Materials for Energy[PHY563]

IV: Electrochemical Energy Materials & Catalysis

20/01/2021

Jean-François Guillemoles,

Nathanaelle Schneider

Objectives and outline

• Energy conversion and storage

• Basics of electrochemistryo Definitionso Electrochemical reaction driving forceo Ionic conduction

• Basics of catalysiso Key notions: activation energy, catalytic species, activity, selectivity, mechanismo Significance and main applications

• Applications:o Materials for supercapacitorso Materials for batteries (Insertion and conversion materials, tutorial 10/02)o Materials for fuel cells (H2, 10/02)o Related issues : Corrosion ( 12/02) , Photoelectrochemistry, Electrocatalysis ( tutorial)

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INTRODUCTION

Background on energy storage

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Energy mix evolution and perspectives

Source : GMO Solar Power Europe 2016

Increasing share of renewables

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Energy consumption – Necessity of storage

Source : https://www.rte-france.com/fr/eco2mix/eco2mix-consommationFluctuating demand

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Energy storage

Mostly PSH

• Heat storage

• Solar thermal

• Molten salts

• Phase Change Materials

• Mechanical storage

• PSH - Pumped Storage Hydroelectricity

• CAES - Compressed Air Energy Storage

• Flywheels

• Electrochemical storage

• Supercapacities

• Batteries

ELECTROCHEMICAL ENERGY STORAGE AND MORE

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How would you store electricity?

• Types of electrochemical storage you know?

• Can you estimate the energy contained in a cell?

• Its power?

• What is it that you don’t know/ don’t understand about electrochemicalstorage?

o Principles

o Material issues

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ELECTROCHEMICAL ENGINES

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Key figures

Source: Fundamentals of Materials for Energy and Environmental Sustainability, Edited by D. Ginley, D. Cahen

• Capacitor - electrical energy stored as surface charge

• Battery - electrical energy stored as chemical energy

• Fuel cell = battery where fuel is supplied at one electrode and the oxidant at the other

SUPERCAPACITORS

Invariant electrolyte and electrodes

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What is the driving force?

How much energy can be stored?

What are the issues?

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Supercapacitors

Source : www.storagealliance.org

Solid-state capacitor(conventionnal)

EC electrochemical capacitorHigh surface area electrode + liquid electrolyte

• No electrochemical reactions

• Charges are accumulated at the material surface through the double layer (EDL)

• EDL

Variation of electric potential near a surface, interfacial field

Several descriptions : Helmholtz (1853) > Marcus (Nobel, 1992)

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EDL – Electrical Double Layer

Debye length (Debye radius) λD

= measure of charge carrier net eletrostatic effect in a solution

and how far it persists

DL Diffuse layer – coulombic interaction + thermal motion, electrically screening the first layer

First layer – surface charges

Supercapacitors

• Electrode materialso Optimum pore size to maximize the capability of the electrolyte

o Inputs of material science, nanosynthesis, simulation and modeling

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Supercapacitors

• No structural changeo Much longer lifetimes (millions of cycles), low maintenance

o Higher rate capabilities, almost instantaneous > repetitive fast applications (braking, acceleration)

• Only surface o Limited energy storage capability (0.1 – 1 Wh./kg)

o Variation of the voltage

• High cost installation

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BATTERIES EVOLUTION

Batteries type I

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Invariant electrolytes

How to make a battery?

• What are the basic ingredients in a battery?

• What are the desired properties of each component?

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Batteries

Ancient technologies with new materials

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1899« Jamais contente »

1920Wireless communication

TodayTesla roaster

TodayWireless communication

Batteries

Evolution of batteries

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Positive electrode

Negative electrode

electrolyte

e-

2020 Many systems Commercial battery types , sodium-sulfur, redox flow

Quite costly for large scale, stationary applications ~ $ 1000/kWh

Difficulties with large power/long term storage /Cyclability => solid state reactions

Lead battery still cheapest

Batteries

Evolution of batteries

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Batteries

Commercial applications

1991LiCoO2/Graphite

2005LiCoO2/Sn-Co-C

Nano-negative

2006LiFePO4/Graphite

Nano-positive

2004Li(Co, Mn,Ni)O2/Graphite

+20%Volumic energy

4 times more powerfull

+60%Mass energy

Very rapid industrial applications

POTENTIAL (ΔE, Volt)Nature of the redox coupleExtent of reaction

25

Batteries

Tarascon, cours Collège de France (2011)

