Electrochemical Quartz Crystal Nanobalance Research Articles

Two Types of Platinum Dissolution in Acid Media: An Electrochemical Nanogravimetric Study

Smooth and platinized platinum electrodes in contact with sulfuric acid solutions were studied using electrochemical quartz crystal nanobalance (EQCN) technique at different temperatures. Two types of dissolution processes have been observed. A platinum loss was detected during the reduction of platinum oxide, the extent of which depends on the positive potential limit and the scan rate, and to a lesser extent on the temperature. The platinum dissolution during the electroreduction of oxide is related to the interfacial place exchange of the oxygen and platinum atoms in the oxide region. At elevated temperatures two competitive processes take place at high positive potentials: a dissolution of platinum and platinum oxide formation. These phenomena are of importance regarding the long-term stability of proton exchange fuel cells.

Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper

5-Methoxy-2-(octadecylthio)benzimidazole (MOTBI) monolayer was self-assembled on fresh copper surface obtained after etching with nitric acid at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) were established using impedance studies. The optimum conditions are methanol as solvent, 10 mM concentration of the organic molecule and an immersion period of 24 h. The MOTBI SAM on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy and it is inferred that chemisorption of MOTBI on copper surface is through nitrogen. Corrosion protection ability of MOTBI SAM was evaluated in aqueous NaCl solution using impedance, electrochemical quartz crystal nanobalance, potentiodynamic polarization and weight-loss studies. While bare copper showed a charge-transfer resistance (Rct) value of 1.89 kΩ cm2 in 0.20 M NaCl aqueous environment, the Rct value for SAM covered copper surface is 123.4 kΩ cm2. The MOTBI SAM on copper afforded corrosion inhibition efficiency of 98–99% in NaCl solution in the concentration range and in the temperature range studied. The SAM functions as a cathodic inhibitor. Quantum chemical calculations showed that MOTBI has relatively small ΔE between HOMO and LUMO and large negative charge in its benzimidazole ring, which facilitate formation of a polymeric [Cu+-MOTBI] complex on copper surface.

Copper underpotential deposition on TiO 2 electrodes: A voltammetric and electrochemical quartz crystal nanobalance study

In this work, the electrogravimetric behavior of copper electrodeposition on TiO 2 electrodes was analyzed. Copper electrodeposition was carried out in 0.1 mol L − 1 H 2SO 4 using several concentrations of CuSO 4. The voltammetric curve displays a redox processes. The first redox process occurs in the region of − 0.30 at 0.1 V (vs. saturated calomel electrode, SCE) and it is related to bulk Cu electrodeposition and stripping. For this cathodic process, it was observed that the mass gain increases both as the sweep rate decreases and as the concentration of copper increases. The second redox process, which occurs between − 0.1 V and 0.35 V (vs. SCE), the stripping charge (and mass) are independent of both sweep rate and CuSO 4 concentration and, finally, there is a saturation charge (and saturation mass) as the deposition time is increased. From the saturated mass, obtained using an electrochemical quartz crystal nanobalance, for this electrodeposition process (248 ng cm − 2 ) a roughness factor of 1.8 was calculated for the TiO 2 film.

Electrocatalysis in oscillatory kinetics of anodic oxidation of formic acid: At Pt; nanogravimetry and voltammetry studies on the role of reactive surface oxide

Following earlier works from our laboratory, we report further experiments on oscillatory behavior in anodic oxidation of H·COOH and H·COO− anion at a low roughness Pt electrode studied by means of: (a) galvanostatic polarization; (b) linear-sweep voltammetry coupled with (c) nanogravimetry using an electrochemical quartz-crystal nanobalance (EQCN). Employment of the latter enables a complementary aspect of oscillatory processes in interfacial electrochemistry to be examined, viz. in situ mass changes at the electrode surface that can be related quantitatively to recordable passages of charge in the time-domain of each oscillation. Such measurements also provide evidence that the sharp current spikes observed at critical potentials in the cyclic voltammetry of H·COOH oxidation at Pt are correlated with special conditions required for onset and maintenance of oscillations. By means of the above complementary procedures of electrochemical surface science, we attempt to elucidate the changes of states of the electrode interfaces involved in the recorded electrochemical periodicity in terms of concepts of electrocatalysis and electrochemical surface science, taking into account the role of: (a) positive feedback associated with (b) an electrocatalytic step and (c) coupling between surface-reaction steps involving surface oxide formation and reductive reaction with an absorbed intermediate such as chemisorbed CO.

