arXiv subjects

Patrice Simon

Publications and source records attributed to Patrice Simon.

13 recordsLinked to original sources

arXiv2025

The 2D Materials Roadmap

Over the past two decades, 2D materials have rapidly evolved into a diverse and expanding family of material platforms. Many members of this materials class have demonstrated their potential to deliver transformative impact on fundamental research and technological applications across different fields. In this roadmap, we provide an overview of the key aspects of 2D material research and development, spanning synthesis, properties and commercial applications. We specifically present roadmaps for high impact 2D materials, including graphene and its derivatives, transition metal dichalcogenides, MXenes as well as their heterostructures and moir\'e systems. The discussions are organized into thematic sections covering emerging research areas (e.g., twisted electronics, moir\'e nano-optoelectronics, polaritronics, quantum photonics, and neuromorphic computing), breakthrough applications in key technologies (e.g., 2D transistors, energy storage, electrocatalysis, filtration and separation, thermal management, flexible electronics, sensing, electromagnetic interference shielding, and composites) and other important topics (computational discovery of novel materials, commercialization and standardization). This roadmap focuses on the current research landscape, future challenges and scientific and technological advances required to address, with the intent to provide useful references for promoting the development of 2D materials.

cond-mat.mtrl-sci↗

arXiv2021

Carbon-carbon supercapacitors: Beyond the average pore size or how electrolyte confinement and inaccessible pores affect the capacitance

Carbon-carbon supercapacitors are high power electrochemical energy storage systems which store energy through reversible ion adsorption at the electrode-electrolyte interface. Due to the complex structure of the porous carbons used as electrodes, extracting structure-property relationships in these systems remains a challenge. In this work, we conduct molecular simulations of two model supercapacitors based on nanoporous electrodes with the same average pore size, a property often used when comparing porous materials, but different morphologies. We show that the carbon with the more ordered structure, and a well defined pore size, has a much higher capacitance than the carbon with the more disordered structure, and a broader pore size distribution. We analyze the structure of the confined electrolyte and show that the ions adsorbed in the ordered carbon are present in larger quantities and are also more confined than for the disordered carbon. Both aspects favor a better charge separation and thus a larger capacitance. In addition, the disordered electrodes contain a significant amount of carbon atoms which are never in contact with the electrolyte, carry a close to zero charge and are thus not involved in the charge storage. The total quantities of adsorbed ions and degrees of confinement do not change much with the applied potential and as such, this work opens the door to computationally tractable screening strategies.

cond-mat.mtrl-sci↗

arXiv2021

Mesoscopic simulations of the in situ NMR spectra of porous carbon based supercapacitors: Electronic structure and adsorbent reorganisation effects

In situ NMR spectroscopy is a powerful technique to investigate charge storage mechanisms in carbon-based supercapacitors thanks to its ability to distinguish ionic and molecular species adsorbed in the porous electrodes from those in the bulk electrolyte. The NMR peak corresponding to the adsorbed species shows a clear change of chemical shift as the applied potential difference is varied. This variation in chemical shift is thought to originate from a combination of ion reorganisation in the pores and changes in ring current shifts due to the changes of electronic density in the carbon. While previous Density Functional Theory calculations suggested that the electronic density has a large effect, the relative contributions of these two effects is challenging to untangle. Here, we use mesoscopic simulations to simulate NMR spectra and investigate the relative importance of ion reorganisation and ring currents on the resulting chemical shift. The model is able to predict chemical shifts in good agreement with NMR experiments and indicates that the ring currents are the dominant contribution. A thorough analysis of a specific electrode/electrolyte combination for which detailed NMR experiments have been reported allows us to confirm that local ion reorganisation has a very limited effect but the relative quantities of ions in pores of different sizes, which can change upon charging/discharging, can lead to a significant effect. Our findings suggest that in situ NMR spectra of supercapacitors may provide insights into the electronic structure of carbon materials in the future.

