Study On Preparation Of Titanium Sub-oxides Of Magneli Phases And Application For Oxygen Evolution Reaction

Magneli phases materials are a series of titanium sub-oxides with the formula of TinO2n-1, where n is between4and10. These materials are electrically conductive and resistant to strong acid and alkali and the conductivity decreases with n increasing, which engage the phases a great promising in electrochemical applications.Magneli phases were prepared using high temperature reduction method with rutile TiO2as raw material and decomposed ammonia as reducing atmosphere. The most conductive phase Ti4O7was obtained by reducing rutile for3hours at1050℃. The prepared materials were dark blue. SEM images showed the particles were porous and grain diameters distributed nonuniformly because powder materials sintered under high temperature, leading to low BET surface area of1.99m2/g. The electrochemical behaviors of Ti4O7electrode in acidic and alkaline electrolytes were detected by cyclic voltammetry and the tests showed that Ti4O7electrode had low activity for both oxygen and hydrogen evolution reactions in sulfuric acid, while the electrode was active for oxygen evolution reaction in KOH electrolyte. The current density of oxygen evolution reaction reached68mA/cm2at the potential of0.8V (vs. Hg/HgO), combined with polarization curves, which told that Ti4O7electrode had comparable catalytical activity for oxygen evolution reaction with graphite electrode in alkaline electrolyte.Spinel catalyst CoFe2O4was prepared using Ti4O7as catalyst supporter. The catalytical performance of the prepared CoFe2O4/Ti4O7electrode was studied through linear sweep voltammetry, chronoamperometry and AC impedance. The results indicated that the CoFe2O4/Ti4O7electrode had great catalytical activity for oxygen evolution reaction (OER) compared with Ti4O7electrode considering that the ORR current density for CoFe2O4/Ti4O7was105mA/cm2, while it was only4mA/cm2for Ti4O7electrode at the potential of0.6V (vs. Hg/HgO). The effects of mass rate between Ti4O7and CoFe2O4to catalytical performance were studied and the results showed that the increased content of CoFe2O4brought more active spots for electrocatalytical reaction and also led to Ohm resistance of the electrode increasing. Polarization and chronoamperometry curves told that when the mass rate between Ti4O7and CoFe2O4was2:1, the catalysts performed better than other mass rates. An electrolytic bath was constructed to explore the prospect of electrolysis of water application, using nickel sheet as hydrogen evolution electrode, the prepared CoFe2O4/Ti407as OER electrode and6mol/L concentrated KOH as electrolyte. The electrolytic bath ran at a constant current of100mA/cm2for over300h without performance declining. The bath voltage was elevated for only50mV, which indicated that the CoFe2O4/Ti4O7electrode was quite stable for use as OER electrode in electrolysis of water.