Surface activation of the nickel-based materials is an important step to create NiOOH compound on the surface and initiate the electrochemical activity. For instance, NiOOH compound has to be originated on the surface to initiate the electrochemical activity. Similarly, the investigated NiO nanostructures

in this study were activated by MCC950 price applying cyclic voltages for 50 times in 1 M KOH electrolytes (the utilized scan rate was 100 mV/s). The cyclic voltammetric behaviors of NiO NPs and NFs are shown in Figure 3. In the voltammograms of the nickel oxide nanoparticles and nanofibers, the cathodic and anodic peaks EPZ5676 cost corresponding to Ni(II)/Ni(III) couple are observed at about 0.35 and 0.42 V (vs. Ag/AgCl), respectively. Rabusertib order As the chemical composition and the grain size are similar in both nanostructures, the same behavior was obtained as shown in the figure. Typically, these peaks refer to the formation of NiOOH in accordance with

these reactions [27–29]: (2) (3) Figure 3 Consecutive cyclic voltammogram of the synthesized NiO NPs and NFs in 1 M KOH at scan rate of 50 mVs −1 . Increasing the number of potential sweeps results in a progressive increase of the current density values of the cathodic peak because of the entry of OH− into the surface layer, which leads to the progressive formation of a thicker NiOOH layer corresponding to the NiO/NiOOH transition [24]. It is noteworthy mentioning that the formed NiOOH layer is responsible for the electrocatalytic activity of nickel-based electrocatalysts [17, 24]. The linear scan voltammograms for the methanol oxidation on the NiO NPs and NFs surfaces in different methanol concentrations are shown in Figure 4. The methanol-containing electrolyte was previously purged with argon. The onset potential is an important indicator among the invoked parameters to demonstrate the electrocatalytic activity. The onset potential indicates the electrode overpotential. In other words, the onset

potential can be utilized to evaluate the efficacy of the electrocatalyst. In methanol electrooxidation, more negative onset potential indicates high activity and less overpotential. Generally, PIK3C2G the main reason behind increasing the onset potential is the OH− and CO adsorbed layer on the surface of the electrodes, this gas layer leads to overpotential [30]. Sometimes, carbon monoxide is an intermediate compound in the methanol electrooxidation; it accumulates on the surface of the electrode until further oxidation step to carbon dioxide occurs. Usually, adsorption of CO appears to take place with the formation of islands of adsorbate [31], and electroactivity appears to be restricted to the outsides of these islands. Accordingly, good catalytic activity is related with the rate of CO removal and/or skipping formation of CO intermediate. From the obtained results, the onset potentials are 0.