The Study On Properties Of Preventing Manganese Depositing On Coated Titanium Anodes

In the current study, the contamination of titanium anode by Mn²⁺ in the seawaterelectrolysis antifouling process was discussed. At first, the environmental factors wasinvestigated, then the purpose of experimental study was to discuss titanium anode whichhave the highest electrochemical properties and preventing manganese deposit property, aswell as by the preparation technology. At last, the mechanism of manganese deposit to theanode was discussed.Based on the analysis of the existing de-active titanium anode, the process of manganesedepositing to the anode was simulated. Current efficiency, anodic polarization curvemeasurements, electrochemical impedance spectroscopy (EIS) investigation and cyclicvoltammetry (CV) were used to obtain information about the electrochemical properties ofmanganese deposited anode. The crystal structure of the coated anode was examined by X-raydiffraction. The surface and morphology of the coatings were characterized by scanningelectron microscopy and electronic probe microanalysis (EPMA).The effects of natural environment factor on preventing manganese deposit wereanalyzed according to the change of seawater environment. (1) It has been found thatmanganese dissolved in seawater causes an anodic deposit to form which likewise increasesthe operating cell voltage and lowers operating current efficiency; (2) temperature affectpreventing manganese deposit to anode in a quite complex way, and see temperature positiveto the growth of preventing manganese deposit while negative to current efficiency, at thesame time, it accelerated the process of anodic degrading; (3) If the pH of solution was acidic,operating cell has a low current efficiency, but the electrode was prone to de-active; what'smore, increasing current efficiency in neutral solution; however, in alkaline solution, thecurrent efficiency becomes very weak by the build-up of a very slight manganese deposit onthe anode and the electrochemical properties would decreased; (4) In the process ofelectrolysis, large current density correlate to the increasing of concentration of activechlorine, for it relates to the preventing manganese deposit; (5) In view of the decompositionof the hypochlorite, the stronger the stirring,, the lower the current efficiency, but thepreventing manganese deposit and electrochemical properties may be reduced.The paper deals with the research on the modification of anode coatings by doping otherelement, the purpoes of experimental study was to obtain titanium anode which have the highest electrochemical properties and preventing manganese deposit. The experimentalresults indicate that: (1) The addition of Ir elements proved to be very effective in improvingthe electrochemical activities of Ti / RuTiCoO_x spinel coatings, reducing cracks forming anddeactivation speed of anode coatings, which is propitious to prolong service life. Theexperiment shows that the electrochemical properties of anode coating doping Sn elementswere not improved greatly. The current efficiency of anodes coating doping Ir, Sn has beenincreased in electrolyte solution contained manganese. (2) The current efficiency of rutilestructure anode coatings is relatively low, the electrochemical properties not to be high. Thechlorine evolution voltage and current efficiency of anode coating doping Pd have beenincreased in electrolyte solution contained manganese. The anode after electrolyzing hasbetter electrochemical properties. On the contrary, anode coatings doping Mn have inferiorelectrochemical properties.Finally, based on the analysis of the existing de-active titanium anode, results indicatedthat the manganese ion in the seawater dominantly induced the degradation of the anodecoatings. On the one hand, electrolysis of seawater containing dissolved manganese ironcaused deposits to form MnO₂ on the anodes, which rapidly increased the impedance of anodeand reduced the efficiency of the cell; on the other hand, the formation of MnO₂ disorderedthe uniform distribution of the electricity on the anodes surfaces, which leaded to thebreakage and invalidation of anode coatings.