A study of the hydrogen absorption and desorption reactions in palladium electrodes using the potential step method

A thin film of Ni(II)¯Al(III) layered double hydroxide hybridized with an amphiphilic anionic Ru(II) complex ((N(C2H5)4)2[Ru(CN)4(dc18bpy)]:dc18bpy=4,4ʹ-octadecyl2,2ʹ-bipyridine) was prepared by the Langmuir¯Blodgett (LB) method. Hybridization was performed by spreading a chloroform solution of (N(C2H5)4)2[Ru(CN)4(dc18bpy)] onto an aqueous suspension of Ni(II)¯Al(III) layered double hydroxide. The film was deposited onto a solid substrate such as an ITO electrode and mica. Atomic force microscopic (AFM) observation on the deposited film confirmed that about 9.0 nm thick Ni(II)¯Al(III) layered double hydroxide particles were uniformly adsorbed by the monolayer of Ru(II) complex. Cyclic voltammograms on an ITO electrode modified with a single layer of the hybrid film gave quasireversible reduction¯oxidation peaks due to Ni(II)/Ni(III) in a phosphate buffer at pH 7.67. When the mononucleotide of guanosine 5ʹ-monophosphate (GMP) was added in an electrolyte solution, the increase of oxidation current above 800 mV (vs SCE) was observed at the expense of the reduction peak of Ni(III). The results indicate that Ni(II) in the layered double hydroxide lattice acts as a mediator in oxidation of GMP. The modified electrode shows great enhancement in the oxidation of GMP in comparison with a bare ITO electrode.