Electrochemical Quartz Crystal Microbalance Technique Research Articles

Downsizing nanoarchitectonics of multilayered MXenes electrocatalysts towards real time ion tracking via EQCM and electrocatalytic applications

Since their discovery, engineering two-dimensional (2D) MXene materials have attracted rapid interest in both energy storage and conversion applications. Among the several techniques being introduced for enhancing material properties, downsizing is one among the interesting approaches. Downsizing involves the deliberate scaling down of active 2D materials, such as MXenes, systematically. Although major studies are focused on the electrochemical applications of single layered MXene flakes, curiosity in evaluating the downsized multilayered MXenes for electrochemical applications motivates this project. Thus, in the current study, the multilayered bulk MXenes are sequentially stepped down to smaller multilayered fragments at definite time intervals, and subsequently the potential of this procured heterogeneous polydispersed solution are evaluated towards electrochemical applications without any further post-treatments. Real time monitoring of lithium-ion exchange in the downsized MXene materials at various time intervals was tracked using the electrochemical quartz crystal microbalance technique, where the downsized MXene system exhibited water-assisted lithium-ion transfer behavior. Increase in mass exchange was found to increase with increase in downsized MXene systems, thus making it very interesting towards ion storage applications. Further, downsized MXene electrocatalyst material delivered the lowest onset potential for hydrogen production among the set of catalysts studied. In short, this study outlines and pioneers some interesting observations regarding both energy storage and catalytic applications of multilayered downsized MXenes, thereby opening up new possibilities for facile, rapid and cost-effective material fabrication approaches.

Role of Surface Terminations for Charge Storage of Ti3C2Tx MXene Electrodes in Aqueous Acidic Electrolyte.

In this study, we used 2-Dimmensionnal Ti3C2 MXene as model materials to understand how the surface groups affect their electrochemical performance. By adjusting the nature of the surface terminations (Cl-, N/O-, and O-) of Ti3C2 MXene through a molten salt approach, we could change the spacing between MXene layers and the level of water confinement, resulting in significant modifications of the electrochemical performance in acidic electrolyte. Using a combination of techniques including in-operando X-ray diffraction and electrochemical quartz crystal microbalance (EQCM) techniques, we found that the presence of confined water results in a drastic transition from an almost electrochemically inactive behavior for Cl-terminated Ti3C2 to an ideally fast pseudocapacitive signature for N,O-terminated Ti3C2 MXene. This experimental work not only demonstrates the strong connection between surface terminations and confined water but also reveals the importance of confined water on the charge storage mechanism and the reaction kinetics in MXene.

Role of Surface Terminations for Charge Storage of Ti3C2Tx MXene Electrodes in Aqueous Acidic Electrolyte

AbstractIn this study, we used 2‐Dimmensionnal Ti3C2 MXene as model materials to understand how the surface groups affect their electrochemical performance. By adjusting the nature of the surface terminations (Cl‐, N/O‐, and O‐) of Ti3C2 MXene through a molten salt approach, we could change the spacing between MXene layers and the level of water confinement, resulting in significant modifications of the electrochemical performance in acidic electrolyte. Using a combination of techniques including in‐operando X‐ray diffraction and electrochemical quartz crystal microbalance (EQCM) techniques, we found that the presence of confined water results in a drastic transition from an almost electrochemically inactive behavior for Cl‐terminated Ti3C2 to an ideally fast pseudocapacitive signature for N,O‐terminated Ti3C2 MXene. This experimental work not only demonstrates the strong connection between surface terminations and confined water but also reveals the importance of confined water on the charge storage mechanism and the reaction kinetics in MXene.

Probe the Dynamic Adsorption and Phase Transition of Underpotential Deposition Processes at Electrode-Electrolyte Interfaces.

Electrochemical scanning tunneling microscopy (EC-STM) and electrochemical quartz crystal microbalance (E-QCM) techniques in combination with DFT calculations have been applied to reveal the static phase and the phase transition of copper underpotential deposition (UPD) on a gold electrode surface. EC-STM demonstrated, for the first time, the direct visualization of the disintegration of (√3 × √3)R30° copper UPD adlayer with coadsorbed SO42- while changing sample potential (ES) toward the redox Pa2/Pc2 peaks, which are associated with the phase transition between the Cu UPD (√3 × √3)R30° phase II and disordered randomly adsorbed phase III. DFT calculations show that SO42- binds via three oxygens to the bridge sites of the copper with sulfate being located directly above the copper vacancy in the (√3 × √3)R30° adlayer, whereas the remaining oxygen of the sulfate points away from the surface. E-QCM measurement of the change of the electric charge due to Cu UPD Faradaic processes, the change of the interfacial mass due to the adsorption and desorption of Cu(II) and SO42-, and the formation and stripping of UPD copper on the gold surface provide complementary information that validates the EC-STM and DFT results. This work demonstrated the advantage of using complementary in situ experimental techniques (E-QCM and EC-STM) combined with simulations to obtain an accurate and complete picture of the dynamic interfacial adsorption and UPD processes at the electrode/electrolyte interface.

