ESSEE 4 4 th European Summer School ELECTROCHEMICAL
- Slides: 68
ESSEE 4 4 th European Summer School ELECTROCHEMICAL ENGINEERING PRINCIPLES of ELECTROCATALYSIS Sergio Trasatti Department of Physical Chemistry and Electrochemistry University of Milan, Italy University of Milan, Department of Physical Chemistry & Electrochemistry
POTENTIALITY OF ELECTROCHEMISTRY • Conversion of chemical energy into electrical energy (power sources) • Conversion of electrical energy into chemical energy (electrolyzers) University of Milan, Department of Physical Chemistry & Electrochemistry
Electrolyzers E R P Batteries Fuel Cells R R E E P P University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCHEMICAL PROCESS R + ne = P AMOUNT OF ELECTRICITY Additional specific reactant University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTRICAL ENERGY Power sources: Production Electrolyzers: Consumption V x Q V x I x t AIM Power sources Maximum I with maximum V Electrolyzers Maximum I with minimum V University of Milan, Department of Physical Chemistry & Electrochemistry
INTENSIVE ELECTROCHEMICAL PROCESSES Process Production Mt/y Consumption k. Wh/kg Chlor-Alkali 32 3 Aluminium 16 13 Chlorate 1. 7 5 University of Milan, Department of Physical Chemistry & Electrochemistry
Electrochemical Polarization V = E ± overpotentials Overpotential: Energy dissipation to overcome reaction resistances University of Milan, Department of Physical Chemistry & Electrochemistry
COMPONENTS OF ΔV V = E ± S ± IR ± DVt (+) for electrolyzers (-) for power sources University of Milan, Department of Physical Chemistry & Electrochemistry
THE ΔE TERM Meaning Thermodynamic potential difference Strategy It can only be modified by modifying the nature of electrode processes Example Chlorine-hydrogen cell ΔE = 1. 35 – (-0. 84) = 2. 19 V Chlorine-oxygen cell ΔE = 1. 35 – 0. 39 = 0. 96 V University of Milan, Department of Physical Chemistry & Electrochemistry
THE IR TERM Meaning Ohmic drops in the electrodes and in the solution between the electrodes Strategy - Increase the conductivity of electrode materials. - Decrease the interelectrode distance. - Avoid formation of bubble curtains at electrodes. University of Milan, Department of Physical Chemistry & Electrochemistry
THE IR TERM IR j an j cat University of Milan, Department of Physical Chemistry & Electrochemistry
BUBBLE EFFECT Ohmic drop Surface blocking Mass transfer University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTRODE OHMIC DROP Sn. O 2 + Ir. O 2 University of Milan, Department of Physical Chemistry & Electrochemistry
THE Ση TERM Meaning Sum of anodic and cathodic overpotentials Strategy Search for materials with low values of overpotential University of Milan, Department of Physical Chemistry & Electrochemistry
THE ΔVt TERM Meaning Unstability: increase with time of the ΔV applied to the reactor Strategy Search for stable materials Compromise between stability and activity University of Milan, Department of Physical Chemistry & Electrochemistry
STABILITY PERFORMANCE J. Divisek et al. , Int. J. Hydrogen Energy 15 (1990) 105 University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Hetrogeneous Catalysis at Electrodes University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS General Variation of electrode reaction rate at constant potential Specific Effect of electrode material on the electrode reactin rate University of Milan, Department of Physical Chemistry & Electrochemistry
ELETTROCATALYSIS Search for new materials and/or new operating conditions in order to Improve : activity efficiency selectivity Reduce : investment costs operational costs Increase : life time Avoid : pollution University of Milan, Department of Physical Chemistry & Electrochemistry
