complex. The atomic structures and formation energies of Li+(DMF)n(PVDF)m complexes, shown in Figure 1, demonstrate that Li+ tends to coordinate up to three DMF molecules rather than directly binding PVDF, indicating that the interaction Li+-DMF is stronger than the interaction of Li+ with PVDF. Increasing the number of ligands, e.g. n+m > 4, Li+(DMF)n complex interacts with PVDF as the second solvation shell. Moreover, our molecular dynamics simulations confirm that the amount of DMF molecules coordinating Li+ affects the mobility of Li+ through PVDF chains. Our results represent a step forwarding in

Published: November 01 2023, In face-to-face conversations, listeners gather visual speech information from a speaker's talking face that enhances their perception of the incoming auditory speech signal. This auditory-visual (AV) speech benefit is evident even in quiet environments but is stronger in situations that require greater listening effort such as when the speech signal itself deviates from listeners' expectations. One example is infant-directed speech (IDS) presented to adults. IDS has exaggerated acoustic properties that are easily discriminable from adult-directed speech (ADS). Although IDS is a speech register that adults typically use with infants, no previous neurophysiological study has directly examined whether adult listeners process IDS differently from ADS. To address this, the current study simultaneously recorded EEG and eye-tracking data from adult participants as they were presented with auditory-only (AO), visual-only, and AV recordings of IDS and ADS. Eye-tracking data were recorded because looking behavior to the speaker's eyes and mouth modulates the extent of AV speech benefit experienced. Analyses of cortical tracking accuracy revealed that cortical tracking of the speech envelope was significant in AO and AV modalities for IDS and ADS. However, the AV speech benefit [i.e., AV > (A + V)] was only present for IDS trials. Gaze behavior analyses indicated differences in looking behavior during IDS and ADS trials. Surprisingly, looking behavior to the speaker's eyes and mouth was not correlated with cortical tracking accuracy. Additional exploratory analyses indicated that attention to the whole display was negatively correlated with cortical tracking accuracy of AO and visual-only trials in IDS. Our results underscore the nuances involved in the relationship between neurophysiological AV speech benefit and looking behavior.