ELECTROCHEMICAL DEPOSITION OF POLYBORATE MONOLAYERS AT AG(111) ELECTRODES

Non-Faradaic electrodeposition of polyborate monolayers at Agr(111) in aqueous solutions containing sodium berate (Na2B4O7) is reported. Ele ctrodeposition is characterized by a very sharp voltammetic wave with half-wave potential E-1/2 approximate to -1.2 V vs Hg/Hg2SO4 and surfa ce charge density sigma 20 +/- 5 mu C/cm(2). X-ray photoelectron spect roscopy and electrochemical quartz crystal microbalance measurements d emonstrate that monolayer formation occurs at potentials positive E-1/ 2. The voltammetric behavior suggests that electrodeposition is associ ated with the polymeric condensation of B(OH)(4)(-) and B(OH)(3), both species produced by the dissociation of B4O72- in the bulk solution ( B4O72- + 7H(2)O reversible arrow 2B(OH)(4)(-) + 2B(OH)(3)). The depend ence oi: the voltammetric wave shape on scan rate is consistent with t he nucleation and growth of an ordered polyborate monolayer. Depositio n of the monolayer is also observed in boric acid/NaOH solutions, stro ngly supporting the proposed mechanism.