Electrochemical Quartz Crystal Microbalance Study Research Articles

Electrochemical quartz crystal microbalance study of underpotential deposition of mercury on iridium metal and iridium oxide

AbstractTo evaluate the properties of an Ir‐based catalyst (IrOx), which is the anode in polymer electrolyte membrane‐type water electrolysis, a new method for estimating the electrochemical surface area (ECSA) is required. ECSA evaluation using the underpotential deposition of mercury (Hg‐UPD) can be applied to metals and oxides. However, research regarding Hg‐UPD is needed because several Hg(II)/Hg(I) redox reactions occur simultaneously, and direct evidence of Hg‐UPD on IrOx has not been reported. We previously confirmed the Hg‐UPD phenomenon on Ir polycrystalline films using the electrochemical quartz crystal microbalance (EQCM) method. However, measurements on IrOx electrodes were not performed. In this study, Ir and IrOx electrodes are prepared by the sputtering method, and their Hg deposition behavior observed by EQCM. We quantitatively confirm Hg‐UPD on Ir metal surfaces and provide new evidence of Hg‐UPD on the IrOx surface. These results contribute to establishing the ECSA evaluation of various Ir‐based catalysts.

Exploring the possibility of aluminum plating/stripping from a non‐corrosive Al(OTf)3‐based electrolyte

Rechargeable aluminum batteries offer a promising candidate for energy storage systems, due to the Aluminum (Al) abundance source. However, the development of non‐corrosive electrolytes, facilitating reversible Al plating/stripping, is a critical challenge to overcome. This study investigates the feasibility of aluminum plating on a platinum substrate using a non‐corrosive trifluoromethanesulfonate (Al(OTf)3)/N‐methylacetamide (NMA)/urea electrolyte. This electrolyte was proposed earlier as an alternative chloroaluminate‐based ionic liquid, but Al plating/stripping was not proved. In this work, various techniques, including cyclic voltammetry, scanning electron microscope/energy‐dispersive X‐ray spectroscopy, operando optical microscopy and electrochemical quartz crystal microbalance (EQCM), gas chromatography (GC), and X‐ray photoelectron spectroscopy were employed to understand the Aluminum plating and stripping behavior. While cyclic voltammetry indicates redox activity on Pt, further analysis reveals no significant plating. Instead, hydrogen evolution reaction, promoted by the water‐residue, dominates the observed current, confirmed by operando microscopy and GC measurements. EQCM studies suggest the concurrent adsorption/desorption of Al(OH)2+ and Al3+ ions on the Pt electrode. Further drying the electrolyte reduces the hydrogen evolution, but plating of metallic Al remains elusive. These findings highlight the need for further optimization of the electrolyte composition to achieve efficient Al plating/stripping.

Effects of Polydopamine Incorporation on the Nanostructure and Electrochemical Performance of Electrodeposited Polypyrrole Films

Polypyrrole films are commonly prepared as conductive electrode surfaces for a variety of applications. Recently, there has been increasing interest in improving the adhesive properties and biocompatibility of polypyrrole electrodes via the incorporation of bioinspired polydopamine within the polymer scaffold. However, very little is currently known about the structural effects of polydopamine incorporation during the electropolymerisation of hybrid films. In this work, we combine electrochemical quartz crystal microbalance studies, fundamental electrochemical characterisation, atomic force microscopy, and a suite of spectroscopic techniques in order to correlate changes in the structure and performance of polypyrrole–polydopamine films to the structural modifications of the nanostructure induced by polydopamine incorporation. The results indicate that polydopamine incorporation greatly increases the rate of hybrid film deposition, as well as improving adhesion, surface homogeneity, and wettability, with no compromise in charge transfer properties. Polydopamine incorporation is strongly suggested to occur in non-connected domains within a predominantly polypyrrole-like scaffold. We propose a two-step model of co-polymerisation and the subsequent surface adhesion of hybrid films. Results are expected to be of broad general interest to researchers utilizing polypyrrole and polydopamine to prepare tailor-made electrodes for biosensing and catalysis.

