Electrode Surface Charge Research Articles

Size polydisperse model ionic liquid under confinement: A molecular dynamics study

The performance of an electric double-layer capacitor is strongly influenced by the choice of electrolyte, and the use of ionic liquid (IL) mixtures as an electrolyte has shown great promise. In this study, a model IL made of a mixture of anions and size-polydisperse cations in equal numbers and confined between two electrodes is investigated by means of molecular dynamics simulations. In particular, using the extent of size-polydispersity (characterized by polydispersity index, δ) as a control parameter, we systematically explore its effect on the local structure, charge profile, ion size distribution in the vicinity of electrode surfaces, and differential capacitance. It is observed that the charge density profiles near cathode, i.e., region comprising both Stern and diffused layers, are significantly affected under the variation of δ in addition to the electrode charge density. Ion population, ordering of different-size cations, and its effective size in the vicinity of electrodes under neutral and applied potential conditions are also quantified. An interesting observation is that the effective cation size in the Stern layer decreases with increasing value of δ in the case of moderate to strong electrode surface charge density. This behaviour can be qualitatively understood from the interplay of enthalpic and entropic forces in the system. Finally, a non-monotomic dependence of capacitance on δ is observed with maximum value of capacitance at a rather small value of δ(≈3%) for the model system.

Modulating zero charge potential of Zn-doped N, P-containing carbon electrodes for efficient copper ion electrosorption

Nitrogen/phosphorus (N/P) doped carbon materials exhibit enhanced electro adsorption capability in capacitive deionization (CDI) applications. However, the incorporation of N/P atoms may introduce electron-withdrawing groups to the electrode surface, impacting the potential of zero charge (EPZC) and thereby influencing its electro adsorption efficiency. This research explores the modulation of electrode surface charge by varying the N/P doping composition. Specifically, it presents a Zn and N/P co-doped carbon material employed as the CDI cathode, showcasing selective adsorption of Cu2+ ions. Under a voltage of 1.2 V, the adsorption capacity achieves 250 mg/g in a 500 mg/L Cu2+ ion solution. Furthermore, it demonstrates outstanding cycling stability, maintaining an adsorption capacity of 233 mg/g even after 21 cycles. This investigation introduces an innovative approach for EPZC adjustment and offers a fresh theoretical framework for fabricating high-performance CDI electrodes.

The Role of Alkali Cations on the Selectivity of 5-Hydroxymethylfurfural Electroreduction on Glassy Carbon.

In the past decade, organic electrosynthesis has emerged as an atom- and energy-efficient strategy for harvesting renewable electricity that provides exceptional control over the reaction parameters. A profound and fundamental understanding of electrochemical interfaces becomes imperative to advance the knowledge-based development of electrochemical processes. The major strategy toward an efficient electrochemical system is based on the advancement in material science for electrocatalysis. Studies on the complex interplay among electrode surface, electrolyte, and transformation intermediates have only recently started to emerge. It involves acquiring atomic-scale insights into the electrochemical double layer, for which the identity and concentration of composing ions play a crucial role. In this study, we present how the identity and concentration of alkali cations impact the selectivity of aldehyde functionality electroreduction. As a case-study transformation, we set the electrochemical conversion of 5-hydroxymethylfurfural (HMF), a promising biomass-derived feedstock for the sustainable production of polymer or fuel precursors. Our findings reveal a consistent trend of the selectivity shift towards 2,5-bis(hydroxymethyl)furan (BHMF) as a function of cation size and concentration, rationalized by specific cation adsorption at the glassy carbon (GC), followed by the increase in the electrode surface charge density.

