Spray deposition of sulfonated cellulose nanofibers as electrolyte membranes in fuel cells

Abstract

Nanocellulose is a promising new membrane material for fuel cells, with much lower cost and environmental impact compared with Nafion or Aquivion. It is mechanically strong, is an excellent hydrogen barrier and has reasonable proton conductivity. Here, sulfonation of cellulose nanofibers is performed to enhance the conductivity (up to 2 × 10− 3 S cm− 1) without compromising the membrane integrity, and fuel cells are fabricated with 30 µm-thick “paper” membranes. The hydrogen crossover current is two orders of magnitude lower than for Nafion fuel cells with equivalent thickness, but the power density is rather low. Spray-coating is used to deposit 8 µm-thick membranes directly onto the electrocatalyst layer, in a process analogous to 3D printing or additive manufacturing. The resulting paper fuel cell has high current density (> 0.8 A cm− 2) and power density (156 mW cm− 2) under standard measurement conditions (H2/air; 80°C; 95% RH; 0.1 MPa), attributed to decreased membrane resistance. The cost of the spray-painted cellulose membranes is calculated to be ~ 50 $ m− 2, which is much lower than that of Nafion, even without taking into consideration economies of scale. This new concept in electrochemical energy conversion paves the way for the mass production of affordable, recyclable fuel cells. Graphic abstract

Cellulose Nanocrystals Crosslinked with Sulfosuccinic Acid as Sustainable Proton Exchange Membranes for Electrochemical Energy Applications

“…The structure of cellulose containing a high proportion of hydroxyl functional groups on the surface provides a convenient starting point for chemical modification. Recently, we combined chemical sulfonation of CNFs to increase the conductivity (from 0.05 to 2 mS/cm) with the fabrication of thin membranes (8 µm) to minimize the membrane resistance, achieving an industrially relevant power density of 156 mW/cm 2 in a fuel cell setting [ 18 ]. However, the durability and mechanical stability of such membranes in a humid environment, and the much lower conductivity compared to Nafion ® , remain as significant issues moving forward.…”

“…In previous work, we demonstrated that the PEMs fabricated from pure CNF and CNC possess intrinsic proton conductivity (0.05 and 4.6 mS/cm, respectively), but the values measured were much lower than the benchmark ionomers, such as Nafion ® [ 16 ]. Another important finding was that the nanocellulose PEMs displayed remarkably low hydrogen permeability compared to Nafion ® , in principle enabling the fabrication of much thinner membranes in which the lower specific resistance can compensate for the lower proton conductivity [ 16 , 18 ].…”

Cellulose Nanopaper: Fabrication, Functionalization, and Applications

“…Bayer et al synthesized a sulfonated cellulose nanofiber (S-CNFs) membrane and successfully introduced it into a "paper fuel cell" as a substitute for Nafion (Fig. 7 b) [ 153 ]. The resulting paper fuel cell had high current density (> 0.8 A cm −2 ) and power density (156 mW cm −2 ) under standard measurement conditions (H 2 /air; 80 °C; 95% RH; 0.1 MPa), which was due to the enhanced conductivity of S-CNFs film.…”

“…7 a The preparation process of BC-CNT-NZ, the detailed configuration of SCMFC and its compartments, and the role of BC-CNT-NZ in SCMFC [ 152 ]. b Photographs of S-CNFs paper, paper fuel cells and the power density of paper fuel cells [ 153 ]. c Schematic structure of the organic solar cell on CNCs substrates (left) and image of an assembled solar cell (right) [ 111 ].…”

Sulfonated Cellulose Membranes Improve the Stability of Aqueous Organic Redox Flow Batteries

“…[ 24 ] Recently, Bayer et al used oxidatively sulfonated cellulose nanofibrils to produce membranes for fuel cells, and were able to achieve a high power density of 160 mW cm −2 by using spray coating to produce thin membranes from the material, thus decreasing the resistance of the device. [ 25 ]…”