Structural properties and antisite defect formation in monoclinic Li2FeSiO4 – a DFT aspect

Properties of monoclinic Li2FeSiO4, which is a prominent candidate for future use as a cathode in lithium ion batteries, have been investigated by DFT+U method, using GGAPBE approximation, plane wave basis set and periodic boundary conditions. All calculations were performed in an antiferromagnetic state, which has been found to be energetically slightly more stable than ferromagnetic. Optimized lattice parameters and atomic coordinates have been compared to the literature data in order to verify the model. In addition, a particular attention was paid to the possibility of the formation of an antisite defect, which was introduced as the interchange between Fe and Li ions at both Li1 and Li2 crystallographic positions. The concentration of defect was varied from 0 to 25 molar per cent. Changes of structural, energetic, and magnetic properties of monoclinic Li2FeSiO4 upon increase of Li1-Fe and Li2-Fe antisite defect concentration have been analyzed and discussed in light of available experimental results

Theoretical analysis of tungsten carbide properties as electrocatalyst support for hydrogen electrode reactions

Elektrokatalizatori na bazi platine su uobičajeni za katalizu reakcija vodonične elektrode (engl. hydrogen evolution reaction - HER i hydrogen oxidation reaction - HOR) u različitim sistemima za konverziju energije, kao što su elektrolizeri i gorivne ćelije. Zbog visoke cene platine teži se povećanju specifične površine, da bi se poboljšalo iskorišćenje i smanjila ukupna cena katalizatora. Uobičajeni pristup koji se trenutno koristi u PEM sistemima (engl. PEM - polymer electrolite membrane ili proton exchange membrane – elektrolizeri ili gorivne ćelije sa polimernom membranom propusnom za protone kao elektrolitom) podrazumeva dispergovanje Pt-čestica dimenzija 5-10 nm na odgovarajućoj podlozi (ugljenik), ali u ovom slučaju jezgro Ptnanocestice ostaje nedovoljno iskorišćeno. Idealno iskorišćenje platine se postiže distribucijom platine u obliku monosloja (ML) na inertno provodno jezgro, što podrazumeva stvaranje posebne klase nano-strukturnih katalizatora nazvanih ''jezgroomotač'' (engl. core-shell). Na ovaj način postiže se smanjenje potrošnje platine za jedan red veličine. Karbidi prelaznih metala (engl. transition metal carbides – TMC)nalikuju grupi platinskih metala po elektronskim svojstvima i dimenzijama elementarne ćelije, što je podstaklo ispitivanje katalitičke aktivnosti za reakcije vodonične elektrode. Volfram-karbid (WC) pokazuje slične osobine kao i platina u smislu elektronske strukture i hemisorpcije vodonika. Ipak, dobijene gustine struje izmene su manje za 2-3 reda veličine u odnosu na platinske površine, čineći WC atraktivnim samo kao podlogu za katalizator. S druge strane, sinergijski efekat izmedju Pt i WC-podloge u smislu povećanja katalitičke aktivnosti se često spominje u literaturi, međutim, priroda ovog sinergizma nije u potpunosti razjašnjena. Pored platine, ostali metali platinske grupe su atraktivni za ispitivanje kao deo sličnih sistema, koji bi predstavljali neplatinske katalizatore. Ipak, tanki slojevi prelaznih metala do sada nisu sistematski ispitivani u smislu predviđanja i objašnjenja katalitičke aktivnosti i stabilnosti u uslovima reakcija vodonične elektrode kao neophodnog uslova za primenu. U ovom radu su, uz pomoć teorije funkcionala gustine (engl. Density functional theory - DFT) sistematski ispitani tanki slojevi metala (Cu, Ru, Rh, Pd, Ag, Ir, Pt i Au) na WC-podlozi. Posebna pažnja je posvećena monosloju i dvosloju Pt i Pd, uz analizu činilaca interakcije sa WC-podlogom na nivou elektronske strukture. Ispitivanje je prošireno i na monoslojeve drugih prelaznih metala, pri čemu je ukazano na mogućnost predviđanja stabilnosti do sada neispitanih sistema putem veze jačine vezivanja na WCpodlozi i kohezivne energije kao unutrašnjeg svojstva metala. U nastavku je diskutovana mogućnost predviđanja katalitičke aktivnosti površina na osnovu DFT izračunatih veličina, i konstruisana je vulkanska kriva koja povezuje DFT izračunate energije adsorpcije vodonika sa eksperimentalno dobijenim gustinama struje izmene, s obzirom na jednostavan pristup koji se više puta pokazao praktično primenljivim. Poseban osvrt napravljen je na aktivnost Pd i Pt tankih slojeva i na pojam i poreklo sinergije sa WC-podlogom. Od analiziranih monoslojeva najviše pažnje su privukli CuML/WC i RhML/WC, s obzirom na predviđenu aktivnost praktično jednaku Pt(111). Nijedan od ovih sistema nije do sad ispitivan kao katalizator za reakcije vodonične elektrode, a CuML/WC nije eksperimentalno ni pripremljen. Na osnovu teorijske analize, pre svega termodinamičkih, svojstava ovih sistema, ukazano je na mogućnost