Polyoxometalate-Modified Boron-Doped Diamond Electrodes

Polyoxometalates were immobilized on a boron-doped diamond (BDD) surface modified by a photochemical modification method. The BDD surface was first modified with allyltriethylammonium bromide (ATAB) to form surface quaternary ammonium groups. The ATAB-BDD was then immersed in a phosphomolybdic acid (H3PMo12O40, denoted as PMo12) solution to fabricate PMo12-adsorbed ATAB-BDD (PMo12-ATAB-BDD). The electrostatic interaction between PMo12 and the quaternary ammonium group on ATAB-BDD is considered to be critical to the stable immobilization. Polyoxometalate-modified BDD was also fabricated from phosphonic-acid-terminated BDD. BDD was first modified with vinylphosphonic acid (VPA), followed by the reaction of the surface phosphonic acid groups with ammonium molybdate to generate a lacunary phosphomolybdic acid (PMox) group. Although the coverage of the PMox group on PMox-BDD was less than that of PMo12-ATAB-BDD, PMox-BDD was found to be more stable to potential cycling than PMo12-ATAB-BDD, indicating that covalent modification methods are effective for creating stable functional groups on diamond. (C) 2012 The Japan Society of Applied Physics