Effect of surface modification extent of carbon nanotubes on electrocatalytic performance of carbon nanotubes supported Pt catalyst

Based on the synthesis and purification of carbon nanotubes (CNTs), CNTs were treated with concentrated HNO3 solution at 50, 75, and 100 degrees C for 5 h. After CNTs were treated in concentrated HNO3 solution at 75 degrees C for 5 h, suitable amount of hydrophilic O-containing surface groups would be formed so that the average size of the Pt particles deposited on the CNTs surface is small, about 3.7 nm, leading to the good electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation. If the treatment temperature is as low as 50 degrees C, the amount of the hydrophilic O-containing surface groups formed on CNTs is small so that the Pt particles formed on CNTs would be easy to aggregate. If the treatment temperature is as high as 100 degrees C, the amount of the hydrophilic O-containing surface groups formed on CNTs is large and the CNTs would be opened. Then, the Pt particles formed on CNTs would be concentrated near the fractures and form large Pt particles, leading to the low electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation.