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: [email protected] / Corresponding author: Prof. S.M. Lyth [email protected] / The Lyth Lab: https://sites.google.com/view/lythlab/