njihovog dobijanja u uslovima visokog vakuuma, kao i na očekivanu postojanost u uslovima rada vodonične elektrode. Opšti trendovi reaktivnosti na kraju su prodiskutovani i s tačke gledišta vodonik-supstrat interakcije na nivou elektronske strukture i dat je bliži uvid u činioce koji tu interakciju određuju. Dobijeni rezultati ukazali su na mogućnost dobijanja nove klase katalizatora za reakcije vodonične elektrode, zasnovane na pogodnom izboru kombinacije tankog sloja metala i podloge, koji uopšte ne sadrže platinu.Platinum based electrocatalysts are commonly used in catalysis of hydrogen electrode reactions (hydrogen evolution – HER and hydrogen oxidation - HOR) in different energy conversion systems, such as electrolyzers and fuel cells. For the reasons of high cost of platinum, efforts are made to enchance its utilization by broadening its specific surface. A typical state-of-the-art approach in PEM devices is based on dispersion of Pt-nanoparticles (5-10 nm) over appropriate support, such as carbon but in such arrangement Pt nanoparticle core still remains unexploited. Ideal Pt utilization is achieved when it is distributed in a form of monolayer (ML) over an inert conducting core, involving formation of a new class of nanostructured electrocatalysts called coreshell. In comparison to Pt-nanoparticles, Pt consumption is reduced by an order of magnitude. The transition metal carbides (TMC) are similar to Pt-group metals as far as electronic properties, as well as elemental cell dimensions are considered, what made them attractive for investigations of electrocatalytic activity towards hydrogen electrode reactions. Tungsten carbide (WC) shows similar properties as platinum, considering electronic properties and hydrogen chemisorption. However, obtained exchange current densities are still 2-3 orders of magnitude smaller than these on clean Pt-surfaces, limiting interests in WC to be applied as a catalyst support only. On the other side, synergy between Pt and WC-support in terms of increase of catalytic activity has been discussed in numerous studies, but its nature has not been completely clarified so far. Besides platinum itself, other platinum group metals are also attractive for investigations as part of similar systems, representing platinum-free catalysts. However, no systematic studies considering transition metal overlayers, prediction and explication of their catalytic activity, as well as stability in conditions of hydrogen electrode operation, have been published yet. In this work, thin layers of transition metals (Cu, Ru, Rh, Pd, Ag, Ir, Pt and Au) on WC support have been systematically investigated using Density Functional Theory (DFT). Special attention has been paid to Pd and Pt monolayer and bilayer, including factors determining metal-support interacton on the level of electronic structure. The research then has been extended to other transition metal monolayer systems, the correlation between metal-support binding energy and cohesive energy as intrinsic property of metals has been pointed out, and futher used to predict stability of systems which have not been examined experimentally so far. Hereinafter, the possibility to predict catalytic activity of surfaces from DFT calculations has been discussed, and the volcanic curve, correlating DFT calculated hydrogen adsorption energies with experimentally obtained exchange current densities, has been constructed, taking into account the simplicity and proved practical applicability of that approach. In particular, activity of Pd and Pt overlayers, the concept, as well as the origin of the synergy with WC-support, have been extensively discussed. On the other hand, among analyzed monolayers, CuML/WC and RhML/WC were the most interesting, because of their predicted catalytic activity practically equal to Pt(111). Neither of these systems has been examined yet as a catalyst for hydrogen electrode reactions, and CuML/WC has not even been prepared experimentally. Based on theoretical analysis of, basically thermodynamical, properties, the possibility to obtain these systems in UHV conditions, as well as expected stability in conditions of hydrogen electrode operation, have been pointed out. Finally, general reactivity trends have been considered from the point of view of hydrogen-substrate interactions, on the level of electronic structure, and the factors determining this interaction have been discussed. In general, results of this dissertation implied the possibility to obtain a new class of hydrogen electrode reaction catalysts, based on suitable combination of thin metal layer and the support, not containing platinum at all

An insight into the efficient dimethoate adsorption on graphene-based materials—a combined experimental and dft study

