Jing Xu

Faraday Technology Inc. is a research, development and engineering firm developing electrochemical innovations based has pulse/pulse reverse electrolytic principles [1]. One of Faraday’s current activities is directed towards the development of an innovative REACH-compliant plating process for deposition of functional chrome coatings, based on replacement of the conventional hexavalent chromium plating chemistry with a non-toxic trivalent chromium chemistry. Hexavalent chromium plating has been used for many decades to produce hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium has come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers’ health. Faraday has demonstrated that the chrome coatings prepared using the FARADAYIC(R) Process in a trivalent chromium chemistry have equivalent functional properties to chrome coatings produced with a hexavalent chromium bath. The data demonstrates equivalent or superior: 1) plating rate, 2) Knoop hardness, 3) current efficiency, 4) hydrogen embrittlement behavior, 5) adhesion, 6) corrosion resistance, 7) porosity, 8) thickness, 9) Taber Abrasion, Ball on Flat Reciprocating and Dithering wear resistance, with no hexavalent chromium formation in the bath. This paper will discuss the 2013 EPA Green Chemistry Challenge Award winning work on the development of a REACH-compliant plating process for wear resistant, functional coatings from a single, simple-to-control trivalent-based electrolyte. Specifically, this paper will discuss electrochemical deposition approaches to improve (decrease) the wear index of the chrome coating, to meet the performance from conventional chrome coating processes. Acknowledgements: This study is supported by the US Army (W911NF-11-2-0014) and private sources. [1] E. J. Taylor “Adventures in Pulse/Pulse Reverse Electrolytic Processes: Explorations and Applications in Surface Finishing” J. Applied Surface Finsihing, 3(4), 178-189 (2008).  

Faraday Technology Inc. is a research, development and engineering firm developing electrochemical innovations based has pulse/pulse reverse electrolytic principles [1]. One of Faraday’s current activities is directed towards the development of an innovative functional REACH compliant chrome plating process based on a trivalent chromium electrolyte to replace hexavalent chromium plating. Hexavalent chromium plating has been used for many decades to provide hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium has come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers’ health. Faraday has demonstrated that the chrome coatings prepared using the FARADAYIC(R) Process have equivalent functional properties to the coatings produced with a hexavalent chromium bath. The data demonstrates equivalent or superior: 1) plating rate, 2) Knoop hardness, 3) current efficiency, 4) hydrogen embrittlement behavior, 5) adhesion, 6) corrosion resistance, 7) porosity, 8) thickness, 9) Taber Abrasion, Ball on Flat Reciprocating and Dithering wear resistance, and with no hexavalent chromium formation in the bath. Therefore, this paper will discuss the 2013 EPA Green Chemistry Challenge Award winning work on the development of a REACH compliant functional trivalent chromium plating process from a single, simple-to-control trivalent-based electrolyte to replace hexavalent chromium plating. Acknowledgements: This study is supported by the US Army (W911NF-11-2-0014) and private sources. [1] E. J. Taylor “Adventures in Pulse/Pulse Reverse Electrolytic Processes: Explorations and Applications in Surface Finishing” J. Applied Surface Finsihing, 3(4), 178-189 (2008).  

