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

Abstract

Nanocellulose is a sustainable material which holds promise for many energy-related applications. Here, nanocrystalline cellulose is used to prepare proton exchange membranes (PEMs). Normally, this nanomaterial is highly dispersible in water, preventing its use as an ionomer in many electrochemical applications. To solve this, we utilized a sulfonic acid crosslinker to simultaneously improve the mechanical robustness, water-stability, and proton conductivity (by introducing -SO3−H+ functional groups). The optimization of the proportion of crosslinker used and the crosslinking reaction time resulted in enhanced proton conductivity up to 15 mS/cm (in the fully hydrated state, at 120 °C). Considering the many advantages, we believe that nanocellulose can act as a sustainable and low-cost alternative to conventional, ecologically problematic, perfluorosulfonic acid ionomers for applications in, e. fuel cells and electrolyzers.

Covalent Crosslinking of Colloidal Cellulose Nanocrystals for Multifunctional Nanostructured Hydrogels with Tunable Physicochemical Properties

“…Samples from 1% CNC crosslinked by 10% GA and 1% EC were used to determine the absorption capacity because xCNCs at these crosslinker concentrations showed the highest CA and degree of crosslinking. It was observed that all xCNC samples retained their structural stability over the entire observation period of 24 h, contrary to pure CNC aerogels that collapsed within 30 min and completely redispersed after immersion in water for 1 h, indicating that exposed OH groups on the surface of CNCs are not available to be hydrated by water due to crosslinking as reported by Selyanchyn et al All four samples exhibited absorption capacity beyond 100 g of water per gram of aerogel (Table ), suggesting that the crosslinking process did not prevent the penetration of water through the xCNC network. Pure CNC samples were not analyzed because their aerogel structures disintegrated in water within 30 min of immersion.…”

“…25 In another recent study, a sulfosuccinic acid crosslinker was used to improve the mechanical properties, water-stability, and proton conductivity of CNC-based proton exchange membranes. 26 However, there are still limited studies that address the chemical crosslinking of CNCs, particularly "non-functionalized" or pristine colloidal CNCs.…”

“…In a study, hydrazone crosslinking between hydrazide-functionalized CNCs and aldehyde-functionalized CNCs was used to produce highly porous ultra-lightweight “all-CNC” aerogels with superabsorbent and excellent shape recovery properties, superior to those of physically crosslinked CNC (xCNC) aerogels . In another recent study, a sulfosuccinic acid crosslinker was used to improve the mechanical properties, water-stability, and proton conductivity of CNC-based proton exchange membranes . However, there are still limited studies that address the chemical crosslinking of CNCs, particularly “non-functionalized” or pristine colloidal CNCs.…”

Recent Developments on Bioinspired Cellulose Containing Polymer Nanocomposite Cation and Anion Exchange Membranes for Fuel Cells (PEMFC and AFC)

“…Proton conductivity measurement results of different ratios of CNC−SSA membranes ( c ) 80 °C and ( d ) 120 °C. Mechanisms governing membrane development and proton conduction in ( e ) CNC and ( f ) cross-linked CNC [ 111 ].…”

“…Comparing CNC-Tri to CNC treated by imidazole, it was observed that CNC-Tri had improved thermal characteristics [110]. Selyanchyn et al investigated the impact of sulfosuccinic acid (SSA) cross-linking with CNC with different ratios [111]. SSA contained a core sulfonic acid moiety (-SO 3 − H + ) and two dangling carboxylic acid moieties, which can enhance proton transport behavior after proper crosslinking with CNC.…”