Electrophoretic Protein Deposition as a Tool for In Situ Co-Crosslinking Enzyme Immobilization: An Electrochemical/Quartz Crystal Microbalance Study

Electrophoretic deposition is a powerful tool for depositing materials onto a substrate by using an electric field; its application in biotechnological areas, namely, electrophoretic protein deposition (EPD), is the most promising for, e.g., fabricating novel amperometric biosensors. Unfortunately, EPD suffers from several drawbacks due to coupled parasite electrochemical processes damaging the deposit; moreover, the nature of the deposition process, the deposit, and its stability are still controversial and unknown. The present research presents a deep investigation of the EPD processes conducted by using several electroanalytical techniques and an electrochemical quartz crystal microbalance (EQCM); notably, EPD was used here as a novel tool for performing an electrophoretically assisted, classical enzyme immobilization technique like co-crosslinking, thus permitting the immobilization of the desired protein in situ, i.e., exclusively onto the deposition electrode. An electrochemical study permitted the acquisition of useful insights about electrophoresis processes as well as solvent discharge and gas evolution at the deposition electrode; further, the use of appropriate current or potential pulse sequences, as investigated and improved in this study, together with fine-tuned chemical conditions, allowed the optimization of this novel EPD approach. Moreover, an EQCM study gave useful insights into the kinetics of the process, permitting a quantitative estimate of the deposit.

Electrodeposition of Transition Metal Dichalcogenide Thin- Films from Non-Aqueous Solvents

Transition metal dichalcogenides (TMDCs) are an interesting group of 2D materials characterised with a layered structure analogous to graphene and they possess unique electronic and optical properties, especially when in the few- and mono-layer form. Developing scalable techniques for depositing TMDCs is a major challenge which needs to be overcome to fabricate functional devices with these materials. Electrodeposition is an industrially relevant technique that has some key advantages over other conventional deposition methods. It is a low cost and easily scalable technique and could be used for obtaining complex nanoscale features and for depositing over topologically demanding surfaces. Even though the electrodeposition of MoS2 has been achieved both in aqueous and non-aqueous electrolytes, not much progress has been made in the deposition of other TMDC materials. Tungsten based TMDCs such as WS2 and WSe2 are shown to be very promising materials in different applications, however electrodepositing them remains extremely challenging. One of the major obstacles here is developing electrochemically active precursors which are compatible with the electrolyte system and able to deliver both the tungsten and chalcogens to the electrolyte. Controlling and optimizing the deposition process to obtain few- and mono-layer TMDCs is another challenge. In addition, the choice of substrates for deposition is very important, especially for direct growth of ultra-thin TMDCs. Electrodeposition, being a bottom-up deposition method, would benefit from an atomically thin and smooth substrate such as graphene for depositing few- and mono-layer TMDCs.Here we present non-aqueous electroplating as a scalable alternative technique for tungsten-based TMDC deposition, with WS2 and WSe2 as examples. Tailored single source precursors were developed to use in non-aqueous electrolytes. WS2 was electrodeposited from dichloromethane (CH2Cl2) using the [NEt4]2[WS2Cl4] precursor. WSe2 was then electrodeposited from acetonitrile (CH3CN) electrolyte using [WSeCl4] as the precursor. Electrochemical quartz crystal microbalance (EQCM) studies were performed to optimize the deposition process and to probe the mechanism of precursor electrochemistry. Electrochemical deposition parameters were then carefully adjusted to obtain few- and mono-layer TMDCs. Patterned graphene electrodes were used as an atomically thin and smooth platform for the deposition of few- and mono-layer WS2. Few-layer TMDC films obtained on graphene were found to be much smoother than films deposited on other standard substrates such as titanium nitride (TiN) or Pt. These TMDC/graphene structures gave interesting 2D heterostructures which are technologically important for different applications.This work was funded by EPSRC grant references EP/V062689/1, EP/V062387/1 and EP/P025137/1

