Electrochemical Quartz Crystal Microbalance Research Articles

An Aqueous Electrolyte Regulator for Highly Stable Zinc Anode Under −35 to 65 °C

AbstractThe reversibility and long‐term cycling stability of aqueous zinc‐ion batteries (AZIBs) in a wide temperature range have rarely been explored. Herein, diethylene glycol monoethyl ether (DG) is introduced as an electrolyte additive to enhance Zn performance within a wide temperature range of −35 to 65 °C. Operando synchrotron Fourier transform infrared spectroscopy analysis combined with molecular dynamics simulations reveal that the introduction of DG disrupts the initial hydrogen bonding network of the aqueous electrolyte, restructuring the solvation structure surrounding Zn2+ ions and mitigating water‐induced parasitic reactions. Adding DG reduces the freezing point of the aqueous electrolyte without compromising its incombustibility. Moreover, operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D) and X‐ray photoelectron spectroscopy demonstrated that the coordinated DG and OTF− undergo reductive decomposition, forming a self‐healing solid electrolyte interphase comprising an inorganic/organic ZnF2‐ZnS, which can effectively suppress the notorious side reactions and guide the uniform Zn deposition. Consequently, the symmetric Zn/Zn cells demonstrate excellent cycling stability for 3500 h under 1 mA cm−2 at 25 °C, and for 1000 h under 1 mA cm−2 at both −35 and 65 °C. Full batteries with a DG‐containing electrolyte exhibit a long lifespan of 5000 cycles at 2 A g−1.

Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising method for decentralized ammonia synthesis using renewable energy. An organic electrolyte is utilized to combat the competing hydrogen evolution reaction, and lithium is plated to activate the inert N2 molecule. Ethanol is commonly used as a proton shuttle to provide hydrogen to the activated nitrogen. In this study, we investigate the role of ethanol as a proton shuttle in an electrolyte containing tetrahydrofuran and 0.2 M lithium perchlorate. Particularly designed electrochemical experiments show that ethanol is necessary for a good solid-electrolyte interphase but not for the synthesis of ammonia. In addition, electrochemical quartz crystal microbalance (EQCM) demonstrates that the SEI formation at the onset of lithium plating is of specific importance. Chemical batch synthesis of ammonia combined with real-time mass spectrometry confirms that protons can be shuttled from the anode to the cathode by other species even without ethanol. Moreover, it raises questions regarding the electrochemical nature of Li-NRR. Finally, we discuss electrolyte stability and electrochemical electrode potentials, highlighting the role of ethanol on electrolyte degradation.

Label-free genosensing of dengue serotypes with an electrodeposited reduced graphene oxide-tris(bipyridine)ruthenium(II)

Constructing a label-free electrochemical transducer platform without compromising inherent biocompatibility against specific bioreceptor remains challenging, particularly probing nucleic acid hybridization at electrode interface without external redox-mediator. Here, we show that electrochemically reduced graphene oxide-tris(bipyridine)ruthenium(II) (ErGO-TBR) nanosheets electrodeposited on carbon screen printed electrode can quantify hybridization of clinically important target sequences specific to serotypes of dengue virus (DENV) non-structural 1 (NS1) protein. Different variables including deposition potential, time, and electrolytic composition were optimized for fabrication of label-free transducer platform. Structural and electrochemical properties of ErGO-TBR/SPE were comprehensively elucidated using microscopic and spectroscopic techniques. Electrochemical quartz crystal microbalance (EQCM) analysis reveals the growth of electrodeposited redox-active species on the electrode interface. Surface functional group investigations suggested that TBR deposited on the basal and edges of ErGO substrate via electrostatic and π-π interactions. Functionalization of bio-affinity layer (B) on ErGO-TBR/SPE enables better loading of probe DNA (PDNA) toward specific detection of DENV target DNA (TDNA) with an ultralow detection limit promising for clinical diagnosis. Scalable chronoamperometry-based redox-active surface growth, customizable bioactivation strategy and external mediator-less probing of nucleic acid hybridization make the present system suitable for other translational application in healthcare diagnosis.

