Proton Conduction in Nanocellulose - Paper Fuel Cells
Authors: Bayer Thomas , Cunning Benjamin Vaughan , Selyanchyn Roman , Nishihara Masamichi , Fujikawa Shigenori , Sasaki Kazunari , Lyth Stephen Matthew 
Published: February 2020

Fuel cells are the key technology towards establishing a hydrogen energy based society, as they convert the chemical energy of hydrogen into electricity with high efficiency, and without emitting harmful exhaust gases. Polymer electrolyte membrane fuel cells (PEMFCs) are already successfully commercialized and are being used in e.g. fuel cell vehicles such as the Toyota MIRAI and the Honda Clarity Fuel Cell. However, the aim for next-generation PEMFCs is to operate at temperatures above the boiling point of water, therefore new membrane materials are needed. Stable operation at high temperature, sufficient high proton conductivity, high gas barrier as well as low cost are essential requirements.

Cellulose is the most abundant biopolymer on earth, and has been utilized in various forms by mankind for thousands of years. Cellulose polymer units form nanofibrils during biosynthesis, with diameters of several tens of nanometers and lengths of up to a few microns. These group together to form micro- and macrofibrils. In 1977 nanofibrils were successfully observed for the first time by Turbak et al., kick-starting the field of nanocellulose science. Paper made from nanocellulose has intriguing properties such as high tensile strength (214 MPa), high gas barrier and thermal stability up to 150°C.1–3 During the fabrication process of nanocellulose, acid group functionalities (i.e. carboxyl and sulfonic acid groups) are introduced,4,5which increase hydrophilicity, and additionally act as proton donors and acceptors, thus enabling proton conduction.

We investigated nanocellulose for its suitability as fuel cell membrane in PEMFCs for the first time. Two different nanocellulose materials were characterized for their morphology and chemical composition, as well as mechanical properties and gas barrier. Nanocellulose membranes showed four times higher tensile strength compared to the industry standard membrane Nafion and a roughly three orders of magnitude lower hydrogen permeability. A maximum proton conductivity of 4.7 mS/cm at 120°C and 100% RH was observed. For the first time, nanocellulose membranes were assembled into membrane electrode assemblies and operated as hydrogen fuel cell. We will report latest results of our research.

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2. Nair, S. S., Zhu, J., Deng, Y. & Ragauskas, A. J. High performance green barriers based on nanocellulose. Sustain. Chem. Process.2, 1–7 (2014).

3. Nogi, M. et al. High thermal stability of optical transparency in cellulose nanofiber paper. Appl. Phys. Lett.102, 181911 (2013).

4. Lin, N. & Dufresne, A. Nanocellulose in biomedicine: Current status and future prospect. Eur. Polym. J.59, 302–325 (2014).

5. Barbosa, L. et al. A Rapid Method for Quantification of Carboxyl Groups in Cellulose Pulp. BioResources
8, 1043–1054 (2013).

Figure 1