Palladium Nanoparticles Grown by Using Successive Ionic Layer Adsorption and Reaction Method: Ethanol Electrooxidation and Electrochemical Quartz Crystal Microbalance Studies

A facile wet chemical method namely successive ionic layer adsorption and reaction (SILAR) is implemented to grow palladium nanoparticles on graphite substrate. The grown Pd nanoparticles are successfully applied for electrooxidation of ethanol in alkaline solution. The electrocatalytic activity of grown Pd nanoparticles is studied by performing cyclic voltammetry (CV) measurements. Electrooxidation of ethanol by Pd nanoparticles is shown to be affected by growth parameters such as precursor concentration and number of SILAR growth cycles. Excessive growth of Pd nanoparticles due to large number of SILAR growth cycles shifts the pattern of cyclic voltammograms from period-one cyclic voltammograms to high order periodic/aperiodic cyclic voltammograms. Pd nanoparticles are also grown on gold coated quartz crystal and implemented to track any mass changes that occur during electrochemical surface oxidation/reduction over Pd nanoparticles, with and without ethanol in alkaline solution. To measure the mass changes occurring during CV measurements electrochemical quartz crystal microbalance (EQCM) is implemented in situ along with potential scanning.

Decoupling of the Impedance of Solid-Electrolyte Interface and Plated Lithium: Implications for Anode-Free Lithium Metal Battery Technology

The understanding of the impedance response during the cycling process of the “anode-free” lithium metal batteries is ambiguous in the literature. Herein, we report on a combined electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy study to decouple the various contributions of the impedance response of an anode-free battery. This decoupling is achieved by a comparison of the evolution of electrochemical impedance spectroscopy spectra in two- and three-electrode cells during the Li plating–stripping processes. The observed high- and medium-frequency loops of the impedance spectra can be unambiguously assigned to the charge transfer in the solid-electrolyte interface and the plated lithium layers, respectively.

Hybrid potentiodynamic/potentiostatic electrodeposition of thin and compact tin dioxide on indium tin oxide electrodes

Electrodeposition of conformal and compact SnO2 films on transparent conductive oxides (TCOs) has been hardly achieved thus limiting its application in fully solid solar cells such as those based in perovskite absorbers. Here are presented high-quality n-type semiconducting tin (VI) oxide (SnO2) thin films, successfully grown using a hybrid potentiodynamic/potentiostatic approach on both ITO and FTO coated glass substrates after a detailed optimization that included both annealing steps between eletrodepositions. A solution chemistry study together with a spectrophotometric analysis was useful to determine the one-hour time window of stability for the chosen electrolyte as source of tin. Formation mechanisms based in thermodynamic data and accumulated mass measurements using an electrochemical quartz crystal microbalance (EQCM) are discussed. From the EQCM study the growth rate of films was also estimated in good agreement with high resolution transmission electron microscopy (HR-TEM) analysis. Field emission scanning electron microscopy (FE-SEM) images and X-ray diffraction (XRD) data revealed that substrates are well-covered, crystalline, conformal and free of defects (e.g. without pinholes). The absence of these defects was also well supported by cyclic voltammetry measurements using the ferricyanide/ferrocyanide redox couple. XPS also confirmed the presence of Sn4+ in optimized films. From the optical properties, after carefully eliminating the influence of oscillations due to interference, a direct bandgap energy at 3.60 eV can be deduced. Another indirect bandgap energy at 3.30 eV can also be possible. The hybrid potentiodynamic/potentiostatic protocol to prepare SnO2 paves a way to prepare compact, transparent and well covering films suitable as electron transporting layer (ETL) for applications in both photoelectrochemical and solid-state solar cells.

Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry Study.