Electrochromic WO3 Films: Nanotechnology Experiments in Instrumental Analysis and Physical Chemistry Laboratories

This experiment teaches students the methodology of investigating novel properties of materials using new instrumental techniques: atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), voltammetric techniques (linear potential scan and chronoamperometry), and light reflectance measurements. The unique capabilities of each of these techniques are utilized in a combined effort to control and monitor synthesis of electrochromic nanostructured films and then to investigate and analyze film properties. The experiments are designed to demonstrate the penetration of chemical species into solids and its practical implications. It is shown that the intercalation of ions into solid materials through solid-state diffusion is sufficiently fast, even at room temperature, that it can be recorded in real-time by nanogravimetry (EQCN), voltammetric methods, and light reflectance. The high performance of electrochromic films is achieved owing to the formation of nanostructured WO3 with nanoparticles of 20–30 nm in size. The diameter of nanoparticles can be controlled by changing deposition potential and is examined by tapping-mode AFM imaging. The subject of the experiment is of high practical importance for studies of properties of new materials discovered recently in various fields of nanotechnology. The interests in electrochromic materials stem from applications in digital displays and smart windows. At present, in many laboratories in the world, extensive research studies are under way to develop new materials for such applications. The proposed experiment introduces a new concept of intercalation and also shows how to control nanoparticle deposition and how to measure nanomolar quantities of H+ ions inserted in WO3 nanoparticles. In addition, students learn modern instrumental techniques.

In Situ Stress and Nanogravimetric Measurements During Underpotential Deposition of Pb on (111)-Textured Au

The surface stress associated with the underpotential deposition (upd) of lead on (111)-textured Au is examined, using the wafer curvature method, in acidic perchlorate supporting electrolyte. The surface stress is correlated to 0, the fractional Pb coverage, by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance (EQNB). The gravimetric results are similar to the data found in the literature, showing an electrosorption valency of 2 and the formation of a hexagonal close-packed monolayer of Pb. The complete Pb monolayer causes an overall compressive surface stress change of about -1.2 N m -1 . The stress-coverage curve can be divided into two linear regions separated by a plateau. The region at low to intermediate coverage is caused by the formation of Au-Pb bonds which decrease the charge density and reduce the tensile surface stress inherent to the clean Au surface. In the second linear region at high coverage, the Pb adlayer compresses and behaves as a free-standing elastic film with a biaxial modulus close to that for Pb (111) in the bulk. The plateau that separates these two linear regions corresponds to the stress relaxation hump that appears in the stress-potential curve. This stress relaxation is attributed to island coalescence.

Characterisation and humidity-sensing properties of aluminium (oxy)-hydroxide films prepared by cathodically induced precipitation

Abstract Cathodically induced precipitated aluminium (oxy)-hydroxide films, prepared using hydrogen-sorbing palladium electrodes, have been characterised and their humidity-sensing electrical properties studied. Infrared (IR) spectroscopy demonstrated that the films are hygroscopic, and this property allows their use as the active component in a humidity sensor. Films formed as bridging precipitates between twin palladium electrodes were tested for electrical parameter response to relative humidity changes. A linear correlation with impedance is obtained on application of a 100 mV applied ac signal amplitude at 1 kHz. The linearity of response is comparable to commercial sensors. Cathodically induced precipitate films contain 24 wt% aluminium and 10 wt% sulfate, the balance being oxygen and hydrogen. As-deposited films are amorphous, but change to a crystalline form after heat treatment at high temperature. XRD patterns taken as films are heated reveal transformation into γ-Al2O3, followed by production of α-Al2O3 at temperatures greater than 1100 °C. An electrochemical quartz crystal nanobalance (EQCN) study demonstrated that dissolution of the precipitate is possible at positive potentials.