Certain aspects of the interpretation of rotating ring-disk electrode, RRDE, data for the oxygen reduction reaction, ORR, in aqueous electrolytes under forced convection have been examined. This presentation will highlight three specific topics: • The correct interpretation of the fraction of the oxygen consumption that generates H₂O₂(aq), as extracted from the ratio of ring current to disk current denoted as X_H2O2 , A plot of this ratio vs ω^-1/2, where ω is the rotation rate of the disk, should be linear and, with a slope proportional to k₃ /X_H2O2 where k₃ is the rate constant for the reduction of solution-phase hydrogen peroxide¹. • Changes in the electrocatalytic activity of Pt for the oxygen and hydrogen peroxide reduction reactions (ORR, and HPRR, respectively) in an aqueous acidic electrolyte induced by the adsorption of bromide, as a model impurity, have been investigated using chronoamperometric techniques. Significant drops in the diffusion-limited currents for O₂ reduction, as well as an increase in the measured H₂O₂(aq) at the ring were induced by the presence of 10 M KBr, and could only be observed for _Br- > 0.25 regardless of E_step. This behavior was found to be consistent with a simple blockage of surface active sites by adsorbed bromide, as predicted by the attenuation model proposed by Levart. • An analysis of O₂ ^- generation at the disk and subsequent oxidation at the ring (see Figure 1) of a RRDE, which undergoes a subsequent second-order dismutation². Acknowledgements: This research was supported by a grant from NSF: CHE-1412060 References 1. N. S. Georgescu, A. J. J. Jebaraj and D. Scherson, ECS Electrochemistry Letters, 4, F39 (2015). 2. Z. Feng, N. S. Georgescu and D. A. Scherson, Analytical Chemistry, 88, 1088 (2016). Figure 1

A primitive model involving the combined use of coulometric and in situ differential reflectance spectroscopy data collected simultaneously¹ has been applied to examine oxide formation on the surface of Pt(poly) electrodes in aqueous 0.1M HClO₄ as a function of the applied potential. Analysis of experimental data assumed sequential formation of two different kinds of oxides, PtOH in the low and PtO, in the high potential regions, denoted as Ox1 and Ox2, respectively. The potential dependence of the coverages of each of these species, theta_Ox1 and theta_Ox2, was obtained by solving the following set of coupled equations: The symbol theta_bare   in Eq.(1) represents the coverage of the bare, i.e. non-oxidized surface sites, Q_n, is the charge determined from the integration of the oxide reduction peak following the method reported by Novak² and the factor 2 in Eq.(2) accounts for the stoichiometry of the oxide. Lastly the symbol -deltaR/R =-[R(E_ref)-R(E_sam)]/R[E_ref], R(E_ref) and R(E_sam) are the reflectance values recorded at the reference potential, E_ref, set at 0.05 V, and at any arbitrary sampling potential, E_sam, respectively³ represents the differential reflectance, where A(E), B(E) and C(E) are coefficients that account for changes in the optical signal of each of the types of sites induced by the applied potential.¹ Shown in jagged line in Fig. 1 is a plot of -deltaR/R vs potential, E, for Pt(Poly) in 0.1M HClO₄ recorded at a scan rate of 10 mV/s. The solid smooth line in this figure was obtained from the analysis of the model specified above which yielded values of theta_Ox1, theta_Ox2, and theta_bare vs E, for Pt(poly) in 0.1M HClO₄ in Fig. 2. REFERENCES A. J. J. Jebaraj, D. Scherson, Anal. Chem., 86, 4241, (2014). D. M. Novak, B. Conway, J. Chem. Soc. Faraday Trans. 77, 234, (1981). J. Xu, D. Scherson, Anal. Chem., 85, 2795, (2013). Figure 1

A method is herein described that allows the coverage of the two forms of oxide believed to form on polycrystalline Pt, Pt(poly), surfaces in aqueous solutions to be determined based on the analysis of in situ differential reflectance spectroscopy, ΔR/R, and voltammetric data recorded simultaneously. The model employed assumes ΔR/R can be expressed as the sum of contributions due to each type of surface site, i, represented by the product of their potential dependent coverage, θ_i(E), and a linear function of E obtained empirically. Values of θ_i(E) for the unoxidized and oxidized sites are calculated by solving a system of three non-linear equations that relate θ_i(E) to the charge associated with the formation of the oxide layer based on coulometric analyses and accepted values for the number of electrons transferred for each of the oxides. Data collected for Pt(poly) electrodes in aqueous 0.1 M HClO₄ was found to be consistent with the coexistence of the two forms of Pt oxide and unoxidized sites on the surface over a potential range extending from ca. 1.0 to 1.25 V.