Number of exchanged electric charges (Coulombs)

POTENTIAL potential : choice

of redox couple

CAPACITY capacity: system exchanging more than 1 electron

CAPACITY (Q, Coulomb, Faraday, Ah)Nature of the redox coupleQuantity of atoms

Nernst equation

Chemical and electrochemical engines

A chemical reactioncan be separated in 2 electrochemical half

reactions

• For one mole

• At each electrode:

Electrode equilibrium: Nernst

• Electric potentials of solution and metal:

• Ideal Solution

• Nernst law:

Losses

(1) Activation overpotential : Potential barrier of redox reaction => reduced by additional potential

(2) Concentration overpotential: Concentration depletion at electrode = > local potential shifted from equilibrium

(3) Conduction overpotential : Ohmic drop

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Issues

• Electrode overpotential: reversibility

• Series resistance : power efficiency

• Cyclability and stability (See Lecture on material degradation)

• LCA

Material issues

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Ox

Strong

Weak

Red

Weak

Strong

Potentiel redox

(Volts) Semi-réactions

H+

Zn(s)Zn2+

H2(g)

Batteries

• Why Lithium batteries?

PHY563 – N. Schneider 31Tarascon, cours Collège de France (2011)

> Small ionic radius

rapid diffusion >> Power

> Works in aqueous medium

>> Thermodynamic limit at 1.2 V

> Lightest metal (6.9g), d= 0.53g.cm-3

> Most electropositive element

>> ΔE 3 – 4V

> High chemical reactivity (water)

>> Organic electrolytes (non aqueous)

Highest energy mass density

BATTERIES TYPE I : LITHIUM TECHNOLOGIES

Invariant electrolytes/redox electrodes

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Li - metal

PHY563 – N. Schneider 33Tarascon, cours Collège de France (2011)

Li-metal > negative electrode = metal Li

Discharge:TiS2 + e- + Li+ TiLiS2Li Li+ + e-

Batteries

• Lithium batteries

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Rocking chair batteries - intercalation

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Li-ion: electrodes = Li+ intercalation compounds

anodecathode

Rocking chair batteries - intercalation

PHY563 – N. Schneider 39http://electronics.howstuffworks.com/everyday-tech/lithium-ion-battery1.htm

Conventions

• Anode: negatively charged electrode

• Cathode: positively charged electrode

Li Battery at equilibrium

• Negative electrode

Li° Li+ + e- or LixC6 e Li+ + e e- + Lix-eC6

• Positive electrode

e Li+ + e e- + LixMOy Lix+eMOy

• In all cases :

o µLi = µLi+ + µe at each electrode

o µLi+ is constant through electrolyte (equilibrium)

o Hence: V = µeanode - µe

cathode = -µLianode + µLi

cathode

• µLi is related to the formation energy of the electrode

o e.g. O2+ Co +Li LiCoO2

o i.e. µLi + µO2 + µCo = DGf ; µLi° = 0

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In this system the electrolyte is « invariant »While electrodes are the « redox » solids

Potential and material properties

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Single-phase systemex: LixTiS2

Two-phase systemex: LixFePO4

PHY563 – N. Schneider 42From JM Tarascon

Li-technologies – electrode materials

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Li-technologies – electrode materials

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LiMnO2/LiCoO2 : 10% less capacity advantage : cost & green

to achieve higher capacities : design materials in which the metal-redox oxidation state can change reversibly by 2 units :

Mn+2/Mn

Preserving frame work structure Molecular masses similar to 3d metal-layer oxides (ex : LiMnO2 or LiCoO2)

Not W, Mo ou Nb : heavy V-based oxides L3V2O5-Li3V3O8

Cr6+/Cr3+

LiMnO2 : structural instability upon cycling : substitution by Cr : Li1+X Mn0.5Cr0,5O2

Capacity : 190 mAhg-1

Mn : stabilize the layered structureCr : large capacity due to oxidation state that changes from +3 to +6

But Cr : presents major toxicity & pricing issues

BATTERIES TYPE I: ALTERNATIVES

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Invariant electrolytes/redox electrodes

