Mechanism of electrochemical reduction of hydrogen peroxide on copper in acidic sulfate solutions

Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Langmuir (Impact Factor: 4.38). 10/2007; 23(19):9911-8. DOI: 10.1021/la7013557
Source: PubMed

ABSTRACT Hydrogen peroxide is a commonly used oxidizer component in chemical mechanical planarization slurries, used in the processing of Cu metallization in microelectronics applications. We studied the electrochemical reduction of hydrogen peroxide on Cu in 0.1 M H2SO4 solutions using methods including cyclic voltammetry, rotating disk electrode experiments, surface-enhanced Raman spectroscopy, and density functional theory (DFT) calculations. The spectroscopy reveals that the hydrogen peroxide molecule is reduced at negative potentials to form a Cu-OH surface species in acidic solutions, a result consistent with the insight from Tafel slope measurements. DFT calculations support the instability of peroxide relative to the surface-coordinated hydroxide on both Cu(111) and Cu(100) surfaces.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The formation mechanism and resulting structure of trivalent chromium process (TCP) conversion coatings on AA6061-T6 (UNS A96061) and AA7075-T6 (UNS A97075) were investigated. The formation of TCP on both alloys is driven by an increase in the interfacial pH caused by the dissolution of the passivating oxide layer, which leads to an elevated rate of proton-consuming cathodic reactions under open-circuit conditions. These reactions cause the interfacial pH to increase. This pH increase drives the hydrolysis of the fluorometalate precursors in the bath and results in the precipitation of a hydrated metal oxide coating on the surface. The coating appears to have a biphasic structure consisting of a hydrated zirconia (ZrO2 center dot nH(2)O) and chromium hydroxide (Cr[OH](3)) outer layer, and a fluoroaluminate (e. g., KxAlF3+x) interfacial layer. The coating thicknesses on both alloys are in the range of 80 nm to 100 nm. The TCP coating exhibited good stability on both alloys during full immersion testing in both naturally aerated sodium sulfate (Na2SO4) and sodium chloride (NaCl) electrolyte solutions. This was evidenced by no pits forming during immersion in chloride solution. The coating provided corrosion resistance to both alloys as polarization resistance (Rp) increased by about 100X in both Na2SO4 and the Na2SO4 + NaCl. Transient formation of Cr(VI) was detected in the coating on both alloys using Raman spectroscopy after immersion in air-saturated solutions.
    Corrosion -Houston Tx- 12/2013; 89(12):1205. DOI:10.5006/1041 · 2.91 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC's performance. Cell polarization, power density, stability, and durability tests are used in the membranes' evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load.
    12/2012; 2(3):478-92. DOI:10.3390/membranes2030478
    This article is viewable in ResearchGate's enriched format
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This work presents a methodology to analyze hydrogen peroxide reduction reaction (HPRR) studied by rotating disk electrode (ROE). Generally the Koutecky-Levich equation is used to determine the kinetic parameters of an electrochemical reaction. This equation is not applicable to electrochemical reactions with a complex reaction mechanism. The HPRR is an example of these complex reactions because the H2O2 reduction, H2O2 decomposition and O-2 reduction may take place simultaneously on the electrode surface. In the current work the mass transport equations of H2O2 in the electrolyte and the reaction equations on the electrode surface are solved simultaneously under the steady state conditions to derive a specific equation for HPRR. The new equation shows the same linear relationship between the inverse of the current density (j(-1)) and the inverse square root of the rotation frequency (omega(-1/2)), but the slopes and the intercepts of the lines are shown to be functions of the reaction rate constants involved in the HPRR. One of the most important results of the work is the possibility to determine the hydrogen peroxide decomposition rate constant directly from RDE data. Prediction of simultaneous reduction of H2O2 and O-2 on the electrode and suggestion a mechanism for HPRR are other advantages of the derived equation when compared with Koutecky-Levich equation.
    Electrochimica Acta 12/2013; 114:551-559. DOI:10.1016/j.electacta.2013.10.094 · 4.09 Impact Factor