Heat and mass transfer of molten carbonates at charged electrode interface and its anisotropic behavior: A molecular dynamics study

Molten carbonates are broadly used in fuel cells with potential applications in reducing CO2 emission, while their heat and mass transfer properties near a charged electrode surface are less well understood. Using molecular dynamics (MD) simulations, the heat and mass transfer properties of molten Na2CO3-K2CO3 salts at charged nickel surfaces are revealed in this study. Simulation results indicates that when surface charge density increases, molten salt’s thermal transport exhibit anisotropic behavior: the interfacial thermal resistance show strong dependence on the surface charge while heat transfer parallel to surface is not sensitive to the surface charge. As for interfacial mass transfers, the shear viscosity of the carbonate tends to rise with external electric field, while the corresponding ion diffusion does not vary very much and exhibit position-dependent behavior. To further explore this, we find that the anisotropy of this heat and mass transfer properties is primarily attributed to the nonuniform ion distribution in the direction perpendicular to nickel surface with the increasing of charge, while the interatomic correlation does not vary much as surface charge increases. These results have suggested that the anisotropy of heat and mass transport properties of molten salt near electrode, which should be taken care of when modelling the macroscopic heat and mass transport of molten carbonate fuel cells in particular.

The Impact of Concentration and Electric-Field Dependent Susceptibilities on Electrolyte Models

Electrolytes have a significant role in a range of scientific and technological fields such as fundamental electrochemistry, biochemical systems, semiconductors, and industrial devices. A widely used mathematical framework for describing electrolytes is based on Poisson-Nernst-Planck-type equations and their successors[1], but the Poisson equation assumes a constant dielectric susceptibility. However, recent research has developed a thermodynamically consistent model for the dielectric susceptibility that accounts for its dependence on both concentration and electric field [5,6]. This allows for the inclusion of the dependency of the susceptibility on salt concentration in liquid electrolytes, referred to as dielectric decrement[2,3,4], as well as the decline in susceptibility for large electric fields[8], known as dielectric saturation.The research findings highlight the importance of considering the variable dielectric susceptibility in electrolyte models, particularly in relation to the decrease in dielectric permittivity in front of a charged electrode surface[7]. The study demonstrates the impact of the concentration and electric-field-dependent susceptibility on the overall equation system for electrochemical double layers. By providing insights into the theoretical aspects of the approach, the researchers aim to contribute to the development of more accurate and comprehensive models of electrolytes that consider the complex interplay of various factors.

In Situ Surface X-Ray Diffraction Studies of the Electrochemical Double Layer on Pt(111)

The molecular structure of the electrochemical double layer is an important fundamental topic in interfacial electrochemistry. It has received renewed interest in the last years, because of its influence on many electrochemical reactions and the emergence of ab initio molecular dynamics simulations that allow a detailed description of the interface structure and dynamics [1,2]. In the measurements presented here, we investigated the properties of the electrochemical double layer on Pt(111) via in situ surface X-ray diffraction (SXRD), a technique that is well-established for single crystal studies [3-7].Platinum electrodes are widely used as electrocatalysts, for example as cathodes in proton exchange membrane fuel cells due to their high ORR reactivity. The single-crystalline Pt(111) surface, which is a well studied model system, is especially interesting for studies of the electrochemical double layer. Recent electrochemical measurements revisited this system and found evidence for a double layer structure that strongly deviated from the traditional Gouy-Chapman-Stern model and indicated a complex structural influence of water [8,9]. The water structure within the electrochemical double layer is also of major interest in computational studies. For non-adsorbing, aqueous electrolyte the electrode surface charge can be partly compensated by a layer of oriented water molecules due to their dipole moment. For potentials around the potential of zero charge (PZC), a potential-dependent orientation of water molecules with respect to the electrode surface was suggested [1,2,10].To investigate the arrangement and orientation of the water molecules near the Pt(111) surface we used in situ SXRD methods, focussing on X-ray reflectivity (XRR) and crystal truncation rod (CTR) analysis. These methods allow to acquire detailed information about the electrode surface structure as well as the electrochemical double layer. By measuring multiple CTR sets at different surface potentials, information on the potential-dependence of the interface processes can be obtained. The experiments were performed at beamline ID31 of the European Synchrotron Radiation Facility using high photon energies of 75 keV, which provide very large data sets. This allows significantly improved structural modeling as compared to conventional SXRD. The studies employed an electrochemical hanging-meniscus X-ray diffraction cell that allows for SXRD measurements of fast dynamic systems in a well-defined electrochemical environment. We will report results on the water structure in the double layer obtained in perchloric acid at potentials around the PZC.We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft via project no. 418603497 and the BMBF via 05K19FK3 and 05K22FK1.

