Activity and stability of RuO2-coated titanium anodes prepared via the alkoxide route

Abstract

Titanium anodes with an active RuO2 coating of two different thicknesses were prepared from the oxide suspended in ethanol ("ink" method), while the oxide itself was synthesized by the hydrolysis of ruthenium ethoxide in an ethanolic solution (alkoxide route). The morphology of prepared oxide was examined by scanning electron microscopy. The electrochemical properties of the prepared Ti/RuO2 anodes, involving their cyclic voltammetric behavior in H2SO4 and NaCl solutions, activity in the chlorine and oxygen evolution reaction, impedance behavior in H2SO4, and stability during electrolysis in dilute chloride solutions, were investigated. The performances of the anodes are compared to those of a Ti/RuO2 anode prepared by the sol-gel procedure from an oxide sol obtained by the forced hydrolysis of ruthenium chloride in acid solution. The anodes prepared via the alkoxide route showed a higher capacitance and activity for the chlorine evolution reaction than the anode prepared by the inorganic sol-gel procedure. The results of the stability test showed that the utilization of the coating active material is better when the anodes were prepared via the alkoxide route than via the inorganic sol-gel procedure, particularly for anodes with a smaller mass of coating. The different rates of loss of activity indicate a degradation mechanism for the anodes prepared via the alkoxide route in which electrochemical dissolution of RuO2 from the coating surface prevails over the growth of an insulating TiO2 layer in the coating/Ti substrate interphase. The effect of RuO2 dissolution from the coating surface increases with increasing coating mass.

Titanske anode sa aktivnom prevlakom od oksida rutenijuma dve različite debljine, formirane su od oksida dobijenog hidrolizom rutenijum(III)-etoksida u etanolskom rastvoru ("ink" metoda). Morfologija dobijenog oksida ispitivana je skenirajućom elektronskom mikroskopijom. Ispitivana su elektrohemijska svojstva formiranih anoda, koja podrazumevaju ciklično-voltametrijsko ponašanje u rastvorima H 2SO4 i NaCl, aktivnost u reakcijama izdvajanja hlora i kiseonika, impedansno pona- šanje i stabilnost tokom elektrolize razblaženih rastvora hlorida. Karakteristike dobijenih anoda upoređene su sa karakteristikama anode formirane sol-gel postupkom iz oksidnog sola dobijenog forsiranom hidrolizom rutenijum(III)-hlorida u kiseloj sredini (5 mol dm-3HCl). Anode formirane alkoksidnim postupkom imaju veću kapacitivnost i aktivnost za reakciju izdvajanja hlora od anode dobijene sol-gel postupkom iz neorganskog sola. Rezultati testa stabilnosti u rastvoru hlorida pokazuju da je iskorišćenje aktivnog materijala prevlake takođe bolje kod anoda dobijenih alkoksidnim postupkom, naročito za anodu sa manjom debljinom prevlake. Rezultati ukazuju na to da u mehanizmu gubitka aktivnosti anoda dobijenih alkoksidnim postupkom elektrohemijsko rastvaranje oksida rutenijuma sa površine prevlake preovlađuje u odnosu na rast izolatorskog sloja oksida titana u međufazi prevlaka/ titanska podloga. Efekt rastvaranja RuO2 sa površine je izraženiji kod prevlake veće debljine.