**3. Results and discussion**

### **3.1 Atomic force microscopy**

AFM images, **Figure 3**, reveal that the samples are organized as bundles of nanofibrils. In some places, individual nanofibrils can be found on the mica surface, which enabled measuring their diameter. **Figure 3a** and **c** show the relief images of the nanofibrils before and after chemical surface modification whereas **Figure 3b** and **d** show 3D AFM images. This analysis indicates that the average diameters of original nanofibrils and modified nanofibrils are 6.6 ± 1.6 nm and 5.6 ± 1.1 nm, respectively.

Overall, AFM results suggest that chemical modification has not changed the morphology of the nanofibrils, which exhibit diameters in the order of 6.0 nm.

#### **3.2 Elementary analysis**

**Table 1** shows CHN results at several reaction times for the functionalization of CNFs with EMMN. This reaction occurs through nucleophilic vinylic substitution (SNV) of the ethoxy group with the malononitrile group in the polymer chain [28].

As shown in **Table 1**, the 8-hour reaction (Reaction 3) yielded the highest nitrogen content and is, therefore, the most effective in functionalizing and

**121**

**Figure 3.**

*respectively.*

**Table 1.**

*room temperature.*

nitrogen content.

due to compound degradation.

*Electrochemical Behavior of Cellulose Nanofibrils Functionalized with Dicyanovinyl Groups*

incorporating the malononitrile (dicyanovinyl) group into the nanocellulose chain. Increasing the reaction time to 24 h led to a decrease in nitrogen content, probably

*Elementary analysis results for several times of reaction between CNFs and EMMN at 1:3 molar ratio and* 

*AFM for pure and modified CNFs in relief (a and c) and 3D (b and d - 2 microns × 2 microns × 15 nm),* 

**Sample Time (h) C (%) H (%) N (%)** Pure nanocellulose — 40.55 6.13 0.017 Reaction 1 2 40.66 5.69 0.280 Reaction 2 4 41.23 6.07 0.810 Reaction 3 8 38.86 5.50 0.920 Reaction 4 24 39.39 6.13 0.760

For the best experimental condition (Reaction 3), the effect of stoichiometry and temperature on reaction yield was investigated. In this case, the same conditions used in Reaction 3 were used, with 1:2 stoichiometry at room temperature and, subsequently, 1:3 stoichiometry at 70 °C. Both assays exhibited a decrease in

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

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

#### **Figure 3.**

*Nanofibers - Synthesis, Properties and Applications*

The content of carbon (C), hydrogen (H), and nitrogen (N) in samples of pure and modified nanocellulose was determined by elementary analysis with a Perkin

The thermogravimetric analysis (TG) of pure and modified nanocellulose was performed on a TG-DSC (Netzsch, model STA 409; PC – Luxx), with 50 mL min-1

All electrochemical measurements were performed in a conventional threeelectrode electrochemical cell. A platinum plate and Ag/AgCl were used as counter electrode and reference electrode, respectively. The working electrode comprised an ultrathin layer of catalyst (pure and modified nanocellulose) under the pyrolytic graphite layer (0.070 cm and 23.0 mm diameter) of a rotating disk electrode (RDE). The 1% w/v aqueous suspension of pure and modified nanocellulose was prepared by ultrasonic dispersion in methanol. A 10 μL aliquot of this suspension was pipetted onto the surface of the pyrolytic graphite substrate. Then, the solvent was left to evaporate in a desiccator. Later, a 10 μL aliquot of Nafion® solution was pipetted onto the catalytic layer in order to attach the polymer layer to that of pyrolytic graphite. The electrochemical behavior of pure and modified nanocellulose was monitored by means of cyclic voltammetry and polarization curves. The potentials applied to the electrodes during the assays were controlled by an Autolabpotentiostat/galvanostat. The electrolyte was saturated with pure argon (Ar) and CO2 depending on the assay. Polarization curves were obtained using an RDE with potential ranging from

AFM images, **Figure 3**, reveal that the samples are organized as bundles of nanofibrils. In some places, individual nanofibrils can be found on the mica surface, which enabled measuring their diameter. **Figure 3a** and **c** show the relief images of the nanofibrils before and after chemical surface modification whereas **Figure 3b** and **d** show 3D AFM images. This analysis indicates that the average diameters of original nanofibrils and modified nanofibrils are 6.6 ± 1.6 nm and

Overall, AFM results suggest that chemical modification has not changed the morphology of the nanofibrils, which exhibit diameters in the order of 6.0 nm.

**Table 1** shows CHN results at several reaction times for the functionalization of CNFs with EMMN. This reaction occurs through nucleophilic vinylic substitution (SNV) of the ethoxy group with the malononitrile group in the polymer chain [28]. As shown in **Table 1**, the 8-hour reaction (Reaction 3) yielded the highest nitrogen content and is, therefore, the most effective in functionalizing and

nitrogen flow, 25–720 °C analysis interval, and 10 °C min−1 heating rate.

−2.0 to 1.0 V vs. Ag/AgCl and a scanning rate of 5 mV s-1.

**2.3 Elementary analysis**

**2.4 Thermal analysis**

Elmer model 2400 instrument.

**2.5 Electrochemical analysis**

**3. Results and discussion**

**3.1 Atomic force microscopy**

5.6 ± 1.1 nm, respectively.