Multiscale modelling of species transport in hydrophilic Nafion®-coated Cu catalysts for CO2 electro-reduction

Ionomers such as Nafion are being used for engineering the microenvironment of the CO2RR towards selectivity to higher hydrocarbons. Their cationic exchange qualities mitigate homogeneous bicarbonate reactions, providing favourable conditions for production of C2-C3 products. The proximity of Nafion® layers to the negatively charged electrode surface results in complex effects that have yet to be explored computationally. We combine mass transport equations and density functional theory (DFT) calculations to model the hydrophilic moieties in Nafion® layer on a 1D planar copper electrode. We vary the Nafion® layer thickness in the thick film regime (200–1100 nm), the ionic strength of supporting aqueous electrolyte and the applied voltage to investigate the concentration profile of participating species within the Nafion® layer. We find that the bicarbonate ion concentration and local pH decrease with decreasing thickness which makes thinner films better at mitigating bicarbonates at the cost of a relatively lower pH. We observe the breakdown of Donnan exclusion effects with higher ionic strength electrolytes which allows diffusion of both co-ions and counter-ions, promoting the bicarbonate reactions. Further, we find that the pKa of Nafion® generally increases as the local dielectric constant of the reaction medium decreases. This is primarily due to the accumulation of K+ and production of low dielectric constant products such as ethanol, albeit their concentrations are low on planar Cu electrodes. The lower permittivity of the reaction medium weakens the exclusion forces and changes the morphology of Nafion® which ultimately impacts its ability to mitigate homogeneous bicarbonate reactions.

Reinforcement of Positive Electrode-Electrolyte Interface without Using Electrolyte Additives Through Thermoelectrochemical Oxidation of LiPF6 for Lithium Secondary Batteries.

Owing to the limited electrochemical stability window of carbonate electrolytes, the initial formation of a solid electrolyte interphase and surface film on the negative and positive electrode surfaces by the decomposition of the electrolyte component is inevitable for the operation of lithium secondary batteries. The deposited film on the surface of the active material is vital for reducing further electrochemical side reactions at the surface; hence, the manipulation of this formation process is necessary for the appropriate operation of the assembled battery system. In this study, the thermal decomposition of LiPF6 salt is used as a surface passivation agent, which is autocatalytically formed during high-temperature storage. The thermally formed difluorophosphoric acid is subsequently oxidized on the partially charged high-Ni positive electrode surface, which improves the cycleability of lithium metal cells via phosphorus- and fluorine-based surface film formation. Moreover, the improvement in the high-temperature cycleability is demonstrated by controlling the formation process in the lithium-ion pouch cell with a short period of high-temperature storage before battery usage.

Selective electrochemical determination of dopamine using Thioglycolic acid modified gold electrode

This study was aimed to investigate the selective electrochemical determination for dopamine based on thioglyolic acid-modified gold electrode. Negatively charged Au electrode surface was created by making Thioglycolic acid film through thiol functional group. Greater oxidation current and less overpotential was observed for the oxidation of dopamine in phosphate buffer solution of pH 8.0 at thioglyolic acid-modified gold electrode than bare Au electrode due to the electrostatic attraction between the negatively charged thioglyolic acid-modified gold electrode surface and positively charged dopamine. The electrochemical behavior of dopamine at the thioglyolic acid-modified gold electrode showed a linear response from 0.05 to 100.0 µM and the limit of detection is 0.01 µM using chronoamperommetry. The proposed thioglyolic acid-modified gold electrode shows good repeatability and promising application in dopamine hydrochloride injection sample.

