Quartz Crystal Microbalance Technique Research Articles

Niobium Electroreduction from Ionic Liquids Using Fluoride Based Precursors

Niobium belongs to the group of refractory metals, and shows advanced properties such as a high melting point and a good hardness, due to the strong interatomic bonds [1,2]. Furthermore, niobium exhibits excellent chemical and corrosion resistance [3]. This makes niobium coatings very attractive for a broad spectrum of applications [4]. Due to the low standard potential, it is not possible to electrodeposit niobium from aqueous solutions. Ionic liquids (ILs) are a good alternative, and first studies have demonstrated the general feasibility of Nb metal deposition from NbF5 containing ILs [5-7]. However, layers deposited from standard ionic liquids like 1-butyl-1-methylpyrrolidinium bistrifluoromethylsulfonyl imide (BMP TFSI) often still are not dense, show cracks, have residual ionic liquids incorporated, and contain Nb subhalides [5]. The use of different precursors like NbCl5 and other ionic liquids, particularly those based on a triflate anion, has been reported [8-10]. In our own research, we recently studied in detail the electrochemical reduction of NbCl5 in TFSI-based ionic liquids [11]. In this work, the electrochemical behavior of NbF5 in different ionic liquids was studied with the electrochemical quartz crystal microbalance technique (EQCM). A network analyzer was used to measure the admittance between the two Au electrodes (one serving as working electrode) of 10 MHz quartz resonators in parallel to the electrochemical measurements. This permitted to extract both changes in resonance frequency and damping of the quartz. The latter is particularly important in ionic liquids, as local changes in the electrolyte composition due to a reduction process are often associated with damping changes. Experiments were carried out at different temperatures, using pulsed electrodeposition and pulsed ultrasound techniques. The application of ultrasound can significantly enhance mass transport and thereby prevent precursor depletion and fluoride enrichment at the surface. On the downside, there is a risk of accelerated electrolyte degradation [11, 12]. Figure 1a shows an example for a successful deposition from a 0.25 M NbF5 solution in an alkylammonium IL electrolyte. A reasonably well adhering layer was obtained even at room temperature that however still contained some fluoride ions at the surface, and was very rough. According to the XPS measurements in Figure 1b and c, an average composition of NbF0.6 was obtained at the surface. Figure 1. a) Photograph of layer deposited from 0.25 M NbF5 b) XPS spectrum (F1s) c) XPS spectrum (Nb 3p5/2,3/2) References [1] S. Zein El Abedin, H.K. Farag, E.M. Moustafa, U. Welz-Biermann, F. Endres. Phys. Chem. Chem. Phys., 7, 2333 (2005). [2] N. Borisenko, A. Ispas, E. Zschippang, Q. Liu, S. Zein El Abedin, A. Bund, F. Endres, Electrochim. Acta, 54, 1519 (2009). [3] V.-H. Pham, S.-H. Lee, Y. Li, H.-E. Kim, K.-H. Shin, Y.-H. Koh, Thin Solid Films, 536, 269 (2013). [4] F. Cardarelli, Int. J. of Refractory Metals & Hard Materials, 14, 3655 (1996). [5] P. Giridhar, S. Zein El Abedin, A. Bund, A. Ispas, F. Endres, Electrochim. Acta, 129, 312 (2014). [6] S. Krischok, A. Ispas, A. Zühlsdorff, A. Ulbrich, A. Bund, F. Endres, ECS Trans., 50(11), 229 (2012). [7] A. Vacca, M. Mascia, L. Mais, S. Rizzardini, F. Delogu, S. Palmas, Electrocatalysis, 5, 16 (2014). [8] E. Freydina, and J. G. Abbott, ECS Trans., 75 (15), 639 (2016). [9] O. B. Babushkina, E. O. Lomako, and W. Freyland, Electrochim. Acta, 62, 234 (2012). [10] Endrikat, N. Borisenko, A. Ispas, R. Peipmann, F. Endres, A. Bund; under revision. [11] L. Seidl, L. Asen, G. Yesilbas, P. Fischer, F. Kühn, and O. Schneider, ECS Trans., 86 (14), 3 (2018). [12] J. D. Oxley, T. Prozorov, and K. S. Suslick, J. Am. Chem. Soc., 125 (37), 11138 (2003). Figure 1