Nanogravimetric studies of tungsten oxide thin films obtained by the polymeric precursor method

In this work, the intercalation/de-intercalation process of Li + ions in the tungsten oxide matrix was investigated. The reaction mechanism involved was also investigated. The WO 3 films, prepared by the polymeric precursor method, were deposited on a Pt covered quartz crystal using the dip-coating technique. The electrolyte was 0.1 mol L − 1 LiClO 4 in acetonitrile. The morphology and structure of the deposit was accomplished by scanning electron microscopy and X-ray diffraction, respectively. In the electrochemical quartz crystal nanobalance results, it was observed that the mass transport as well as the kinetic processes involved are facilitated in the films cycled at lower potential sweep-rates. The mass variation data as a function of the charge variations in the anodic and cathodic regions indicate the participation of solvent molecules (acetonitrile) during the Li + ion intercalation/de-intercalation process. This was confirmed by the development of a model of the species flux as a function of the potential.

PH-induced mass and volume changes of perchlorate-doped polypyrrole

The mass change of polypyrrole (PPy) due to ion transport was investigated in NaClO 4 of various pHs, using an electrochemical quartz crystal nanobalance (EQCN). It was disclosed that the mass of perchlorate-doped PPy (PPy-ClO 4) varies with solution pHs. While the mass was increased with lowering pH in general, the greatest mass changes were observed in the pH range of ca. 1.0–2.0 and 10.5–11.5. The magnitude of mass changes with pH was proportional to the film thickness of PPy-ClO 4. Repeated acid/base treatments in between pH 1.0 and 11.3 resulted in the retention of ca. 78% of the initial mass response after 100 cycles, which can be compared with ca. 65% retention of the electrochemically induced mass change. In situ atomic force microscopic (AFM) images of PPy in NaClO 4 revealed that the volume increase of 12.6% occurs in a solution of pH 1.0, relative to the volume in a solution of pH 11.3.

In Situ Stress and Nanogravimetric Measurements during Underpotential Deposition of Bismuth on (111)-Textured Au

The surface stress associated with the underpotential deposition (upd) of bismuth on (111)-textured Au is examined, using the wafer curvature method, in acidic perchlorate and nitrate supporting electrolyte. The surface stress is correlated to Bi coverage by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance. The mass increase measured in the presence of perchlorate is consistent with the (2 x 2) and (p x square root 3)-2Bi adlayers reported in the literature. ClO(4)(-) does not play a significant role in the upd process. The complete Bi monolayer causes an overall surface stress change of about -1.4 N m(-1). We attribute this compressive stress to the formation of Bi-Au bonds which partially satisfy the bonding requirements of the Au surface atoms, thereby reducing the tensile surface stress inherent to the clean Au surface. At higher Bi coverage, an additional contribution to the compressive stress is due to the electrocompression of the (p x square root 3)-2Bi adlayer. In nitric acid electrolyte, NO(3)(-) coadsorbs with Bi over the entire upd region but has little fundamental impact on adlayer structure and stress.

CO electrooxidation on a polycrystalline Pt electrode: A wall-jet EQCN study

Abstract Pre-adsorbed and bulk (continuous) CO oxidation on a polycrystalline Pt electrode were examined in a wall-jet electrochemical quartz crystal nanobalance (EQCN) setup, using both differential and integral evaluation of the EQCN data, to get further insights into the kinetics and mechanism of this important fuel-cell related electrocatalytic reaction. The hydrogen underpotential adsorption–desorption features in the base cyclic voltammogram of a Pt film are accompanied by significant changes in the electrode mass due H-upd induced desorption–adsorption of anion. In the double-layer region small capacitive currents are accompanied by comparatively large reversible mass changes indicating anion adsorption/desorption (96.5 g mol−1 assigned to bisulfate). OH and oxygen electrosorption from water at potentials more positive of 1.0 V result in relatively small variations in the electrode mass (16 g mol−1 for PtOH and ca. 9 g mol−1 for PtO formation, respectively). The CO-adlayer stripping first leads to the electrode mass decrease in the “pre-peak” region, followed by a fast mass increase within the main stripping peak due to re-adsorption of bisulfate anion (91 g mol−1). A mass-transport limited current for bulk CO oxidation under continuous flow of CO-saturated electrolyte leads to negligible mass changes (0–1 g mol−1) in the PtO region, suggesting that bulk CO oxidation is mediated by electroformed PtO.