cond-mat.mtrl-sci↗

arXiv2021

On the effect of surface functional groups on the structural and dynamical properties of an ionic liquid confined in zeolite templated carbons studied through molecular simulations

Porous carbons are used in a wide range of applications, including electrochemical double layer capacitors for energy storage, in which electrolyte ion properties under confinement are crucial for the performance of the systems. While many synthesis techniques lead to the presence of surface functional groups, their effect on the adsorption and diffusion of electrolyte ions is still poorly understood. In this study we investigate the effect of surface chemistry on dynamical and structural properties of adsorbed ions through molecular dynamics simulations of a neat ionic liquid in contact with several zeolite templated carbons. The steric and specific influence of functional groups is explored using three structures: a structure without any functional groups; a structure with ester, hydroxyl, anhydride acid and carboxyl functional groups; and a structure where the oxygen and hydrogen atoms are replaced by carbon atoms. We show that the functionalization has a limited impact on the structure of the confined electrolyte but affects the diffusion coefficients, and that the relative importance of the structure and chemical nature of the functional groups is not the same depending on the ion type and property considered.

cond-mat.mtrl-sci↗

arXiv2020

Ionic liquids under confinement: From systematic variations of the ion and pore sizes towards an understanding of structure and dynamics in complex porous carbons

We use molecular simulations of an ionic liquid in contact with a range of nanoporous carbons to investigate correlations between ion size, pore size, pore topology and properties of the adsorbed ions. We show that diffusion coefficients increase with the anion size and, surprisingly, with the quantity of adsorbed ions. Both findings are interpreted in terms of confinement: when the in-pore population increases additional ions are located in less confined sites and diffuse faster. Simulations in which the pores are enlarged while keeping the topology constant comfort these observations. The interpretation of properties across structures is more challenging. An interesting point is that smaller pores do not necessarily lead to larger confinement. In this work, the highest degrees of confinements are observed for intermediate pore sizes. We also show a correlation between the quantity of adsorbed ions and the ratio between the maximum pore diameter and the pore limiting diameter.

cond-mat.mtrl-sci↗

arXiv2019

On the development of an original mesoscopic model to predict the capacitive properties of carbon-carbon supercapacitors

We report on the development of an original mesoscopic lattice model to predict structural, dynamical and capacitive properties of carbon-carbon supercapacitors. The model uses input from molecular simulations, such as free energy profiles to describe the ion adsorption, and experiments, such as energy barriers for transitions between lattice sites. The model developed is approximately 10,000 times faster than common molecular simulations. We apply this model to a set of carbon structures with well-defined pore sizes and investigate the solvation effect by doing simulations with neat ionic liquids as well as acetonitrile-based electrolytes. We show that our model is able to predict quantities of adsorbed ions and capacitances in a range compatible with experimental values. We show that there is a strong dependency of the calculated properties on the pore size and on the presence or absence of solvent. In particular, for neat ionic liquids, larger capacitances are obtained for smaller pores, while the opposite trend is observed for organic electrolytes.

cond-mat.mtrl-sci↗

arXiv2019

A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte

Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of 2D materials that draw attention as energy storage materials. So far, MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution, but most other MAX phases have not been explored. Here, a redox-controlled A-site-etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX phase precursors with A elements Si, Zn, and Ga. A negative electrode of Ti3C2 MXene material obtained through this molten salt synthesis method delivers a Li+ storage capacity up to 738 C g-1 (205 mAh g-1) with high-rate performance and pseudocapacitive-like electrochemical signature in 1M LiPF6 carbonate-based electrolyte. MXene prepared from this molten salt synthesis route offer opportunities as high-rate negative electrode material for electrochemical energy storage applications.

physics.app-ph↗

arXiv2018

Towards more efficient supercapacitors: when experiments and simulations uncover the mechanisms on the nanometer scale

