Electrocatalytic properties and stability of titanium anodes activated by the inorganic sol-gel procedure

Abstract

The properties of activated titanium anodes, RuO2-TiO2/Ti and RuO2--TiO2-IrO2/Ti, prepared from oxide sols by the sol-gel procedure, are reviewed. RuO2 and TiO2 sols were synthesized by forced hydrolysis of the corresponding chlorides in acid medium. The morphology of the prepared sols was investigated by transmission electron microscopy. The chemical composition of the RuO2 sol was determined by X-ray diffraction and thermogravimetric analysis. The loss of electrocatalytic activity of a RuO2-TiO2/Ti anode during an accelerated stability test was investigated by examination of the changes in the electrochemical characteristics in the potential region of the chlorine and oxygen evolution reaction, as well as on the open circuit potential. These electrochemical characteristics were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and polarization measurements. The changes in electrochemical characteristics of the anode prepared by the sol-gel procedure were compared to the changes registered for an anode prepared by the traditional thermal decomposition of metal chlorides. The comparison indicated that the main cause for the activity loss of the sol-gel prepared anode was the electrochemical dissolution of RuO2, while in the case of thermally prepared anode the loss was mainly caused by the formation of an insulating TiO2 layer in the coating/Ti substrate interphase. The results of an accelerated stability test on RuO2-TiO2/Ti and RuO2--TiO2-IrO2/Ti anodes showed that the ternary coating is considerably more stable than the binary one, which is the consequence of the greater stability of IrO2 in comparison to RuO2.

U radu je dat je pregled svojstava aktiviranih titanskih anoda, RuO2-TiO2/Ti i RuO2--TiO2-IrO2/Ti, dobijenih sol-gel postupkom od neorganskih oksidnih solova. RuO2 i TiO2 solovi dobijeni su forsiranom hidrolizom odgovarajućih hlorida metala u kiseloj sredini. Morfologija dobijenih solova ispitivana je transmisionom elektronskom mikroskopijom. Hemijski sastav RuO2 sola ispitivan je difrakcijom x-zraka i termogravimetrijskom analizom. Mehanizam gubitka elektrokatalitičke aktivnosti RuO2-TiO2/Ti anoda ispitivan je praćenjem promena elektrohemijskih svojstava anode u reakcijama izdvajanja hlora i kiseonika, kao i na potencijalu otvorenog kola, tokom degradacije anode. Ove elektro-hemijske karakteristike anode ispitivane su metodama ciklične voltametrije, spektroskopije elektrohemijske impedancije i polarizacionim merenjima. Promene u elektrohemijskim svojstvima anode dobijene sol-gel postupkom poređene su sa promenama koje su registrovane za RuO2-TiO2/Ti anodu dobijenu tradicionalnim postupkom termičke razgradnje hlorida metala. Na osnovu ovih ispitivanja proizilazi da je osnovni uzrok gubitka elektrokatalitičke aktivnosti anode dobijene sol-gel postupkom elektrohemijsko rastvaranje RuO2, dok je uzrok degradacije anode dobijene termičkom razgradnjom rast neprovodnog TiO2 sloja u međufazi prevlaka/titanska podloga. Rezultati ubrzanog testa stabilnosti RuO2-TiO2/Ti i RuO2-TiO2-IrO2/Ti anode pokazuju da je trojna prevlaka znatno stabilnija od dvojne, zbog veće stabilnosti oksida iridijuma u poređenju sa oksidom rutenijuma.