A nanogravimmetric investigation of the charging processes on ruthenium oxide thin films and their effect on methanol oxidation

The charging processes and methanol oxidation that occur during the oxidation–reduction cycles in a ruthenium oxide thin film electrode (deposited by the sol–gel method on Pt covered quartz crystals) were investigated by using cyclic voltammetry, chronoamperometry and electrochemical quartz crystal nanobalance techniques. The ruthenium oxide rutile phase structure was determined by X-ray diffraction analysis. The results obtained during the charging of rutile ruthenium oxide films indicate that in the anodic sweep the transition from Ru(II) to Ru(VI) occurs followed by proton de-intercalation. In the cathodic sweep, electron injection occurs followed by proton intercalation, leading to Ru(II). The proton intercalation/de-intercalation processes can be inferred from the mass/charge relationship which gives a slope close to 1gmol−1 (multiplied by the Faraday constant) corresponding to the molar mass of hydrogen. From the chronoamperometric measurements, charge and mass saturation of the RuO2 thin films was observed (440ngcm−2) during the charging processes, which is related to the total number of active sites in these films. Using the electrochemical quartz crystal nanobalance technique to study the methanol oxidation reaction at these films was possible to demonstrate that bulk oxidation occurs without the formation of strongly adsorbed intermediates such as COads, demonstrating that Pt electrodes modified by ruthenium oxide particles can be promising catalysts for the methanol oxidation as already shown in the literature.

Interactions of adsorbed albumin with underpotentially deposited copper on gold piezoelectrodes

The adsorption of a model protein, bovine serum albumin (BSA), on Au electrodes was investigated using the Cu adatom probe method and Electrochemical Quartz Crystal Nanobalance (EQCN) technique. The adsorption of BSA was confirmed by AFM imaging and has been found to be controlled by kinetics. Using the Cu adatom probe method, we were able to reconstruct the entire BSA adsorption transient Θ BSA vs. t. The adsorption rate constant k 1, determined from this transient is k 1 = 2.45 × 10 5 L mol − 1 s − 1 . We have found that the bulk Cu 0 deposition process is blocked by BSA adsorption and it decays exponentially with time during BSA adsorption. It ceases completely when a full monolayer of BSA is formed. In contrast to that, the mass associated with Cu-u.p.d. decreases only to ca. 50% of that in the absence of BSA, indicating that Cu adatoms can penetrate (wedge) into the space between the surface Au atoms and the adsorbed BSA molecules. In addition to that, we have found that the degree of penetration of Cu adatoms can be controlled by the applied deposition potential. By selecting a sufficiently cathodic potential, we were able to deposit a full Cu-u.p.d. monolayer, independent of the BSA surface coverage extending from Θ BSA = 0 to Θ BSA ≈ 1. The positive shift of Cu ad desorption peak potential E p, observed in the presence of adsorbed BSA, has been interpreted in terms of Frumkin exchange interaction forces between Cu ad and BSA ad, on the basis of our earlier theoretical model, expanded here to include adsorbed species in two monolayers. This expansion is possible owing to the fast rate of Cu adatom penetration in the interfacial region. From the plots of E p vs. Θ BSA, the presence of strong attractive interactions between Cu ad and BSA ad was deduced. These interactions result in a super-shift of the Cu-u.p.d. desorption peak potential, corresponding to the exchange interaction coefficient g M,X < − 4, indicating on a possibility of the formation of a stable interface complex.

Electrochemical quartz crystal nanobalance and chronocoulometry studies of phenylalanine adsorption on Au

The interfacial adsorption behaviour of the amino acid, phenylalanine (Phe), was studied at a polycrystalline Au surface in 0.05 M KClO 4 using cyclic voltammetry, chronocoulometry (CC) and electrochemical quartz crystal nanobalance (EQCN) frequency measurements. The frequency was observed to decrease with increasing concentration of Phe, indicating that the frequency measurements were following analyte adsorption directly. Both CC and EQCN frequency measurements showed a two-stage adsorption process, consistent with the molecule being adsorbed in the horizontal position at negative potentials, but rearranged to the more upright position at potentials more positive to the potential of zero charge. From the slopes at the onset of each of these two regions in plots of change in mass from the EQCN frequency measurements versus the surface charge density from CC measurements, the calculated molar mass corresponded to that of Phe displacing adsorbed water molecules for EQCN measurements made with small bulk concentrations of Phe (i.e., <1 × 10 −4 mol L −1). The adsorption process from CC measurements for Phe, described using the Henry adsorption isotherm, gave Gibbs energies of adsorption (Δ G ADS) ranging from −18 to −35 kJ mol −1 over the potential range of −0.6 to 0.6 V. The observed decrease in frequency of the EQCN measurements with additions of aliquots of amino acid and the substantial Δ G ADS values suggests that Phe adsorbs onto the surface via chemisorption. Surface concentrations (1.2 × 10 −10 mol cm −2) were in excellent agreement between the EQCN and CC measurements for small bulk concentrations of Phe (4.0 × 10 −5 mol L −1), in very good agreement with previously published results at the Au(1 1 1) surface. Thus, for small bulk concentrations of analyte, these electrochemical techniques complement one another to enhance our knowledge of the behaviour of thin organic films at electrode surfaces.