Revisited insights into charge storage mechanisms in electrochemical capacitors with Li2SO4-based electrolyte

This paper provides a comprehensive overview of the recent state of the art in research on a neutral, water-based electrolyte, i.e., 1 mol⋅L−1 Li2SO4 solution, for sustainable electrochemical capacitors. The fundamental physicochemical properties of aqueous electrolytic solutions (conductivity, viscosity, etc.) are discussed together with the electrochemical performance of carbon-based electrochemical capacitors. In addition to a critical review of the recent findings in the field, the paper discusses new data obtained with the operando approach; the discussion is supported by recent findings from the electrochemical quartz crystal microbalance, Raman spectroscopy and scanning electrochemical microscopy techniques. In this respect, interesting results concerning specific and selective ion adsorption have been obtained. In addition, a post-mortem analysis of carbon electrodes (N2 adsorption) subjected to an ageing protocol is presented. Furthermore, the influence of an anti-ageing additive (tocopherol) on the electrode material and electrolyte has been investigated. Finally, the mechanisms governing capacitive- and redox-based interfacial interactions are proposed.

Mechanisms of Fibrinogen Adsorption on Silica Sensors at Various pHs: Experiments and Theoretical Modeling.

The adsorption kinetics of human serum fibrinogen at silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance (QCM) techniques. Measurements were performed at pH 3.5, 4, and 7.4 for various ionic strengths. The experimental data were interpreted in terms of a hybrid random sequential adsorption model. This allowed the mass transfer rate coefficient for the OWLS cell and maximum coverages to be determined at various pHs. The appearance of different, pH-dependent mechanisms of fibrinogen adsorption on silica substrates was confirmed. At pH 3.5 the molecules mostly adsorb in the side-on orientation that produces a low maximum coverage of ca. 1 mg m-2. At this pH, the kinetics derived from the OWLS measurements agree with those theoretically predicted using the convective-diffusion theory. In consequence, a comparison of the OWLS and QCM results allows the water factor and the dynamic hydration of fibrinogen molecules to be determined. At pH 7.4, the OWLS method gives inaccurate kinetic data for the low coverage range. However, the maximum coverage that was equal to ca. 4 mg m-2 agrees with the QCM results and with previous literature results. It is postulated that the limited accuracy of the OWLS method for lower coverage stems from a heterogeneous structure of fibrinogen monolayers, which consist of side-on and end-on adsorbed molecules. One can expect that the results acquired in this work allow development of a robust procedure for preparing fibrinogen monolayers of well-controlled coverage and molecule orientation, which can be exploited for efficient immunosensing purposes.

Experimental and density functional theory study on humidity sensing properties of copper phthalocyanine (CuPc)

The quartz crystal microbalance (QCM) technique was applied to investigate humidity sensing properties of a copper phthalocyanine (CuPc) thin film prepared by drop cast method. The humidity adsorption and desorption kinetics of (CuPc) thin film was evaluated. The QCM and electrical measurements results showed that humidity sensing properties of CuPc is very sensitive to humidity changes and reversible adsorption/desorption performance which is an indicative of a good humidity sensor even at room temperature. Reproducible experimental results indicated that CuPc thin films have an abundant potential for humidity sensing applications at ambient temperature. According to the first-principle density functional theory calculations, the promising humidity sensing properties of CuPc can be attributed to the considerable charge transfer from the water molecule into Cu atom.

(Invited) Electrochemical “Zinc-Ion” Storage at Nanostructured Manganese Oxides: Mechanistic Insights from 2D Interfaces to Advanced 3D Electrode Architectures