In situ reflection absorption UV-visible spectroscopy was used to detect solution phase products generated during the oxidation of bromide on the surface of a polycrystalline platinum rotating disk electrode, Pt(poly) RDE, as a function of the applied potential and rotation rate, ω, in 0.01M KBr in 0.1M HClO₄ aqueous solutions. The experimental set up employed for these measurements was similar to that described by Shi et al.¹ involving, in this case, a Cary 60 spectrophotometer and a modified set of reflection optics. The data collected were analyzed by theoretical simulations (COMSOL 4.3) that account for the formation of tribromide in solution using diffusion coefficients and homogeneous rates constants for the bromide|tribromide reaction reported earlier in the literature^{2, 3}, expect for the diffusion coefficient of bromide which was adjusted to achieve a better fit, i.e. D_Br ^- =2.66 ×10^-5 cm²/s, as opposed to D_Br ^- =2.08 ×10^-5 cm²/s as reported in the literature⁴. Statistical analyses of the I_lim vs √ω (E = 1.4 V vs RHE), data yielded both for the experimental (see black symbols) and theoretical data (red symbols) best fit straight lines with virtually identical slopes and close to zero intercepts (see caption, Fig. 1). Shown in black symbols in Fig. 2, are potential difference UV visible reflection absorption spectra recorded simultaneously at a wavelength, λ = 266 nm, which corresponds to the absorption maxima of the peak associated with tribromide in solution.² Also shown therein (see red symbols) are the results of the theoretical simulations. Although the slopes of the linear fits seem in very good agreement, the experimental results appear higher than the theoretical ones. The most likely origin of this effect relates to changes in the intensity of the reflected light induced both by the adsorption of bromide and the formation of a layer of oxide on the Pt surface at the high potentials at which the oxidation of bromide was monitored⁵. REFERENCES Shi, P.; Scherson, D. A., Anal. Chem. 2004, 76, 2398. Liu, Q.; Margerum. D.W. Environ. Sci. Technol. 2001, 35, 1127. I. Ruff. J. Phys.Chem. 1972, 76, 2957. J. Newman. Electrochemical Systems; third edition John Wiley & Sons. Inc., Hoboken, NJ, 2004. Zhao, M.; Scherson, D. A; Anal. Chem. 1992, 64, 3064.

Normal incidence reflectance spectra (λ = 635 nm) data were acquired from a Pt disk of a rotating Pt|Pt ring-disk electrode in 0.1 M HClO₄ solutions containing bromide in the μM range, while scanning the disk potential linearly and measuring the diffusion limited bromide oxidation current at the ring. Analysis of the results obtained made it possible to correlate quantitatively the relative intensity of the reflected light, R, with the bromide coverage, i.e. the fraction of the surface covered by bromide, assuming the remaining areas of the Pt disk are covered by adsorbed hydrogen, using empirical functions to account for the potential dependence of the optical signals for each of the two surface regions. This technique opens new prospects for monitoring in real time the coverage of bromide and perhaps other adsorbed species during the course of a faradaic process under well-defined conditions of mass transport control.

A porous Teflon ring|solid disk electrode is herein described specifically designed for acquiring online mass spectrometric measurements under well-defined forced convection created by liquid emerging from a circular nozzle impinging on the disk under wall-jet conditions. Measurements were performed for the oxidation of hydrazine, N₂H₄, in a deaerated phosphate buffer electrolyte (pH 7) on Au, a process known to yield dinitrogen as the product. The N₂⁺ ion currents, measured by the mass spectrometer, i(N₂⁺), as well as the corresponding polarization curves recorded simultaneously displayed very similar s-like shapes when plotted as a function of the potential applied to the Au disk. In fact, the limiting currents observed both electrochemically and spectrometrically were found to be proportional to [N₂H₄]. However, the limiting values of i(N₂⁺) did not increase monotonically with the flow rate, ν_f, reaching instead a maximum and then decreasing to values independent of ν_f. This behavior has been attributed in part to hindrances in the mass transport of gases through the porous materials.