Transient conformation changes of albumin adsorbed on gold piezoelectrodes

The adsorption of bovine serum albumin (BSA) on Au piezoelectrodes was investigated using Electrochemical Quartz Crystal Nanobalance (EQCN), redox ion probe, and tapping-mode AFM techniques. The high ionic conductance of Au|BSA films, owing to the presence of voids, allowed for extensive studies of the templated deposition of cadmium and electrocatalytic nitrate reduction processes. Changes in BSA conformation in the adsorbed state were found to occur on completion of Cd-upd formation in the presence of nitrate ions. The conformational transition was reversible and BSA film integrity was preserved, as confirmed in multiple scan experiments and by carrying out Quartz Crystal Immittance (QCI) measurements. No change in the resonance admittance modulus versus frequency was observed. We have found that triggering of BSA conformational transition is not associated with bulk-Cd 0 nucleation and growth. Mechanistic considerations have led to the conclusion that BSA conformation changes are due to BSA adjustment to the changing electric field distribution in Au|BSA film associated with formation of surface complexes of partially charged Cd-upd with NO 2 − changing electrode charge and local pH increase caused by the electrocatalytic nitrate ion reduction. This mechanism is corroborated by the fact that in other Cd(II) solutions, not containing NO 2 − anions, conformational transitions in Au|BSA films were not observed.

Electrochemical quartz crystal nanobalance (EQCN) studies of the adsorption behaviour of an enzyme, mandelate racemase, and its substrate, mandelic acid, on Pt

The adsorption behaviour of the enzyme, mandelate racemase (MR), and its substrate, ( S)-mandelic acid (MA), was studied at a polycrystalline Pt surface in pH 7.4 phosphate buffer at 294 K using the electrochemical quartz crystal nanobalance (EQCN) technique of simultaneous cyclic voltammetry (CV) and frequency measurements. It was shown that the EQCN frequency measurements did not directly monitor the molar mass of the adsorbed protein at anodic potentials, but instead measured changes in the surface oxide in the absence and presence of adsorbed protein. However, at a potential characteristic of the double layer for platinum, EQCN frequency measurements gave a measure of the extent of solvent displacement by the adsorbed protein. The adsorption process was modelled using the Langmuir adsorption isotherm. The values for the Gibbs energy of adsorption, Δ G ADS, obtained with these EQCN frequency measurements gave excellent agreement within experimental uncertainty with those obtained from the simultaneous CV measurements for both the enzyme and substrate, and showed the enzyme to have a greater affinity for the surface than the substrate molecule. The maximum surface concentrations from CV and EQCN frequency measurements gave excellent agreement for the two techniques and showed MA to be adsorbed in a tilted orientation with monolayer coverage. On the other hand, the surface concentrations showed the presence of ∼2.5 monolayers of enzyme from charge transfer CV measurements, while the frequency results showed the presence of a densely packed monolayer from the “footprint” of solvent displacement by the adsorbed enzyme molecules on the electrode surface. The two techniques provide valuable complementary information on the interfacial behaviour of molecules.

Electrochemical quartz crystal nanobalance to detect solvent displacement by pH-induced conformational changes of proteins at Pt.