Alkaline Zn/MnO2 cells remain a popular energy-storage technology due to their low cost and benign components, yet they lack the long-term rechargeability and high-power capability required in many present and emerging applications. The benefits inherent to the coupling of zinc and manganese oxide (MnOx) electrodes can be translated to a new generation of rechargeable “zinc-ion” batteries that incorporate mild-pH Zn2+-containing electrolytes. By pairing such electrolytes with particular nanostructured forms of MnOx that undergo reversible Zn2+-based redox reactions, the rechargeability of Zn/MnOx systems can be extended to hundreds or thousands of cycles. We are exploring two particular MnOx polymorphs—layered, birnessite-type and cubic-spinel ZnMn2O4—for zinc-ion storage, where these oxides are expressed as nanoscale coatings on 3D carbon nanofoam (CNF) architectures. Such electrode designs enable high oxide-normalized capacity delivered at moderate-to-high rates and over hundreds of charge–discharge cycles. When Na+ or Li+ salts are added to the Zn2+-based aqueous electrolyte, pseudocapacitive reactions at the MnOx become active to provide pulse-power functionality at time scales approaching those for electrochemical capacitors [1]. Electrochemical charge storage in zinc-ion electrolytes may follow multiple pathways, including direct Zn2+ insertion/association at MnOx or via proton-insertion reactions that drive the formation of Znx(OH)y(SO4)z salts at the MnOx surface. We use ex situ characterization (diffraction, spectroscopy, and microscopy) of electrochemically conditioned MnOx–CNF electrodes to show that the latter reaction is dominant for birnessite-type MnOx, where the reversibility of Znx(OH)y(SO4)z formation/dissolution is promoted by the pore–solid architecture of the CNF [2]. These findings are further confirmed by scanning-probe microscopy and quartz-crystal microbalance techniques at planar MnOx–carbon electrodes that mimic the interfaces in MnOx–CNF. Insights from these investigations inform the design of advanced electrode architectures for high-performance, rechargeable zinc-ion batteries. [1] “Combining Battery-Like and Pseudocapacitive Charge Storage in 3D MnOx@Carbon Electrode Architectures in Zinc-Ion Cells.” J.S. Ko, M.B. Sassin, J.F. Parker, D.R. Rolison, and J.W. Long, Sustain. Energy Fuels, 2 (2018) 626–636. [2] J.S. Ko, M.D. Donakowski, M.B. Sassin, J.F. Parker, D.R. Rolison, and J.W. Long, MRS Comm., in press (2019).

Effective Pre-Electrochemical Treatment of Cu EQCM Electrode on Lithium Electrodeposition/Dissolution Processes

Lithium has been extensively expected as one of the most ideal anode materials of the next generation lithium-based batteries, because of its higher theoretical specific capacity (3860 mA h g-1) and its most negative redox potential (-3.04 V vs. SHE). On the lithium anode surface, however, it is well-known that the dendrite, which further leads to poor battery performance and short circuit, forms in charging. In addition, solid electrolyte interphase (SEI), which is generated by decomposition of electrolytes and/or solvents, also accumulates on the anode surface during the anode reaction. An ideal SEI layer is expected to be higher and lower conductive for lithium ion and electron, respectively, and it is flexible and has a relatively uniform flat surface with an appropriate thickness, in order to avoid dendrite formation [1]. During the electrochemical reaction, on the other hand, electrochemical quartz crystal microbalance (EQCM) technique gives us information not only of mass change on the electrode surface but also resonance resistance change, which shows surface area change of the electrode [2,3] and/or density and viscosity change at the electrode/electrolyte solution interface [4,5]. Using this technique, we found that the pre-electrochemical treatment of the Cu EQCM electrode strongly effects on the lithium electrodeposition/dissolution processes. Acknowledgements: This work was totally supported by the Advanced Low Carbon Technology Research and Development Program (ALCA), specially promoted research for innovative next generation batteries (SPRING) from the Japan Science and Technology (JST).

A potential-responsive affinity-controlling 2-2′-dithiodibenzoic acid/polyaniline hybrid film with high ion exchange capability and selectivity to cadmium ions

A potential-responsive 2-2′-dithiodibenzoic acid (DTSA)/Polyaniline (PANI) hybrid film with high ion-exchange capability and selectivity to cadmium ions was successfully fabricated on electrode by a one-step cyclic voltammetry (CV) method. S–S bonds in the DTSA serve as a gate that can be controllably opened and closed to let cadmium ions get in and out of the hybrid film when changing its redox state, and the PANI mainly enhanced the conductivity of the hybrid film. The working mechanism of the film is proposed and identified via the electrochemical quartz crystal microbalance (EQCM) technique, X-ray photoelectron spectroscopy (XPS), Raman and density functional theory (DFT) computations. As a result, the obtained hybrid film exhibited high selectivity towards cadmium ions even in the presences of other cations. More interestingly, over 240% of its initial capacity was retained after 25 consecutive cycles and maintained in the following cycles. Furthermore, the regeneration rate of the hybrid film retains 99% of its initial value even after 30 cycles. It is expected that such a potential-responsive film can be applied for the removal and recovery of cadmium ions from wastewater in various industrial processes.

