Effect of the pH of the preparation medium on the microstructure and electrocatalytic activity of carbon nanotubes decorated with PtSn nanoparticles for use in methanol oxidation

Carbon nanotubes (CNTs) decorated with PtSn nanoparticles (PtSn/CNT) were prepared by the microwave-assisted ethylene glycol reduction method and characterized by atomic adsorption spectroscopy, X-ray diffraction and transmission electron microscopy. Results indicated that the loading efficiency of the metal catalyst, and the degree of alloying and morphology of the PtSn nanoparticles were significantly affected by the solution pH value of the metallic ions in the ethylene glycol. The required composition of the PtSn/CNT catalysts could be obtained by adjusting the pH value to about 5, which is almost the isoelectric point of the acid-treated CNTs. The size of the PtSn nanoparticles decreased with the pH value in the range 2 to 7, but they became large and agglomerated when the pH value was greater than 7. Electrocatalytic activity tests indicated that the PtSn-CNTs prepared at pH 5 had the best catalytic performance towards methanol oxidation. The improvement in catalytic activity was mainly attributed to a high loading efficiency and control of particle shape and size distribution.