Preparation of Novel Biodegradable Cellulose Nanocrystal Proton Exchange Membranes for Direct Methanol Fuel-Cell Applications

Abstract

The material processing procedure of cellulose nanocrystals (CNCs) was investigated for use as a proton exchange membrane (PEM) of direct methanol fuel cells (DMFCs). The CNCs were prepared from pulp via the sulfuric acid hydrolysis homogenization method. Novel biodegradable and environmentally friendly PEMs with good proton conductivity and mechanical properties were successfully prepared by grafting cytidine monophosphate, taurine, and cysteine onto CNC backbones. The DMFC operation test demonstrated that the modified films had a good power output performance and lower methanol permeability comparable to those of the available commercial membrane, which was nonbiodegradable and involved toxic fluorination. Their high performance and environmental friendliness indicated that the modified films might have potential applications in DMFCs.

Modified Cellulose Proton-Exchange Membranes for Direct Methanol Fuel Cells

“…Therefore, MCC and CNC have been used to develop PEM for fuel cell applications. Huang et al grafted CNCs with biomass-derived cytidine monophosphate (CMP), taurine (TAU), and cysteine (Cys) to improve their proton conductivity for DMFC applications [ 130 ]. During grafting, CNCs are first transformed into 2,3-dialdehyde cellulose (DAC) by the action of an oxidant (NaIO 4 ).…”

“…During grafting, CNCs are first transformed into 2,3-dialdehyde cellulose (DAC) by the action of an oxidant (NaIO 4 ). Then, acetic acid functioned as a catalyst to enable nucleophilic primary aldehyde groups on DAC to interact with the changed molecules in a Schiff-base process [ 130 , 131 , 132 ]. Hemiacetal may be generated by the influence of a possible cross-linking between the hydroxyl (−OH) on CNCs and the aldehyde groups (CHO) on DAC, which augments the tensile characteristics of the membrane [ 103 , 130 ].…”

“…Then, acetic acid functioned as a catalyst to enable nucleophilic primary aldehyde groups on DAC to interact with the changed molecules in a Schiff-base process [ 130 , 131 , 132 ]. Hemiacetal may be generated by the influence of a possible cross-linking between the hydroxyl (−OH) on CNCs and the aldehyde groups (CHO) on DAC, which augments the tensile characteristics of the membrane [ 103 , 130 ]. Additionally, the tensile strength can be improved by the interfacial interaction between the CNC and polymer.…”

“…The proton transfer distance was shortened by the addition of CMP, TAU, and Cys to the membrane. The decreased substitutional degree and exchangeable proton capacity of the modified membranes resulted in a lower ion-exchange capacity (IEC) value (between 0.0344 and 0.3267 mmol g −1 ) than that of the Nafion117 membrane (between 0.345 and 0.95 mmol g −1 ) at 20 and 80 °C, respectively [ 130 ]. Figure 1 b–f show the power density and polarization curves of the Nafion117 and modified membranes.…”

“…The highest power density was measured for the TAU3-DAC membrane (34.05 mW/cm 2 ). The obtained power density of the other TAU3-DAC membrane was approximately 97.4% of the Nafion117 membrane performance [ 130 ]. In another approach, Zhao et al developed a new proton conductive membrane with 2,6-diaminopurine grafted onto CNC [ 133 ].…”