Recent work has shown that ion-selective components may be transferred from nanoemulsions (NEs) to endow polymeric membranes with ion-selective sensing properties. This approach has also been used for nanopipette electrodes to achieve single-entity electrochemistry, thereby sensing the ion-selective response of single adhered nanospheres. To this date, however, the mechanism and rate of component transfer remain unclear. We study here the transfer of lipophilic ionic compounds from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS) films by chronoamperometry and quartz crystal microbalance. Thin-film cyclic coulovoltammetry measurements serve to quantify the uptake of lipophilic species into blank PVC-DOS membranes. Electrochemical quartz crystal microbalance data indicate that the transfer of the emulsion components is insignificant, ruling out simple coalescence with the membrane film. Ionophores and ion-exchangers are shown to transfer into the membrane at rates that correlate with their lipophilicity if mass transport is not rate-limiting, which is the case with more lipophilic compounds (calcium and sodium ionophores). On the other hand, with less lipophilic compounds (valinomycin and cation-exchanger salts), transfer rates are limited by mass transport. This is confirmed with rotating disk electrode experiments in which a linear relationship between the diffusion layer thickness and current is observed. The data suggests that once the nanoemulsion container approaches the membrane surface, transfer of components occur by a three-phase partition mechanism where the aqueous phase serves as a kinetic barrier. The results help better understand and quantify the interaction between nanoemulsions and ion-selective membranes and predict membrane doping rates for a range of components.

The effects of local graphitization on the charging mechanisms of microporous carbon supercapacitor electrodes

The electrochemical quartz crystal microbalance (EQCM) technique has been used to study the charge mechanisms in two TiC-derived nanoporous carbons (CDC), synthesized at 800 ℃ and 1100 ℃. These two carbons have a similar pore size and porous volume, but the CDC prepared at 1100 °C shows a more graphitic microstructure. The EQCM study revealed that the charge storage mechanism in the CDC-800 is mainly controlled by a counter-ion adsorption process, while an expanded ion-exchange process was observed for the CDC-1100. Combined with the potential of zero charge (PZC), these measurements suggest a strong interaction between the anions and graphitic carbon. For the first time, we provide experimental evidence that the local carbon structure affects the charge storage mechanism of the electrical double-layer capacitance in high surface area porous carbons.

Towards Rechargeable Aluminum-Ionic Liquid Batteries for Low-Temperature Space Applications

Batteries operating reliably at low temperatures are required to power robotic spacecraft, particularly those that embark on planetary science missions1. For example, Mars surface missions have typical temperature targets of -40 to -60 °C, while surface mission concepts to the outer planets or Ocean Worlds, such as Europa, have targets down to -180 °C. At low temperatures, state-of-the-art lithium-ion batteries suffer from lithium plating and dendritic growth on the graphite anodes, severe capacity loss associated with sluggish ion diffusion in crystalline transition metal cathodes, and kinetic limitations2. While organic electrolyte mixtures have been developed that enable moderate low-temperature performance, new battery concepts, including those using ionic liquid electrolytes, are needed to enable new paradigms in low or ultra-low temperature space missions. Recently, rechargeable aluminum batteries have been developed that use chloroaluminate-containing ionic liquid electrolytes, which may be suitable alternatives to lithium-based batteries when used under extreme temperatures. Aluminum metal is also distinguished by its high energy density, safety, low cost, and sustainability, which are also key properties for space applications.Herein we present, for the first time, results towards rechargeable Al-batteries designed specifically for low-temperature space missions that demonstrate high capacity retention, long-term cyclability, and favorable electrochemical kinetics at low temperatures down to -40 °C. We focus on the development of ionic liquid electrolytes with mixed anion-cation compositions to impart disorder and disrupt crystallization, while pairing them with functionalized graphite and conducting polymer cathodes.3 , 4 The resulting aluminum batteries were characterized by variable-temperature and rate cyclic voltammetry (CV), galvanostatic cycling, electrochemical impedance spectroscopy (EIS), and solid-state nuclear magnetic resonance (NMR) spectroscopy to understand their reaction mechanisms and factors limiting their rate performance. The ionic liquid electrolyte mixtures were also characterized by a combination of differential scanning calorimetry (DSC) and electrochemical methods to understand their freezing points and electrochemical stability. The results provide fundamental insights into the design of positive electrode materials and ionic liquid electrolyte mixtures in novel batteries for low-temperature space applications.References Bugga, R. V.; Brandon, E. J., Energy Storage for the Next Generation of Robotic Space Exploration. Electrochemical Society Interface 2020, 29 (1), 59-63.Jones, J.-P.; Smart, M. C.; Krause, F. C.; Bugga, R. V., The Effect of Electrolyte Additives upon Lithium Plating during Low Temperature Charging of Graphite-LiNiCoAlO2 Lithium-Ion Three Electrode Cells. Journal of The Electrochemical Society 2020, 167 (2), 020536.Schoetz, T.; Kurniawan, M.; Stich, M.; Peipmann, R.; Efimov, I.; Ispas, A.; Bund, A.; Ponce de Leon, C.; Ueda, M., Understanding the charge storage mechanism of conductive polymers as hybrid battery-capacitor materials in ionic liquids by in situ atomic force microscopy and electrochemical quartz crystal microbalance studies. Journal of Materials Chemistry A 2018, 6 (36), 17787-17799.Xu, J. H.; Turney, D. E.; Jadhav, A. L.; Messinger, R. J., Effects of Graphite Structure and Ion Transport on the Electrochemical Properties of Rechargeable Aluminum–Graphite Batteries. ACS Applied Energy Materials 2019, 2 (11), 7799-7810.

