**2.4 Thermal analysis**

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

### **2.5 Electrochemical analysis**

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