The electrochemical quartz crystal nanobalance (EQCN) techniques of simultaneous measurements of frequency and cyclic voltammetry (CV) were used to investigate protein adsorption behavior resulting from pH-induced conformational changes at the Pt electrode at 298 K. The adsorption behavior of holo- and apo-alpha-lactalbumin was studied in electrolyte solutions of pH < 2, 7.4, and 11. The EQCN frequency measurements did not directly monitor the mass of the adsorbed protein at anodic potentials, but instead, at a potential characteristic of the double layer for platinum, gave a measure of the extent of solvent displacement by the adsorbed protein (i.e., a "footprint"), which correlated well with known pH-induced conformational changes of the protein. Simultaneous CV charge transfer measurements provided information on the number of layers of protein adsorbed to the surface. This ability of the EQCN to detect solvent displacement by protein adsorption is potentially useful for biosensors to detect and to monitor protein conformational changes in the bulk and during the adsorption process. The Langmuir adsorption isotherm provided the Gibbs energy of adsorption, DeltaG(ADS), and showed excellent agreement between the CV and EQCN frequency measurements.

Electrochemical quartz crystal nanobalance study of the adsorption/displacement phenomena of proteins and lipids on Pt.

The electrochemical quartz crystal nanobalance (EQCN) was used to measure the adsorption behavior of a series of lipids (stearate, oleate, linoleate, and gamma-linolenate) on a Pt surface from a phosphate buffer pH 7.0 solution at 295 K and to investigate their adsorption/displacement behavior with the proteins, beta-lactoglobulin and alpha-lactalbumin, which are known to cause fouling during milk processing. The EQCN technique and the complementary technique of cyclic voltammetry measured simultaneously provided information on the efficiency of solubilization of the proteins by these lipids. Excellent agreement was obtained for the surface concentration of adsorbed lipid from the surface charge density from cyclic voltammetry measurements and the change in mass from the EQCN frequency measurements. The Gibbs energy of adsorption showed the lipids to have a strong affinity for the platinum surface. Addition of protein to a preadsorbed lipid layer showed alpha-lactalbumin to be able to coadsorb with the lipids, while beta-lactoglobulin was able to desorb some of the unsaturated lipids but appeared to coadsorb with the saturated lipid, stearate. Addition of lipid to a preadsorbed protein layer showed the unsaturated lipids to be able to displace some of the protein. A comparison of the desorption ability of the lipids showed stearate to be very inefficient at removing protein, while the other three lipids were able to remove each of the proteins, with the order of efficiency for protein desorption being oleate > linoleate > gamma-linolenate.

Effects of Thiourea on Anodic Dissolution of Au and Surface Oxidation Behaviour in aq HClO4Studied by Means of an EQCN

Anodic dissolution of Au is facilitated by the presence of thiourea owing to formation of strongly complexed Au ions. The present paper reports studies of this process using cyclic voltammetry (CV), chronopotentiometry and chronoamperometry, usefully complemented by nanogravimetry employing an electrochemical quartz-crystal nanobalance (EQCN). The molar masses per faraday for Au dissolution were determined from EQCN measurements, coupled with information derived from CV, chronopotentiometry and chronoamperometry, and clearly indicate that Au becomes dissolved over the potential range 0.45—0.65 V vs RHE via a 1e− oxidation process in 0.5 M HClO4 solution containing thiourea. The peak potential for Au dissolution in the presence of thiourea is about 600 mV less positive than that in the presence of Br− or Cl− (1.20 V vs RHE for Br− and 1.39 V vs RHE for Cl−). The linear relationship between anodic peak currents at about 0.630 V vs RHE and square-root of the sweep rate indicates that the Au dissolution process is diffusion-controlled. The anodic current efficiency for Au dissolution is 93%.

Electrochemical Quartz Crystal Nanobalance (EQCN) Studies of Protein Interfacial Behavior at Pt

The interfacial behavior of a variety of proteins ranging in molar mass from 2500 to 340 000 g mol-1 was studied at a Pt electrode surface at 298 K using the electrochemical quartz crystal nanobalance (EQCN) technique of simultaneous measurements of frequency and cyclic voltammetry (CV). It was shown that the EQCN frequency measurements did not directly monitor the molar mass of the adsorbed protein at anodic potentials but instead measured changes in the surface oxide in the absence and presence of adsorbed protein. However, at a potential characteristic of the double layer for platinum, EQCN frequency measurements gave a measure of the extent of solvent displacement by the adsorbed protein. The values for the Gibbs free energy of adsorption, ΔGADS, obtained with these EQCN frequency measurements gave excellent agreement within experimental uncertainty with those obtained from the simultaneous CV measurements for all proteins studied. The adsorption process was modeled using the Langmuir adsorption isoth...