Synthesis and characterization of novel chitosan-sodium pyruvate polymer and its derivatives for corrosion feature evaluation of Cu-Ni alloy

In this research, developing a novel chitosan-Schiff base and its derivatives is a distinct and appealing synthetic route for green corrosion inhibitors to lower the rate of Cu-Ni alloy industrial corrosion. Cu-Ni alloy is a material of choice for condensers and heat exchangers, where seawater is used as a coolant and in desalination plants. Therefore, a novel chitosan-sodium pyruvate (Chi-SP) polymer was successfully prepared through the condensation reaction of chitosan with sodium pyruvate. (Chi-SP) polymer is tailored into the hydrophobic core of β-cyclodextrin (CD) by two routes (chemically and physically) to give a novel Chi-SP/β-CD inclusion complex (IC), Chi-SP/β-CD physical mixture (PM), respectively. Further, A composite of Chi-SP encapsulating titanium oxide (TiO2) with nanometer size has been synthesized by a one-pot reaction. The physicochemical properties and the corrosion inhibition efficiency (CIE) of Chi-SP, Chi-SP/β-CDIC, Chi-SP/β-CD PM, and Chi-SP/TiO2 were performed. The corrosion rate (CR) and inhibitor efficiency (IE) of Cu-Ni alloy in HCl (1 M) using Chi-SP, PM, IC, and the nanocomposite were found to be (82.53, 61.63, 65.56, and 62.94) % and (54.1, 65.7, 63.5, and 65)%, respectively. These findings reveal that the Chi-SP/TiO2 molecules have many polar hydroxyl groups which can contribute to the chemisorption and physisorption of the inhibitor on the alloy surface. As well as, the TiO2 in an aqueous solution convert into Ti4+ (cation ions) adsorbed on the negatively charged electrode surface, which increases the adsorption of the nanocomposite on the electrode surface and increases the protection layer.

A Voltammetric Sensor Based on Aluminophosphate Zeolite and a Composite of Betulinic Acid with a Chitosan Polyelectrolyte Complex for the Identification and Determination of Naproxen Enantiomers

A voltammetric sensor was developed based on a glassy carbon electrode with aluminophosphate zeolite finely dispersed on its surface, modified with a polyelectrolyte complex of chitosan with succinyl chitosan and betulinic acid, for the selective detection and determination of naproxen enantiomers. The electrochemical and analytical characteristics of the sensor were studied, and the effective electrode surface area (A = 9.8 ± 0.5 mm2) and charge transfer resistance (Ret = 649.9 ± 0.4 Ω) were calculated. In determining naproxen enantiomers, calibration characteristics are linear in the range from 2.5 × 10–5 to 1 × 10–3 M with limits of detection of 1.1 × 10–7 and 1.5 × 10–7 M and limits of quantification of 3.6 × 10–7 and 4.9 × 10–7 M for R- and S-naproxen, respectively. The sensor is more sensitive to R-naproxen (∆Ep = 60 mV, ipR/ipS = 1.40). The proposed sensor was used to recognize and determine naproxen enantiomers in human urine and plasma samples. Statistical evaluation of the results by the standard addition method showed that there was no systematic error.

Local cation-tuned reversible single-molecule switch in electric double layer

The nature of molecule-electrode interface is critical for the integration of atomically precise molecules as functional components into circuits. Herein, we demonstrate that the electric field localized metal cations in outer Helmholtz plane can modulate interfacial Au-carboxyl contacts, realizing a reversible single-molecule switch. STM break junction and I-V measurements show the electrochemical gating of aliphatic and aromatic carboxylic acids have a conductance ON/OFF behavior in electrolyte solution containing metal cations (i.e., Na+, K+, Mg2+ and Ca2+), compared to almost no change in conductance without metal cations. In situ Raman spectra reveal strong molecular carboxyl-metal cation coordination at the negatively charged electrode surface, hindering the formation of molecular junctions for electron tunnelling. This work validates the critical role of localized cations in the electric double layer to regulate electron transport at the single-molecule level.