Unveiling the charge storage mechanisms of Co-based perovskite fluoride in a mild aqueous electrolyte.

This study is an in-depth exploration of the charge storage mechanisms of KCoF3 in 1 M Na2SO4 mild aqueous electrolytes via an array of ex situ/in situ physicochemical/electrochemical methods, especially the electrochemical quartz crystal microbalance (EQCM) technique, showing a combination of conversion, insertion/extraction and adsorption mechanisms. Specifically, during the first charge phase, Co(OH)2 is formed/oxidized into amorphous CoOOH and Co3O4, and then CoOOH undergoes partial proton extraction to yield CoO2, which is simultaneously accompanied by the transformation of Co3O4 into CoOOH and (hydrated) CoO2. During the first discharge process, the partial insertion of H+ into (hydrated) CoO2 leads to the formation of CoOOH and Co3O4, with the conversion of Co3O4 into CoOOH and both Co3O4 and CoOOH undergoing further transformations into (hydrated) Co(OH)2via the insertion of H+. This work offers valuable references for the development of aqueous energy storage.

2D Germanane‐MXene Heterostructures for Cations Intercalation in Energy Storage Applications

AbstractHeterostructures offer an exceptional possibility of combining individual 2D materials into a new material having altered properties compared to the parent materials. Germanane (GeH) is a 2D material with many favorable properties for energy storage and catalysis, however, its performance is hindered by its low electrical conductivity. To address the low electrochemical performance of GeH, a heterostructure of GeH and Ti3C2Tx is fabricated. The Ti3C2TX is a layered material belonging to the family of MXenes. The resulting heterostructure (GeMXene) at a defined mass ratio of GeH and Ti3C2Tx shows superior capacitive performance that surpasses that of both pristine materials. The effect of the size of cations and anions for intercalation into GeMXene in different aqueous salt solutions is studied. GeMXene allows only cation intercalation, which is evidenced by the gravimetric electrochemical quartz crystal microbalance (EQCM) technique. The capacitive performance of the GeMXene is compared in neutral, acidic, and alkaline electrolytes to determine the best electrochemical performance. This unleashes the potential use of GeMXene heterostructure in different electrolytes for supercapacitors and batteries. This work will pave the way to explore the heterostructures of other 2D materials such as novel MXenes and functionalized germanane for highly energy‐storage efficient systems, and beyond.

Coupling Uniform Pore Size And Multi‑Chemisorption Sites: Hierarchically Ordered Porous Carbon For Ultra‐Fast And Large Zinc Ion Storage

AbstractConstructing hierarchically ordered macro/meso−microporous structures of carbonaceous cathode with matchable pore size and adequate active sites is significant toward large Zn2+ storage, but remains a formidable challenge. Herein, a new perspective is reported for synthesizing phosphorus and nitrogen dual‐doped hierarchical ordered porous carbon (PN‐HOPC) by eliminating the micropore confinement effect and synchronously introducing multi‐chemisorption sites. The interconnected macropore can effectively facilitate long‐distance mass transfer, and meso−microporous wall can promote accessibility of active sites. Density functional theory (DFT) calculations identify that the P and N co‐doping markedly contributes to the reversible adsorption/desorption of zinc ions and protons. Consequently, the optimized PN‐HOPC exhibits outstanding Zn2+ storage capabilities in terms of high capacity (211.9 mAh g−1), superb energy density (169.5 Wh kg−1), and ultralong lifespan (99.3% retention after 60 000 cycles). Systematic ex situ measurements integrating with in situ Raman spectroscopy and electrochemical quartz crystal microbalance (EQCM) techniques elucidate that the superior electrochemical capability is ascribed to the synergistic effect of the Zn2+, H+, and SO42− co‐adsorption mechanism, as well as invertible chemical adsorption. This study not only provides new insights to design advanced carbon materials toward practical applications but also sheds lights on a deeper understanding of charge storage mechanism for zinc‐ion capacitors (ZICs).