Electrocatalysis ELECTRONIC FACTORS Primary vs. Secondary Effects Primary Effects Chemical interactions between electrode surface and reactants, intermediates and/or products Secondary Effects Non-specific interactions between electrode surface and reactants, intermediates and/or products University of Milan, Department of Physical Chemistry & Electrochemistry
Generalized Kinetic Equation University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Primary Effects University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Hydrogen Evolution on Metal Electrodes University of Milan, Department of Physical Chemistry & Electrochemistry
BASIC CONCEPTS OF OXYGEN EVOLUTION ON OXIDE ELECTRODES MO + x. H 2 O MO 1+x + 2 x. H+ + 2 xe (formation of higher oxide) MO 1+x MO + x/2 O 2 (higher oxide decomposition) University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Oxygen Evolution on Oxide Electrodes University of Milan, Department of Physical Chemistry & Electrochemistry
“Volcano” curves in CATALYSIS CO + 3 H 2 → CH 4 + H 2 O University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Examples of Experimental Assessment University of Milan, Department of Physical Chemistry & Electrochemistry
Electrocatalytic Activity Relative Evaluation University of Milan, Department of Physical Chemistry & Electrochemistry
ELETTROCATALYSIS Relative Assessment of Activity j DV 1 1 2 2 DV DV ln j DV 1 2 ln j University of Milan, Department of Physical Chemistry & Electrochemistry ln j
ELECTROCATALYSIS Electronic vs. Geometric Factors Electronic Factors Structure and chemical composition of materials Geometric Factors Surface area of materials (morphology) University of Milan, Department of Physical Chemistry & Electrochemistry
Real Surface Area Effect I. J. Brownand S. Sotiropoulos, J. Appl. Electrochem. , 30 (2000) 107 University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Intensive vs. Extensive Quantities Independent of surface area extension Extensive Quantities Dependent on surface area extension University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Intensive Quantities Tafel slope Reaction mechanism Point of zero charge Surface chemistry University of Milan, Department of Physical Chemistry & Electrochemistry
MECHANICAL vs. CHEMICAL ACTIVATION h /V Ni-Raney sand blas smo oth ted N i Ni Log (j/m. A cm-2) University of Milan, Department of Physical Chemistry & Electrochemistry
EFFECT OF SURFACE CRYSTALLOGRAPHIC ORIENTATION Ag University of Milan, Department of Physical Chemistry & Electrochemistry
EFFECT OF PARTICLE SIZE (110) particle size University of Milan, Department of Physical Chemistry & Electrochemistry
EFFECT OF PREPARATION University of Milan, Department of Physical Chemistry & Electrochemistry
Ir. O 2+Rh. Ox Mixed Oxides H 2 Evolution University of Milan, Department of Physical Chemistry & Electrochemistry
Sn. O 2 + Ir. O 2 Mixed Oxides Cl 2 Evolution University of Milan, Department of Physical Chemistry & Electrochemistry
General Trends in Research Better dispersion Maximize surface area Specific technology Better mixing Synergetic effects Composite materials University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS University of Milan, Department of Physical Chemistry & Electrochemistry
ESSEE 4 4 th European Summer School ELECTROCHEMICAL ENGINEERING THE END Thank you for your attention University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Transition Metal Oxides: A Technological Breakthrough University of Milan, Department of Physical Chemistry & Electrochemistry
University of Milan, Department of Physical Chemistry & Electrochemistry
BRINE ELECTROLYSIS Na. Cl + H 2 O + 2 e ½Cl 2 + Na. OH + ½H 2 Anode: Graphite 2 Cl- Cl 2 + 2 e H 2 O ½O 2 + 2 H+ + 2 e Graphite is consumed University of Milan, Department of Physical Chemistry & Electrochemistry