Proton is Essential or Not: A Fresh Look on Pseudocapacitive Energy Storage of PANI Composites.

Protonation has been considered essential for the pseudocapacitive energy storage of polyaniline (PANI) for years, as proton doping in PANI chains not only activates electron transport pathways, but also promotes the proceeding of redox reactions. Rarely has the ability for PANI of storing energy without protonation been investigated, and it remains uncertain whether PANI has pseudocapacitive charge storage properties in an alkaline electrolyte. Here, this work first demonstrates the pseudocapacitive energy storage for PANI without protonation using a PANI/graphene composite as a model material in an alkaline electrolyte. Using in situ Raman spectroscopy coupled with electrochemical quartz crystal microbalance (EQCM) measurements, this work determines the formation of -N= group over potential on a PANI chain and demonstrates the direct contribution of OH- in the nonprotonation type of oxidation reactions. This work finds that the PANI/graphene composite in an alkaline electrolyte has excellent cycling stability with a wider operation voltage of 1V as well as a slightly higher specific capacitance than that in an acidic electrolyte. The findings provide a new perspective on pseudocapacitive energy storage of PANI-based composites, which will influence the selection of electrolytes for PANI materials and expand their application in energy storage fields.

Electrodeposition of Silver in Cyanide-Free Solution Containing Pyrimidine Derivative as a Complexing Agent

Pyrimidine derivatives, for example, 2,4-pyrimidinedione (uracil), 1-methyluracil and 5-methyluracil (thymine) can bind with metal ions in alkaline solution. 5-methyluracil (thymine) as complexing agent in electroplating solution has not been investigated due to low solubility in water. The aims of this study were to determine the potential of 5-methyluracil (thymine) as complexing agent for cyanide-free silver electroplating solution. The influence of complexing agent and polyethyleneimine on the silver electrodeposition reaction were studied. Several methods which are electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS) have been used to study the electrochemical behavior of cyanide-free silver electroplating solution. The surface morphology and brightness of silver deposits obtained from each cyanide-free silver electroplating solution were evaluated. A semi-bright deposit was obtained from thymine and uracil-complexing silver solution while matte deposit from 5,5-dimethylhydantoin-complexing silver solution. A bright silver deposit could be obtained in the presence of polyethyleneimine. The reduction current value decreases as the amount of polyethyleneimine added increases due to inhibition effect on the silver electrodeposition reaction. The results of electrochemical quartz crystal microbalance measurement showed that the addition of polyethyleneimine in thymine-complexing silver solution does not significantly affect the resonance frequency change.

Electrically Controlled Adsorptive Membranes with Tunable Affinity for Selective Chromium (VI) Separation from Water.

Ionic contaminants such as Cr(VI) pose a challenge for water purification using membrane-based processes. However, existing membranes have low permeability and selectivity for Cr(VI). Therefore, in this study, we prepared an electrically controlled adsorptive membrane (ECAM-L) by coating a loose Cl--doped polypyrrole layer on a carbon nanotube substrate, and we evaluated the performance of ECAM-L for Cr(VI) separation from water. We also used electrochemical quartz crystal microbalance measurements and molecular dynamics and density functional theory calculations to investigate the separation mechanisms. The adsorption and desorption of Cr(VI) could be modulated by varying the electrostatic interactions between ECAM-L and Cr(VI) via potential control, enabling the cyclic use of the ECAM-L without additional additives. Consequently, the oxidized ECAM-L showed high Cr(VI) removal performance (<50 μg/L) and treatment capacity (>3500 L/m2) at a high water flux (283 L/m2/h), as well as reusability after the application of a potential. Our study demonstrates an efficient membrane design for water decontamination that can selectively separate Cr(VI) through a short electric stimulus.