Influence of ferrocyanide on the long-term stability of poly(butyl viologen) thin film based electrochromic devices

High bleaching/coloring electrochemical reversibility is crucial for practical applications of an electrochromic material. In this study, ferrocyanide-containing poly(butyl viologen) (PBV:fc) thin films were prepared by electropolymerization, and subsequently investigated and compared their redox properties by using the electrolyte with and without the addition of potassium ferrocyanide (K4Fe(CN)6). Electrochemical and electrochromic properties of the PBV:fc thin films were studied by using cyclic voltammetry (CV) and UV–Vis spectroscopy techniques. The mass changes of the PBV:fc thin films during their redox reactions were studied by using electrochemical quartz crystal microbalance (EQCM) technique. In addition, the scanning electrochemical microscope (SECM) studies confirmed the stable anion insertion/extraction of Fe(CN)64− within a PBV:fc thin film. The obtained results indicate that the redox reversibility of the PBV:fc thin film can be effectively improved by the addition of K4Fe(CN)6 in the electrolyte. It is deduced that the enhancement of bleaching/coloring stability of the PBV:fc thin film is affected by Fe(CN)64− charge balance during the reactions. Complementary electrochromic devices (ECDs) using the PBV:fc and Prussian blue (PB) thin films were fabricated. Finally, the ECD with the electrolyte containing K4Fe(CN)6 shows the superior transmittance modulation stability than the one without K4Fe(CN)6.

Theoretical investigation of the chlorophyll nucleus adsorption monitored with Quartz Crystal Microbalance technique: New insights on physicochemical properties

In this work, adsorption isotherms of magnesium chloride (MgCl2) and magnesium nitrate (Mg (NO3)2) onto tetraphenylporphyrin molecules (H2TPP) are achieved at three temperatures using the Quartz Crystal Microbalance (QCM) method. The equilibrium data expressing the adsorbed quantity of Magnesium per unit of adsorbent area provide interesting information to explain the adsorption mechanism. In fact, statistical physics treatment is applied to attribute new investigations to the complexation process. Some physicochemical parameters are deduced from the analytical models established by the theoretical formalism. It is found that the model describing the layer by layer (LBL) adsorption is the best to reproduce the experimental isotherms of magnesium nitrate on porphyrin. The interaction between magnesium chloride and porphyrin is explained by a mono-layer adsorption expression. The adsorption mechanisms are characterized by an energetic investigation which demonstrates that a physisorption occurs for the Mg(NO3)2-H2TPP system whereas the adsorption of MgCl2 onto H2TPP is characterized by chemical interactions.

Silica nanoparticles as copper corrosion inhibitors

Nanoparticle suspensions (or ‘nanofluids’) employed as heat transfer fluids (HTF) enhanced the thermal conductivity and the effectiveness of the heat exchangers as well as efficacy of thermal energy storage (TES) platforms by augmenting the effective specific heat capacity of various solvents. In prior studies, molten salt nanofluids also reduced corrosion by 50% (compared to that of neat molten salts and pure molten salt eutectics). Here, we demonstrate that silica nanoparticle suspension could be beneficial not only from the point of higher rates of heat transfer and thermal energy storage but also as corrosion inhibitors of copper substrates, that are typically used for thermal systems (e.g., HTF and TES). Combined use of Quartz Crystal Microbalance (QCM) technique and atomic force microscopy indicate a significant lowering of the corrosion rates (up to 4 times) when only 10% of the surface is covered by silica nanoparticles with a nominal diameter of 10 nm. These results are attributed to the negative surface potential of silica nanoparticles. As a result when the nanoparticles precipitate on the copper surface and form surface ‘nano-fins’—they preferentially prevent negatively charged ions (such as chlorine ions) from approaching the metal surface and thereby serve as an impediment from increasing the metal dissolution rate. This counter-intuitive behavior occurs even when the nanofins are formed randomly (i.e., without forming a uniform coating) and are sparsely dispersed on the copper substrate. This phenomenon of reduced corrosion is attributed to be another manifestation of the ‘nano-Fin Effect (nFE)’.

