Polyoxometalate-Modified Boron-Doped Diamond Electrodes

Abstract

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.