GRAPHITE ANODES An Cat IR University of Milan, Department of Physical Chemistry & Electrochemistry
DIMENSIONALLY STABLE ANODES DSA® Graphite replaced by insoluble materials H. Beer H. B. Beer. J. Electrochem. Soc. 127 (1980) 303 C S. Trasatti, Electrochim. Acta 45 (2000) 2377 University of Milan, Department of Physical Chemistry & Electrochemistry
DIMENSIONALLY STABLE ANODES (DSA®) Silver Jubilee celebrated in 1989 at the Spring Meeting of the Electrochemical Society, Los Angeles University of Milan, Department of Physical Chemistry & Electrochemistry
INDUSTRIAL PERFORMANCE University of Milan, Department of Physical Chemistry & Electrochemistry
Chlor-Alkali Cells APPLIED VOLTAGE Breakdown Graphite DSA University of Milan, Department of Physical Chemistry & Electrochemistry
1971 - First Paper in the Open Literature University of Milan, Department of Physical Chemistry & Electrochemistry
TRANSITION METAL OXIDE ELECTRODES Applications Chlorine evolution Oxygen evolution Hydrogen evolution Electroorganic reactions p. H sensors Supercapacitors Oxygen reduction CO 2 reduction Ozone electrosynthesis University of Milan, Department of Physical Chemistry & Electrochemistry
TRANSITION METAL OXIDES ü Dioxides (Ru. O 2, Ti. O 2) ü Spinels (Co 3 O 4) ü Perovskites (La. Ni. O 3) ü Pyrochlores (Bi 2 Ru 2 O 7) University of Milan, Department of Physical Chemistry & Electrochemistry
ACTIVATED ELECTRODES Active layer Support University of Milan, Department of Physical Chemistry & Electrochemistry
Morphology of Active Layers Effect of precursor and Calcination Temperature 300°C Ru. O 2 500°C Ru. Cl 3 • x H 2 O Ru(NO)(NO 3)3 • x H 2 O University of Milan, Department of Physical Chemistry & Electrochemistry
PROPERTIES OF ACTIVE LAYERS Techniques of Characterization ü XRD, SEM, TEM, AES, XPS, RBS, IRS, SIMS, ICPES, NRA, Radiotracer ü Voltammetry, potential step, point of zero charge, impedance. Structure, morphology, surface area, stability, surface composition, acid-base behaviour University of Milan, Department of Physical Chemistry & Electrochemistry
Morphology of Active Layers Surface Charge total = outer + inner University of Milan, Department of Physical Chemistry & Electrochemistry
CYCLIC VOLTAMMETRY Electrochemical Spectrum University of Milan, Department of Physical Chemistry & Electrochemistry
OXIDE ELECTRODES Surface charge and surface concentation of active sites MOx(OH)y + d. H+ + de ↔ MOx-d(OH)y+d University of Milan, Department of Physical Chemistry & Electrochemistry
TRANSITION METAL OXIDE ELECTRODES Voltammetric analysis • Surface area • Morphology • Porosity • Surface composition • Stability University of Milan, Department of Physical Chemistry & Electrochemistry
SURFACE CHARGE University of Milan, Department of Physical Chemistry & Electrochemistry
MIXED OXIDE ELECTRODES Surface Charge vs. Composition University of Milan, Department of Physical Chemistry & Electrochemistry
SURFACE SEGREGATION IN MIXED OXIDES Ru. O 2+Ir. O 2 (Ir) Co 3 O 4+Ru. O 2 (Ru) Ir. O 2+Sn. O 2 (Ir) Ru. O 2+Zr. O 2 (Zr) Ir. O 2+Ta 2 O 5 (Ta) Ru. O 2+Ti. O 2 (Ti) Ru. O 2+Pt. Ox (Pt) Ni. Ox+Fe. Ox (Ni) Ni. Ox+Co 3 O 4 (Ni) Rh. Ox+Ru. O 2 (Rh) University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCHEMICAL SURFACE ANALYSIS University of Milan, Department of Physical Chemistry & Electrochemistry
SURFACE vs. BULK COMPOSITION University of Milan, Department of Physical Chemistry & Electrochemistry
Normalization to Unit Real Surface Area University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTRODE STABILITY TEST University of Milan, Department of Physical Chemistry & Electrochemistry
ELECTROCATALYSIS Oxide Electrodes: Redox Relais University of Milan, Department of Physical Chemistry & Electrochemistry
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