Developing Tin Anodes for Aqueous Batteries

Aqueous batteries based on metal anodes present an attractive alternative to lithium-ion for long-duration energy storage due to their low-cost, high-safety, and theoretically high energy density. Still, despite many efforts towards development and commercialization, metal anode systems remain hampered by irreversible hydrogen evolution (HER), detrimental shape change, and passivation during cycling. Recognizing the immediacy required to enable the renewable energy transition, our research is focused on developing alternative anode chemistry based on Tin (Sn) for aqueous batteries.Sn metal has been used in aqueous battery systems as additives or current collectors to mitigate side reactions due to its high overpotential for HER. However, little attention was paid to its potential use as a redox active material in aqueous electrolytes. In this talk, we will discuss our efforts to develop Sn as an aqueous anode with high capacity and cyclability. We will first present our development of pouch cells to enable aqueous cells while minimizing the side reactions from cell components other than the active materials. Preliminary data demonstrate the feasibility of using Sn as anode active materials via a 4-electron process in aqueous systems. To investigate the mechanism and improve the Coulombic efficiency, we perform operando X-ray diffraction (XRD), rotating ring disk electrochemistry (RRDE), electrochemical quartz crystal microbalance (EQCM), and 117Sn nuclear magnetic resonance (Sn-NMR) on the Sn system. Lastly, we will show our improvement based on the mechanistic understanding that enables Sn-based full cells with high Coulombic efficiency, high areal capacity, high utilization rate and long capacity retention.

New Mechanism Insights on Ca-Ion Storage in Small Molecular Crystal

Rechargeable calcium-ion batteries have become intriguing alternatives for grid-scale energy storage devices. However, the strong electrostatic interaction caused by the intrinsic divalent nature of Ca2+ leads to sluggish ion diffusion kinetics, thus resulting in low capacity. Herein, a small molecular crystal organic material is employed as the electrode material for the aqueous calcium-ion batteries. This kind of organic material could not only bypass the sluggish ion diffusion through carbonyl enolization but also avoid electrode inevitable dissolution due to the intermolecular hydrogen bonding, and flexible structure. In addition, the robust crystal structure allows fast Ca-ion diffusion and storage. Electrochemical characterization including electrochemical quartz crystal microbalance combined with first-principles density calculations and in(ex)-situ spectroscopy methods reveals the whole Ca-ion storage mechanism at the atomistic and macroscopic levels. The reversible enolization redox process, diffusion path, and structure change of molecular crystals have been clearly clarified. Consequently, the materials yield a premier rate capability (70.2 mAh g−1 at 5 A g−1), and excellent cycling stability (retention of 80.3% over 1000 cycles at 2 A g−1). This study extends the boundary of molecular crystal systems for battery chemistry to construct high-performance multivalent ion batteries.

Methods for Calibrating the Electrochemical Quartz Crystal Microbalance: Frequency to Mass and Compensation for Viscous Load

The main output from an Electrochemical Quartz Crystal Microbalance is a frequency shift. This note describes how to separate the mass- and viscous load contributions to this shift by a calibration procedure. The mass calibration is made by electroplating from a copper sulfate solution in ethanol/water with 100% current efficiency. An estimate of viscous load is obtained by measuring the energy dissipation and is related to frequency change using the Kanazawa–Gordon equation. Two approaches are discussed: either by performing calibration experiments in a series of water–glycerol mixtures or by following oscillations in frequency and dissipation by collecting data during the stabilization phase of the experiment.

Kaolinite surface charges developed in cyclohexane suspension with dissolved Span 80 or bitumen: Electrodeposition and adsorption/desorption studies