Morphology and atomic configuration control of heavy metal attraction modified layer on screen-printed electrode to enhance electrochemical sensing performance

The sensitivity of screen-printed electrochemical (SPE) sensors is heavily dependent on the selection of appropriate modifiers that can optimize the chemical (functional ligands, surface charge, binding energy) and physical (morphological structure) properties of the sensor surface. This study aimed to investigate the impact of these chemical and physical factors on the sensitivity of modified SPEs for the detection of lead and cadmium. The study employed anodic stripping voltammetry to evaluate the sensing performance of SPEs modified with different modifiers, including cellulose acetate, chitosan, Nafion, nylon-6, and silver nanoparticles. Results showed that metal-attracting functional groups and surface charged electrode were the dominant factors affecting the sensitivity of SPEs in heavy metal sensing. Specifically, negatively charged electrode surfaces and metal-attracting -SO32- ligands, as found in Nafion-modified SPE, were identified as the key factors in improving sensor selectivity, rather than the rough physical morphology of the SPE, which was believed to provide more metal detection sites. This conclusion was supported by the combination analyses of electrochemical impedance spectroscopy, electrochemically active surface area and computational molecular binding energy of bare and modified SPEs. The findings of this study provide valuable insights for selecting appropriate SPE modifiers and designing sensor architectures for heavy metal detection.

Exploring the electrosorption and surface charge amplification at the ionic liquid/cavity interface: Influence of imidazolium alkyl chain length and the size of the spherical cavities of the porous electrode

The surface charge amplification (SCA) phenomenon at the ionic liquid/cavity interface has been investigated as a result of co-ion electrosorption due to increasing the alkyl chain length of imidazolium. Three types of ionic liquids with different imidazolium alkyl chain lengths inside the different-sized spherical cavities of porous electrodes have been studied using the coarse-grained model within the framework of classical density functional theory (CDFT). Our results show that selectivity occurs at lower potentials for ionic liquids with longer cation chain lengths in smaller cavities. The significant point is that at low negative surface potentials for asymmetric ionic liquids, the electrosorption of anions as co-ions occurs in some spatial regions that are made possible by the accidental orientation of cations in the first layer in the vicinity of the cavity surface. This is evidence of the SCA phenomenon for asymmetric ionic liquids at the ionic liquid/cavity interface. Moreover, the comparison of results, especially the normalized screening strength in the first layer indicates that the smaller cavities containing the ionic liquid with cations that have longer alkyl chains amplify the electrode surface charge more.

Interfacial behaviour of oligodeoxynucleotides prone to G-quadruplex formation on negatively charged electrode surface monitored by electrochemical probes

Development of analytical tools enabling discrimination amongst various structures of nucleic acids attracts interest due to diverse biological functions and prospective biotechnological applications of the latter. In this work, two electrochemically active compounds, copper porphyrin complex Cu-TMPy2PP and base-modified deoxyguanosine triphosphate conjugate bearing 3-nitrophenyl moiety (dGNPTP), were used as probes to study electrode potential effects on oligodeoxynucleotides (ODNs) of various sequences and abilities to form secondary structures (including unstructured single strands, duplexes, guanine quadruplexes, i-motifs) at the surface of hanging mercury drop electrode (HMDE). Our experiments revealed formation of less dense adsorbed layers by G-rich ODNs with the propensity to fold into G-quadruplexes (G4), compared to layers formed by other studied sequences. Strikingly, the G4-forming ODNs were significantly more susceptible to desorption from the HMDE surface during its polarization to highly negative potentials compared to other ODNs. Negative potential-induced desorption of the ODNs from HMDE was further confirmed by gel electrophoresis. Application of the electrochemical probes offers a useful method for further research of DNA conformations and transitions taking place in solution and at electrically charged surfaces.

