Preparation of a titanium metal electrode with a nitrogen-doped one-dimensional titanium oxide surface layer for the support of catalysts

Abstract

A Ti metal electrode with nanostructured titanium oxide that possesses high electrical conductivity, a large specific surface area and the capacity for supporting catalysts was prepared by a simple solution and heat treatment. A precursor of the electrode that possesses one-dimensional hydrogen titanate, H₂Ti₃O₇, 600 nm in thickness was produced by soaking the metal in 5 M NaOH at 60 °C and subsequently in a 0.5 mM HCl solution at 40 °C. The treated metal had a high specific surface area approximately 100 times higher than theoretical flat surface, but its scratch resistance was low. The heat treatment of the hydrogen titanate at 650 °C for 1 h under air increased the scratch resistance markedly, but resulted in the development of an electric insulated surface layer that was composed of anatase and rutile. In contrast, when heat-treated under an N₂ atmosphere, the hydrogen titanate was transformed into anatase containing a small amount of Ti₄O₇, TiN, TiN_xO_1−x and Ti₂N, which exhibited a relatively higher electrical conductivity that was in the range of semiconducting materials. It was also shown that the treated metal immobilized 1,1′-ferrocenylbis(phosphonic acid) by forming a Ti–O–P bond and thereby induced a high electric current upon cyclic voltammetry, although the treated metal before the ferrocene modification showed almost no electric current. Thus, the treated Ti metal is expected to be useful as an electrode for various types of electrochemical systems due to its high specific surface area, electrical conductivity and large capacity for supporting catalysts.