Sulfonic acid-crosslinked nanocellulose as a novel polymer electrolyte membrane for hydrogen fuel cells

SELYANCHYN OlenaGraduate School of Integrated Frontier Sciences, Department of Automotive Sciences, Kyushu University

HYDROGEN FUEL CELL

anode

cathodeelectrolyte (PEM)

gas diffusion layerbipolar plate

H2

H2

O2

O2

Cell n

Cell n-1

Cell n+1

Fuel cell - core technologi`cal element of the sustainable “Hydrogen society”

Barriers of wide deploymet:> Cost of hydrogen fuel> Lack of infrastructure (e.g. fuelling stations)> Cost of fuel cells (Pt in electrocatalyst, bipolar plates and proton exchange membrane)

Benchmark materials for PEM - perfluorinated sulfonic acid ionomers: Nafion®, Aquivion®, 3M®

Proton conductivity ~ 100 mS/cmIEC ~ 0.9 mmol [H+]/gCost ~ US$600 to 1200 per m2

C CF2

F2 F2 F2

F2F2C

FC

O CFC

6.6 n

C SO3HO

CF3

C

Nafion®

Disadvantages: high-cost, degradation, non-recyclable

Development of low-cost and efficient PEM based on nanocellulosePurpose of this work:

Proton exchange membrane fuel cell (PEMFC)

RESEARCH MATERIAL: NANOCELLULOSE

Main types of NC: - cellulose nanocrystals (CNC) - cellulose nanofibers (CNF)

Characteristic properties: - high mechanical strength - low density & high surface area - non toxicity & biodegradability - flexibility

Membranes features - uniform thickness in casted membranes (aqueous solution) - natural drying (no extra energy) - suitable for mass production - flat and stable after hot-pressing

Nanocellulose can be obtained from various types of plants by mechanochemical processing or directly in bacteria: - strong acid treatment - mechanical shearing - grown in microorganisms

Nanocellulose

Molecular structure

nanocrystals nanofibers

strong acid treatment mechanical shearing

OHO

OH

HOO

O

HOOH

OH

OO

OH

HO

OO

HO OH

OHOHOH

OH

n

Cellobiose

Glucose

Ordered (crystalline) domains

Disordered (amorphous) regions

Conventionalcellulose(microfibers)

Lignin

CelluloseHemicellulose

Plant cell wallmechanical, chemical tretment

Higher plants, bacteria,simple animals (e.g. tunicates)

“Eco-friendly, low-cost material for fuel cell applications”

crosslinked cellulose

MODIFICATION APPROACH: SULFONIC ACID CROSSLINKING

OOH

HOO O

HO OH

OH

OO

OH

HOO O

HO OH

OHOH OH∗∗

OOH

HOO O

HO OH

OH

OO

OH

HOO O

HO OH

OHOH OH∗∗

HO

O S

O

OHOO

OH

OOH

HOO O

HO OH OO

OH

HOO O

HO OH

OH OH∗∗

O

HOO O

HOOH

OH

OO

HOO O

HO OH

OHOH OH∗∗

OO

SO

OO

O

OHO

O

SO

OO

O

HO

+

ester bo

nds

hydrogen-bonds

130 ºChot-press

(oven)

Sulfosuccinic acid

sulfonic group

hydroxyl group

One-step approach

Crosslinking: one-step reac-tion between mixed acid and nanocellulose results in a formation of multiple ester bonds disrupting the natural hydrogen-bonding network of cellulose.

Hypothesis: surface of nano-cellulose covered with suffi-cient amount of sulfonic acid group (strong proton con-ducting moiety) will make a good proton conductor.

nanofiber-based

nanocrystal-based

MACROSCOPIC & MICROSCOPIC MORPHOLOGY

[hot-pressed]

CNF paperConventional paper 3%-SSA@CNF Membranes of 3-30 microns in thickness are distinctively differ-ent from conventional cellulosic membranes (e.g. paper), free- standing and self supporting.

Maximum concentration of SSA in CNF ~ 10 wt%, up to 50 wt% can be blended with CNC

5 x 5 cm

O.Selyanchyn, R.Selyanchyn & S.M.Lyth* Front.Energy.Res. 2020, doi.org/10.3389/fenrg.2020.596164

Bayer, 2016 (TP)

Seo, 2009 (IP) Lin, 2013 (TP)

Jiang, 2015 (IP)Gadim, 2016 (IP)

Vilela, 2016 (TP)

Vilela, 2017 (TP)Wang, 2019 (TP)

Ni, 2018 (IP) Ni, 2018 (IP) Cai, 2018 (IP) Zhao, 2019 (IP)

Etuk, 2020 (TP)

Vilela, 2020 (TP)

Zhao, 2019 (IP)

Guccini, 2019 (TP)

Di, 2019 (IP)

Tritt-Goc, 2020 (?)Tritt-Goc, 2019 (?)