Nanotribological Performance Factors for Aqueous Suspensions of Oxide Nanoparticles and Their Relation to Macroscale Lubricity

Quartz crystal microbalance (QCM) measurements of nanotribological properties of statistically diverse materials combinations of nanoparticles and substrate electrodes in aqueous suspensions are reported and compared to macroscale measurements of the same materials combinations for a subset of the nanoparticle combinations. Four ceramic nanoparticles, TiO2, SiO2, Al2O3, and maghemite (γ-Fe2O3) and ten substrate materials (Au, Al, Cr, Cu, Mo, Ni, Pt, SiO2, Al2O3, and SS304) were studied. The QCM technique was employed to measure frequency and motional resistance changes upon introduction of nanoparticles into the water surrounding its liquid-facing electrode. This series of experiments expanded prior studies that were often limited to a single nanoparticle - solid liquid combination. The variations in QCM response from one nanoparticle to another are observed to be far greater than the variation from one substrate to another, indicating that the nanoparticles play a larger role than the substrates in determining the frictional drag force levels. The results were categorized according to the direction of the frequency and motional resistance changes and candidate statistical performance factors for the datasets were generated. The performance factors were employed to identify associations between the QCM atomic scale results and the macroscale friction coefficient measurements. Macroscale measurements of friction coefficients for selected systems document that reductions (increases) in motional resistance to shear, as measured by the QCM, are linked to decreases (increases) in macroscale friction coefficients. The performance factors identified in the initial study therefore appear applicable to a broader set of statistically diverse samples. The results facilitate full statistical analyses of the data for identification of candidate materials properties or materials genomes that underlie the performance of nanoparticle systems as lubricants.

Cellulose Nanofiber Nanosheet Multilayers by the Langmuir–Blodgett Technique

We describe a systematic approach for producing cellulose nanofiber (CNF) nanosheets using the Langmuir-Blodgett (LB) technique. The CNFs were obtained from sulfuric acid hydrolysis of commercially available microfibrillated cellulose. Needle-like CNFs, negatively charged by grafted sulfate groups, were maintained at the air-water interface, assisted by amphiphilic polymer, poly( N-dodecyl acrylamide) (pDDA). The CNFs produced a stable monolayer. The surface pressure increased steadily with a high collapse pressure of 50 mN m-1 when spread with formic acid and pDDA. The composite monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. Upstroke and downstroke transfer ratios of the films were, respectively, unity and 0.88, indicating that full coverage was achieved by the monolayer even for more than 200 layers. Results obtained using atomic force microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy showed that CNF nanosheets possess well-defined layer structures with average monolayer thickness of 5.3 nm. The relative amount of CNFs in the nanosheets was calculated as 62.6 wt % using the quartz crystal microbalance technique. The as-prepared nanosheets are optically transparent to visible light and have high hydrophobicity. In fact, the nanosheet transparency was higher than 88% at 600 nm wavelength for 24 layers. A miniscule amount of pDDA enables demonstration of free-standing CNF nanosheets with 1 cm width and 45.6 nm thickness (23 layers).

Rapid and real-time detection of arginine enantiomers by QCM sensor having a Calix[4]arene receptor bearing asymmetric centers

This paper describes the sensing studies of a chiral calix[4]arene receptor (5) having (R)-2-phenylglycinol moiety for arginine enantiomers (D-/L-arginine) by using Quartz Crystal Microbalance (QCM) technique. The initial experiments have revealed that the chiral calix[4]arene 5 coated QCM (CCC-QCM) sensor showed good sensing for arginine enantiomers, such that it has exhibited higher sensing towards D-arginine than that of L-arginine. It has been determined that the sensitivity, limit of detection values of CCC-QCM sensor for the D-/L-arginine solutions as 0.024/0.023 Hz/μM and 0.38/1.29 μM, respectively. On the other hand, the racemic mixture studies were optimized using the response surface methodology with central composite design. Consequently, it has been demonstrated that the QCM sensor modification with a calix[4]arene receptor bearing asymmetric centers provided rapid, real-time, sensitive and effective sensing of arginine enantiomers.