Supercapacitors are energy storage devices able to deliver electricity with a high power. They consist of porous carbon electrodes in a concentrated electrolyte. Charged is stored by the adsorption of ions at the electrode surface. Nanoporous carbons allow to store more electricity thanks to a charging mechanism that differs from carbons with larger pores. This mechanism has recently been uncovered by combining in situ experiments (nuclear magnetic resonance, electrochemical quartz microbalance) and molecular simulations.

physics.chem-ph↗

arXiv2017

Capacitance of Nanoporous Carbon-Based Supercapacitors is a Trade-Off Between the Concentration and the Separability of the Ions

Nanoporous carbon-based supercapacitors store electricity through adsorption of ions from the electrolyte at the surface of the electrodes. Room temperature ionic liquids, which show the largest ion concentrations among organic liquid electrolytes, should in principle yield larger capacitances. Here we show by using electrochemical measurements that the capacitance is not significantly affected when switching from a pure ionic liquid to a conventional organic electrolyte using the same ionic species. By performing additional molecular dynamics simulations, we interpret this result as an increasing difficulty of separating ions of opposite charges when they are more concentrated, i.e. in the absence of a solvent which screens the Coulombic interactions. The charging mechanism consistently changes with ion concentration, switching from counter-ion adsorption in the diluted organic electrolyte to ion exchange in the pure ionic liquid. Contrarily to the capacitance, in-pore diffusion coefficients largely depend on the composition, with a noticeable slowing of the dynamics in the pure ionic liquid.

cond-mat.mtrl-sci↗

arXiv2016

Multi-scale modelling of supercapacitors: From molecular simulations to a transmission line model

We perform molecular dynamics simulations of a typical nanoporous-carbon based supercapacitors. The organic electrolyte consists in 1-ethyl-3-methyl--imidazolium and hexafluorophosphate ions dissolved in acetonitrile. We simulate systems at equilibrium, for various applied voltages. This allows us to determine the relevant thermodynamic (capacitance) and transport (in-pore resistivities) properties. These quantities are then injected in a transmission line model for testing its ability to predict the charging properties of the device. The results from this macroscopic model are in good agreement with non-equilibrium molecular dynamics simulations, which validates its use for interpreting electrochemical impedance experiments.

cond-mat.mtrl-sci↗

arXiv1998

A Cellular Automaton Model for Bi-Directionnal Traffic

We investigate a cellular automaton (CA) model of traffic on a bi-directional two-lane road. Our model is an extension of the one-lane CA model of {Nagel and Schreckenberg 1992}, modified to account for interactions mediated by passing, and for a distribution of vehicle speeds. We chose values for the various parameters to approximate the behavior of real traffic. The density-flow diagram for the bi-directional model is compared to that of a one-lane model, showing the interaction of the two lanes. Results were also compared to experimental data, showing close agreement. This model helps bridge the gap between simplified cellular automata models and the complexity of real-world traffic.

cond-mat.stat-mech↗

arXiv1998

A Simplified Cellular Automaton Model for City Traffic

We systematically investigate the effect of blockage sites in a cellular automaton model for traffic flow. Different scheduling schemes for the blockage sites are considered. None of them returns a linear relationship between the fraction of ``green'' time and the throughput. We use this information for a fast implementation of traffic in Dallas.

cond-mat.stat-mech↗

arXiv1997

Two-lane traffic rules for cellular automata: A systematic approach

Microscopic modeling of multi-lane traffic is usually done by applying heuristic lane changing rules, and often with unsatisfying results. Recently, a cellular automaton model for two-lane traffic was able to overcome some of these problems and to produce a correct density inversion at densities somewhat below the maximum flow density. In this paper, we summarize different approaches to lane changing and their results, and propose a general scheme, according to which realistic lane changing rules can be developed. We test this scheme by applying it to several different lane changing rules, which, in spite of their differences, generate similar and realistic results. We thus conclude that, for producing realistic results, the logical structure of the lane changing rules, as proposed here, is at least as important as the microscopic details of the rules.

cond-mat.stat-mech↗