**3.2 Elementary analysis**

**120**

*AFM for pure and modified CNFs in relief (a and c) and 3D (b and d - 2 microns × 2 microns × 15 nm), respectively.*


#### **Table 1.**

*Elementary analysis results for several times of reaction between CNFs and EMMN at 1:3 molar ratio and room temperature.*

incorporating the malononitrile (dicyanovinyl) group into the nanocellulose chain. Increasing the reaction time to 24 h led to a decrease in nitrogen content, probably due to compound degradation.

For the best experimental condition (Reaction 3), the effect of stoichiometry and temperature on reaction yield was investigated. In this case, the same conditions used in Reaction 3 were used, with 1:2 stoichiometry at room temperature and, subsequently, 1:3 stoichiometry at 70 °C. Both assays exhibited a decrease in nitrogen content.

A more accurate way to measure reaction yield is by estimating the degree of substitution (DS), which can be obtained from Eq. (1):

$$DS = \frac{M\_{g\_{\rm ul}} \cdot \%N}{100 M\_N - M\_{\rm val} \cdot \%N} \tag{1}$$

Where DS is the degree of substitution, Mglu the molar mass of the glucose monomer (162 g/mol), MN the molar mass of the nitrogen atom, Mmal the molar mass of the malononitrile group introduced into the cellulose (77 g), and %N the nitrogen content determined by elementary analysis.

By means of Eq. (1), Reaction 3 exhibits the highest DS value: 0.12. Despite not being very high, this value is close to those reported in the literature for reactions in which amino groups are introduced into the nanocellulose chain [29, 30]. For instance, the nitrogen content found in the functionalization reaction of cellulose nanocrystals with propargylamine was 0.79% [29]. Another study involving nanocellulose amination with 2-hydroxy-3-chloro-propylamine yielded a nitrogen content of 0.9% and a degree of substitution of 0.11 [30].

#### **3.3 Thermal analysis**

**Figure 4** shows the thermogravimetric analysis for pure and modified CNFs as well as the derivatives of the thermogravimetric curves (dTG). The thermal behavior of both materials exhibits a single decomposition event between 305 °C and 390 °C, with pure CNFs exhibiting greater loss of mass at the end of the process (**Figure 4**). The peak corresponding to maximum mass loss for the functionalized CNFs occurs at a temperature approximately 20 °C lower (Tmax = 349.05 °C) than that for pure CNFs (Tmax = 369.34 °C), as shown in **Figure 3**. Similarly, the beginning of the decomposition process for the modified CNFs also occurs at a temperature approximately 20 °C lower (Tinitial = 306.21 °C) than that for pure CNFs (Tinitial = 327.87 °C).

**123**

**Figure 5.**

*Electrochemical Behavior of Cellulose Nanofibrils Functionalized with Dicyanovinyl Groups*

the functionalized cellulose as compared to that of pure cellulose [31].

The drop in the decomposition temperature of the modified CNFs may be due to a decrease in crystallinity when the dicyanovinyl group was introduced. There are reports in the literature of cellulose exhibiting lower thermal resistance when carbamate groups are introduced, which indicates a decrease in thermal stability of

**Figure 5** shows cyclic voltammetry profiles for the CNFs electrocatalysts with and without mode modification at 5 mv/s scanning rate and applied potential ranging from −1.5 to 1.5 (vs Ag/AgCl). Conductivity of the electrocatalyst increases when cyan groups are introduced, as shown by the increase in area and current density. This increase in conductivity has a positive effect concerning the use of the

CO2 conversion, whether thermal or electrochemical, is associated with high energy consumption due to CO2 being a very stable molecule. In the case of electrochemical reduction of CO2, the source of energy is electricity. It is possible to reduce CO2 completely by applying a higher potential. However, an appropriate catalyst can significantly reduce energy consumption and increase end-product selectivity. **Figure 6** shows the polarization curves for pure and modified CNFs in an atmosphere of Ar and CO2. It is possible to observe that CNFs modification with cyan groups increases current density of the CO2 reduction reaction, which implies a higher CO2 conversion rate in the products. It also points to the onset potential for CO2 reduction shifting to more positive values as compared to those observed for pure CNFs. This may be attributed to adsorption/desorption of reaction intermediates in

The use of CNFs modified by the dicyan group has improved the catalytic efficiency of the electrocatalyst, thereby promoting CO2 reduction, probably due to higher availability of active sites in its fibrillar structure, especially cyan groups on the surface.

*Cyclic voltammetry for CNFs pure and modified at a scanning rate of 5 mV s-1; electrolyte: K2SO4 0.5 Mol/L* 

*saturated with Ar at 25 °C. currents normalized by the geometric area of the electrode.*

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

electrocatalyst as cathode in CO2 reduction.

the polymer interface due to the presence of the cyan group.

**3.4 Electrochemical analysis**

**Figure 4.** *TG and dTG curves for CNFs pure and modified.*

The drop in the decomposition temperature of the modified CNFs may be due to a decrease in crystallinity when the dicyanovinyl group was introduced. There are reports in the literature of cellulose exhibiting lower thermal resistance when carbamate groups are introduced, which indicates a decrease in thermal stability of the functionalized cellulose as compared to that of pure cellulose [31].