Adsorption of sodium and lithium ions onto helicenes molecules: Experiments and phenomenological modeling

Fundamentally, isotherm curves of adsorption can provide reasonable information to explain the mechanism of the adsorption process. Thus, equilibrium data in which the variation of adsorption quantity is expressed versus the concentration of Sodium chloride or Lithium chloride on hepta-Helicenes were collected under various experimental conditions (temperature, pH, etc) by using Quartz Crystal Microbalance (QCM) technique. The experimental results show that the adsorption process attains a saturation level when a limited number of layers was adsorbed. For modeling analysis, advanced models established in light of a statistical physics treatment describing the adsorption process have been tested and discussed in this paper. Based on the experimental results, the adsorption mechanism was interpreted theoretically via the chosen model parameters. It is interesting to note that the numbers n1 and n2 of bonded ions per site values of the two studied ions are similar. In addition, this parameter had a linear tendency with temperature for the two ions. This showed that the thermal agitation has the same effect on the two adsorbed ions. The adsorption mechanism was characterized by energetic parameters showing that the adsorption of Sodium and Lithium on Hepta-Helicenes was physisorption with a tendency toward a chemisorption process. Thanks to the adopted model, three classical thermodynamic functions have been calculated and interpreted to describe macroscopic thermodynamic potentials of the investigated process.

Entropy-Driven Mechanisms between Disulfide-Bond Formation Protein A (DsbA) and B (DsbB) in Escherichia coli.

A disulfide-bond formation system for nascent proteins in the Escherichia coli periplasm contains efficient electron transfer systems for the catalysis of oxidation. This electrochemical system has interesting implications in vivo. Disulfide bonds are formed by disulfide-bond formation protein A (DsbA), which contains two reactive cysteines. DsbA is reoxidized by a membrane protein, disulfide-bond formation protein B (DsbB), which has four catalytic cysteines. The oxidation of DsbA by DsbB seems energetically unfavorable on the basis of the redox potential. The oxidizing power of ubiquinone (UQ), which endogenously binds with DsbB, is believed to promote this reaction. However, using UQ-deficient DsbB, it was found that the oxidation of DsbA by DsbB proceeds independently of UQ. Thus, the reaction mechanism of DsbA oxidation by DsbB is under debate. In this study, we used the quartz crystal microbalance technique, which detects the intermediate complex between DsbA and DsbB during DsbA oxidation as a change in mass, to obtain kinetic parameters of DsbA oxidation under both the oxidized and reduced states of UQ at acidic and basic pH. In addition, we utilized sodium dodecyl sulfate polyacrylamide gel electrophoresis mobility shift assay technique to determine the pKa of the cysteine thiol groups in DsbA and DsbB. We found that DsbA oxidation proceeded independently of UQ and was greatly affected in kinetics by the shuffling of electrons among the four cysteine residues in DsbB, regardless of pH. These results suggest that DsbA oxidation is driven in an entropy-dependent manner, in which the electron-delocalized intermediate complex is stabilized by preventing a reverse reaction. These findings could contribute to the design of bio-inspired electrochemical systems for industrial applications.

Organic vapor sensing properties and characterization of α-naphthylmethacrylate LB thin films

Determination of organic vapor sensing properties of α-Naphthylmethacrylate (α-NMA) monomer based Langmuir-Blodgett (LB) thin films was aimed in this study. LB thin film fabrication was performed on quartz glass and quartz crystal substrates in order to investigate the characterization and organic vapor properties of α-NMA materials by using UV-Visible, Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance (QCM) techniques. π-A isotherm graph was taken and a suitable surface pressure value were primarily determined as 13 mN m−1 for successful α-NMA LB thin film fabrication. Transfer ratio value was found to be ≥ 0.93 for quartz glass and quartz crystal substrates. The typical frequency shift per layer was obtained as 16.93 Hz/layer and the deposited mass onto a quartz crystal was calculated as 271.30 ng/layer (1.02 ng mm−2). The sensing responses of α-NMA LB films against dichloromethane, chloroform, toluene and m-xylene were measured by QCM system. Dichloromethane created the maximum shift in the resonance frequency than other organic vapors used in this study. Results exhibited that α-NMA LB thin films were potential candidates for organic vapor sensing applications, especially high sensitive detection of dichloromethane at room temperature.

