Adsorption of ions on Cd(0001) electrode from ionic liquids at different temperatures

http://www.ester.ee/record=b4621577*es

Metalli–vesilahuse ja metalli–ioonse vedeliku elektrilise kakskkihi arvutuslik uurimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKäesolevas teadustöös uurisime metalli ja vesilahuse ning metalli ja ioonse vedeliku vahelist elektrilist kaksikkihti, keskendudes pindkihi dipoolse struktuuri analüüsile. Hindasime selle komponente elektrilise kaksikkihi kompaktses osas, mis jääb Helmholtzi välise kihi ja metalli pindkihi vahele. Alustasime pindkihi struktuuri ning elektrilise kaksikkihi diferentsiaalmahtuvuse arvutusliku uuringuga vismuti, galliumi ja elavhõbeda pinnal vesilahustes. Saadud tulemused kinnitavad molekulide adsorptsiooni olulist rolli elektrilise kaksikkihi omaduste kujunemisel. Seejärel kogusime arvutuslikke andmeid metalli ja ioonse vedeliku pindkihi struktuuri kohta, ning uurisime kuidas see määrab pindkihi dipoolse ehituse ning diferentsiaalmahtuvuse. Kasutasime ioonse kaksikkihi mudelit, mis sobib nii vastasioonide adsorptsiooni tõttu tekkinud dipooli kui ka anioonide ja katioonide vastastikuste mõjutuste tõttu tekkinud dipooli kirjeldamiseks. Süsiniku pinnal paiknevat ioonpaari käsitlevas uuringus näitasime, et kovalentne side vähendab oluliselt dipoolmomenti väärtust ning potentsiaalilangust elektroodi–elektrolüüdi pindkihis, mille tulemusena suureneb elektrimahtuvus. EMImBF4 ioonassotsiaatide võrdlemisel kulla, vismuti ja süsiniku pinnal selgus, et elektrolüüdikihi dipool mõjutab oluliselt mahtuvuse elektroodi potentsiaalist sõltuvuse kõvera kuju. Põhimõtteline erinevus vesilahuse ja ioonse vedeliku elektrilise kaksikkihi omaduste vahel tuleneb nende molekulaarse ja ioonse struktuuri erinevusest. Esitatud andmed annavad kasulikku teavet vesilahuse ja ioonvedeliku adsorptsiooni kohta erinevatel metallidel. Teave nende tegurite vastastikuste mõjude kohta võib aidata leida seoseid metalli ja elektrolüüdi pindkihi struktuuri ning pindkihtide toimimise vahel energia muundamise ja salvestamise seadmetes.In this thesis, we investigated the electrical double layer at metal–aqueous solution and metal–ionic liquid interfaces. For both aqueous and ionic liquid interfaces, we focused on the characteristics of interfacial dipole created at metal–electrolyte interface. We analysed its components on the example of the compact layer – the region between the outer Helmholtz plane and the interface. We started with a computational investigation of interfacial structure and differential capacitance of the electrical double layer at Bi, Ga, and Hg electrodes in aqueous electrolyte solution. The obtained results stress the significant role of the interfacial water layer in the interfacial properties of a metal surface–electrolyte solution interface. Then we gained computational insights into the structure of the metal–ionic liquid interfaces and how it determines the interfacial dipole as well as the differential capacitance. We introduced an ionic bilayer model that accounts for the dipole formed due to the adsorption of counter-ions as well as for the dipole formed due to anion–cation interplay. In a study of an ionic pair at circumcoronene surface, we showed that the covalent bonding significantly reduces the interfacial dipole moment value as well as the potential drop at an electrode–electrolyte interface, thus, leading to the capacitance increase. Comparison of the behaviour of EMImBF4 ionic associates at gold, bismuth and circumcoronene surfaces revealed that electrolyte layer dipole composition and structure play a crucial role in determining the shape of the capacitance vs. electrode potential curve. The conceptual difference between the properties of the aquoues and ionic liquid electrical double layers is dictated by the difference in their molucular and ionic structures. The reported data provide useful information on the water and ionic liquid adsorption on the metal surfaces. The enlighten interaction mechanisms may help to find links between the interfacial structure of the metal–electrolyte interfaces and their performance in energy conversion and storage devices

On the thickness of the double layer in ionic liquids

In this study, we examined the thickness of the electrical double layer (EDL) in ionic liquids using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. We focused on the BF4- anion adsorption from 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid on the Au(111) surface. At both DFT and MD levels, we evaluated the capacitance-potential dependence for the Helmholtz model of the interface. Using MD simulations, we also explored a more realistic, multilayer EDL model accounting for the ion layering. Concurrent analysis of the DFT and MD results provides a ground for thinking whether the electrical double layer in ionic liquids is one- or multi-ionic-layer thick

Predictions of Physicochemical Properties of Ionic Liquids with DFT

Nowadays, density functional theory (DFT)-based high-throughput computational approach is becoming more efficient and, thus, attractive for finding advanced materials for electrochemical applications. In this work, we illustrate how theoretical models, computational methods, and informatics techniques can be put together to form a simple DFT-based throughput computational workflow for predicting physicochemical properties of room-temperature ionic liquids. The developed workflow has been used for screening a set of 48 ionic pairs and for analyzing the gathered data. The predicted relative electrochemical stabilities, ionic charges and dynamic properties of the investigated ionic liquids are discussed in the light of their potential practical applications

Density Functional Theory Study of Ionic Liquid Adsorption on Circumcoronene Shaped Graphene

Carbon materials have a range of properties such as high electrical conductivity, high specific surface area, and mechanical flexibility are relevant for electrochemical applications. Carbon materials are utilized in energy conversion-and-storage devices along with electrolytes of complementary properties. In this work, we study the interaction of highly concentrated electrolytes (ionic liquids) at a model carbon surface (circumcoronene) using density functional theory methods. Our results indicate the decisive role of the dispersion interactions that noticeably strengthen the circumcoronene–ion interaction. Also, we focus on the adsorption of halide anions as the electrolytes containing these ions are promising for practical use in supercapacitors and solar cells