Formation of lithiated gold and its use for the preparation of reference electrodes \u2014 an EQCM study

Lithiated gold wires can be used to build reference electrodes with outstanding potential stabilities over several days and even over the course of one year. These electrodes are well suited for investigations in the context of lithium-ion batteries (LIBs). In this work, a detailed procedure for the preparation of such electrodes with tailored mechanical properties, which can be fitted gastight into electrochemical cells using commercially available fittings, is given. The electrochemical lithiation process is studied using the electrochemical quartz crystal microbalance (EQCM) technique, and the differences in lithiation of wire type and thin film type gold electrodes are discussed. All experiments were carried out with two different electrolytes, namely, a LiPF6 and a lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based electrolyte, and we conclude that for a higher lithiation rate and long-term stability, the use of LiTFSI-based electrolyte in the preparation phase is beneficial. The EQCM data provides a better insight in the analysis of film formation processes, like the buildup of the solid electrolyte interphase (SEI) during the lithiation, the rate of deposition of metallic lithium, or additional information on the kinetics of Li-Au alloy formation.

EQCM study of intercalation processes into electrodeposited MnO2 electrode in aqueous zinc-ion battery electrolyte

In this work manganese oxide films were obtained by electrodeposition and their electrochemical and mass transfer processes in aqueous zinc-ion battery electrolyte were studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Cyclic voltammograms and corresponding mass variation curves of manganese oxide during charge-discharge processes were examined simultaneously on Au-coated quartz crystal electrodes. The investigations were conducted in aqueous electrolytes of different composition (2 M ZnSO4 and 2 M ZnSO4 + 0.1 M MnSO4). Monitoring of electrode mass variation during potential cycling provides direct evidence that redox processes in MnO2 electrodes co-occur with intercalation of protons and zinc ions. Combined CV and EQCM studies reveal that electrodeposited films of MnO2 are unstable in 2 M ZnSO4 electrolyte. The repeated potential cycling in Zn-containing electrolytes leads to rapid deterioration of electrode capacity in the few initial cycles due to the Zn2+ insertion into subsurface structures of MnO2 and blocking of electroactivity of MnO2 film on Au substrate. On the other hand, reversible processes of intercalation of protons and zinc ions occur in 2 M ZnSO4 + 0.1 M MnSO4 electrolyte. Two main steps of mass increase during the discharging process, taking place at 1.4 V (vs. Zn/Zn2+) and in the potential range (1.3–1.0) V were demonstrated by EQCM. The first step of mass increase is mainly related to the intercalation of H+ (as H3O+), whereas the second step of mass increase is mainly associated with formation of surface compounds like zinc sulfate hydroxide salts.