Sriruangrungkamol, 2020 (TP)

Rogalsky, 2018 (TP)

Gadim, 2014 (TP)

0 10 20 30 40 50 60 70 80 90 100

0.1

1

10

100

Prot

on c

ondu

ctiv

ity (m

S⋅cm

-1)

Cellulosic material content (%)

20

85

30

30

90

90

60

94

80

Tri 9%

Tri 13%

Tri 16%

Tri 20%

S-CNC/Tri/PVA

CNC(75%)/Im

MFC@SSA

CNC with residualsulfonic groups

CarboxylatedCNF

Unmodified BC, CNF (hydrated)

BG 60%

BG 80%

BG 80%PANI 6.4%

BC/PMOEPBC/PMOEP

CNF with residualsulfonic groups

CNF@SSA

AMPS-g-BC

Composites with low content of cellulose

BC/Nafion

MFC/RDP

BC/Fucoidan/Tannic acid

CNC(78%)/Im

PSS/BC

BC/Nafion

MFC/NafionBC/PMACC

BG 95%

25%SSA@CNC

9%SSA@CNF

3 x 3 cm

CNC 3%SSA@CNC 7%SSA@CNC 10%SSA@CNC 20%SSA@CNC

2 μm20 μm 2 μm

μ10 μm 10 μm

9%SSA@CNF bottom surface

9%SSA@CNF top surface

SSA@CNF [hot-press] CNF paper [hot-press]

Conventional paper

1 μm 1 μm

2 μm

CNC surface 7%SSA@CNC surface

0 10k 20k 30k 40k 50k 60k

0

-10k

-20k

-30k

Z'' /

Ω

Z' / Ω

20% RH

40% RH

60% RH80% RH

100% RH

0 10k 20k 30k 40k 50k0

-10k

-20k

-30k

-40k

-50k

Z'' /

Ω

Z' / Ω

40°C

50°C

60°C

70°C80°C

90°C 0.04 0.05

0.13

1.03

1.73Conditions:90 ºC, 95% RH1

0.1

Prot

on c

ondu

ctiv

ity (m

S/cm

)

CNF 3%-SSA 5% 7% 9%

Lower thickness of nanocellulose PEMs is possible due to material properties + high gas barrier- Thickness of the CNF and SSA@CNF membranes is below 10 µm- State-of-art Nafion in Toyota Mirai: 2008 (~50 µm); 2017 (14 µm); goal for 2020 - 10 µm

PROTON CONDUCTIVITY OF CROSSLINKED MEMBRANES

Strong dependence of σ on relative humidity, weaker dependence on temperature (9%-SSA@CNF). Crosslinking of the CNF with SSA resulted in ca. 40 times increased proton conductivity compared to unmodified CNF sample.

(PRELIMINARY RESULTS ): COMPARISON WITH LITERATURE

- Results of this work compared to literature shows that utilization of asid crosslinked nocellulose allows substantial increase in the proton conductivity and fabrication of thinner membranes.

- Considering high gas barrier of nanocellulose membranes PEMs with competitive properies (specific resistance, chemical & mechanical stability) can be fabricated, that are environmentally friendly and have substantially lower cost compared to benchmarks (e.g. Nafion).

CONCLUSIONS & FUTURE WORK1. Nanocellulose is a promising biopolymer platform for the development of novel PEM for fuel cell applications.2. Structural integrity of the organic acid crosslinked cellulose nanofiber and nanocrystal membranes was proven in the region of sub-10 micron thicknesses.3. Morphological features (SEM), chemical structure (FTIR) and swelling behaviour in water suggest a promising material with competitive proton conductivity. Future experiments: mechanical properties, proton conductivity at high temperatures, chemical stability in hot water, O2 and H2 permeability, fuel cell performance.

MACROSCOPIC & MICROSCOPIC MORPHOLOGY

ACKHOWLEDGEMENT: Kyushu University Platform of Inter/Transdisciplinary Energy Research Support Program for Doctoral Students

E-mail: olenaselyanchyn@gmail.com / Corresponding author: Prof. S.M. Lyth lyth@i2cner.kyushu-u.ac.jp / The Lyth Lab: https://sites.google.com/view/lythlab/