Li-S and Li-air batteries

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Challenges on Li-air battery:- avoid undesired

reactions (LiO2, …) : need for electro-catalyst,

- avoid dendriticreplating of Li

- non floodingelectrolyte

- Li anode protection from air

- scrubbing system for the air

Tarascon, cours Collège de France (2011)

Na technology

PHY563 – N. Schneider 51Tarascon, cours Collège de France (2011)

Na vs Li

(+) cost(Na2CO3 0.1€/kg vs. Li2CO3 3.5€/kg)abundant

(-) potential -0.3Vcapacity (rionique)

Na technology

PHY563 – N. Schneider 52Tarascon, cours Collège de France (2011)

• Na/S – high T system

o Large scale batteries

o Mature

o Safety issues

Vegetal alternatives

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Organic material 1

(electroactive with high potential

3 V vs Li+/Li0)

Non-aqueous electrolyteElectrode (+) Electrode (-)

Li++ -

e e

Organic material 2

(electroactive with low potential

0.5 V vs Li+/Li0)

BIOMASS

From P. Poizot, LRCS

ex: rhodizonate(maïs)

Alternatives

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Esta

blis

hed

Futu

re

NATURE|Vol 451|7 February 2008

BATTERIES TYPE II

Invariant electrodes/redox electrolytes

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• Li batteries:

Invariant electrolyte and redox electrodes

• Other batteries could have redox electrolyte and invariant electrodes

Exemple : concentration Cu cell

Still other case with electrolytes redox and inert electrodes (e.g., graphite) > Redox flow

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Redox electrolytes

Redox flow batteryPower : surface area of the electrodes

Energy : amount of liquid electrolyte(size of storage tanks)

Power and Energy separated

Redox flow batteries

• Reactants are liquid and heldin large tanks high energy-storage capacity

• Key-element = membraneo Separated two solutions +

selective (only 1 ion) or anio(catio)ic (only anion or cation)

o If mix of electrolytestreatment of solutions (cost)

• Different systems: Fe/Cr, V/Br, Zn/Br, VRB (all V-species, lessinterdiffusion issues)

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Redox flow batteries

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Vanadium Redox Batteries (VRB)

o Negative: V2+/V3+ ; positive: V4+/V5+ , acidic sol.

o 4 ions form the same element Less interdiffusion issues

Redox flow batteries

Advantages Disadvantages

Large lifetimePower/Energy are decoupledSeasonal storage possible

Low specific energy and powerHigh costSelf discharge

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CATALYSIS

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Catalysis

• What is a catalyst?

• Which type of catalyst exist?

• Is it relevant?

• Some examples

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Catalysis – fundamental notions

• Catalysis = increase of chemical reaction rate due to the participation of an additional substance (catalyst) : thermodynamics / kinetics

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Ea = activation energy

= transition state

k = A.e-Ea/RT (Arrhenius)

o

oo

Catalyzed reaction : ≠ intermediates/ transition stateslower Ea

o = intermediate

Catalysis – fundamental notions

• Different types of catalysis

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HETEROGENEOUS Cat. and reactants in different phasesHOMOGENEOUS Cat. and reactants in the same phase, usually liquid

(+) Good contact with reactants(+) Ease of characterization/tuning(-) Catalyst needs to be separated after the reaction(-) Difficult catalyst recovery

ENZYMATIC Cat. is an enzyme

(+) Most highly efficient systems(+,-) Highly specific

(+) Little difficulty in separating and recycling the catalyst(-) Lower effective concentration of catalyst

Ni Raney: Ni/Al

Wilkinson cat.: RhCl(PPh3)3

Polyneuridine AldehydeEsterase

catalyst

loading (mol%)

activity (mol.s-1, quantity converted/time, or TOF (turn-over frequency

selectivity ability to yield a particular product

stability TON (turn-over number)

Catalysis – fundamental notions

• Catalyst selectivity

= ability to yield a particular product

Catalysis – fundamental notions

• Five steps of a heterogeneous catalytic reaction

Catalysis – fundamental notions

• Adsorption / physisorption / chimisorptionPhysisorption:

Exothermic (10-40 kJ.mol-1)low / no Eaweak interaction (VdW)f(P), f (specific area)

Chimisorption:exothermic, Qads = Ebond (60-120 kJ.mol-1)High Eastrong interaction (OM overlaping)f(P), f(surface nature, defects, active sites)

