**Abstract**

Cellulose is considered one of the most important renewable sources of biopolymers on Earth. It has attracted widespread attention due to its physical– chemical characteristics, such as biocompatibility, low toxicity, biodegradability, low density, high strength, stability in organic solvents, in addition to having hydroxyl groups, which enable its chemical modification. In this study, cellulose nanofibrils (CNFs) were functionalized with dicyanovinyl groups through nucleophilic vinylic substitution (SNV) and used as electrocatalyst in electrochemical of carbon dioxide (CO2) reduction. Results indicate that introducing dicyanovinyl groups into the structure of nanocellulose increases electrocatalytic activity as compared to that of pure nanocellulose, shifting the onset potential of the electrochemical CO2 reduction reaction to more positive values as compared to those for the reaction with argon. The atomic force microscopy (AFM) images show no changes in the morphology of CNFs after chemical modification.

**Keywords:** cellulose nanofibrils, nucleophilic vinylic substitution, electrochemical CO2 reduction

#### **1. Introduction**

The most abundant biopolymer on Earth, cellulose displays wide chemical variability due to the functionalization capability of its hydroxyl groups, via chemical and physical reactions. Moreover, cellulose exhibits diverse morphologies, found in the hierarchical constructions that constitute plants. Cellulose is mainly found in plant cell walls, but it can also be found in other living beings, such as bacteria, fungi, and even in some species of sea mammals [1, 2].

From the standpoint of chemical structure, this biopolymer belongs to the carbohydrate group, classified as a linear polysaccharide consisting of β-D-glycopyranose units joined by β-1,4 glycosidic bonds. As a result, cellulose exhibits a high molecular weight ranging from about 50,000 to 2.5 million g/mol, depending on its source [3]. The repetitive unit of cellulose, known as cellobiosis, is a cellulose dimer (**Figure 1**).

**Figure 1.** *Molecular structure of cellulose.*

Each of these individual chains clusters into larger units, called fibrils or microfibrils, which in turn clump together and form cellulose fibers. This organization may present amorphous regions, in which fibers exhibit an undefined arrangement, or highly organized segments with fibers arranged parallel to each other. Notwithstanding other arrangements, crystalline and amorphous stretches constitute the most common fiber configurations in the polymeric structure of cellulose [1].

The degree of polymerization (DP) of this semi-crystalline biopolymer varies according to the raw material used to obtain it and the method used for its extraction. For instance, wood pulp has a DP between 10,000 and 15,000 glycosidic units, while values for cellulose of bacterial origin range from 2,000 to 6,000 [4].

At nanoscale, cellulose can be obtained by chemical or physical methods or both. Cellulose nanofibrils are usually obtained by physical methods, e.g., high shear rate mechanical treatment, whereas cellulose nanocrystals are usually obtained by chemical methods, e.g., acid hydrolysis. The difference between mechanically-produced nanocellulose and chemically-produced cellulose is that the former can reach a length of up to 2 μm, while the latter, in addition to being crystalline, exhibits a length of the order of 150 nm [5, 6].

Besides its physical–chemical properties, such as low cost, biodegradability, renewability, low toxicity, and stability in organic solvents, nanocellulose exhibits a high aspect ratio and a high specific surface area. These properties combined promote its use in nanocomposites [7–9], hydrogels and aerogels [10, 11], biomedical products [12, 13], pharmaceuticals [14], environmental applications [15], and electrochemistry. In the latter case, it is used mainly in sensors [16], transistors, and solar cells [17, 18].

The introduction of strong electron withdrawing groups such as malononitrile groups in dyes and polymers has been reported in the literature [19, 20], and the presence of these groups leads to Intramolecular Charge Transfer (ICT), increasing the electron density in dicyano groups.

Electrochemical CO2 reduction is not only an effective way of lowering CO2 concentrations in the atmosphere, but it is also advantageous. CO2 can be effectively reduced to renewable fuels, such as ethanol, methane, and methanol, which can contribute to meeting today's growing demand for renewable energy sources [21, 22]. So, some studies on CO2 reduction catalysis have used conducting polymers as polyethylenimine (PEI) [23], and polyaniline (Pan) [24] that causes an effect of reducing catalytic overpotential and increasing current density and efficiency, besides increased

**119**

**Figure 2.**

*CNF functionalization with EMMN.*

*Electrochemical Behavior of Cellulose Nanofibrils Functionalized with Dicyanovinyl Groups*

of selectivity for CO2 reduction was observed for Cobalt phthalocyanine with poly-

In this study, cellulose nanofibrils were functionalized with dicyanovinyl groups, from use ethoxymethylene-malononitrile (EMMN) as chemical modifier, for use in the electroreduction CO2, whose excessive presence in the environment can cause serious problems, such as the greenhouse effect and, consequently,

In a flask, 0.5 g (3.1 mmol) by mass of an aqueous dispersion of 3% w/v CNFs (SuzanoPapel & Celulose) was placed under agitation. At that point, sodium hydroxide (NaOH) solution (0.1 M; Vetec; 97%) was added by means of a pipette (dropwise) until pH 10 was reached. The mixture was left under agitation for 30 minutes. Afterwards, EMMN (1.14 g; 9.3 mmol; Sigma Aldrich; 98%) was added to the mixture and left to react at room temperature (**Figure 2**), varying the reaction time and keeping the stoichiometry at 1:3 molar ratio (nanocellulose:malononitrile). The effect of stoichiometry and temperature on the reaction efficiency was evalu-

After the programmed reaction time, the reaction medium was placed in a sintered glass funnel (no. 4) and rinsed with acetone (Vetec; 99.5%), ethanol (Vetec; 99.5%), methanol (Vetec; 99.8%), and distilled water until neutral pH was reached. The sample was then placed in an amber glass bottle and stored in a

AFM was conducted on a Dimension ICON microscope (Bruker). The sample was prepared by dripping 5 microliters of a solution containing the CNFs on a mica surface. The mica was cleaved twice right before applying the solution dropwise onto the surface and left to dry for 1 hour at room temperature. To prevent CNFs from dragging, intermittent contact mode with a rectangular silicon probe was used

(cantilever spring constant = 40 N/m; oscillation frequency = 330 kHz).

*DOI: http://dx.doi.org/10.5772/intechopen.96181*

**2.1 Nanocellulose functionalization**

ated for the best experimental condition.

**2.2 Atomic force microscopy**

climate change [26, 27].

**2. Method**

refrigerator.

4-vinyl pyridine polymers (CoPc – P4VP) [25].

*Electrochemical Behavior of Cellulose Nanofibrils Functionalized with Dicyanovinyl Groups DOI: http://dx.doi.org/10.5772/intechopen.96181*

of selectivity for CO2 reduction was observed for Cobalt phthalocyanine with poly-4-vinyl pyridine polymers (CoPc – P4VP) [25].

In this study, cellulose nanofibrils were functionalized with dicyanovinyl groups, from use ethoxymethylene-malononitrile (EMMN) as chemical modifier, for use in the electroreduction CO2, whose excessive presence in the environment can cause serious problems, such as the greenhouse effect and, consequently, climate change [26, 27].