A novel label-free electrochemical immunosensor for detection of surfactant protein B in amniotic fluid

The deficiency of Surfactant Protein B (SPB) in Amniotic Fluid (AF) has been associated with severe respiratory pathologies in newborns such as respiratory distress syndrome (RDS). Early-stage diagnosis of these respiratory complications by monitoring the SPB in AF could be a significant clinical tool and the first step toward adopting efficient therapy. In this work, we report the development of a novel sensitive electrochemical immunosensor for the detection of SPB in human AF samples. The surface biofunctionalization steps were characterized by using Electrochemical Impedance Spectroscopy (EIS), cyclic voltammetry, and quartz crystal microbalance techniques. The performance of the immunosensor was investigated by EIS, showing a linear dynamic range between 2 ng/mL and 2000 ng/mL and a limit of detection of 0.1 ng/mL. The immunosensor was also selective and specific to other surfactant proteins presented in AF. To the best of our knowledge, this is the first developed electrochemical biosensor for SPB detection. More significant, the immunosensor developed is simpler than the traditional enzyme-linked immunosorbent assay, and present a higher sensitivity for SPB, indicating that it could be a promising alternative approach for SPB detection in the clinical diagnosis.

Effects of Local Graphitization on the Charging Mechanisms of Capacitive Microporous Carbon Supercapacitor Electrodes Application

Electrochemical double layer capacitors (EDLCs) store the charge by reversible adsorption of ions at the electrode/electrolyte interface. The optimization of EDLC performance needs to push further our basic understanding of the ion fluxes that occur during the charging/discharging process. Microporous carbon has been widely used as supercapacitor electrode material thanks to their tunable porosity and high specific surface area. However, most of the porous carbon materials have complex carbon structures, so that the mechanism is still poorly understood.Using electrochemical quartz crystal microbalance technique (EQCM) technique, we studied the charge storage mechanisms of two nanoporous carbide-derived carbon (TiC-CDC) electrodes, namely CDC-800 synthesized at 800℃ and CDC-1100 synthesized at 1100℃. These two carbons have a similar porosity but the CDC-1100 sample shows more graphitic carbon microstructure. We found that a counter-ion adsorption process mainly controls the charging mechanism of CDC-800 (“V” shape m vs Q plot), while an expanded ion-exchange and counter-ion adsorption process is obtained for CDC-1100 (“U” shape). We show here that the local carbon structure affects the charging mechanism of electrical double layer capacitance, and a strong interaction between the anions and graphitic carbons explains these different behaviors. Our results provide more insights into the fundamental understanding of the carbon/electrolyte interface and the charge of the electrical double layer capacitance.Figure 1. Electrode mass change versus charge during the polarization of CDC-800 (a) and CDC-1100 (b) coated Au electrodes in 2M EMI-TFSI/ACN electrolyte at the scan rate of 10 mV·s−1. Figure 1

Electropolymerization of thiazole derivatives bearing thiophene and selenophene and the potential application in capacitors

• Three thiazole derivatives bearing thiophene and selenophene were used as monomers for electropolymerization. • Pseudocapacitor performance of deposited polymer layers was investigated on macroelectrode and ultramicroelectrode. • Pseudocapacitor behavior is related to the anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. • The approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion were analyzed. Three thiazole derivatives bearing thiophene and selenophene are synthesized and used as monomers for electropolymerization. The electropolymerization process is studied using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques. Deep understanding is obtained regarding the pseudocapacitor performance of deposited polymer layers by subjecting the macroelectrode and ultramicroelectrode to CV and galvanostatic charging–discharging experiments in three kinds of electrolytes. Notably, the highest specific capacitance is observed in the derivative bearing selenopheno[3,4- d ]thiazole and selenophene in a solution of tetrabutylammonium tetrafluoroborate. Furthermore, the electropolymerization rate is influenced by the kind of chalcogenophene and the CV scan rate. A spectroelectrochemistry experiment reveals the optical and electrochromic behavior of the deposited polymer layers. From these results, the pseudocapacitor performance of the deposited polymer layers is related to anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. The EQCM experiments also reveal these processes during electropolymerization and anion intercalation/deintercalation into the deposited polymer layers. Finally, the approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion are analyzed using the EQCM data.

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.

