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Low-temperature systems water containing systems. e.g. Nafion, heteropolyacids oxoacids and their salts, which show proton conductivity even in the absence of water due to their self-dissociation, e.g. CsHSO 4 ( s =10 -3 S cm -1 above 412 K)

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proton conductors

Low-temperature systems

  • water containing systems. e.g. Nafion, heteropolyacids
  • oxoacids and their salts, which show proton conductivity even in the absence of water due to their self-dissociation, e.g. CsHSO4 (s=10-3 S cm-1 above 412 K)
  • blends of organic compounds exhibiting basic sites with acids, e.g. H3PO4 or H2SO4.
  • Xerogels- amorphous materials obtained by drying of the inorganic gels synthesised using sol-gel route.
  • High temperature systems
  • oxides, hydroxides and apatites

Proton conductors

slide2

Proton conductivity of some water containing compounds

The loss of water, which in most cases takes place at temperatures close to the boiling point of water, results in a decrease in conductivity

slide4

Nafion

Heteropolyacid with Keggin structure

(e.g. H3PO4x12WO3)

Poly (2-acrylamido-2-methyl-1-propane sulphonic acid)

slide6

Polymer electrolytes

  • Acidic groups (-COOH, -SO3H) in side or main chain (part of the polymer bachbone),
  • e.g. poly (acrylic acid), PAMPS
  • Complexes of polymer with salt or acid: polymer with basic sites in a chain is a solvent for the dopant
  • Polymer gels- three component systems, combining polymer matrix swollen with dopant solution in an an apropriate solvent

Polymers which may be applied in proton conducting systems should fulfil some requirements, such as:

‑ chemical and thermodynamic stability

‑ specific protonic conductivity

‑ conductivity range depending on the perspective application, i.e. 10‑1‑ 10‑3 S cm‑1 for fuel cells and 10‑5‑ 10‑7 S cm‑1 for sensors or electrochromic devices

‑ properties independent of the humidity level

‑ thin film configuration.

The use in electrochromic devices requires also high transparency of membranes

slide7

Gel electrolytes

Polymers:

Acrylic and methacrylic polymers (PMMA, PAN,PGMA,PAAM), poly (vinylidene fluoride), poly (vinyl chloride), PEO

Solvents:

Propylene carbonate, ethylene carbonate, N, N-dimethylformamide, glymes, N-vinylpyrrolidone

Acids:

Phosphoric acid and its acidic esters, sulfuric acid, sulphonic acids, phosphonic acids, heteropolyacids

slide8

Structure of glycidyl methacrylate and products of its reaction with phosphoric acid

G.Zukowska, V. Robertson, M. Marcinek, K.R. Jeffrey, J. R. Stevens

J.Phys.Chem. B 10 (2003)5797

mechanism of proton transport in polymer electrolytes
Mechanism of proton transport in polymer electrolytes

Grotthus

Fast exchange of protons („hoping”) between neighbouring molecules

Vehicle

Transport of a proton as a part of a bigger species (e.g. anion)

dmf h 3 po 4 based gels
DMF-H3PO4 based gels

Protonation of DMF

Proton transport according to Grotthus mechanism

pc h 3 po 4 based gels
PC-H3PO4 based gels

Auto-dissociation of H3PO4 in PC

Vehicle transport at low acid concentration,

Grotthus at high (30-40%) concentration

conductivity of liquid and gel electrolyes based on pmma pc h 3 po 4
Conductivity of liquid and gel electrolyes based on PMMA-PC-H3PO4

 - gels

- liquid

a)50% mas. H3PO4

b)26% mas. H3PO4

c)19.5% mas. H3PO4

conductivity of liquid and gel electrolytes based on pgma dmf h 3 po 4
Conductivity of liquid and gel electrolytes based on PGMA-DMF-H3PO4

 - gels

 - liquid

a)50% mas. H3PO4

b)44% mas. H3PO4

c)38% mas. H3PO4

d)26% mas. H3PO4

e)8% mas. H3PO4

e*)5% mas. H3PO4

GMA (glycidyl methacrylate) reacts with phosphoric acid with formation of acidic phosphates (stronger acids than H3PO4) which results in increase in conductivity

slide15
NMR measurements of the diffusion of deuterons in the DMF/phosphoric acid mixtures and in the PGMA/DMF/H3PO4 gels.

K.R. Jeffrey, G.Z. Zukowska, and J.R. Stevens

J. Chem. Phys. 119 (2003)2422

The coefficients decrease with acid concentration

and with the introduction of the polymer gel.

slide16

A comparison of the diffusion coefficients for the deuterons and phosphorus in the samples containing 40% phosphoric acid with and without the polymer matrix

The measurements were made using the static magnetic field gradient NMR technique. The diffusion coefficients for the deuterons are about a factor of three greater than that for phosphorus in comparable samples. The influence of the gel is to reduce the diffusion coefficient.

slide17

(a)

(b)

Influence of the type of proton donor on conductivity in electrolytes based on PMMA-PC-DMF (a) and PVdF-DMF (b)

- PWA, - diphenyl phosphate, - H3PO4

electrochromic device

+

+

+

+

+

Transparent conductor

Electrochromic layer

Electrochromic layer

Transparent conductorprzewodnik

Electrolyte

Glass

Glass

-

-

-

-

-

ions

Electrochromic device

According to Granqvist