Electrosynthesis and characterisation of novel poly(Nile blue)-deep eutectic solvent/Prussian blue nanoparticle modified electrodes and their biosensing application

• Ethaline deep eutectic solvent (DES) for electropolymerisation of Nile blue (NB). • Poly(Nile blue) formed on Prussian blue nanoparticles on glassy carbon electrodes. • Electrochemical quartz crystal microbalance study of polymerisation process. • Electrochemical and surface characterisation of DES polymer modified electrodes. • Tyrosinase immobilised on PNB ethaline film gives superior biosensing of catechol. Electropolymerisation of Nile blue to form films of the redox polymer poly(Nile blue) (PNB) in ethaline deep eutectic solvent, by potential cycling, on Prussian-blue nanoparticle (PBNP) modified glassy carbon electrodes (GCE) is described. For comparison, PNB films were also prepared in aqueous solution. The performance of the novel composite modified electrodes was evaluated electrochemically (cyclic voltammetry, electrochemical impedance spectroscopy, and fixed potential amperometry). An electrochemical quartz crystal microbalance was used to quantify the amount of the polymer film deposited in ethaline and to investigate the polymerisation mechanism. The nanostructured morphology was examined using transmission electron microscopy and scanning electron microscopy. PNB ethaline /PBNP/GCE and PNB aqueous /PBNP/GCE were used as support for immobilising the enzyme tyrosinase for the biosensing of catechol, the biosensor configuration with the PNB film formed in ethaline being significantly more sensitive than that with the PNB film made in aqueous solution.

Electrochemical quartz crystal microbalance studies on specific adsorption of nanoparticle stabilizers on platinum surface

• Phosphinate reduces mass change of adsorbate film on Pt at the double layer region. • Phosphinate suppresses reduction of Pt to zero-valent and growth of metal particles. • Citrate adsorbs on Pt and increases adsorption strength of coadsorbed oxygen. • Citrate inhibits Cu electrodeposition on Pt while phosphinate has a minor effect. • Suberate adsorbs more than citrate on Pt to prevent nanoparticle aggregation. Phosphinate and citrate ions are effective stabilizers for aqueous phase synthesis of platinum-based nanoparticles. In the present study, specific adsorption/desorption of stabilizers on platinum surface was investigated using an electrochemical quartz crystal microbalance (EQCM). Cyclic voltammetry combined with EQCM revealed that phosphinate ion reduces mass change of adsorbate film on Pt at the double layer region and it was oxidized by water and oxygen species producing anodic current above 0.2 V vs. Ag/AgCl. Phosphinate stabilizes positively charged platinum species rather than metallic species, which leads to size reduction of metal nanoparticles. Density Functional Theory calculation indicated that phosphinate adsorbs on Pt via two oxygen atoms (though coadsorbed water might change the structure) and the interaction strength increases with increasing positive charge on Pt surface. Meanwhile, citrate increased adsorption strength of oxygen on Pt in a weakly acidic condition. Electrodeposition of copper on Pt was significantly suppressed in the presence of citrate. The capping effect of citrate and oxygen on metallic surface helps dispersing nanoparticles.

Exploring the mechanical stability of manganese oxide as an electrocatalyst via in-situ surface stress and electrochemical quartz crystal microbalance studies

We report in this study on the combination of resonance frequency shift measurements with the use of Electrochemical Quartz Crystal Microbalance (EQCM), alongside in-situ electrochemical surface stress (ESS) analysis, which provides a comprehensive description of both the microscopic and macroscopic processes occurring on the surface of the oxygen reduction reaction (ORR) electrocatalyst. The resonance frequency shift was measured on an Au/MnOx electrode in both de-oxygenated and O2 saturated electrolytes. The results obtained with the use of frequency shift measurements (with the use of EQCM) are in good agreement with the interpretations of the data originated from the surface stress response. It was found that the structural changes identified by the surface stress led to the insertion and release of water molecules into and out of the manganese-oxide film. These findings are used to explain the mechanical failure of the electrocatalyst film subsequent to multiple charge/discharge cycles, hence revealing an additional valuable information on the poor mechanical stability of the manganese-oxide film. Moreover, the presence of oxygen in the electrolyte resulted in mass changes, being qualitatively similar to those recorded in de-oxygenated electrolyte, albeit with different intensities during the ORR, further validating the proposed catalytic mechanism.

