Sol-gel processing of ordered MnO2 structures
 toward enhanced O2 reduction catalysis for air batteriesPoster presented at Meeting Point of the Science and Practice in the Fields of Corrosion, Materials and Environmental Protection - XX YuCorr International Conference (May 21-24, 2018, Tara Mountain, Serbia

Friedrich, Bernd

Mihailović, Marija

Panić, Vladimir

Stevanović, Jasmina

Stopić, Srećko

Central Repository of the Institute of Chemistry, Technology and Metallurgy (CER)

Marija Mihailović1, Jasmina Stevanović1, Srećko Stopić2, Vladimir Panić1, Bernd Friedrich21Institute оf Chemistry, Technology and Metallurgy, University of Belgrade, Department of Electrochemistry, Njegoševa 12, 11000 Belgrade, Serbia2Institut für Metallurgische Prozesstechnik und Metallrecycling, RWTH Aachen University, Intzestraße 3, 52056 Aachen, DeutschlandThe catalysis of electrochemical oxygen reaction (ECOR), as an essential reaction occurring in energy conversion systems, such as fuel cells or metal–airbatteries, is still to be improved. The improvement relates to the synthesis of the catalysts other than Pt onto which rather slow ECOR would take placewith acceptable rate and stable activity and cyclability of the catalyst. Newest investigation revealed that composite oxides based on MnO2 are ofsufficient activity to replace Pt in ECOR. Ordered structures and hierarchical distribution of the oxide components, incorporated within other non-expensive and noble-metal-free elements are the main goals of the synthesis routes. The present work reports the synthesis of ordered MnO2-basedstructures by combined sol–gel (SG) processing and ultrasonic spray pyrolysis (USP): CeO2|MnO2 and LaSrCoO3|MnO2. These SG–USP materials areinvestigated for their ECOR activities in alkaline solution.Metal-air batteries attracted much attention recently due to extremly high energy density compared to other rechargable batteries. The high specific energy density is a result of the coupling of a reactive metal anode to an air electrode. Cathode must be able to sustain an ORR, aswell as oxygen oxidation reaction if battery is rechargeable. Fig.2 Block diagram of a fuel cell (H2 could also be hydride, methanol, ethanol, formic acid etc.) [https://en.wikipedia.org/wiki/Fuel_cell]Fuel cells requires a continuous source of fuel and oxygen (usually from air) to sustain the operation. EXPERIMENTALThe MnO2 sol was obtained through a procedure in which the aqueous solution of KMnO4 reacted with of methanol after continuous agitation at magneticstirrer. The precipitate was rinsed with water and subjected to ultrafiltration in several stages in order to obtain homogeneous dispersion. Ultrafiltration wascarried out using Amicon Stirred Cell at the pressure of 3.5 bar at the magnetic stirring rate of 300 rpm, while the dispersion had pH value of 8.4. The solidphase sponateneously split into two phases: the gel was precipitated at the membrane (magnetically unstable MnO2 phase), stable colloidal dispersionabove membrane (magnetically stable MnO2 phase). Both, the stable and unstable phase were separately sampled and dried at 120oC for 9 hours.MnO2@CeO2 was synthetized to reach the nominal composition of 1:1 oxide mass ratio. The precursor for CeO2 was Ce(SO4)2 *4H2O, which simultaneouslyhydrolyzed in presence of CH3OH and KMnO4 water solution. Upon change of thecolour of a mixture from yellow-purple to dark brown, the precipitate wasrinsed with C2H5OH and dried afterwards at 110oC for 24 hours.Thin layers of stable and unstable MnO2, as well as MnO2@CeO2, applied to glassy carbon (GC) working electrode, were electrochemically examined in O2saturated 0.1M KOH by CV and LSV techniques.Fig.1 Metal-air battery  (Li could also be Al, Zn etc.) [http://slideplayer.com/slide/3452993/]-0,2 0,0 0,2 0,4-0,020,000,020,040,06I/ mAE/V vs. Hg/HgO stable MnO2 phase unstable MnO2 phase MnO2@ CeO2 in N2-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5-0,15-0,10-0,050,000,050,100,150,20I/ mAE/V vs. Hg/HgO MnO2@ CeO2 in N2 MnO2@ CeO2 in O2-1,6 -1,4 -1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8-0,35-0,30-0,25-0,20-0,15-0,10-0,050,000,05I/ mAE/V vs. Hg/HgO unstable MnO2 phase MnO2@ CeO2 in O2 stable MnO2 phaseFig. 3: CV responses in deaerated 0.1MKOH indicate similar low-current featurelessshapes for all samples . There is a strongindication of different conductivities sincethe CVs are of different inclination. CeO2considerably improves the MnO2conductivity, especially with respect tomagnetically insensitive sample.Fig. 4: MnO2@CeO2 shows remarkableactivity toward ORR in alkaline solution,with a potential region similar to otherelectrocatalysts known upon ORR activity.Fig.5: Although the MnO2 content in aMnO2@CeO2 thin layer is a half of thatin MnO2 pure layers, ORR currents arehigher with respect to magneticallyunstable MnO2 phase. The reactionstarts at the potential of about 100 mVmore positive values than in the caseof pute MnO2. The ORR activity apearsconsiderably affected by magneticstate of MnO2.

Sol-gel processing of ordered MnO2 structures  toward enhanced O2 reduction catalysis for air batteries

 CER - Central Repository of the Institute of Chemistry;  Technology and Metallurgy

Mihailovic, Marija

Stopic, Srecko

RWTH Publications

Sol-gel processing of ordered MnO2 structures toward enhanced O2 reduction catalysis for air batteries

Publikationsserver der RWTH Aachen University

http://cer.ihtm.bg.ac.rs//bitstream/id/6257/XX yucorr_MMihailovic.pdf

Sol-gel processing of ordered MnO2 structures toward enhanced O2 reduction catalysis for air batteries

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Central Repository of the Institute of Chemistry, Technology and Metallurgy (CER)

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