Nanocellulose electrolyte membranes for fuel cells Stephen Lyth University of Strathclyde, UK
Cellulose is the most abundant biopolymer on the planet, making a cheap and sustainable resource. Meanwhile, cellulose nanofibers and nanocrystals are promising new nanomaterials derived from cellulose. Nanocellulose has many potential uses in energy applications, replacing more expensive polymers and petrochemicals. Polymer electrolyte fuel cells (PEFCs) convert hydrogen to electricity without emitting carbon dioxide. They will play an important part in the coming hydrogen economy. However, their operation relies on sulfonated fluoropolymer electrolytes such as Nafion. These are expensive, ecologically damaging to produce, and difficult to recycle. Moreover, their production involves per- and polyfluoroalkyl substances (PFASs), otherwise known as “forever chemicals”. We propose the use of nanocellulose as a sustainable alternative to sulfonated fluoropolymers in PEFCS. As such we fabricated paper-like membranes from nanocellulose and investigated their properties. We found that nanocellulose membranes have a tensile strength three times higher than Nafion, making them strong enough to withstand the pressurized conditions in a fuel cell. We also found that nanocellulose membranes have three orders of magnitude lower hydrogen permeability than Nafion, meaning that they can effectively separate the oxygen and hydrogen gases at the cathode and anode, respectively. Most importantly, we found that nanocellulose membranes can conduct protons and are therefore suitable to be used as ionomer materials. We reported the world’s first PEFCs using sustainable nanocellulose electrolyte membranes to replace Nafion, in 2016. To improve the fuel cell performance, we functionalized nanocellulose with sulfonic acid groups to increase the proton conductivity, whilst developing very thin membranes using spray deposition to decrease the membrane resistance. More recently we have used acidic crosslinkers to simultaneously increase the mechanical strength, durability, and proton conductivity. These innovations have resulted in cheap cellulose-based fuel cells with practically relevant power densities, paving the way for the mass production of sustainable, affordable, and recyclable fuel cells. References 1. Proton Conductivity in Cellulosic Materials: A Review, O. Selyanchyn, R. Selyanchyn, S. M. Lyth, Frontiers in Energy Research: Fuel Cells, 8, 596164 (2020) 2. High Temperature Proton Conductivity in Nanocellulose: Paper Fuel Cells, T. Bayer, Roman Selyanchyn, Shigenori Fujikawa, K. Sasaki, and S. M. Lyth*, Chemistry of Materials, 28 (13), 4805–4814 (2016) 3. Spray Deposition of Sulfonated Cellulose Nanofibers as Proton Conducting Membranes for Fuel Cells, T. Bayer, B. Cunning, R. Selyanchyn, B. Smid, S. Fujikawa, K. Sasaki, S. M. Lyth*, Cellulose, 28, 1355–1367 (2021) 4. Cellulose Nanocrystals Crosslinked with Sulfonic Acid as Sustainable Proton Exchange Membranes for Electrochemical Energy Applications, O. Selyanchyn, T. Bayer, D. Klotz, R. Selyanchyn, K. Sasaki, S. M. Lyth, Membranes 12 (7), 658 (2022)
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