Pre-Electrochemical Treatment Effect of Cu Eqcm Electrode on Lithium Electrodeposition/Dissolution Processes

Lithium has been extensively expected as one of the most ideal anode materials of the next generation lithium-based batteries, because of its higher theoretical specific capacity (3860 mA h g-1) and its most negative redox potential (-3.04 V vs. SHE). On the lithium anode surface, however, it is well known that the dendrite, which further leads to poor performance and short circuit, forms. In addition, solid electrolyte interphase (SEI), which is generated by decomposition of electrolytes and/or solvents, also accumulates on the anode surface during the anode reaction. An ideal SEI layer is expected to be higher and lower conductive for lithium ion and electron, respectively, and it is flexible and has a relatively uniform flat surface with an appropriate thickness, in order to avoid dendrite formation [1]. During the electrochemical reaction, on the other hand, electrochemical quartz crystal microbalance (EQCM) technique gives us information not only of mass change on the electrode surface but also resonance resistance change, which shows surface area change of the electrode [2,3] and/or density and viscosity change at the electrode/electrolyte solution interface [4,5]. Using this technique, we found that the pre-electrochemical treatment of Cu EQCM electrode strongly effects on the lithium electrodeposition/dissolution processes. Acknowledgements This work was totally supported by the Advanced Low Carbon Technology Research and Development Program (ALCA), specially promoted research for innovative next generation batteries (SPRING) from the Japan Science and Technology (JST).

Vibrating Powders: Eqcm Measurement of Potential Dependent IrO2 Mass Changes for Voltage Reversal Tolerant PEMFC Anodes

Oxygen evolution reaction (OER) catalysts are used to protect carbon components of polymer electrolyte membrane fuel cell (PEMFC) anodes during transient fuel starvation conditions such as start-up/shut-down [1]. OER catalysts such as IrO2 or RuO2 promote the oxidation of water instead of the corrosion of carbon components [1, 2]. However, the conditions in a PEMFC during normal operation (ca. 0 V and low pH) can induce instability in these metal oxides. IrO2 in particular can form soluble Ir3+ species [3] that migrate across the membrane electrode assembly and deposit on the cathode causing poisoning of the oxygen reduction reaction (ORR) catalyst (typically Pt/C). Currently, OER catalysts for reversal tolerant anodes (RTAs) are investigated using prototype MEA single unit cell testing which is time consuming and expensive to perform [4]. Previously, our group investigated the dissolution of different IrO2 based powder catalysts using a potential stepping stress test. The dissolution of Ir3+ from this test was compared with reversal tolerance of a membrane electrode assembly fabricated using the same IrO2 catalyst [5]. To further investigate the dissolution of IrO2 powders, we have devised a series of experiments (with potential cycling between 0.05 to 1.2, 1.4 and 1.6 V, at 100 mV s-1 30 times each and 298 K) using the electrochemical quartz crystal microbalance (EQCM) technique. The EQCM uses a vibrating quartz crystal and measures its frequency (inversely proportional to crystal mass) as a function of potential. Our method was validated using a commercially available IrO2 powder (Alfa Aesar) heat treated in air at 350, 450 and 550°C which improves durability while negatively effecting OER activity [6]. The powders were deposited (24 μ cm-2) onto a gold EQCM crystal to investigate the dissolution behavior as a function of particle size, crystallinity and electrode potential. The untreated IrO2 exhibited a large irreversible increase in vibration frequency indicating a loss of mass during the initial polarization from 1.2 to 0.05 V. The increase was on the order of 400 to 700 Hz or -7.1 to -12.4 μg cm-2 assuming a perfectly uniform and rigid layer (figure a). This frequency increase could equally be due to loss of adhesion from the surface, a change in the rigidity of the layer or dissolution of Ir3+. To confirm that frequency changes were not due to adhesion or rigidity of the film, samples of the electrolyte were taken from near the electrode surface and Ir3+ concentration was determined by inductively coupled plasma mass spectrometry (ICP-MS). We observed that the frequency of the untreated IrO2 increased by ca. 90 Hz (-1.6 μ cm-2) during a single polarization from 0.05 V to 1.2 V (figure a). Birss et al. reported the formation of an iridium oxo-hydroxide which causes a mass increase when polarizing to 0 V [6]. Conversely, the frequency of heat treated layers first decreased by ca. 200-500 Hz (1.4 to 3.5 μg) then increased again when polarizing to 1.6 V. Heat treatment induced IrO2 crystallinity changes could account for this difference in frequency response. From the first cycle to the last, there was a frequency gain for untreated IrO2 and a frequency loss for all of the heat treated IrO2 catalysts; suggesting Ir3+ dissolution and increased IrO2 layer rigidity or coverage respectively. The capacitive current of the untreated catalyst decreased slightly over the course of the test and was more than five times higher than the 550°C heat treated catalyst in its cyclic voltammogram (figure c and d). The main challenge to using EQCN for powder catalyst investigation is producing layers with consistent and repeatable frequency behavior. In this work, the IrO2 deposition conditions were tightly controlled and each experiment was repeated to ensure the consistency of the results. If these obstacles can be overcome, EQCN presents a novel, rapid and powerful tool to learn about the potential dependent reactions taking place using a myriad of catalyst materials. Ralph TR, Hudson S, Wilkinson DP (2006) ECS Trans 1:67–84.Patterson TW, Darling RM (2006) Electrochem Solid-State Lett 9:A183–A185.Danilovic N, Subbaraman R, Chang K-C, et al (2014) J Phys Chem Lett 5:2474–2478.Makharia R, Kocha S, Yu P, et al (2006) ECS Trans 1:3–18.Moore CE, Eastcott J, Cimenti M, Kremliakova N, Gyenge EL (2019) J Power Sources in review da Silva GC, Perini N, Ticianelli EA (2017) App Cat B: Env 218 287–297.Birss VI, Elzanowska H, Gottesfeld S (1991) J Electroanal Chem and Interfac Electrochem 318:327–333. Figure 1

