In the current work, graphene oxide (GO) samples were prepared at room temperature from graphite flakes using a modified Hummer's method to produce metal-free electrocatalysts. The effect of the duration of the oxidation process on the structural, chemical and physical characteristics of the GO samples was evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ion-exchange capacity (IEC) measurements and Field-emission scanning electron microscopy (FESEM). Electrochemical behavior of the GO samples towards hydrogen adsorption/reduction (HAR) reactions was evaluated using a typical three-electrode electrochemical cell at room temperature under N2 atmosphere. Increasing the oxidation time from 3 h to 5 h resulted in dramatic decreases in the number of epoxy and carboxyl groups, interlayer spacing (~ 9.5%) and also in the IEC (~ 1.8 times) of the GO samples. Moreover, increasing the oxidation time resulted in a remarkable increase in the size of the GO sheets along two dimensions (~ 1.5 times) and also in electrochemical surface area (ECSA) of GO (~60%). CV studies revealed that increasing the oxidation time results in an increase in the current response of GO samples towards HAR reaction, indicating an enhancement in the electrochemical activity of GO. This was attributed to the formation of larger GO samples with improved electronic network.
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