The development of highly efficient methods for removing hazardous substances from the environment attracts increasing attention. Understanding the basic principles of the removal processes using graphene materials is equally essential to confirm their application efficiency and safety. (2) Methods: In this contribution, adsorption of pesticide dimethoate (DMT) on graphene-based materials has been investigated on the molecular level. (3) Results: The experimental results’ analysis revealed a cooperative binding mechanism of the DMT on the adsorption sites of investigated materials—graphene oxide (GO) and industrial graphene (IG). The adsorption data were analyzed using various adsorption isotherms to determine the thermodynamics of the adsorption process. The experimental results were correlated with Density Functional Theory (DFT) calculations of DMT adsorption on the model surfaces that appropriately describe the graphene materials’ reactive features. (4) Conclusions: Considering experimental results, calculated adsorption energies, optimized adsorption geometries, and electronic structure, it was proposed that the dispersive interactions determine the adsorption properties of DMT on plain graphene sites (physisorption). Additionally, it was shown that the existence of vacancy-type defect sites on the surfaces could induce strong and dissociative adsorption (chemisorption) of DMT. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Supplementary information for the article: Milović, M.D., Vasić Anićijević, D.D., Jugović, D., Anićijević, V.J., Veselinović, L., Mitrić, M., Uskoković, D., 2019. On the presence of antisite defect in monoclinic Li2FeSiO4 – A combined X-Ray diffraction and DFT study. Solid State Sciences 87, 81–86. https://doi.org/10.1016/j.solidstatesciences.2018.11.008

Supplementary information for: [https://doi.org/10.1016/j.solidstatesciences.2018.11.008]Related to: [http://dais.sanu.ac.rs/123456789/4552

Testing the electrochemical behavior of BPA on GC, WO3 and MWCNT electrodes

Bisphenol A (BPA) is an organic compound used in large scale at the plastics industry and as a precursor in the synthesis of polycarbonates and epoxy resins, which lead to frequent detections of BPA in surface waters. Therefore, it is necessary to develop and improve methods for BPA detection and monitoring. The electrochemical behavior of Bisphenol A at WO3 and carbon-based electrodes, like glassy carbon (GC) and multi-walled carbon nanotubes (MWCNT), were compared using cyclic voltammetry (CV). Therefore, WO3 nanoparticles were obtained by hydrothermal method and characterization was done using XRDP. The results showed that the responses of the WO3 electrode were 30 times larger compared to another examined electrode. This implies that WO3 electrode can be useful for the detection BPA in nature media

Energy savings in electrolytic hydrogen production – comparison of binary and ternary activators

Ideja rada predstavlja poboljšanje elektrokatalitičke aktivnosti konvencijalnih elektroda za alkalnu proizvodnju vodonika dodavanjem jonskih aktivatora na bazi d-metala. Predstavljena je in situ metoda za aktivaciju elektroda koja omogućava poboljšanje kod reakcije izdvajanja vodonika jer ne zahteva predhodni korak čišćenja elektroda što doprinosi dodatnim uštedama procesa. U radu su predstavljeni ekperimentalno dobijeni rezultati kao i teorijske osnove vezane za kombinovanje razlicitih d-metala u cilju dobijanja kvalitetne prevlake na elektrodi.The idea of improvement of electrocatalytic activity of conventional electrodes for alkaline hydrogen evolution by in situ electrodeposition of selected d-metals has been attracting the attention of researchers for about two decades. These efforts already resulted in a number of economical solutions that enable better catalytic performances and higher energy efficiency compared to the state-of-the-art catalytic materials. In this contribution, we pay a particular attention to the processes on the atomic level, and (electro)chemical factors in general, that enable observed improvement of the electrocatalytic activity of the systems activated with in situ ionic activators, using a combination of experimental and computational techniques11th International Conference on Renewable Electrical Power Sources : November 2-3, Belgrade, 2023

TEM and DFT study of Indocyanine green adsorption on a silver nanoparticle surface

U ovom radu, transmisionom elektronskom mikroskopijom (TEM) i teorijskim proračunom (DFT), izučavana je adsorpcija boje Indocijanin zeleno (ICG) na površini nanočestica srebra (AgNPs). Studija je pokazala da su dobijene hibridne nanočestice sastava Ag-jezgro-ICG-omotač. TEM merenjima potvrđeno je formiranje omotača boje oko AgNPs debljine ~ 3 do 4 nm, dok su HRTEM merenja pokazala mikrostrukturne promene AgNPs usled adsorpcije boje ICG. Teorijskim proračunom utvrđeno je da se molekul ICG boje vezuje kovalentno za atom Ag, na površini AgNPs, preko svoje SO3− grupe.Here we present the TEM and DFT study of hybrid nanoparticles consisting of an Ag core and Indocyanine green (ICG) shell. TEM measurements revealed the formation of a distinctive ~ 3 to 4 nm thick halo around the particles, while HRTEM measurements show microstructural changes in NPs. The DFT calculations were used to investigate the energetics of interaction between ICG molecule and Ag-surface. The obtained data indicate a strong interaction between Ag-atom from NPs surface and SO3− group of ICG molecule.59th Meeting of the Serbian Chemical Society; June 1-2, 2023, Novi Sad, Serbi