Controllable Production of Ag/Zn and Ag Particles from Hydrometallurgical Zinc Solutions

Ag/Zn and Ag particles have been successfully produced from electrolytes simulating zinc process solutions containing a high zinc concentration (65 g/L) and a negligible silver concentration (0.5–50 ppm) using a facile and sustainable electrodeposition-redox replacement (EDRR) method. Results show that the particle size and chemical composition of the deposited Ag/Zn and Ag particles can be readily controlled by varying the operating parameters such as replacement time and agitation. Electrochemical quartz crystal microbalance (EQCM) studies supported with SEM-EDS and TEM results indicate that the EDRR process consists of three regions: (I) zinc pulse deposition; (II) redox replacement between the Ag+ ions and the deposited Zn, formation of a Zn/Ag alloy structure, and competing Zn oxidation by H+ ions; and (III) further replacement between Ag+ ions and Zn (alloy) formed in the previous stage and possible silver reduction by hydrogen. The Zn (alloy) has a higher reduction potential which hinders the competing H+ reduction and sequentially improves the utilization efficiency of the sacrificial metal (Zn). Furthermore, by using the EDRR method, Ag/Zn particles could be successfully obtained from solutions with an extremely low Ag concentration of 0.5 ppm. The promising results demonstrate the feasibility of producing Ag-based functional materials utilizing trace amounts of Ag from zinc process solutions.

Anion Exchange and Water Dynamics in a Phosphonium-Based Alkaline Anion Exchange Membrane Material for Fuel Cells: An Electrochemical Quartz Crystal Microbalance Study.

The anion exchange and water dynamics of a phosphonium-based alkaline anion exchange membrane (AAEM) during the methanol oxidation process have been studied with the electrochemical quartz crystal microbalance (EQCM). The viscoelastic effects of the phosphonium-based AAEM in water and the optimal film thickness for EQCM analysis were identified by acoustic impedance analysis. The phosphonium-based AAEM exhibited stronger mechanical toughness in water when compared to a quaternary-ammonium-based membrane that was studied previously. From the simultaneous measurement of the electrochemical response and the frequency changes of the quartz crystal oscillator, water ingress/egress to/from the AAEM film was found to accompany the hydrogen adsorption/desorption, Pt oxidation process, and methanol oxidation process. The in situ study of AAEM films helps illustrate the critical role that water transport plays in electrochemical processes during the operation of anion exchange membrane fuel cells. The generated CO32- and HCOO-, during methanol oxidation, were absorbed into the AAEM film, replacing the OH- in the film, as shown by the decrease in frequency after one potential cycle. The exchange of OH- by CO32- and HCOO- was found to be reversible. These results provide insights into the anion exchange processes in membranes and emphasize the importance of characterizing the hydrated membranes under electrochemical conditions.

(Invited) Challenges in Reversible Electrodeposition and Stripping of Lithium Peroxide for Li-Air Batteries