In this study, we investigated the surface charges of kaolinite particles suspended in cyclohexane with or without the addition of Span 80 or bitumen. Kaolinite particles did not carry a net charge when dispersed in cyclohexane. They were found to acquire positive charges after adding Span 80 and negative charges after adding bitumen. Furthermore, when Span 80 was removed from the cyclohexane solution, the kaolinite surface charges disappeared, but when bitumen was removed, the kaolinite particles remained negatively charged. Our investigations showed that the bitumen adsorbed on the kaolinite surface caused the negative surface charges of kaolinite in cyclohexane. This was different from the widely accepted conventional charging mechanism which states that solid particles in a nonpolar organic liquid acquire charges due to the formation of reverse micelles from added surfactants, such as Span 80, and the reverse micelles house and stabilize free opposite charges to maintain the net particle surface charge. On the other hand, bitumen-coated kaolinite could carry net charges in cyclohexane due to the selective dissolution of charge-carrying species induced by an external electric field. Our electrochemical quartz crystal microbalance with dissipation (EQCM-D) measurements showed that about 3.7 wt% of the adsorbed bitumen was desorbed from kaolinite surface under a 5 V external electric field. Elemental analysis showed that the carbon content on the surface of bitumen-coated kaolinite particles decreased from 4.43 wt% for suspended kaolinite particles to 4.21 wt% for kaolinite particles deposited on the electrodes. Both measurements revealed shedding of bitumen from the bitumen coating layer on kaolinite surface.

Highly Localized Charges of Confined Electrical Double‐Layers Inside 0.7‐nm Layered Channels

AbstractA confined electrical double‐layer (EDL) inside nanoporous electrodes has a large capacitance and deviates from traditional ones. Unfortunately, its capacitive mechanism is still unclear. Herein, expanded vertical graphene/diamond (EVG/D) films with regular and ordered 0.7‐nm layered channels are designed and synthesized to serve as an ideal model for understanding confined EDL. A clear overall picture of confined EDL is provided at an atomic resolution with the aid of in situ electrochemical Raman spectroscopy, electrochemical quartz crystal microbalance (EQCM), and density functional theory (DFT) calculations combined with three‐dimension reference interaction site method (3D‐RISM). It is especially interesting that the induced charges in electrode hosts are highly localized with a density far higher than that on a traditional EDL and even close to those of ion batteries. It is proposed that such a high localization of induced charges plays an essential role in the high energy storage efficiency of confined EDL capacitance. This work not only provides a previously unexplored way to refine the mechanism of confined EDL, but also further lays the foundation for understanding the functions of nanoporous or layered materials in electrochemical energy storage.

An electrochemical study of the dissolution behavior of gold in a novel glycine-thiosulfate system

Ammonia-free thiosulfate systems are known for their non-toxicity, low reagent consumption, and excellent leaching efficiency in gold extraction studies. This study proposes a novel and environmentally friendly glycine-thiosulfate system and comprehensively investigates the dissolution behavior of gold through the application of electrochemical methods. Electrochemical quartz crystal microbalance (EQCM) has demonstrated that the anodic dissolution of gold is predominantly influenced by the forms of copper(II)-glycine complexes as catalysts, and the presence of Cu(C2H4NO2)3− complex in strong alkaline has enhanced dissolution rate of gold, in contrast to Cu(C2H4NO2)20 complex in near-nurture condition. Such excellent catalytic capability of the Cu(C2H4NO2)3− complex for gold dissolution can be attributed to the lowest corrosion potential, slighter passivation behavior, and rapid electron transfer from the analysis of corrosion electrochemistry (OCP, PDP, and EIS) and advanced spectrum technologies (LA-ICP-MS and XPS). The dissolution of gold in the novel glycine-thiosulfate system undergoes a typical ligand exchange process (Au+→Au(C2H4NO2)2−→Au(S2O3)23−), and the formation of passivation species on the gold surface is predominantly formed by Au(I)-glycine coordination, rather than the sulfur-containing products from thiosulfate decomposition. Based on these results, the proposed two electrochemical reaction mechanisms will contribute to the optimization of leaching conditions in the novel glycine-thiosulfate system.

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.

Aqueous Polyelectrolyte Electrodeposition: The Effects of Alkyl Substitution and Varying Supporting Electrolyte Concentrations on the Deposition Efficiency

AbstractThe controlled growth of surface‐modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non‐electroactive polymers. Hence, we investigate the counterion‐induced electrodeposition of polyelectrolytes: three quaternized poly(N,N‐dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in‐house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between “hydrophobicity” and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings.

Electrode Potential-Dependent Studies of Protein Adsorption on Ti6Al4V Alloy.