Investigation of Solvent Effects on Electrochemical Quartz Crystal Microbalance (eQCM) Studies of Carbon Nanomaterials

The electrochemical quartz crystal microbalance (eQCM) technique provides a direct assessment on the behavior of electroadsorbed ions and a fundamental understanding of charge-storage mechanisms. Though recent efforts have illustrated changes in measurements as a function of electrolyte composition, our work describes the effects of solvent choice on the eQCM measurement itself. Results comparing aqueous, polar aprotic, and polar protic solvents with model substrates will be presented.

Electrodes for Membrane Surface Science. Bilayer Lipid Membranes Tethered by Commercial Surfactants on Electrochemical Sensors.

Commercial surfactants, which are inexpensive and abundant, were covalently grafted to flat and transparent electrodes, and it appears to be a simple functionalization route to design biomembrane sensors at large-scale production. Sparsely tethered bilayer lipid membranes (stBLM) were stabilized using such molecular coatings composed of diluted anchor-harpoon surfactants that grab the membrane with an alkyl chain out of a PEGylated-hydrogel layer, which acts as a soft hydration cushion. The goal of avoiding the synthesis of complex organic molecules to scale up sensors was achieved here by grafting nonionic diblock oligomers (Brij58 = C xH2 x+1(OCH2CH2) nOH with x = 16 and n = 23) and PEO short chains ((OCH2CH2) nOH with n = 9 and n = 23) from their hydroxyl (-OH) end-moiety to a monolayer of -Ar-SO2Cl groups, which are easy to form on electrodes (metals, semiconducting materials, ...) from aryl-diazonium salt reduction. A hybrid molecular coating on gold, with scarce Ar-SO2-Brij58 and PEO oligomers, was used to monitor immobilization and fusion kinetics of DOPC small unilamellar vesicles (SUV) by both quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. Using flat and transparent thin chromium film electrodes, we designed biosensors to couple surface sensitive techniques for membranes, including X-ray reflectivity (XRR), atomic force microscopy (AFM) with subnanometer resolution, and optical microscopy, such as fluorescence recovery after photobleaching measurements (FRAP), in addition to electrochemistry techniques (cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)). The advantages of this biomembrane-sensing platform are discussed for research and applications.