Thanks to a high theoretical energy density combined to a relatively high operation voltage around 3 Volts versus Li+/Li, the non-aqueous Li-Air battery is a good candidate for future electric cars with an increased driving range. In principle, this battery relies on the reversible electrochemical reaction between the metallic Li and the gaseous O2 in presence of a non-aqueous electrolyte where Li+ ions and dissolved O2 molecules diffuse and react to form the ideal discharge product lithium peroxide Li2O2. However, this apparently simple reaction process appears to be more complicated when put into practice.Considering the Li-O2 discharge process, there are two main models proposed in the literature to explain the Oxygen Reduction Reaction which were unified in a single mechanism process where Li2O2 formation goes through a surface reaction or/and a solution reaction1, depending on system parameters such as the applied potential or the solvent properties. Using an electrochemical quartz crystal microbalance (EQCM) we studied the products formed in discharge as well as the reversibility of the reactions from a mass point of view during cycling.2 Regarding the Li-O2 charge process, the Li2O2 decomposition occurring is a rather sluggish and incomplete process. A lot of efforts was made in this area by the research community, and several approaches were proposed to facilitate and fasten the Li2O2 decomposition: the use of solid state catalyst of several kind (doped carbon, non-precious materials...) or soluble catalysts also called redox mediators, such as for example TTF3 (tetrathiafulvalene), TEMPO4 (2,2,6,6-tetramethylpiperidinyloxyl), Cobalt Bis(terpyridine)5, lithium iodide6 (LiI). The mobile redox mediators, electron-hole transfer agents, aid the oxidation of Li2O2 as has been reported previously. In our EQCM study we activated in situ the TTF and confirms its usefulness on the mass reversibility of the deposition/dissolution of Li2O2 during cycling2. Later on, we performed a detailed study of the effect of LiI redox mediator on the formation and decomposition of Li2O2.7 We showed that the solvent could drastically change the mechanism of decomposition during charge8. Finally, we will discuss the parameters able to influence the most the deposition and stripping of Li2O2 in a non-aqueous medium. Reference s : 1 L. Johnson, C. Li, Z. Liu, Y. Chen, S. A. Freunberger, J. M. Tarascon, P. C. Ashok, B. B. Praveen, K. Dholakia, P. G. Bruce, Nature Chemistry, 6, 1091 – 1099 (2014). 2 S. Schaltin, G. Vanhoutte, M. Wu, F. Bardé, J. Fransaer, Phys. Chem. Chem. Phys. , 17, 12575 – 12586 (2015). 3 Y. Chen, S. A. Freunberger, Z. Peng, O. Fontaine, and P. G. Bruce, Nature Chemistry, 5, 489 – 494 (2013). 4 Y. Hase, J. Seki, T. Shiga, F. Mizuno, H. Nishikoori, H. Iba, K. Takechi, Chem. Commun., 52, 12151 – 12154 (2016). 5 Koffi P.C. Yao, J. T. Frith, S. Youssef Sayed, F. Bardé, J. R. Owen, Y. Shao-Horn, N. Garcia-Araez, J. Phys. Chem. C, 120 (30), 16290 – 16297 (2016). 6 Y. Qiao, S. Wu, Y. Sun, S. Guo, J. Yi, P. He, H. Zhou, ACS Energy Letters, 2, 8, 1869 – 1878 (2017). 7 M. Tulodziecki, G.M. Leverick, C.V; Amanchukwu, Y. Katayama, D.G. Kwabi, F. Bardé, P. Hammond, Y. Shao-Horn, Energy Environ. Sci., 10, 1828, (2017). 8 G. Leverick, M. Tułodziecki, R. Tatara, F. Bardé, Y. Shao-Horn, Joule, Vol. 3, Issue 4, 1106-1126, (2019).

Electrochemical quartz crystal microbalance study of magnesium porphine electropolymerization process

Material and charge balances in the course of the electropolymerization process of the non-substituted Mg(II) porphine (MgP) at a low oxidation potential from its acetonitrile solutions of various concentrations have been studied via the in situ electrochemical quartz crystal microbalance method (EQCM). Thus, registered electrode mass increase due to the MgP oxidation at its surface has been used, in combination with in situ spectroelectrochemical data, for determination of the key parameters of the polymerization process and of the magnesium polyporphine films deposited on the electrode surface: current efficiency of the film deposition process, average charge spent for transformation of a monomer molecule into monomer unit inside the film, number of monomer units inside the deposited film, average number of valence bonds per one monomer unit inside the film. Besides, the EQCM method applied to the discharge process of the electropolymerized film has allowed us to estimate the average charging (oxidation) degree of the monomer unit inside the film at the polymerization potential and the degree of the solvent participation in the course of the polymer’s redox transitions. It has been established that the number of bonds between porphine units is within the range of 2.2 to 2.4, with its slight increase for films deposited at higher monomer concentrations. Conclusions on the structure of polyporphine chains have been made.