Enhancing proton transport in cross-linked poly(vinyl alcohol)/sulfosuccinic acid membranes by adding TEMPO-oxidized lignocellulose nanofibrils

The membranes based on poly(vinyl alcohol) (PVA) and sulfosuccinic acid (SSA) are an interesting alternative for use in proton exchange membrane fuel cells (PEMFC), due to their low cost. Nevertheless, it is necessary to enhance their electrochemical performance for their use. This research aims to understand the effect of the addition of TOLCNFs with different lignin content on the physicochemical properties of PVA/SSA-based membranes, proton transport, and their performance as electrolytes in a laboratory PEMFC. For this, TEMPO-oxidized lignocellulose nanofibrils (TOLCNFs) were produced from Pinus radiata pulp that was delignified using oxidative treatments. TOLCNFs with a lignin content of 29.7% (TOLCNF-0), 21.8% (TOLCNF-0.75), 16.9% (TOLCNF-2), and 9.7% (TOLCNF-5) were obtained by varying oxidative treatment times. Membranes of PVA, SSA, and 5% (w/w) TOLCNF were prepared. The addition of TOLCNF changed the structure of the PVA/SSA membrane, promoting cross-linking between the fibrils. Furthermore, they increased the water absorption capacity (W) and decreased the swelling (S). The proton transport by diffusion through the membranes was hindered by the addition of the TOLCNFs. Despite that, the TOLCNFs promoted proton conductivity through the membranes, due to the increase in their water absorption capacity, hydrophilicity, cross-linking, and W/S ratio. Notably, the PVA/SSA/TOLCNF-0 and PVA/SSA/TOLCNF-2 membranes exhibited the highest proton conductivity over the entire temperature range studied (40–110 °C). Finally, the incorporation of the TOLCNFs improved the performance of the PVA/SSA membrane as an electrolyte in a laboratory PEMFC, with the TOLCNF-0 proving to be the best filler for the PVA/SSA membrane.

Graphical abstract