Oxygen vacancy inducing phase transition during charge storage in MnOx@rGO supercapacitor electrode

Herein, in-situ Raman and electrochemical quartz crystal microbalance techniques combined with density functional theory (DFT) calculations are adopted to prove the charge storage mechanism for high-stability MnOx@graphene microspheres electrode in alkaline electrolyte (KOH). The results reveal that the layered MnO2 phase gradually transformed into the spinel Mn3O4 phase in the process of discharging, accompanied by the insertion of potassium ions. Moreover, the Mn-O bonds length near the potassium ions in [MnO6] octahedral structure becomes longer, while the long unstable Mn-O bonds tend to lose oxygen and create oxygen vacancies, which further transforms the layered structure into stable spinel structure. Furthermore, it is also found that potassium ions can be more easily embedded in the layered MnO2 with oxygen vacancies due to the lower energy demand compared with the pure MnO2. Meanwhile, the MnOx@graphene microspheres electrode exhibits a capacity retention as high as 90% after 10,000 cycles at 10 A g−1, indicating a superior cyclic stability.

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.

Specific carbon/iodide interactions in electrochemical capacitors monitored by EQCM technique

This paper reports on the ion fluxes at the interfaces of various porous carbon electrodes/aqueous solutions of alkali metal cations (Na+, K+ and Rb+) and iodide anions, monitored by an electrochemical quartz crystal microbalance (EQCM).

Characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on gold electrodes

The modification of surfaces by polyethylene glycol (EGn) is an approach used to reduce the antifouling effects of these materials in a biological medium. It has been found that the packing density and conformational order of these molecules in the films are crucial for the inhibition of unspecific protein adsorption. In this work, we present a study of the formation and characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on either poly-oriented or Au(111) single crystal surfaces. The final properties of the formed EG7-SAMs are studied by examining the reductive desorption process as well as the electronic and ionic blocking behaviour of these layers, under different experimental conditions, by using cyclic voltammetry and electrochemical impedance spectroscopy. Additional information of the structure, composition and organization is obtained by absorption-reflection infrared and X ray photoelectron spectroscopies and contact angle measurements. In contrast to the behaviour observed with alkanethiols, the EG7-SAM shows the best final organization at a modification time of 1 h. The antifouling properties of this EG7-SAM against the adsorption of the bovine serum albumin protein in a phosphate saline medium, has been evidenced by using the electrochemical quartz crystal microbalance technique.

In situ analysis of pore size effect of ionic solvation during the formation of double electric layers

Electrochemical quartz crystal microbalance (EQCM) technique was used to characterize the influence of pore size and ion size and, solvation effect on the formation of electric double-layer capacitors (EDLCs). Based on quantitative calculation and analysis, the apparent molecular mass ( M sx ) was calculated from the slope of the electrode mass change ( Δm ) vs. the charge ( ΔQ ) passed in the electrode during charging/discharge. Comparing M sx with the molar mass of bare ion, the value of specific solvation number( x )was deduced. Findings indicate that the formation of double layers at electrode interface by ionic absorption was accompanied by solvation effect. The solvation effect was weakened as the pore size of the electrode decreased, concluding that the pore size effect exist concurrently with solvation effect during ionic adsorption. The pore size effect was influenced by the size of the counter-ions, polarity of solvent molecules and ionic concentrations.

Studying the effects of bismuth on the electrochemical properties of lead dioxide layers by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO2 layers doped with bismuth in contact with sulfuric acid solutions were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers (non-doped and doped with Bi) were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid and they were investigated in sulfuric acid media. Based on the electrochemical and the mass change responses, it is concluded that during the electrodeposition, bismuth influences the structure of the PbO2 formed. Bi(III) also inhibits the oxidation of lead sulfate and affects the reduction kinetics of lead dioxide. During successive cyclization (aging), the presence of bismuth accelerates the hydration of PbO2.

Investigation of the electrochemical behaviour of lead dioxide in aqueous sulfuric acid solutions by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO2 layers in contact with sulfuric acid solutions of different concentrations (1.5–5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H2SO4, the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb2+ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO2 layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the non-conductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