Tailoring Electrode Surface Charge to Achieve Discrimination and Quantification of Chemically Similar Small Molecules with Electrochemical Aptamers (Adv. Funct. Mater. 1/2023)

Tailoring Electrode Surface Charge to Achieve Discrimination and Quantification of Chemically Similar Small Molecules with Electrochemical Aptamers (Adv. Funct. Mater. 1/2023)

The origin of selective electro-adsorption of cations by few-layered 2D MXene electrode

In this work, the few-layered 2D MXene (F-Ti3C2Fx) are developed as highly efficient cation removal electrode by capacitive deionization (CDI). The F-Ti3C2Fx layer is measured as 1.65 nm. It has been demonstrated the large interlayer space, which benefits to adapt the cations. On the other hand, the negatively charged terminal F functional group presenting on the surface of F-Ti3C2Fx offers massive host sites for electro-adsorption of cations. As a result, the F-Ti3C2Fx has exhibited exceptional selectivity on cations. Essentially, the monovalent ion with small hydrated radius is superior to the divalent ion (K+ > Na+ > Li+ > Zn2+) in the single-component solution. However, the divalent ion (Zn2+) has been proven higher electro-adsorption selectivity over monovalent ions in multi-component solutions. This is ascribed to the strong interaction between Zn2+ and F-Ti3C2Fx, and the charge-preferred neutralization on charged electrode surface. Most importantly, the electro-adsorption energy calculated by density functional theory has verified that the surface F functional group benefits to enhance the affinity between cations and F-Ti3C2Fx. Thus, the possible cation removal mechanism of F-Ti3C2Fx electrode is proposed.

Spectro-Electrochemical Investigations of Interfacial Phenomena in Concentrated Hydrogen-Bonded Electrolytes for Electrochemical Energy Storage

Spectro-electrochemistry combines spectroscopic and electrochemical techniques, enabling time-resolved and in-situ measurements of phenomena occurring at charged electrode surfaces. Surface-enhanced Raman spectroscopy (SERS) yields highly specific information about the structure and composition of molecules. Coupling SERS with electrochemical experiments gives insight into changes near the electrode surface under polarization. In-situ SERS and electrochemical measurements are demonstrated to provide information on the electrolyte-electrode interface in three different applications: (1) specific ion adsorption in hydrogen-bonded concentrated electrolytes under polarization, (2) adsorption and charge-transfer mechanisms of redox-active organic in aqueous electrolytes, and (3) charge-transfer reactions of redox-active species in hydrogen-bonded electrolytes.Differential capacitance measurements suggest that surface adsorption is prevalent in deep eutectic solvents (DESs) and more broadly concentrated hydrogen-bonded electrolytes, however, these measurements do not directly probe the surface layer. Therefore, in this study, SERS was employed to investigate potential-dependent changes in the surface layer of the electrode-electrolyte interface where surface adsorption was spectroscopically confirmed. However, this behavior was observed to depend on the charge density and the strength of hydrogen bonding.In situ SERS coupled with electrochemical measurements was also used to probe redox reactions of redox-active molecules at the electrode-electrolyte interface. One study elucidated an adsorption and charge-transfer mechanism for a potential redox-active organic molecule, 4–hydroxy–2,2,6,6–tetramethylpiperidine–1–oxyl (4–hydroxy–TEMPO).1 Nitroxide radicals, such as 4–hydroxy–TEMPO, are of interest for application in redox flow batteries due to their relative stability, and tunability through functionalization. In situ SERS combined with density functional theory (DFT) simulations confirmed the presence of surface–adsorbed species on an Au electrode during the oxidation of 4–hydroxy–TEMPO in an aqueous electrolyte. Direct spectroscopic evidence shows the oxidation of 4–hydroxy–TEMPO leads to the adsorption of the oxidation product, which then undergoes slow rate-limiting desorption from the electrode surface. This information is important for the design of redox flow battery systems that employ nitroxide radical redox-active species, as surface adsorption can affect battery performance.In an H-bonded electrolyte containing redox-active species (methyl viologen and ferrocenedimethanol in ChCl:EG), SERS, electrochemical, and spectrochemical UV-vis techniques were used to study their charge-transfer reactions. UV-vis measurements provide molecular information related to the electronic levels of molecules. UV-vis coupled with SERS allows for the study of changes in the oxidation state of redox-active molecules under electrode polarization.This work demonstrates the importance of spectrochemical measurements in determining phenomena at the electrode-electrolyte interface, particularly in a complex solvent system such as DESs. Emphasis is placed on the coupling spectroscopic techniques with other techniques to determine interfacial structuring and charge-transfer reactions relevant to energy storage applications.(1) Shaheen, N. A.; Ijjada, M.; Vukmirovic, M. B.; Akolkar, R. Mechanism of Electrochemical Oxidation of Nitroxide Radicals in Ethaline Deep Eutectic Solvent. Journal of The Electrochemical Society 2020, 167 (14), 143505–143505. https://doi.org/10.1149/1945-7111/abc439.