- Langmuir model – monolayer- BET (Brunauer, Emmet, Teller) model – multilayers (chimisorbed + physisorbed molecules on top)

Catalysis – fundamental notions

• Catalyst dispersion / active siteso Dispersion = nb accessible atoms / total nb of atoms

o Dispersion can be increased by supported catalysts

o Dispersion can be increased by the use of nanoparticles

Handbook of Heterogeneous Catalysis, Wiley, 2008

Catalysis – fundamental notions

• Supportso Should prevent sintering effects

o Can have acid/base properties bifunctionnal catalysis

o Can allow biphasic systems

o Oxides, Silica, Zeolites (SiAlOxM, M can be a catalyst), graphite, microporous and mesoporous materials (micelles, use of templates)

o Pore size determination: Hg porosimetry, BET

Melero et al, J. Mater. Chem. 2002 12 1664

Silica SiO2

graphite zeolites

SBA-15

Catalysis – fundamental notions

• Accessible sites ≠ active sites : structure-sensitiveo Electronic properties are size-dependent

o Shape may vary during the reaction

o Large particles are not spherical: atoms with ≠ coordinence

74Lin et al, Phys. Rev. Lett. 102, 206801 (2009)

Catalysis – significance and main applications

• Academia

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Fig. 1 Subject area breakdown of Catalysis Science & Technology's 2014 published articles.

Catalysis – significance and main applications

• Industry90% of industrial processes are catalyzed

(1) Bulk chemicals

- polymerisation (Ziegler-Natta)

- oxydation (nitric/sulfuric acid)

- hydrogenation (NH3 Haber-process, methanol)

- carbonylation (acetic acid, Monsanto-process)

(2) Fine chemicals

- olefin metathesis

- Friedel-Craft

- asymmetric synthesis (pharmaceuticals)

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Catalysis – significance and main applications

(3) Energy processing

CO2 reduction

See PC

Fuel cells

metal catalysts at both anode and cathode to catalyze half-reactions

commercial devices: Pt nanoparticles or Pt alloy supported on C black

« main obstacle for larger fuel cellcommercialisation »

research devices: doped C nanotubes, Ni-Cr, Ni-Al or Ni-O alloys

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Source: D. S. Ginley et al, Fundamentals of materials for energy and environmental sustainability-Cambridge University Press (2012)

Catalysis – significance and main applications

(3) Energy processing

Catalytic converters

(petroleum exhaust)

PHY563 – N. Schneider78Source: Handbook of Heterogeneous Catalysis, Wiley, 2008

Reduction (Rh) : NOx N2

Oxydation (Pt) : CO CO2 , HC CO2 + H2Oλ probe + cordierite support + Al2O3 washcoat + CeO2 O2 storage promoters + Pt + Rh

Catalysis – significance and main applications

(3) Energy processing

Catalytic converters

(petroleum refining)

alkylation, cracking, naphta and steam reforming (HC syn-gas)

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( CO, H2 )

( CO, H2 )

( H2O, CH4 )

steam reforming

Water-gas-shiftH2O + CO CO2 + H2

Adjusted syn-gas, H2/CO=2

syn-gas, H2/CO=0.7

Hydrocarbons + H2OFischer-Tropsch

Catalysis – significance and main applications

(3) Energy processing

Fischer-Tropsch

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History

1923 : patent from Franz Fischer and Hans Tropsch(Kaiser-Wilhelm-Institut für Kohlenforschung, Mülheiman der Ruhr)

WWII : ersatz fuel (90% plane, 25% automobile)

50’s : South Africa

70’s : Regain of interest due to oil price increase

currently : Sasol, PetroSA, Linc Energy, Shell

Catalysis – significance and main applications

(3) Energy processing

Fischer-Tropsch

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Sasol-Qatar Petroleum Oryx plant

Catalysis – significance and main applications

(3) Energy processing

Biomass

conversion

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biomass

SyngasSynthetical gas, {CO + H2}

MethanolCH3OH

Cat. Cu/ZnO440°C, 50 atm

GasificationControlled amount of O2

Hydrocarbon chainsCnH2n+2

Fischer-Tropf process

Fischer-Tropf processtypically catalyzed by Co, FeT 300°C

challenges: - control n value- catalyst deactivation- …

Bibliography: Materials for Energy

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Bibliography: Electrochemistry

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Bibliography: Catalysis

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