Possibilities of integrating alkaline electrolyzer with ionic activators in micro combined heat and power systems

The utilization of renewable energy sources such as wind and solar increases the available options for a decentralized electricity grid. Water electrolysis is among the most perspective methods of technical development. Cost reduction in electrolyzers is possible only through the development of electrocatalysts and cathode materials. The primary outcomes of the research were the characterization and testing of ionic activators added in a standard solution of 6M KOH in alkaline electrolyzers and integrated into combined heat and power systems. We found that ionic activators based on d-metals such as Ni, Cu, Co or Cr and Mo salt in a standard solution of 6M KOH improve the reduction in energy consumption by about 18%, compared to a non-activated system. The energy efficiencies of the electrolyzer with an activated system were about 70% on the different applied current densities. Increasing the energy efficiency of the electrolytic process is achieved by thermal integration, that is, by connecting the heat exchanger with the electrolyzer and the fuel cell. By establishing the connection of the heat exchanger with the alkaline electrolyzer with ionic activators and the fuel cell, it is possible to increase energy efficiency by thermal integration of the electrolytic process

Investigation Of Benzophenone-3 Electrochemical degradation On Titanium Electrode

Benzophenone - 3 is a well - known molecular UV filter, main- ly found in commercial cosmetic preparation for sunscreen and skincare. Due t o increased use of sunscreens, it could be found in surface water and wastewater, which could affect the water quality and human health. Research indicates that benzophenone - 3 act as endocrine disruptor and has a carcinogen- ic and mutagenic effect on humans and other living organisms. As such, poses a health risk to all living beings and need to be removed from the environment. Electrochemical techniques for wastewater treatment of organic pollutants show advantages over commercial techniques as practicality , safety, and simple application on both, small and large systems. Aim of the presented research is to examine the possibility of using titanium anode plates for electrochemical degradation of benzophenone - 3 in 0.05M aqueous sodium chloride solution. Elect rolysis was performed in galvanostatic mode at a current density of 25 mA cm - 2 . During 40 minutes of electrolysis, the degradation efficiency of benzo- phenone - 3 is 98.3 %. Additional studies of process kinetics show that degrada- tion of benzophenone - 3 follow s first - order kinetics.Contemporary Materials, Banja Luka Republic of Srpska, September 9-10, 2021

Conjugates of Gold Nanoparticles and Antitumor Gold(III) Complexes as a Tool for Their AFM and SERS Detection in Biological Tissue

Citrate-capped gold nanoparticles (AuNPs) were functionalized with three distinct antitumor gold(III) complexes, e.g., [Au(N,N)(OH)2][PF6], where (N,N)=2,2′-bipyridine; [Au(C,N)(AcO)2], where (C,N)=deprotonated 6-(1,1-dimethylbenzyl)-pyridine; [Au(C,N,N)(OH)][PF6], where (C,N,N)=deprotonated 6-(1,1-dimethylbenzyl)-2,2′-bipyridine, to assess the chance of tracking their subcellular distribution by atomic force microscopy (AFM), and surface enhanced Raman spectroscopy (SERS) techniques. An extensive physicochemical characterization of the formed conjugates was, thus, carried out by applying a variety of methods (density functional theory—DFT, UV/Vis spectrophotometry, AFM, Raman spectroscopy, and SERS). The resulting gold(III) complexes/AuNPs conjugates turned out to be pretty stable. Interestingly, they exhibited a dramatically increased resonance intensity in the Raman spectra induced by AuNPs. For testing the use of the functionalized AuNPs for biosensing, their distribution in the nuclear, cytosolic, and membrane cell fractions obtained from human lymphocytes was investigated by AFM and SERS. The conjugates were detected in the membrane and nuclear cell fractions but not in the cytosol. The AFM method confirmed that conjugates induced changes in the morphology and nanostructure of the membrane and nuclear fractions. The obtained results point out that the conjugates formed between AuNPs and gold(III) complexes may be used as a tool for tracking metallodrug distribution in the different cell fractions