Cuprous oxide surface potential

The electrode potential behaviour of copper in various solutions has been investigated and discussed in considerable detail by Catty and Spooner . According to these workers a large part of the surface of copper electrodes in aerated aqueous solutions is normally covered with a film of cuprous oxide and the electrode potential is usually close to the potential of these film-covered areas. The filmed metal simulates a reversible oxygen electrode at... 

In the light of the present study it is possible to draw up the following interpretation of the interaction of oxygen with cuprous oxide. During the adsorption of the monolayer, the electron transfer imparts a negative potential to the adsorbed film (which probably exists as 0 ) and positive holes are formed in the surface layers. This process has an activation energy of 7 kcal./mole and proceeds with a heat of adsorption (I) of 60-55 kcal./ mole. 

It can be seen from the reactions (10.12) and (10.13) that the oxygen released from cuprous oxide should react with hydronium ions increasing the surface pH. This effect can be confirmed experimentally by probing with pH-sensitive microelectrodes. One of them, Sb SbjOj microprobe, was used in the following experiments. This antimony microelectrode (AME) is reversible with respect to H+ ions and its equilibrium potential is determined unambiguously by the solution pH (see Section 3.4.1). The design ofthe equipment permitted the position of the AME tip to be controlled with an accuracy of 10 pm. The distance of closest approach ofthe AME to the electrode surface. Ax, was arbitrarily taken as zero. 

Summary. An STM study has been initiated to investigate the various processes associated with electrodeposition of Cu-Ni multilayers on Cu(100). The substrates were prepared by electropolishing in phosphoric acid followed by immersion in 10 mmol/1 HCl. A (V2 x V2)R45° adlattice of oxidatively adsorbed chlorine is formed under these conditions. The adlayer stabilizes the surface steps in the <100> direction which corresponds to the close packed direction of the chloride adlattice. In dilute (millimolar) solutions of cuprous ion, reduction occurs under mass transport control with the electrocrystallization reaction proceeding by step flow in the <100> direction. At more negative potentials chloride is partially desorbed. Coincidentally, the highly kinked metal steps become Mzzy and move towards adopting the close-packed <110> orientation of the metal lattice. Preliminary experiments on heteroepitaxial nickel deposition reveal regions where electrocrystallization on Cu(100) occurs via step flow in the <110> direction. 

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