Interactive MD-DFT Model to Predict the Multi-Component Electrolyte Reduction within the Electrical Double Layer

A typical liquid electrolyte for lithium (Li)-ion and Li-metal batteries is a liquid mixture with salt, solvent, and additives. The reduction products of the electrolytes form the solid-electrolyte interphase (SEI) layer, whose composition, heterogeneity and thickness largely determine the Li plating and stripping processes and thus the cycling performance. It is highly desirable to obtain atomistic insights into the reduction reactions of the electrolytes to help predict and control the formation of the SEI layer. The reduction reactions of the liquid electrolyte occur near the charged electrode surface within the electric double layer (EDL). The electrolyte structures within EDL must change under an electric field, which impacts the electrolyte reduction and SEI formation. This has been rarely considered in previous theoretical investigations of the reduction potentials and reduction products.In this work, we have developed an interactive model combining molecular dynamics (MD) simulations and density functional theory (DFT) calculations to predict the multi-component electrolyte reduction within the EDL.[1] First, MD simulations, which can deal with thousands of atoms and even more, are used to capture the dynamics and statistics of the EDL structures. Then DFT calculations are used to compute the reduction products and corresponding reduction potentials of the representative clusters in the EDL. Finally, a formulation was proposed to calculate averaged reduction potential based on DFT-calculated reduction potentials of all the possible Li+-coordinated structures and their distribution probabilities obtained through MD analyses.We have applied this new interactive MD-DFT model to two types of essential multi-component electrolytes, the carbonate-based electrolyte (LiPF6@EC:EMC) and the ether-based electrolyte (LITFSI@DOL:DME). We find in both electrolytes the Li+ ions within the EDL tend to have less coordination with other electrolyte species (salt anion, solvent and additive) compared to those in the bulk electrolyte. For LiPF6@EC:EMC, we reveal that FEC can enter into the EDL region and is favorable to be reduced, which helps form the F-containing SEI component (e.g., LiF). In addition, we have studied the effects of the FEC additive on LiTFSI@DOL:DME at various temperatures. We find that, at -40 °C, the number of F atoms that come near the electrode is largely increased after adding FEC, while no big change is observed at 20 °C. This explains that adding FEC is more effective in forming stable F-containing SEI and in promoting cycling performance at low temperatures.[2] Our simulations have also explained why ether based electrolyte works better than carbonate base electrolyte for Li metal anode. Reference: [1] Qisheng Wu,Yue Qi. Manuscript under preparation, 2022. [2] Akila C. Thenuwara, et al. ACS Energy Lett. 2020, 5, 2411−2420

Tailoring electrode surface charge to achieve discrimination and quantification of chemically similar small molecules with electrochemical aptamers.

Electrochemical biosensors based on structure-switching aptamers offer many advantages because they can operate directly in complex samples and offer the potential to integrate with miniaturized electronics. Unfortunately, these biosensors often suffer from cross-reactivity problems when measuring a target in samples containing other chemically similar molecules, such as precursors or metabolites. While some progress has been made in selecting highly specific aptamers, the discovery of these reagents remains slow and costly. In this work, we demonstrate a novel strategy to distinguish molecules with miniscule difference in chemical composition (such as a single hydroxyl group) - with cross reactive aptamer probes - by tuning the charge state of the surface on which the aptamer probes are immobilized. As an exemplar, we show that our strategy can distinguish between DOX and many structurally similar analytes, including its primary metabolite doxorubicinol (DOXol). We then demonstrate the ability to accurately quantify mixtures of these two molecules based on their differential response to sensors with different surface-charge properties. We believe this methodology is general and can be extended to a broad range of applications.