PHOSPHONIC ACID MONOLAYERS FOR CORROSION PROTECTION OF COPPER: EQCM AND EIS INVESTIGATIONS

Preparation, characterization and application of protective phosphonic acid monolayers formed by 1-Aminohexyl phosphonic acid (AHP), 1,4-butanediphosphonic acid (BDPA), 1-amino-1,3-dimethylbutyl phosphonic acid (ADBP) on copper surface as anticorrosive self-assembled molecular monolayers (SAMs) have been investigated by atomic force microscopy (AFM) analysis, electrochemical impedance spectroscopy (EIS) and in situ electrochemical quartz crystal microbalance (EQCM) techniques. Film formation and growth were monitored by EQCM and the step-by-step construction of monolayer was investigated through measurement of the frequency change, which corresponds to mass change due to the adsorption of molecules. Observed increase in electrode mass suggests that SAMs formed on copper surface by the adsorption of phosphonic acids. Results clearly demonstrate that adsorbed amounts of phosphonic acids were strongly influenced by immersion time and molecular structure. Quantum chemical calculations were performed by semi-empirical PM6 method, in order to explain the relationship between molecular structure and adsorption mechanism. Quantum chemical parameters of phosphonic acids propound that adsorption of molecules on copper surface has a chemical mechanism. Corrosion protection ability of SAMs against the acidic corrosion of copper has been evaluated in 0.1[Formula: see text]M H2SO4 solution. It was found that phosphonic acid SAMs act as protective barrier and the protection efficiencies increased in the following order: [Formula: see text].

Electrodeposition of Platinum Catalyst from Ionic Liquids

Both battery and fuel cell electric vehicles are important building blocks for the transition to sustainable transportation [1]. Fuel cell vehicles have been introduced into the market, but have not yet reached a wide market penetration due to high cost and limited refueling infrastructure. One important cost factor is due to the large amounts of platinum required because of the sluggish kinetics of the oxygen reduction reaction (ORR) [1]. Currently, the main pathway for minimizing the Pt content consists in nanostructuring of Pt and especially by using Pt alloys. Electrodeposition is an effective pathway for the preparation of Pt nanoparticles. By choosing suitable electrolysis conditions one can control the morphology and the size of the obtained particles [2]. Electrodeposition of pure Pt can be accomplished in aqueous solutions [3]. However, aiming at Pt alloys with very reactive alloying elements requires a non-aqueous approach. Especially suitable are ionic liquids (ILs). The main advantages of ILs are a wide electrochemical window, low flammability, a nearly non-existing vapor pressure, and often low toxicity [4, 5]. The electrodeposition of Pt using standard Pt precursors from some ILs has been reported [6-8]. In this study, the deposition of platinum from PtCl4 dissolved in the IL 1-methyl-1-octylpyrrolidinium bis(trifluoromethylsulfonyl)imide (OMP TFSI) was explored on boron doped diamond (BDD) and Au electrodes for the electrochemical quartz crystal microbalance technique (EQCM) at 60 °C. A typical cyclic voltammogram on BDD is shown in Figure 1a. After pulsed electrodeposition (-1.6V vs Pt, 1s, 0V, 4s, 30 minutes total) and transfer of the washed electrode to 0.1 M H2SO4, a characteristic Pt voltammogram was obtained (Figure 1b). EQCM permitted to monitor directly changes in the resonance frequency and damping associated with the Pt(IV) reduction processes. Based on these results, the implications for alloy deposition and application to practical catalyst synthesis are discussed. The project leading to this abstract has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 700127. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation Programme and Hydrogen Europe and Hydrogen Europe Research. Figure 1. Cyclic voltammogram of a) BDD in 50 mM PtCl4 in OMP TFSI at 60°C, 20 mV s-1 b) BDD after Pt deposition in 0.1 M H2SO4, 100 mV s-1 References [1] O. Gröger, H. A. Gasteiger, J.-P. Suchsland, J. Electrochem. Soc., 162, A2605-A2622 (2015). [2] X. Zhang, F. Shi, X. Yu, H. Liu, Y. Fu, Z. Wang, L. Jiang, X. Li, J. Am. Chem. Soc., 126, 3064 (2004). [3] J.V. Zoval, J. Lee, S. Gorer, R.M. Penner, J. Phys. Chem. B, 102, 1166 (1998). [4] M.C. Buzzeo, R.G. Evans, R.G. Compton, ChemPhysChem, 5, 1106 (2004). [5] F. Endres, ChemPhysChem, 3, 144 (2002). [6] D. Zhang, W. C. Chang, T. Okajima, T. Ohsaka, Langmuir, 27, 14662-14668 (2011). [7] P. He, H. Liu, Z. Li and J. Li, J. Electrochem. Soc., 152, E146 (2005). [8] L. Asen, W. Ju, E. Mostafa, S. Martens, U. Heiz, U. Stimming, O. Schneider, ECS Trans., 75, 323 (2016). Figure 1