This article presents the potential-dependent adsorption of two proteins, bovine serum albumin (BSA) and lysozyme (LYZ), on Ti6Al4V alloy at pH 7.4 and 37 °C. The adsorption process was studied on an electropolished alloy under cathodic and anodic overpotentials, compared to the open circuit potential (OCP). To analyze the adsorption process, various complementary interface analytical techniques were employed, including PM-IRRAS (polarization-modulation infrared reflection-absorption spectroscopy), AFM (atomic force microscopy), XPS (X-ray photoelectron spectroscopy), and E-QCM (electrochemical quartz crystal microbalance) measurements. The polarization experiments were conducted within a potential range where charging of the electric double layer dominates, and Faradaic currents can be disregarded. The findings highlight the significant influence of the interfacial charge distribution on the adsorption of BSA and LYZ onto the alloy surface. Furthermore, electrochemical analysis of the protein layers formed under applied overpotentials demonstrated improved corrosion protection properties. These studies provide valuable insights into protein adsorption on titanium alloys under physiological conditions, characterized by varying potentials of the passive alloy.

Research on Growth Behavior of Calcium Carbonate Scale by Electrochemical Quartz Crystal Microbalance

Research on Growth Behavior of Calcium Carbonate Scale by Electrochemical Quartz Crystal Microbalance

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.

Electropolymerization of some amino acids on platinum electrode

This paper studied the anodic oxidation of L-amino acids on smooth platinum and modified Pt electrodes (Pt/AAO). The oxidation of L-amino was carried out by cyclic voltammetry coupled with electrochemical quartz crystal microbalance (EQCM). The Amino acid concentration, pH of the electrolyte and the scan number effects on cyclic voltammetry were examined. Spectroscopic analysis, such as attenuated total reflectance FT infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), characterize the resulting thin film coatings. Scanning electron microscopy (SEM) is used to study the morphology of thin film surfaces and their solubility. Spectroscopic measurements favor L-amino acids electropolymerization into poly-L-amino acids in an irreversible way. The electrosynthesis of poly-L-amino acids was used as a proton receptor for the solid-state pH solid sensor. Keywords. Anodic oxidation, L-amino acids, electropolymerization, pH sensor.

Initial Electrodeposition Behavior of Chromium from Hydrate-Melt Based Trivalent Chromium Baths

Trivalent chromium electrodeposition is expected to substitute the conventional hard chromium electroplating that requires harmful hexavalent chromium. Recently, we revealed that crystalline chromium, which is effective for hard chromium properties, can be electrodeposited from trivalent chromium baths using chloride-based hydrate-melts. Herein, we investigated the initial behavior of the trivalent chromium electrodeposition by in situ analyses using electrochemical quartz crystal microbalance (EQCM) and ex situ characterization of resulting electrodeposits. In the very initial stage of electrolysis, proton reduction proceeds preferentially, resulting in chromium hydroxide precipitation on the electrode due to the local pH increase. Chromium reduction was found to require a few seconds of induction time to start. The transient was interpreted by the Sand equation which also indicated proton depletion near the cathode. In the hydrate-melts, due to the depletion of free water, the high proton mobility due to Grotthuss mechanism is lost, resulting in the suppression of hydrogen evolution after the induction time. This explains why chromium electrodeposits are obtained at extremely high current efficiencies of 60%–80%. Additionally, the proton reduction of the initial electrolysis stage may lead to negative effects, for example, impairing adhesion of chromium electrodeposits.

Feasibility study of amperometric and electrochemical quartz crystal microbalance measurements for in situ state of charge monitoring in vanadium flow batteries

For an efficient flow battery operation, knowledge of the state of charge of the battery is essential. Monitoring the state of charge of both half cells is advantageous concerning a timely detection of crossover processes. We present the first results for amperometric and electrochemical quartz crystal microbalance measurements in a vanadium flow battery test setup. By validating with half cell potential measurements as well as ex situ titration we investigate the applicability of both electrochemical methods for an in situ half cell state of charge monitoring.